• exclusive economic zonea zone extending up to 200 nautical miles (370km) from a nation's territorial waters into the ocean where that nation has jurisdiction over natural resources such as fisheries and energy production. TheExclusive Economic Zone is defined in the United Nations Convention on the Law of the Sea. Also called the EEZ.
• Precipitationany liquid or frozen water that forms in the atmosphere (clouds) and falls back to the Earth (e.g. rain, hail, sleet, and snow).
• A-weightingthe most commonly usedfrequency weighting function for humans that accounts for the fact that human hearing is less sensitive to lowfrequencies; units dB(A) or dBA.
• absorptionAbsorption is the conversion of thewave of energy to other forms of energy. The combined effect ofscattering and absorption is calledattenuation.
• accelerationthe rate of change ofvelocity with respect to magnitude or direction.
• accelerometera device that measures the vibration, or change in motion (acceleration) of a structure or organism. The force caused by vibration or a change in motion causespiezoelectric material within the device to be squeezed, which produces an electrical charge that is proportional to the force exerted upon it. Since the charge is proportional to the(...)
• accuracythe degree of closeness of measurements of a quantity to its actual value.
• acoustic environmentthe composite of all sounds in an environment. The perception of theacoustic environment for each animal will vary depending on its hearing abilities.
• acoustic fish tagatransmitter implanted or attached to a fish to monitor fish movement
• acoustic impedancethe amount of sound pressure generated by a given vibration at a specific frequency.
• acoustic indexa statistic that summarizes several aspects of thedistribution of acoustic energy and information.  Acoustic indices have been developed to estimate characteristics of the acoustic production of biological communities including richness and heterogeneity.
• acoustic lensa delay-and-sum beamformer in which the delays and sums are accomplished by therefraction and concentration of acoustic rays induced by the curved surface of the lens.
• acoustic maskingwhen sounds (masking sounds ormaskers) interfere with an animal’s ability toperceive, detect, or discriminate a different sound.
• acoustic modema wireless communication device used to transmit data and information through the ocean
• acoustic propagation modelsconceptual and numerical models that compute how sound travels through the water, taking into account many variables such as watertemperature,salinity, bottom topography, etc.
• acoustic reflex (AR)the contraction of the middle-ear muscles in response to sound stimulation. The reflex decreases the transmission of vibrational energy to the cochlea.
• acoustic releasea device which holds onto the anchor of a buoyant instrument until it is commanded to release it
• acoustic signatureacoustic characteristics or attributes of asound source that can be used for its identification.
• acoustic telemetryto transmit acoustic signals automatically and at a distance, as between a ground station and an artificial satellite, space probe, or the like, especially in order to record information, operate guidance apparatus, etc
• acoustic thresholdthe received level at which an effect from acoustic exposure may begin to occur.
• acoustic tomographyuses the travel time of sound in the ocean to measure the temperature of the ocean over large areas
• acoustic traumasevere traumatic injury from sound
• acoustical shadowinga condition that occurs when refraction orreflection prevents direct sound waves from reaching a region (called ashadow zone)
• active acousticssound is purposefully generated and received
• acutesevere condition with a sudden onset.
• adaptationan alteration in the structure or function of an organism or any of its parts that results in the organism becoming better fitted to survive and multiply in its environment.
• ADCPAcoustic Doppler Current Profiler; an instrument used to measure the current using acoustic sound and the knowledge of theDoppler effect
• African penguinSpheniscus demersus
• agonistic behavioraggressive or defensive social interaction (such as fighting, fleeing, or submitting) between individuals usually of the same species
• airgunAnairgun is designed to release compressed air, which forms bubbles. The formation of bubbles produces a loud sound that is used to explore the geologic structure of the ocean floor. Airguns primarily produce sound at low frequencies (between 10-500 Hz); however, high frequencynoise is also created. A small airgun that releases 0.16 Liters(...)
• algorithma step-by-step procedure for calculations/solving a problem.
• aliasingwhen ananalog signal is not digitally sampled at a high enough rate, thesignal that is reconstructed from the digital samples will not match the original signal
• alongshore flowA surface current that flowsparallel to the shore.
• Amazon river dolphinInia geoffrensis
• ambient noisebackground sound in the ocean. Examples of sound sources contributing toambient noise include waves, wind, rain, shrimp, earthquakes, volcanoes, and distant sources, such as shipping andairguns.
• ambient soundSound that would be present in the absence of a specified activity;ambient sound is location-specific and time-specific; also known as ambient noise.
• American lobsterHomarus americanus
• American paddlefishPolyodon spathula
• American shadAlosa sapidissima
• amphibiousliving or able to live on land and in the water
• amplitudethe maximum distance that a vibrating particle moves from itsequilibrium; how much themedium is disturbed
• amplitude modulationtheamplitude (signal strength) of a carrierwave is varied in proportion to that of thesignal, while thefrequency andphase remain constant.
• anadromousfish that are born in fresh water, migrate to the ocean to grow into adults, and return to fresh water to spawn.
• analog signala continuous signal that varies with time based on another quantity; it is analogous to another quantity
• anemometera weather instrument that measures wind speed.
• angle of incidencethe angle that theincident wave makes with a lineperpendicular or normal to the reflecting surface
• angle of reflectionthe angle that thereflected wave makes with a line perpendicular or normal to the reflecting surface
• animated frequency spectrumAnanimated frequency spectrum is a series of frequencyspectra that show just the frequencies present at each moment in time. You can see whatfrequencies are associated with each part of a sound.
• annelidworms or wormlike animals of the phylum Annelida, characterized by an elongated, cylindrical, segmented body with movable bristles (orsetae); includes the earthworms, polychaete worms, and leeches.
• Antarctic Convergencea zone in the Southern Ocean that separates the waters surrounding Antarctica from sub-Antarctic regions. Waters around Antarctica are colder and slightly less saline than north of the convergence zone
• Antarctic minke whaleBalaenoptera bonaerensis
• anthropogeniccaused by humans
• Aristotle's lanternclaw-like mouth on a sea urchin that contains five calcium carbonate teeth that are used for feeding
• array elementsa singlehydrophone in a receiving array or a singleprojector (sound source) in a projector array
• arthropodsinvertebrates of the phylum Arthropoda that have jointed appendages and a chitinous, segmentedexoskeleton.Arthropods include insects, spiders, crabs, and lobsters.
• Atlantic croakerMicropogonias undulatus
• Atlantic mackerelScomber scombrus
• Atlantic salmonSalmo salar
• Atlantic spotted dolphinStenella frontalis
• Atlantic Undersea Test and Evaluation Center (AUTEC)a deep-water laboratory located in the Bahamas (in the Tongue of the Ocean (TOTO)) that is instrumented with a variety of acoustic beacons and sensors to provide testing, evaluation, and certification for U.S. Navysubmarine captains and their crews, as well as theaccuracy of their undersea weapons. A Marine Mammal Monitoring (M3R) system(...)
• atmospheric pressurethe force per unit area exerted by the weight of the atmosphere; also known asbarometric pressure.
• attenuatereduce the force or effect of; the gradual loss of fluxintensity through a medium.
• attenuationthe decrease in the intensity of a wave due to the loss of acoustic energy to heat energy
• audiograma graph expressing hearing loss (hearing sensitivity) as a function of frequency
• audiometric curvea graph displaying the range of sounds that humans can hear.
• auditory brainstem response (ABR)Whenever a sound wave is detected by the ear, it triggers a number of neuro-physiological responses along the auditory pathway. An auditory brainstem responsetest is an objective test that measures the electrical potential produced in response to sound stimuli by the synchronous discharge of the first through sixth order neurons in the(...)
• auditory bullaa hollow, bony structure that encloses parts of the middle andinner ear.
• auditory fatiguewhen the intensity level orduration of sound overwhelms thehair cells so they cannot respond to sounds appropriately
• auditory meatus or ear canalan air-filled canal that leads from the ear flap to the ear drum. It helps direct soundwaves to the ear drum.
• auditory systemthe sensory system for hearing, consisting of the ear and thecentral nervous system.
• auditory weighting functiona mathematical equation that compensates for the fact that animals do not hear equally well at all frequencies.
• australsouthern hemisphere
• Australian freshwater crayfishCherax destructor
• automatic gain control (AGC)a system that automatically controls the increase in the amplitude of an electrical signal. “Gain” controls how loud something is before it goes through any processing.
• Automatic Identification System (AIS)an automated tracking system used to electronically identify and locate ships. AIS uses GPS-linked, very highfrequency radio signals that allow for ship-to-ship and ship-to-shore information transfer. Information transmitted includes a ship's name, position, speed, heading, and other information. These details are transmitted multiple(...)
• autonomousexisting and/or functioning independently; with regards to ocean-going vehicles, one which travels at the surface or underwater without requiring input from an operator.
• axial musclesfolded muscle segments that, when contracted, produce a wavelike motion that moves the fish through the water
• backscatterthe deflection of sound in a scattering process through an angle greater than 90 degrees.Backscatter is the term commonly used to describe the return of sound from the seafloor to thereceiver in an activesonar.
• BaijiLipotes vexillifer
• baleenseries of horny plates that hang from the gums of the upper jaw of some large whales (calledMysticetes). Thebaleen is made from the same materials as human hair and fingernails. It is used to filter small bits of food from the water.
• baleen whalesThese largecetaceans are usually more than 9.1 m (30 ft) long and can be found throughout the ocean. Instead of teeth, mysticetes have a series of horny plates called baleen. The baleen is made from the same materials as human hair and fingernails. Thebaleen plates hang from the gums of the upper jaw and are used to filter small bits of(...)
• bandpass filterasignal processing technique that allows a range of frequencies to be heard, while blocking higher and lowerfrequencies.
• bandwidththe frequency span of asignal, calculated as the difference between the highest frequency of a signal and the lowestfrequency of a signal.
• barometric pressurethe force per unit area exerted by the weight of the atmosphere; also known asatmospheric pressure.
• barotraumaThe result of an inability to equalizepressures between the environment and an air-filled area of the body.  This can happen in air (such as ear discomfort and ear drum injury when planes descend or ascend) or in water (such as injuries to lung tissues or middle ears when scuba diving).Barotrauma typically occurs at much lower pressures(...)
• Barth’s myochordotonal organs (Barth’s MCO)thin-walled sensory organ found in the exoskeleton on each leg ofsemi-terrestrial ocypodid crabs.
• basilar membranea membrane in the cochlea of the ear that vibrates in response to sound. As sound vibrations progress down the ear, a fluid wave that is created by the movement of the third ossicle, the stapes, moves thebasilar membrane. The basilar membrane is the part of the cochlea that separates sounds according to their frequency.
• basking sharkCetorhinus maximus
• bathymetrycharting of the sea floor using water depth measurements
• bathythermographan instrument that makes a record of the temperature at various depths in the ocean
• beaconan acoustic signaling device that continually sends out a repetitivesignal. Acoustic beacons, sometimes called pingers, are used to mark the locations of underwater objects.
• beam patterna graphical or other description of the response of atransducer used for sound transmission or reception as a function of the direction of the transmitted or incident sound waves.
• beamforminga general signal processing technique used to control the directionality of the reception or transmission of a signal on an array of sensors. Usingbeamforming during sound transmission, the majority ofsignal energy is transmitted in a specified direction. During sound reception, beamforming allows sensors to predominantly receive energy(...)
• beamforminga signal processing technique for thedirectional transmission or directional reception of a signal.
• bearded sealErignathus barbatus
• bearingmeasurement of direction; the angle, with respect to magnetic north, to where the target is located
• bedrockthe hard, solid rock beneath surface materials such as soil as well as sand and othersediments on the ocean floor.
• bela unit used in the comparison ofpower levels or of intensities of sounds corresponding to anintensity ratio of 10:1.
• beluga whaleDelphinapterus leucas
• benthicliving on the bottom of the sea (or a lake).
• biodiversitya contraction of “biological diversity,” it generally refers to the amount of variability within species, among species, and among ecosystems.
• biofoulingthe accumulation of microorganisms, plants, algae, or small animals on surfaces, causing structural or other functional deficiencies.
• biologically significantan action or activity that affects an animal's ability to grow, survive, or reproduce.
• biomagnificationthe process by which a compound (such as a pollutant or pesticide) increases its concentration in the tissues of organisms as it travels up the food chain. (also known as bioamplification orbiological magnification)
• biomassmeasure of the amount of living material in an area, usually expressed in units of weight per unit volume
• bistatic sonarwhen the sound source and receiver are located in different places
• bivalvean aquatic mollusk that has a compressed body enclosed within a hinged shell, such as oysters, clams, mussels, and scallops.
• black drumPogonias cromis
• black-legged kittiwake Rissa tridactyla
• black rockfishSebastes melanops
• Blainville's beaked whaleMesoplodon densirostris
• blast injuryInjuries that occur as a result of an explosion (blast) which produces ashock wave with rapid shifts to extremely high pressures (compression) followed by lower than ambientpressures (rarefaction).  These suddenpressure extremes can produce direct physical injury to body tissues or indirect injuries from debris or transport of bodies into(...)
• blue-fin tunaThunnus thynnus
• blue rockfishSebastes mystinus
• blue sharkPrionace glauca
• blue whaleBalaenoptera musuculus
• blue whitingMicromesistius poutassou
• bottlenose dolphinTursiops truncatus
• bottom reverberationsound scattering that occurs at or near the sea bottom
• bowhead whaleBalaena mysticetus
• bowridinga common activity of dolphins and other cetaceans in which marine mammals swim infront of a vessel, riding or surfing on thepressure wave created by the vessel
• brisancethe ability to shatter nearby objects because of the rapid release of energy and the rapid increase in pressure by explosives.
• broadbanda soundsignal that includes acoustic energy across a wide range of frequencies.
• Bryde’s whaleBalaenoptera edeni edeni
• bubble feedinga feeding process where whales trap aschool of prey (fish or krill) by blowing a series of bubbles as the whales swim to the surface. The bubbles form a curtain that rises to the surface of the water and concentrates the prey in the center. The whales charge through with their mouths open to engulf the fish or krill.
• bubble frequencythe frequency equal to the reciprocal of the time interval between the shockwave and the first bubblepulse.
• bubble pulsessecondary shock waves of explosions in which the bubbles repeatedly grow larger and smaller.
• buccal cavitythe anterior portion of theoral cavity, also sometimes referred to as the vestibule or entry area of the oral cavity. It is the region bounded by teeth and gums, jaws, and cheeks.
• buoyancythe upward force on a free floating or submerged object, independent of the object's weight; gives submerged objects the weightless appearance.
• burst pulsed soundsa rapid series ofbroadbandclicks similar to those used inecholocation, but with a much shorter interclick interval of 0.5-10ms. Given this very high pulse repetition rate, greater than 300 pulses/second, more clicks are produced per unit time withburst pulsed sounds.
• bycatchthe harvest of fish (or any marine organism) other than the species for which the fishing gear was set
• byssal threadsstring like substance that is secreted by mussels to allow the mussel to attach to hard substrates like rocks
• C-weightingafrequency weighting function that was originally designed to predict the human ear’s sensitivity to tones at high noise levels; however, nearly allnoise measurements for hearing conservation are measured withA-weighting; units dB(C) or dBC.
• calderadepression formed at the summit of a volcano
• California mantis shrimpHemisquilla californiensis
• California sea lionZalophus californianus
• callositiesthick, white patches of hardened skin, called chitin, that are covered with tinycrustaceans, called whale lice." These patches are found on the heads
• calvethe sudden release and breaking away of a mass of ice from a glacier, iceberg, ice front, or ice shelf.
• canine teethsharp, fang-like teeth adapted for capturing and penetrating prey
• Cape fur sealArctocephalus pusillus
• capillariesthe smallest of the network of blood vessels throughout an organism
• carapaceA hard, protective, shell-like outer covering found in crustaceans (e.g. crabs and lobsters) as well as turtles.
• carbon sinkacarbon sink takes up more carbon from the atmosphere than it releases, resulting in a net decrease of carbon in the atmosphere
• cardioida heart-shaped curve generated by a point on a circle that rolls without slipping on another fixed circle of the same diameter.
• Caribbean spiny lobsterPanulirus argus
• catadromousfish that are born in saltwater, migrate into freshwater as juveniles where they grow into adults, before migrating back into the ocean to spawn.
• caudal peduncleThe narrow part of the body to which the caudal fin (or tail) attaches to the body.
• cavitationformation of gas-filled cavities in liquids in motion when the pressure is reduced to a critical value. Lowpressure regions are often created by rotating ship propellers. As the propellers rotate, bubbles form in the water. A loud acoustic sound is created when these bubbles collapse.
• center frequencywhen describing a sonar system, the frequency with the highest intensity, usually listed as the operating frequency of the sonar.
• central nervous systemthe complex of nerve tissues that controls the activities of the body. In vertebrates it comprises the brain and spinal cord.
• cephalopodsquid, cuttlefish, octopods, and nautilus.
• cetaceanorder of mammals that includes whales, dolphins and porpoises
• Channel catfishIctalurus punctatus
• characteristic acoustic impedancethespecific acoustic impedance of aplane wave propagating horizontally.
• characteristic impedancea material property of a medium, defined as thedensity of themedium times the sound speed through the medium.
• chelaehinged, pincer-like claws at the end of certain limbs of some crustaceans and arachnids (e.g. crabs, lobsters, and scorpions). Typically,chelae are curved and sharply pointed and are used for feeding, defense, andcourtship. They can be referred to as claws, nippers, or pincers; legsbearing chelae are calledchelipeds.
• chelipedone of the pair of legs that bears the large chelae in decapodcrustaceans. A male fiddler crab has an enlarged claw or cheliped.
• Chinook salmonOncorhynchus tshawytscha 
• chirpa signal in which thefrequency changes with time; the opposite type of signal is a pure-frequency tone where the frequency remains the same throughout thesignal.
• chordotonal organsfor Crustaceans, they are located at the joint segments and they serve asmechanoreceptors (sensory organs).
• chronicdeveloping over an extendedperiod of time and long-lasting.Chronic conditions are long term in nature, and usually have slow to develop symptoms that potentially worsen over time.
• cichlidsfamily (Cichlidae) of freshwaterfishes found throughout tropical and subtropical waters of the Americas, Africa and parts of Asia
• ciliahair cells of the neuromast
• circumferencethe enclosing boundary (perimeter) of a curved geometric figure, especially a circle.
• circumpolarlocated around or found in one of Earth's polar regions
• Clayboth a grain size (1µm - 3.9 µm) and a type of aluminum silicate mineral
• cleaner shrimpPericlimenes longicarpus
• clicka short pulse of sound, often used to describe pulses produced by toothed whales for echolocation.
• click trainrapid sequence of clicks, produced by whales and dolphins, that are associated with echolocation. Theclicks are emitted from themelon of the whale.
• climatologista scientist who studies climate
• clupeidsfish belonging to the herring family
• coalescedfused or grown together
• cochleathe spiral-shaped chamber within the inner ear that transforms sound waves into nerve impulses. Thecochlea is a fluid-filled organ that houses many structures related to hearing, including the basilar membrane and theorgan of Corti. It is considered the organ of hearing.
• codGadus morhua
• coelenteratesa group of aquatic invertebrates that includes jellyfishes, corals, and sea anemones. They are distinguished by having a saclike body with a single opening ringed with tentacles.
• common carpCyprinus carpio carpio
• Common cockleCerastoderma edule
• common damselfishPomacentrus amboinensis
• common dolphinDelphinus capensis (long-beakedcommon dolphin), Delphinus delphis (short-beaked common dolphin)
• common octopusOctopus vulgaris
• common prawnPalaemon serratus
• communication spacethe area over which one individual can detect the signal of another.
• complementary angletwo angles are complementary when they add up to 90°.
• Comprehensive Nuclear-Test-Ban TreatyTheComprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosions on Earth whether for military or for peaceful purposes. It was adopted by the United NAtions General Assembly in 1996. The treaty contains provisions for monitoring which include acoustic monitoring. The treaty is not yet in force because it has not been ratified by(...)
• conditioned responsea response that becomes associated with a previously unrelated stimulus as a result of pairing the stimulus with another stimulus normally yielding the response.
• conductivity-temperature-depth (CTD)oceanographic tool used to determine the essential physical properties of sea water: conductivity (salinity),temperature, and depth. Depth measurements arederived from measurement ofhydrostatic pressure and salinity is measured from electrical conductivity. The CTD may be incorporated into an array of sampling bottles referred to as a(...)
• conspecificanimals (or plants) belonging to the same species
• contact callssounds produced by closely associated conspecifics (individuals of the same species) as a means of keeping in touch.Contact calls are important for individual, mate, and kin recognition as well as group cohesion and movement coordination. A wide variety of social information can be encoded in the acoustic structure of contact calls.
• continental shelfthe gently sloping undersea region between a continent and the deep ocean.
• continuous wave pulsea single frequency tone when referring tosonar signals
• corticosteroida type of hormone produced by the adrenal glands. Corticosteroids levels may be elevated as a response tostress.
• courtshipbehaviors in animals, that are used to initiate mating
• critical anglethe arrival angle at which a soundwave traveling from one medium to anothermedium will berefracted along the interface of the two media. If a wave traveling from one medium to another medium with a higher speed of sound hits the interface between the twomedia at an arrival angle less than thecritical angle, only reflection will occur; at(...)
• critical bandwidththebandwidth of amasking sound at which thedetection threshold of a tone at the center of the masking sound ceases to increase with increasing width of the masking bandwidth; an estimate of the bandwidth of the auditory filter at thecenter frequency.
• critical habitatspecific geographic area(s) that contains features essential for the conservation of athreatened orendangered species and that may require special management and protection.
• critical ratiothe ratio, indecibels, of the signal power to the noise power in a 1-Hz band (centered at the testfrequency) required to reliably detect asignal at some predetermined level of correctness
• critically endangeredA category on the IUCN Red List of Threatened Species which indicates a taxon is considered to be facing an extremely high risk ofextinction in the wild.
• crustaceansa class of mainly aquatic, gill-breathing arthropods such as crabs, lobsters, shrimp, and barnacles. They usually have a hard exoskeleton and two pairs of antennae.
• cSELmeasurement of the total energy of a sound event over a specified time period, considering both the intensity and duration of exposure. The measurement is performed on the time series data and is displayed inlogarithmic units (e.g., dB SPL).
• ctenophoregelatinous, aquatic invertebrate also known as a "comb jelly". They use rows ofcilia ("combs") to swim. Most species have eight strips, called comb rows, that run the length of their bodies and bear comb-like bands of cilia, called "ctenes". When the cilia beat, those of each comb touch the comb below . The name "ctenophora" means(...)
• cumulative sound exposure levelmeasurement of the total energy of a sound event over a specified time period, considering both theintensity and duration of exposure. The measurement is performed on the time series data and is displayed in logarithmic units (e.g., dB SPL).
• cupulagel-like cover ofcilia in the neuromast
• Cycleone complete vibration of a particle through a wave, e.g., from equilibrium to the crest through equilibrium to the trough and back toequilibrium.
• cylindricalHaving straight parallel sides and a circular or oval cross-section; in the shape or form of a cylinder.
• cylindrical spreadingenergy spreading out from asound source in the shape of a cylinder; no energy radiates above the top or below the bottom of the cylinder
• dB peaka unit of relative pressure when the pressure of the soundwave is characterized as thepeak pressure.
• dB peak-peaka unit of relativepressure when the pressure of the sound wave is characterized as thepeak-to-peak pressure.
• decapod crustaceancrustacean that has five pairs of walking legs, a segmented body, and chitinousexoskeleton. Examples include lobsters, crayfish, crabs, shrimps, and prawns.
• decibela relative unit used to describe sound intensities. Written as dB. See Advanced Topic: Introduction to Decibels.
• decompression sicknessknown as the bends, a condition that occurs in deep-sea divers caused by the formation of nitrogen bubbles in the blood and tissues following a sudden decrease in the surrounding pressure. This occurs when ascending rapidly from a deep dive and is characterized by severe pains in the joints and chest, skin irritation, cramps, and paralysis.
• Deep Scattering Layer (DSL)a region in the water column where there is a high density of marine organisms that reflect sound.
• delphinidcetaceans of the family Delphinidae, the most diverse ofcetacean families. Includes oceanic whales and dolphins, such as,killer whales, pilot whales, common dolphins andbottlenose dolphins
• demersalliving and/or feeding on or near the bottom of seas or lakes.
• densitythe distribution of a quantity (such as mass, electricity, or energy) per unit usually of space (such as length, area, or volume); the degree of compactness or concentration of a substance.
• depredatethe removal and/or damage of netted or hooked fish and bait from fishing gear. Generally, to prey upon, to make a prey of.
• derivedformed or developed from something else; not original. NOTE: different areas of science have more specialized definitions for this term (e.g. in paleontology, derived characteristics means something has evolved to fit a particularpressure).
• detection probability p(D)the probability of correctly deciding on the basis of a statistical test that a signal is present when it is in fact present.
• detection thresholdthe signal-to-noise ratio (SNR) (in decibels) required to achieve a specified probability of detection p(D) for a given probability offalse alarm p(FA) when deciding whether or not a signal is present at a receiver.
• detonationto explode
• diadromousmigrating between saltwater and freshwater to complete a lifecycle.
• dialectvocalizations or calls of cetaceans that arestereotyped, distinctive, and discrete to a particular group orpod.
• dielhaving a 24 hourperiod
• DIFARDirectional Frequency Analysis and Recording device;passive acousticsonobuoy
• Differentiating depthEqual to ten acoustic wavelenghts; the water depth, based on the frequency of thesignal, that determines whether modeling is ocurring in an acoustically deep or shallow water over space and across time.
• diffusethe spreading out of molecules or atoms (or energy), generally away from from higher concentrations
• digital datainformation that is represented in a coded form, as a series of zeros and ones
• digital signala series of samples to represent a continuous analog signal.
• dinner bell "effect"when an underwater sound (or some other stimulant) acts like a dinner bell, alerting and attracting an animal to the presence of a food source.
• directionalproducing or receiving sound only from certain angles or directions
• displacementthe linear distance in a given direction between a point and a reference position.
• distributionthefrequency of occurrence of a specific value in a set of measurements.
• diurnalof or during the day.
• domino damselfishDascyllus trimaculatus
• doppler effectthe raising or lowering of the frequency of a sound due to the motion of the source of the sound relative to the listener. The most common example is the rising frequency of a train whistle as the train approaches.
• dorsalof or pertaining to the upper surface.
• dorsal finthe main fin found on the back of fishes and some marine mammals. Some whales, such as the killer whale, have talldorsal fins, while other whales (i.e. belugas and bowheads) have nodorsal fin.
• downsweepa signal that decreases infrequency over time.
• drummingto vibrate a muscle in, on, or near, theswim bladder that produces a loud, low-pitched grunt sound
• ductsinternal passage involved in the flow of fluids through an organism
• DugongDugong dugon
• durationthe length of a sound in seconds.
• duty cyclethe time period or fraction of one time period in which asignal or system is active
• echinodermmarine invertebrates with tube feet and five-part radially symmetrical bodies. The group includes sea urchins, sea stars, sea cucumbers, brittle stars, and crinoids.
• echo-countingwhen individual (sonar) targets are spaced far enough apart that they can be distinguished from one another, the number of targets are counted (and the number of fish estimated).
• echo-integrationwhen more than one target (e.g. a fish school) is located in an acoustic beam at the same depth, and it is not possible to resolve them separately.  The total acoustic energy backscattered by the school or aggregation is integrated together, and this total is divided by the (previously determined) backscattering coefficient of a single(...)
• echo rangingdetermining the distance to an object by measuring the time between transmitting a sound signal and hearing its echo.
• echo signaturea unique sonar return (reflection) that can be used to identify individual species of marine organisms, such as fish, or other submerged objects
• echolocationa process for locating distant or hard-to-see objects using thereflection of sound waves. The distance of objects or depth of the seafloor can be determined by measuring the time it takes forreflected soundwaves (echoes) to return to the sound source. Some whales and dolphins useecholocation to identify underwater objects and to help find food.
• echosounderan instrument that uses sound echoes to determine the water depth. The instrument emits sound waves that travel to the bottom of the ocean and are reflected back. Depth is determined by timing how long it takes the soundpulse to leave the instrument, travel to the seafloor, and return to thereceiver on the ship.
• echosoundingthe technique of measuring the depth of a body of water by means of anechosounder, an electrical depth sounder that uses sound echoes. The instrument emits sound waves that travel to the bottom of the ocean and are reflected back. Depth is determined by timing how long it takes the sound pulse to leave the instrument, travel to the seafloor,(...)
• ecological risk assessmentthe process of calculating the probability of adverse ecological effects
• ecologythe scientific study of the relationship between organisms and their environment.
• ecotypeecologically distinct groups or communities; in this case, groups exhibiting different dietary specializations and corresponding behavioral adaptions, such as hunting techniques and acoustic repertoires.
• eddyenergetic, swirling, unsteady flows that are found almost everywhere in the ocean
• eDNAorganismal DNA that can be found in the environment.Environmental DNA (eDNA) originates from cellular material shed by organisms (via skin, excrement, etc.), which can be collected and monitored using molecular methods.
• effective source levelthesource level of an array when considered as a singleomnidirectional sound source
• efferentmoving or carrying outward or away from a central part. For example:efferent blood vessels carrying blood away from the heart or efferent nerves carrying signals away from the brain.
• EigenrayPropagating rays that connect thesound source and receiver in ray tracing mdoels.
• elasmobrancha group of cartilaginous fish that comprises the sharks, rays, and skates.
• elasmobranchsa group of fishes, including sharks, rays and skates, that has a skeleton made of cartilage rather than bone; they also do not have a swim bladder.
• electro-physiological responsethe electrical activity of neurons when stimulated (seeauditory brainstem response (ABR)).
• elephant sealMirounga
• endangeredany species that is in danger of extinction
• endemicnative to or prevalent in a particular area or region; not found in other places.
• ensonifiedfilled with sound.
• entanglementwhales, seals, sea lions, and other marine animals may come into contact with lost or active fishing gear, causing the gear to become twisted around their bodies and/or snagged on different body parts. When this occurs, the animal is considered entangled.
• epicenterthe point on the earth's surface (on land or underwater) vertically above the focus of an earthquake.
• Epicenterthe surface location of an earthquake.
• epitheliuma type of body tissue that forms the covering on all internal and external surfaces of he body, lines body cavities and hollow organs, and is the major tissue in glands.
• equal energy hypothesisassumption that sounds of equal SELcum produce an equal risk for hearing loss (i.e., if the SELcum of two sources are similar, a sound from a lower level source with a longer exposureduration may have similar risks to a shorter duration exposure from a higher level source).
• equal latencythe assumption in hearing studies that sounds that are perceived to be equally loud result in equal response times, thereby allowing response time to be a proxy for perceivedloudness.
• equal loudness curvea graph of theperceived intensity (loudness) of sounds. The loudness of a sound is different for different frequencies.
• equilibriumthe rest position of the particles in amedium
• essential fish habitat (EFH)those waters andsubstrate necessary for fish forspawning, feeding, or growth to maturity.
• estuarya coastal body of water formed when freshwater from rivers and streams flows into the ocean, mixing with the seawater.Estuaries and the lands surrounding them are places of transition from land to sea, and from freshwater to saltwater. Although influenced by the tides, estuaries are protected from the full force of oceanwaves, winds, and(...)
• European perchPerca fluviatilis
• European sea bassDicentrarchus labrax
• European spiny lobsterPalinurus elephas
• exoskeletona hard outer structure, such as thecarapace of a lobster or crab, that provides protection or support for an organism (especiallyinvertebrates).
• expendable bathythermographa probe which is dropped from a ship and measures the temperature as it falls through the water. Two very small wires transmit the temperature data to the ship where it is recorded for later analysis. The probe is designed to fall at a known rate, so that the depth of the probe can be inferred from the time since it was launched. By plotting(...)
• explosive sound sourcea device that uses explosive material to generate controlled acoustic energy.
• extantstill existing; not extinct.
• extinctionthe end of an organism or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species (although the capacity to reproduce and recover may have been lost before this point).
• extirpationthe movement of an entirepopulation out of a region
• extrapolateto estimate or expand unknown data based on known facts and/or observations.
• extrapolationusing evidence and inferences from a similar situation to project information about a related event or process.Extrapolation can also be used to apply or transfer experimental observations from a model to the real world.
• false alarmincorrectly deciding on the basis of a statisticaltest that a signal is present when it is in fact absent. Afalse positive.
• false alarm probability p(FA)the probability of incorrectly deciding on the basis of a statistical test that asignal is present when it is in fact absent.
• false killer whalePseudorca crassidens
• false negativean error when one concludes that there is not a real difference between two means when, in fact, there is a difference; also called aType II error.
• false positivean error when one concludes that there is a real difference between two means when, in fact, there is not; also called aType I error.
• far fieldthesound field at a distance from a soundsource array where the wave fronts created by the individual sound sources are in phase
• fat embolia fat globule in the bloodstream that is often caused by physical trauma such as fracture of long bones, soft tissue traum, or burns.
• fathead minnowPimephales promelas
• fecund, prolificfruitful inoffspring or vegetation
• fertilitythe ability to produce offspring; fecundity.Fertility rate is the number of offspring born per mating pair, individual, or population.
• filteringasignal processing technique that selectsfrequencies of interest during the analysis of signals.
• fin whaleBalaenoptera physalus
• finfishteleost bonyfishes, in other words, not sharks/skates/rays, and not shellfish.
• finless porpoiseNeophocaena phocaenoides
• fisherythe industry or occupation devoted to the catching, processing, or selling of fish, shellfish, or other aquatic animals.
• fishestwo or more fish species. For example, if you have three fish species in an aquarium (such as a clownfish, damselfish, and goby), you would say "three fishes." If you have three clownfish (all of the same species), you would say "three fish".
• flukethe two lobes of a whale tail.
• focal animal observationsobservations concentrated on individual animals that record everything they do
• foragingto search for food
• foraging behaviorthe way in which an animal searches for food; the process, or series of actions, that an animal goes through to find food
• FranciscanaPontoporia blainvillei, Also known as: La Plata dolphin, toninha, cachimbo, boto amarelo
• Franciscana dolphinPontoporia blainvillei
• frequencythe rate of repetition of a regular event. The number ofcycles of a wave per second. Expressed in units ofHertz (Hz)
• frequency modulated pulsea tone that changes in frequency over its duration. The frequency change can be from lower to higherfrequency (upsweep) or from higher to lower frequency (downsweep).
• frequency modulationvariation of the frequency of a carrierwave in accordance with the characteristics of a signal.
• Frequency selectivitythe ability of an animal to discern thefrequency of one sound in the presence of sounds of different frequencies.
• frequency spectruma graph of a sound that plots the intensity of each frequency in the sound. Plural is spectra.
• frequency weightinga method for quantitatively compensating for the fact the animals do not hear equally well at all frequencies within theirhearing range.
• fright responseresponding out of fear
• fronta boundary between two water masses with differing properties such astemperature andsalinity
• Full wave equationA partial differential equation that describes how a quantity (e.g. pressure) changes over space and across time.
• fundamental frequencythe lowest frequency in a complex wave.
• ganglion cellsnerve cells that have their cell bodies outside of the central nervous system (the brain and spinal cord). Auditoryganglion cells carry sound information from the inner hair cells to the auditory nerve.s
• gas glanda modification of the inner lining of the bladder, which works with therete mirabile to force gases into the bladder
• Gated Continuous WavesSimple and good Doppler sensitivity but does not have a high BT.
• goldfishCarassius auratus auratus
• goliath grouperEpinephelus itajara
• goose-beaked whaleZiphius cavirostrisalso known as Cuvier's beaked whale
• gray triggerfishBalistes capriscu
• gray whaleEschrichitus robustus
• grazing anglethe angle formed by the incident ray or thereflected ray and the plane(surface).
• Great cormorantPhalacrocroax carbo sinensis
• great white sharkCarcharodon carcharias
• Green sea turtleChelonia mydas
• greenhouse gasa gas that traps heat in the atmosphere.
• grey sealHalichoerus grypus
• gross tonnagea measure of the cargo carrying capacity or the volume of a ship.
• ground truthinformation, or the determination of facts, provided by direct observation.  Often performed to check the accuracy of data or other observations.
• gudgeonGobio gobio
• habitat impedimenta hindrance or obstruction that restricts migratory movements and/or prevents a species from accessing habitat necessary for spawning,foraging, and other activities.
• habituateto become accustomed to something through repeated or prolonged exposure
• haddockMelanogrammus aeglefinus
• hair cellsmechano-transducers that detect energy or pressure changes. They are complex structures that include a cell body on the surface of a membrane. At the base of thehair cell are one or more neural synapses. On the upper surface of the hair cell are hair-like projections calledstereocilia, commonly in bundles. These stereocila bend in(...)
• hakeMerluccius merluccius
• harbor porpoisePhocoena phocoena
• harbor sealPhoca vitulina
• harmonic distortiondistortion of apure tone associated with the presence of undesired harmonics atfrequencies that are a multiple of thefundamental frequency of the signal.
• harmonic frequencythe part of asignal whosefrequency is an integer multiple of the fundamental frequency. Harmonic frequencies are related to each other by simple whole number ratios, for example if the fundamental frequency is f, the harmonics have frequencies of 2f, 3f, 4f, etc.
• hawaiian monk sealMonachus schauinslandi
• Heard Island Feasibility Test (HIFT)an expedition to Heard Island in the southern Indian Ocean during which acoustic sources suspended below a ship transmitted acoustic signals to receivers around the globe. Heard Island was selected because signals transmitted from that location can reach both coasts of North America. HIFT showed that underwater acoustic signals could be(...)
• hearing generalista fish species in which the swim bladder aids very little or not at all in hearing sensitivity
• hearing groupsgroups of marine mammals defined by the generalized range offrequencies that species in the group can hear.
• hearing rangethe range of frequencies the ear of an animal can detect.
• hearing thresholdthe minimumintensity at which a sound of a specificfrequency is reliably detected in absolute quiet conditions. The intensity level varies with frequency. Also calledthreshold of hearing.
• heavy oilvery thick oil that has little to no evaporation and/or dissolution properties and weathers very slowly.Heavy oil is depleted in hydrogen relative tolight oil, and fewer refined products are derived from heavy oil. Cleanup of heavy oils is also very difficult.  Heavy crude oil is an example of aheavy oil.
• hemorrhagesflow of blood from a ruptured blood vessels; excessive bleeding
• herbivorean organism that feeds mostly on plants.
• hermaphroditican animal or plant having both male and female reproductive organs
• Hertzthe unit of frequency; the number of cycles, or wavelengths, in a second (cycles/second)
• hierarchya system or organization in which people, animals, or groups are ranked one above the other according to status or authority.
• High Arcticthe northernmost part of the Arctic, including thecircumpolar Arctic Ocean with its surface ice and its most northerly coastal margins and islands.
• histograma representation of a distribution by means of rectangles whose widths represent class intervals and whose areas are proportional to the corresponding frequencies of occurrence.
• homologoussimilar in position, structure, and evolutionary origin but not necessarily in function.
• hullthe main body of a ship or vessel (most of which goes under the water), including the bottom, sides, and deck but not the masts, superstructure, rigging, engines, and other fittings.
• humpback whaleMegaptera novaeangliae
• hydratewater ice with methane molecules trapped within the ice structure.
• hydraulic hammera large, industrial hammer that is operated by a fluid that is underpressure (hydraulics). Ahydraulic hammer is a modern type of piling hammer used in place of diesel and air hammers for driving steel pipe, precast concrete, and timber piles.
• hydroacousticacoustics in water
• hydrocarbon an organic compound containing only hydrogen and carbon; often occurring in crude oil, natural gas, and coal, as well as plant life.
• hydrodynamicof, relating to, or operated by the force of liquid in motion
• hydrofoila vessel that is lifted partially above the water by wing-like structures mounted on struts below thehull of a boat.
• hydrokineticthe conversion ofkinetic energy produced by flowing water into electricity, or other forms of energy.
• hydrophonean underwater microphone that will listen to, or pick up, acoustic signals. A hydrophone converts acoustic energy into electrical energy and is used in passive underwater systems to listen only.
• hydrophone arrayseveral hydrophones attached to each other at known fixed distances so the location of sound sources can be calculated.
• hydrostatic pressureThe pressure at a point in a fluid at rest due to the weight of the fluid above it.
• hydrothermalrelating to hot water circulation in the ocean crust.
• Hydrothermalrelating to hot water circulation in the ocean crust.
• hydrothermal venta hot spring on the seafloor
• hyperthermiaa condition where the body produces or absorbs more heat than it can dissipate, causing one's body temperature to become elevated to a potentially dangerous level.
• hypothermiaa condition where the body loses heat faster than it can produce it, causing one's body temperature to become dangerously low.
• hypothesisa tentative explanation proposed by a scientist for observations that cannot be explained by existing scientific theories. A careful statement of a tentative or provisional conclusion to be tested.
• ice floea sheet of floating sea ice.
• ice keelthe underwater portion of an ice ridge.
• IESInverted Echosounder; an instrument used to measure thetemperature of the water column at a single point
• immunological responsea bodily defense reaction that recognizes an invading substance (such as a virus, fungus, or bacteria, or a transplanted organ) and produces antibodies specific to that invading substance.
• impulsive sounda broadband signal generated by sound sources such as explosions and airguns in which the sound pressure is very large at the instant of the explosion and then decays rapidly away; theduration of the peakpressure pulse is usually only a few milliseconds.
• incident wavethe wave moving towards thereflector
• Infaunamarine animals that live in the seafloor such as clams or worms
• infrasonicsoundwaves that have afrequency that is lower than what humans can hear (i.e. below about 20 hertz).Baleen whales, such as blue andfin whales, produce these low frequency sounds. The sounds may be used to communicate over long distances and to detect large-scale topography of the seafloor. On land, elephants also use these powerful(...)
• inhomogeneitiesparts that are not the same as the larger whole or not uniform in composition
• inner earthe innermost part of the ear that is surrounded by the skull bone. It contains the organs of balance and hearing. The inner ear contains thevestibular system that helps maintain our balance. It also contains the cochlea that transforms sound waves into nerve impulses that are carried to the brain.
• intensitythe average amount of soundpower (sound energy per unit time) transmitted through a unit area in a specified direction. The unit of intensity is watts per square meter. For simplicity, the magnitude of theintensity is often referred to as the intensity, without specifying the direction in which the sound is traveling.
• inter-click intervalthe time it takes an echolocation signal to be sent out and an echo to return, combined with the time the animal needs to receive and process that echo.
• interface wavea type of wave that is only found at the interface between two dissimilar media such as at the boundary of the sea floor and the ocean
• invertebratean animal that lacks a backbone (marine examples include lobsters, shrimp, squid, clams, crabs, and sea stars).
• ionan atom or a group of atoms that has an electric charge. Positive ions, or cations, are formed by the loss of electrons; negative ions, or anions, are formed by the gain of electrons.
• isochronoushappening at regular intervals
• kelp rockfishSebastes atrovirens
• kerplunkstechnique used by dolphins to drive fish away from protected areas such as sea grass beds. A dolphin will lift its tail and lower body out of the water and crash it down on the water surface. This causes a loud splash and creates a trail of bubbles under the water. The bubbles startle the fish hiding in the seagrass and flush them from their(...)
• keystonea species on which other species in an ecosystem largely depend, such that if it were removed, the ecosystem would drastically change
• killer whaleOrcinus orca
• KinaEvechinus chloroticus
• kinetic energythe energy possessed by a system or object as a result of its motion.
• knotsa unit of speed equal to one nautical mile (1.852 km) per hour, approximately 1.151 mph.
• krillsmall, shrimp-like invertebrates (also calledeuphausiids) that swarm in dense patches within the water column or at the sea surface. They have hard mouths and tail parts that reflect sound.Krill is an important food source for many marine organisms including whales and seals.
• labyrintha complex system of interconnecting bony or membranous cavities, particularly those concerned with hearing and balance
• ladyfishElops saurus
• Lake sturgeonAcipenser fulvescens
• lanugothe soft, downy hair that covers some newborn mammals; in Arctic seals, it is a white fur that is highly prized by seal hunters, most famously associated with the hunting of harp seal pups
• Largemouth bassMicropterus salmoides
• laryngeal sacan inflatable “pouch”, or often a pair of pouches, that are generally locatedventral to thelarynx in many mammals, particularly in primates (but not in humans), hooved mammals (e.g., reindeer, horses, antelopes), and cetaceans. The functions of laryngeal sacs are not completely understood. Like the vocal sacs of frogs, laryngeal sacs may(...)
• larynxthe upper part of thetrachea (air passage) that contains the vocal folds
• lateral linesensory organ, found in fishes, that runs long the length of their body. Thelateral line allows fish to sense movement.
• latitudethe angular distance of a place north or south of the earth's equator, or of a celestial object north or south of the celestial equator, usually expressed in degrees and minutes.
• leachateliquid that has dissolved or entrained environmentally harmful substances that may then enter the environment.
• leopard sealHydrurga leptonyx
• leopard sharkTriakis semifasciata
• LIDARa remote sensing method usingfrequencies of light that penetrate water and are used for mapping clear rivers and shallow coastalbathymetry from the air.
• ligamentsstrong, flexible bands of tissue that hold two or more bones together at moveable joints. They help restrain the movement of bones at the joint.
• light detection and ranginga remote sensing method using frequencies of light that penetrate water and are used for mapping clear rivers and shallow coastal bathymetry from the air.
• light oilvery fluid oil that has a strong odor, high concentrations of soluble, toxic compounds, and a high evaporation rate. Light oils consist largely of benzene and toluene.  Gasoline and diesel fuel are examples of light oils.
• little skateRaja erinacea
• localizedetermine the direction the sound is coming from.
• LOFARLow Frequency and Ranging sonobuoy; a type of passive acoustic sonobuoy
• logarithmicof, relating to, or expressed in terms of logarithms. A logarithm is the power to which a base, such as 10, must be raised to produce a given number.
• Lombard Effectthe unconscious tendency of a person or animal to raise and/or lower their voice when going from a relatively quiet to a noisy environment and vice versa
• Long-spined sea urchinDiadema setosum
• longfin squidLoligo pealeii
• longitudinal wavea disturbance in which the particles and the energy move in the same direction
• loudnesshow loud a person perceives a sound to be. Not the same as the intensity of the sound. The perceivedloudness varies withfrequency.
• lunge-feedinga method of feeding underwater in which the predator moves forward with its mouth open, engulfing the prey along with the water surrounding it.
• Lusitanian toadfishHalobatrachus didactylus
• magnetic resonance imaging (MRI)method of producing a three-dimensional image of object by recording the signals the object emits when placed in a magnetic field
• manateeLarge, herbivorous, aquatic mammal that inhabits warm coastal and inland waters of the southeastern U.S., West Indies, northern South America, and West Africa. Manatees have a robust, rounded body, small head, paddle-shaped flippers, and a flattened, rounded tail. The animals are members of the genus Trichechus.
• mandibleone of the jaw structures of animals. For example, in vertebrates, it is the lower jaw bone; in insects it is one of the anterior mouth parts.
• marine foulingthe accumulation of microorganisms, plants, algae, and/or animals on surfaces immersed in the ocean.  Buildup on marine vessels poses a significant problem.
• marine vibroseisa technique for creating a geophysical survey sound source by displacing a volume of water with a vibrating plate or shell to create a pressurewave. Also called amarine vibrator.
• maskingreduced ability to detect, recognize, or understand sounds of interest because of interference by other sounds
• masking soundssounds that compete with sounds of interest for reception and processing in the ear of an animal. Also known as "maskers".
• mass strandingastranding event where 2 or more animals, excluding mother-calf pairs, unless a third animal strands, strand together in time and place.
• matched-filter processingto detect and classify signals of sound sources within acoustic recordings by comparing against knownsignal (matched filtering).
• matched filteringto detect and classify signals of sound sources within acoustic recordings by comparing against known signals (matched-filter processing).
• meanthe average of a set of measurements defined to be the sum of all of the measurements divided by the number of measurements.
• mechanoreceptorssensory organs that cause response todisplacement, pressure and vibrations
• medianthe "middle" value in the list of numbers. To find themedian, observations are arranged in order from smallest to largest value. If there is an odd number of observations, the median is the middle value. If there is an even number of observations, the median is the average of the two middle values.
• mediumsubstance or material that carries or transports the wave from its source to other locations. In the open ocean, the medium through which the wave travels is the ocean water.
• melonlipid-filled sac in the forehead of whales that helps to focus sound
• Melon-headed whalePeponocephala electra
• mesopelagic boundary communitysmall (less than 4 inches long)fishes, shrimps, and squids that live in the middle of the water column and near islands
• metamorphosisthe process of transformation from an immature form to an adult form.
• methane fluxrate of movement of methane from one reservoir to another, between seafloor sediments and the water column.
• Mid-frequency Active sonarA navalsonar system primarily used to detect submarines, defined as a sonar that emits in the frequencies from 1kHz to 10kHz by the U.S. Navy. Often abbreviated MFA.
• mid-ocean ridgeunderwater mountain chain where new ocean crust is created.
• Mid-ocean ridgeunderwater mountain chain where new ocean crust is created.
• middle earthe air-filled cavity that lies between theouter ear and theinner ear. Themiddle ear contains theossicles which conduct sound vibration from the eardrum to the inner ear.
• migrationmovement of a group of animals from one location to another
• common minke whaleBalaenoptera acutorostrata
• missIncorrectly deciding on the basis of a statistical test that a signal is absent when it is in fact present. Afalse negative.
• mitigateto make (something) less severe or harmful.
• mollusksinvertebrates that possess a soft, unsegmented body and live in aquatic or damp habitats. Many have an external, calcareous shell (although some do not). Phylum Mollusca is the second-largest phylum of invertebrate animals after the arthropods (Arthropoda), and includes gastropods (e.g. snails and slugs),cephalopods (e.g. octopuses), and(...)
• moltto shed the outer covering, or shell, which is then replaced by a new shell that is produced by the organism
• monostatic sonarwhen thesound source andreceiver are located in the same place
• mooringequipment (often consisting of anchors and chains) which holds an item (such as a boat or underwater instrument) stable and secure in one place
• moratoriuma temporary prohibition of an activity.
• moratoriumthe suspension (postponement and/or delay) of a particular activity.
• morphologythe form and structure of an organism or any of its parts
• mudflat fiddler crabUca rapax
• multi-channel seismicsusing multiplehydrophone arrays orstreamers to record the reflected and refracted sounds from an air gun array
• multibeam sonara sonar system that emits soundwaves in a fan shape toward the sea floor and can measure the ocean depth over a wideswath.
• multiyear icesea ice that has survived at least more than one melting season (i.e. one summer). Multiyear ice contains much less brine and more air pockets than first-year ice. Less brine means "stiffer" ice that is more difficult for icebreakers to navigate and clear.
• myctophid fishany of the numerous small, deep-sea fishes of the family Myctophidae that have bioluminescent light organs on the head and sides and that often swim to the surface at night.
• Mysticetesthese largecetaceans are usually more than 9.1 m (30 ft) long and can be found throughout the ocean. Instead of teeth, mysticetes have a series of horny plates called baleen. The baleen is made from the same materials as human hair and fingernails. Thebaleen plates hang from the gums of the upper jaw and are used to filter small bits of(...)
• narial passagesthe air spaces that connect the throat region with the openings of the nose, known as the nares. It is also sometimes referred to as the nasal passages.
• narrowbandsounds made up of only a small range offrequencies
• narwhalMonodon monoceros
• natalgrown, produced, or originating in a particular place or in the vicinity (of, relating to, or present at birth).
• near fieldthe sound field near a sound source array where complex constructive and destructive interference occurs among the wave fronts created by the individual sound sources
• necropsiesthe examination and dissection of a body to determine the cause of death; autopsy
• NeMO NetNew Millennium Observatory Network; a project, which records and transmits daily temperature andpressure readings from Axial Volcano
• Neural impulsesan electrical and chemical signal sent along nerve fibers
• neuromastssmall, sensory receptors of arrangedhair cells located along the lateral line, which respond to motion between the fish and the surrounding water
• new england musselMytilus edilus
• noisean unwanted sound or a sound that interferes with the perception of anothersignal, whether it be through recording or hearing.
• nominalaccording to plan, usual, or expected.
• non-vocal soundssounds made without the use of vocal folds or other body parts whose primary function is moving air for sound production. These sounds are typically made by slapping a body part on the water or land surface, or by forcefully clapping body parts together.Non-vocal sounds may be used to communicate acoustically.
• normal linea line that is perpendicular (makes a 90 degree angle) to a surface
• North Atlantic right whaleEubalaena glacialis
• North Pacific right whaleEubalaena japonica
• Northern bottlenose whaleHyperoodon ampullatus
• Northern elephant sealMirounga angustirostris
• Northern fur sealCallorhinus ursinus
• Northern seahorseHippocampus erectus
• Northern shrimpPandalus borealis
• Atlantic herringClupea harengus
• null decisioncorrectly deciding on the basis of a statisticaltest that a signal is absent when it is in fact absent.
• null hypothesisthehypothesis that there is not a real difference between the means of two data sets.
• Nyquist ratetwice the highest frequency in an analog signal (acousticsignal)
• ocean acidificationa reduction in thepH of the ocean over an extendedperiod of time, caused primarily by uptake of carbon dioxide (CO2) from the atmosphere. When CO2 is absorbed by seawater, chemical reactions occur that reduce seawater pH, carbonateion concentration, and saturation states of biologically important calcium carbonate minerals. These chemical(...)
• ocean frontthe interface between two water masses of different  physical  characteristics
• ocean observatorya networked array of sensor systems that measure the physical, chemical, geological and biological variables in the ocean and seafloor as well as the overlying atmosphere.
• oceanographic variablea characteristic of the ocean that changes
• octave band soundsound over a range of frequencies where the frequency in Hertz of the upper end of the range is twice thefrequency of the lower end.
• octavo-lateralis systemcomprised of the lateral line and inner ear of fish; provides fish with balance, hearing, and the ability to feel vibrations from a distance
• odontocetegroup of mammals that includes the toothed cetaceans. This includes some whales (such assperm whales, orca or killer whales, and beaked whales) as well as all dolphins and porpoises.
• offspringnext generation or baby of a certain species
• olfactory organan organ for smelling
• omnidirectionalhaving nodirectional component; producing or receiving sounds from all directions
• omnivorean organism that eats plants and animals.
• omnivorousorganisms that eat both animals and plants
• opportunistic feedinga type of foraging in which an animal feeds on a wide variety of prey and is able to adapt to whatever food becomes available.
• oral cavitythe mouth, which forms the first chamber of the digestive system. It includes the space surrounded by the lips, teeth, hard and soft palates, cheeks, and tongue. The oral cavity ends at border of the pharynx, which is approximately the line just anterior to the tonsils.
• organ of Cortithe sensory part of theinner ear that converts sound signals into nerve impulses. Located on thebasilar membrane, it contains sensory cells that transform vibrations into neural code for sound processing by the brain. It contains many important cells including the inner and outer hair cells.
• oscarAstronotus ocellatus
• oscillationa flow periodically changing direction.
• ossiclesthree tiny bones - the incus (anvil), malleus (hammer), and stapes (stirrup) - that lie in the middle ear. The ossicles conduct sound across the middle ear to the inner ear by forming a bridge between the eardrum and theoval window.
• otariids or eared sealsfur seals and sea lions that have visible ear flaps. They have an elongated neck and long front flippers. Their hind flippers can be turned forward for walking on land.
• otolithsmall bones in the inner ear which provide balance, and, in fish, aid in hearing
• ototoxiccausing damage to the ear or its nerve supply.
• outer earthe outermost part of the ear that is external to the ear drum ortympanic membrane. It directs sound waves down the air-filled ear canal onto the eardrum.
• oval squidSepiotheutis lessoniana
• oval windowa membrane-covered opening between themiddle ear and theinner ear. The oval window is connected to the third ear ossicle (stapes) and passes sound vibrations to the inner ear.
• overpressureThe pressure in the shockwave from an explosion that exceeds the existing atmospheric or hydrostatic pressure in the medium through which theshock wave is propagating.
• oyster toadfishOpsanus tau
• Pacific humpback dolphinalso known as the Indo-Pacific humpback dolphin; Sousa chinensis
• Pacific Missile Range Facility (PMRF)a U.S. Naval facility off the island of Kauai, Hawaii, that is the world's largest instrumented, multi-dimensional testing and training missile range. It is the only range in the world where submarines, surface ships, aircraft, and space vehicles can operate and be tracked simultaneously. There are over 1,100 square miles of instrumented(...)
• Pacific oysterMagallana gigas
• Pacific white-sided dolphinLagenorhynchus obliquidens
• pack icea large expanse of floating ice
• pack icea large area of floating ice pieces that have been driven together by wind, currents, etc. to form a nearly continuous mass of ice
• pallid sturgeonScaphirhynchus albus
• pan bonethin bone in the back of the lower jaw that helps transmit sound to the middle ear
• parallelbeing an equal distance apart everywhere, extending in the same direction, never meeting or intersecting
• particle motionthe change in position of a particle with respect to time; in acoustics,particle motion is vibratory motion in which the particles move back and forth around an equilibrium point.
• passive acoustic monitoring (PAM)observation method where an acoustic device is deployed in the ocean to capture sounds from the surrounding environment (the instrument does not produce any sounds). The sounds received by the instrument are identified and classified. PAM has become an important tool in observing cetaceans, especially deep-diving species.
• passive acousticslistening to sound sources; sound is only received.
• passive marginthe transition between oceanic and continental landmasses that is not a plate boundary and therefore experiences little to no volcanic or earthquake activity.
• patchinessdegree of irregular, or uneven, appearance or quality.
• peak pressurethe range inpressure between zero and the greatest pressure of the signal.
• peak pressure/0-to-peak pressurethe range in pressure between zero and the greatestpressure of the signal
• peak-to-peak pressurethe range in pressure between the most negative and the most positive pressure of thesignal
• pectoral finsthe uppermost of the paired fins on a fish
• pectoral flipperforelimbs of whales and dolphins that are used for stability and steering. These appendanges are generally flattened and paddle-like.Humpback whales have very large pectoral flippers, reaching 5 m (15 ft) in length.
• pectoral free raysrays that are part of the fishespectoral fins but are free from the actual fin skin. These rays aid in the movement of the fish.
• pectoral girdlethe bony or cartilaginous arch that supports the forelimbs of avertebrate
• peer-reviewedscientific papers that have been subjected to evaluation by highly qualified experts in the field, the reviewers are usually anonymous and check the papers for inconsistencies, invalid conclusions and editorial errors
• peer reviewa process by which a scholarly work (such as a paper or a research proposal) is checked by a group of experts in the same field to make sure it meets the necessary standards before it is published or accepted
• pelagicof, relating to, or living or occurring in the open ocean.
• pelagic speciesorganisms that swim or drift in the water; these organisms are distinct from those living on or in the bottom sediments.
• perceiveto recognize, discern, or understand.
• Periodthe time duration between any point on a wave and the same point on the next wave, e.g., from onewave crest to the next wave crest; the time for a particle to make one complete cycle at a given point
• permanent threshold shift (PTS)a permanent increase in the threshold of hearing (minimumintensity needed to hear a sound) at a specific frequency above a previously established reference level
• perpendicularbeing at right angles
• pHa figure expressing the acidity or alkalinity of a solution on a logarithmic scale on which 7 is neutral, lower values are more acid, and higher values more alkaline (basic).
• pharyngealteeth located in the gill or throat region
• phasethe location of a point within a wave cycle of a repetitivewaveform, measured as the fraction of awavecycle and often expressed as an angle; one cycle is 360º or 2 π radians.
• phocids or true sealsseals, such asharbor seals, that have no visible ear flap. They have a streamlined body with shortfront flippers. Their hind flippers are directed backward and they are not used for walking on land.
• phona unit of loudness for pure tones that accounts for the perceived loudness of tones; the number ofphon of a sound is thedecibel of a sound at 1 kHz that isperceived to be just as loud.
• photophoreslight producing organs that appear as bright spots on various marine animals, includingfishes and cephalopods.
• physiological stressa reaction to a change that requires a physical, mental or emotional adjustment or response.
• piezoelectric effectthe ability of some materials (notably crystals and certain ceramics) to generate electricity in response to applied mechanical stress
• piezoelectric materiala material that produces electrical charges when subjected topressure changes
• pilot whaleGlobicephala spp.
• pingto query (another computer on a network, or in this case, an acoustictransponder) to determine the location of it.
• pink snapperPagrus auratus
• pink snappersPagrus auratus
• pinna, auriclethe ear flap or outer part of the ear that extends from the head. The pinna funnels sound down the outer ear canal to the eardrum.
• pinnipedgroup of mammals that includes seals, sea lions andwalruses
• pitchan up-or-down movement of the front (bow) of a vessel (ship, glider, etc.).
• pitcha shippitch motion is an up or down, front to back motion.
• plainfin midshipmanPorichthys notatus
• plane wavea wave in which the wave fronts are a series of parallel planes.
• planktivorean aquatic organism that feeds on planktonic food, includingzooplankton and phytoplankton.
• planktonrelatively small organisms that drift or float passively in the water and are carried wherever currents and tides take them.Plankton are often microscopic and are an important food source for other aquatic organisms. There are two types of plankton- phytoplankton (plants and autotrophs) and zooplankton (animals).
• plectrumpart of thespiny lobster that is found underneath the files. It is a soft piece of tissue that is found at the base of the antennae. The plecta is what the lobster pulls over the files to produce sound
• pneumaticcontaining or operated by air or gas under pressure.
• poda social group of whales that are clustered together. Some toothed whales, such as orcas travel in large, sometimes stable pods. They may group together to hunt their prey and/or migrate.
• polar bearUrsus maritimus
• pollackPollachius pollachius
• polypssmall marineinvertebrates that have hard, cup-like, limestone skeletons.Polyps live in large colonies where they take-in the calcium from the ocean and to build a hard shell around themselves. The skeletons grow one on top of one another and as a result a coral reef is able to grow.
• populationthe entire collection of individuals or items from which samples are drawn.
• porositya measure of the pore space in a material, often expressed as a percentage of total volume
• potential energythe energy possessed by an object as a result of its position relative to other objects, stresses within itself, its electric charge, or other factors.    
• powerthe rate at which work is done; the amount of energy transmitted over a given amount of time; or instatistics, the probability of rejecting thenull hypothesis in a statistical test when it is false.
• power spectral density levelthe power present in a signal as a function of frequency, measured in units per Hz.
• precisionthe degree to which repeated measurements under unchanged conditions show the same results; reproducibility; repeatability.
• prehensileadapted for seizing, grasping, or holding, especially by wrapping around an object.
• pressurethe amount of force per unit area measured in units of Pascal (which is defined as 1 Newton acting on an area of 1 square meter).
• pressure ridgea ridge produced on floating ice by buckling or crushing under lateral pressure of wind orwaves (tide).
• pressure wavealongitudinal wave in the seafloor or solid Earth (also called a compression wave)
• profilethe change of anoceanographic variable with water depth
• projectoran instrument that sends out sound waves; consists of a transmitter and a transducer
• projector arraysa collection of individual projectors used together to generate a directional sound beam
• propagationthe movement of sound through amedium.
• pulsea short duration broadband signal.
• pulse traina repetitive series of shortduration,broadband signals that are separated in time by a fixed and often constant interval
• pure tonea sound that consists of one singlefrequency
• queen parrotfishScarus vetula
• radionuclidea radioactive atom.
• RAFOS floatsfloating instruments designed to move with a current and track the current's movements
• rainbow troutOncorhynchus mykiss
• ramp-upgradually increasing the sound source level
• rarefactionthe instantaneous, local reduction in density of a gas or other medium resulting from passage of a soundwave.
• Rayleigh waveA Rayleigh wave is asurface wave causing retrograde elliptical particle motion at the surface.Rayleigh waves are one type ofseismic wave produced by earthquakes. Found at an interface between a solid and avacuum or a low-density gas medium such as the Earth’s atmosphere.  Also called groundroll.
• receiversomething that listens for or receives sound; it may or may not record the sound
• receiver-operating-characteristic (ROC) curvea curve that plots the cumulativedistribution functions of the false-alarm probability and the detection probability on the x-axis and y-axis, respectively, to select the optimal detection threshold.
• recesshole, corner or niche. For example, a rockrecess, a place surrounded by rocks where a fish can hide
• rectified diffusionwhen acoustic energy causessupersaturated gas to be pumped into an existing small bubble, making the bubble increase in size
• red drumSciaenops ocellatus
• red grouperEpinephelus morio
• red hindEpinephelus guttatus
• reference unitsthe value against which a relative amount is calculated. For example, a decibel is a relative unit (ratio of measured to reference), therefore a reference unit must be specified to understand the value
• reflected wavethe wave moving away from the reflector
• reflectionthe deflection of the path of a soundwave by an object or by the boundary between two media
• reflectorany boundary between twomedia that causes the reflection of a wave
• refractionthe bending of a sound wave towards a region of slower sound speed.
• repertoiresuite of behaviors that an animal may use in different contexts; in this case, the number of call types that have been distinguished based on categorization of vocal behavior.
• resistanceresistive force is a force whose direction is opposite to the velocity of the body, or of the sum of the other forces; may be referred to as "friction" or "drag".
• resonancewhen sounds of specific frequencies cause air- or fluid-filled organs to vibrate with amplitudes that are large compared to the amplitude of incoming soundwaves
• resonatorsomething that fills with sound and acts as a natural amplifier
• rete mirabilea tightly packed bundle ofcapillaries which works with thegas gland to force gases into the bladder
• reverberant environmentan environment with a large amount ofreverberation. An environment with a large number of echoes.
• reverberationthe total sound reflected by multiplescatterers
• ringed sealPhoca hispida
• rip currenta strong, narrow surface current that flows rapidly away from the shore, returning the water carried shoreward bywaves.
• rise timethe time it takes for the leading edge of an [acoustic]pulse to rise from its minimum to its maximum value.
• risk functioncalculation to predict the probability of a behavioral response based on several factors, including sound received levels
• Risso's dolphinGrampus griseus
• Risso's dolphinGrampus griseus
• Roche’s snake blennyOphidion rochei
• rollthe rotation of a vessel about its longitudinal (front/back) axis.
• rolla ship roll motion in a side-to-side tilting motion.
• root-mean-square pressurethe square root of the average of the square of thepressure of the soundsignal over a given duration. Root-mean-square is often abbreviated rms
• rorqualswhales of the family Balaenopteridae which includes humpbacks, sei, minke, fin, blue and Bryde's whales. They have throat pleats or ventral grooves that expand when the whales gulp large amounts of water while feeding.
• rostrumupper jaw of whales that is elongated and looks like a beak
• sablefishAnoplopoma fimbria
• saffir-simpson hurricane wind scaleThe Saffir–Simpson hurricane wind scale (SSHWS) classifies hurricanes into five categories distinguished by the intensities of their sustained winds. Hurricanes aretropical cyclones in the Western Hemisphere that exceed the intensities of tropical depressions and tropical storms.
• saithePollachius virens
• salinitythe total amount of salt dissolved in seawater; the units most often used are parts per thousand (ppt) but practical salinity unit (psu) is now the accepted standard in oceanography. An average salinity value for seawater is 35 ppt (psu) or 35 parts of salt in 1000 parts of water.
• salt domesa layer of salt in a domed structure that was formed beneath the Earth's surface by the movement of salt over long periods of time.Salt domes are often associated with oil and gas deposits.
• samplea subset of the population.
• sample sizethe number of individuals or items in a subset orsample of thepopulation from which estimates of various statistical measures of the whole population are calculated.
• sampling frequencythe number of samples per second; how often a sample is taken
• sand fiddler crabUca pugilator
• sardinessmall, silvery, slender fish of the herring family that have one short dorsal fin and no scales on their heads
• Sargassum or Gulfweeda type of brown algae (of the genus Sargassum) that have a branching thallus (body) with lateral outgrowths differentiated as leafy segments, air bladders, or spore-bearing structures
• satellite altimetrysatellite radar altimeters measure the ocean surface height (sea level) by measuring the time it takes a radar pulse to make a round-trip from the satellite to the sea surface and back. Features on the sea floor such as mountains add extra pull to Earth's gravity field, drawing more water around them and bulging the sea surface outward. The(...)
• saturatewhen no more of something can be dissolved, or the degree or extent to which something is dissolved or absorbed compared with the maximum possible, usually expressed as a percentage
• scattered/scatteringthe diffusion of thesonar signal in many directions through refraction, diffraction and reflection, primarily due to the material properties of the seafloor.Scattering is one of the causes ofattenuation in sonar, resulting in signal weakening.
• scatterer an object that reflects sound energy, can be a particle in seawater or the sea surface or the seafloor
• scatteringwhen the path of a sound wave is broken up by objects (volume scattering) or the sea floor or sea surface (boundary scattering)
• Scholte wavea surface wave causing elliptical motion at the interface. Found at an interface between a solid and an elasticmedium such as the seafloor and water. Also called ground roll.
• schoola large group of marine animals, for example fish, that swim together. The appearance of a large number of individuals may ward off potential predators.
• Sciaenidaefamily of fishes that contains approximately 270 species distributed in the Atlantic, Pacific, and Indian Oceans. This family is commonly known as the drums, which are renowned for their sound producing ability.
• scientific methodthe orderly process by which scientists ask questions about the natural world and test their observations
• scuttleto sink (a vessel) deliberately.
• sea otterEnhydra lutris
• sea statecondition of the surface of the ocean, measured on a scale 0-9, categorized bywave height.
• Sedimentsolid particles of inorganic or organic material deposited in water on the bottom
• sei whaleBalaenoptera borealis
• seismicrelates to an earthquake, earth vibration or volcano
• seismic reflectiona technique for examining the layers of the seafloor that uses the sound energy that isreflected by different layers in the seafloor.
• seismic refractiona technique for examining the layers of the seafloor that uses the sound energy that is refracted by different layers in the seafloor.
• seismic wavea wave of energy caused by the sudden movement of rock, as in an earthquake, or by an explosion.Seismic waves travel trough the Earth and are recorded by aseismometer.
• seismometeran instrument that records ground movement; used to detect and measure earthquakes
• semi-terrestrialliving mostly on land but requiring water and/or a moist environment (esp. as a breeding site). Most amphibians (e.g. frogs) and many crustaceans (e.g. crabs) are semi-terrestrial.
• sensorineural hearing losshearing loss due to damage to the nerves or inner ear structures
• sensory hair cellsbundles of hair like projections (cilia) located on the surface of theinner ear that become stimulated by movement of theotolith against them. Stimulation of the hair cells results in sending asignal to the brain which is interpreted as sound.
• sequestrationthe process of depositing carbon from the atmosphere in a pool , or reservoir. In terms of carbonsequestration, it presumes a reservoir that is not easily transferable to the atmosphere or only transfers over a long time period.
• setaea stiff hair, bristle, or bristle like part on an organism.
• sexual dimorphismdistinct difference in size or appearance between male and female sexes of an animal
• shadow zonea region of low sound intensity that soundwaves traveling away from a source in the ocean do not reach, usually because the sound waves arerefracted away from that region
• shear waveatransverse wave in the seafloor or solid Earth
• shelf-edged habitatsocean habitat on the edge of thecontinental shelf
• shoala largeschool of fish
• shock wavea fully developed compression wave of largeamplitude, across whichdensity, pressure, and particle velocity change drastically.
• side scan sonarsonar is an acronym for sound navigation and ranging equipment.Sonar systems use soundwaves to detect underwater objects by listening to the returning echoes.Side scan sonar uses the strength of the returning echo, not the travel time, to map the seafloor and identify objects on the seafloor.
• signalsound that is used for a specific task, such as to convey information.
• signal excessthe amount (in decibels) by which the signal- to-noise ratio (SNR) exceeds the detection threshold (DT).
• signal processinganalyzing sounds from a receiver to detect and classify sound sources
• signal processingthe analysis of signals to obtain information.
• signal-to-noise (SNR) ratiothe ratio that compares the received level of a sound signal and the background noise level. For example, it is easy to hear conversations in a quiet room, where the signal-to-noise ratio is high, but it is difficult to hear conversations at a noisy party, where the signal-to-noise ratio is low.
• signature sounda unique sound that is associated with a specificsound source
• signature whistletonal sounds produced by whales and dolphins that are unique to a particular individual and distinct from any other member of the group. Signaturewhistles provide a way to recognize individuals and help maintain group cohesion.
• silver perchBairdiella chrysoura
• sine waveasinusoid; a mathematical curve defined in terms of the sine trigonometric function
• sinusoidasine wave; a mathematical curve defined in terms of the sine trigonometric function
• sireniansgroup of mammals that includes manatees and dugongs
• slippery dick wrasseHalichoeres bivittatus
• smolta young salmon (or trout) at the stage of development when it assumes the silvery color of the adult and is ready to migrate to the sea.
• snapping shrimpAlpheus heterochaelis
• SOFAR channelSOFAR stands for SOund Fixing And Ranging. The sound speed minimum at 800-1000 meters of water depth is called the deepsound channel or, more historically, theSOFAR channel.
• sonaran acronym for SOund Navigation And Ranging equipment. Sonar systems use sound waves to detect underwater objects by listening to the returning echoes. The distance to the object or the seafloor can be calculated by measuring the time between when the signal is sent out and when the reflected sound, or echo, is received.
• waveform interval periodtime betweensonar waveforms
• sonar pulseeach individual component of a sonarsignal
• sonar waveformthe combined components of asonar signal, which includes all thesonar pulses
• sonar waveform durationthe length of time of the sonar waveform
• sonic musclea muscle that is attached to theswim bladder. Rapid flexure of thesonic muscle against the swim bladder produces drum-like sounds commonly associated with courtship and spawning behavior.
• sonic muscle - swim bladdera combined mechanism used by fishes to produce sound. The swim bladder is a gas filled organ primarily used forbuoyancy control and is also important for hearing in somefishes. The sonic muscle is attached to theswim bladder. Rapid flexure of the sonic muscle against the swim bladder produces drum-like sounds commonly associated with(...)
• soniferoussound producing
• sonobuoyinstrument that is dropped into the ocean (from either an aircraft or ship) to record underwater sounds. It includes ahydrophone and a radio transmitter to send sound signals back to the aircraft or ship. The U.S. Navy uses this instrument to listen for enemy submarines.Sonobuoys may also be used to record marine mammal calls and listen for(...)
• sonogramgraphic presentation of a sound. Asonogram plots the frequency vs. time and represents the different intensity of thefrequencies with different colors. It is similar to a contour map or bathymetric map where the different colors represent different water depths. Also called aspectrogram
• sonoluminescencethe production of light as a result of the passing of sound waves through a liquid medium. The soundwaves cause the formation of bubbles that emit bright flashes of light when they collapse.
• sound channelan area of slow sound speed that causes sound waves to become focused at this water depth
• sound channel axisdepth of the minimum sound speed within the sound channel. Sound waves cycle above and below the axis as they move through the sound channel.
• sound exposure level (SEL)thedecibel level of the time integral (summation) of the squared pressure over the duration of a sound event; units of dB re 1 µPa2/s
• sound fieldthe level of sound at different distances and depths from the source
• sound intensity level10 times the logarithm of the ratio of theintensity of a soundwave to a reference intensity; also known as intensity.
• sound level10 times the logarithm of the ratio of the mean-squarepressure of a sound to the square of a reference sound pressure.Sound pressure level will usually be shortened to sound level on the DOSITS website. Sound pressure level is given in relative units named decibels (dB). Sound pressures for transient signals are sometimes given as peak or(...)
• sound receptorsomething that receives sound; sound receiver
• sound sourcesomething that creates sound
• sound spreading lossthe decrease inintensity that occurs when a sound wave expands as it moves away from a source
• Sound Surveillance System (SOSUS)a network of hydrophones mounted on the seafloors of the North Atlantic and North Pacific oceans maintained by the US Navy
• soundscapeacoustic environment as perceived or experienced and/or understood by a listener. (ISO Technical Committee on Acoustics,Noise Subcommittee, ISO 12913-1:2014).
• source arraymultiple sound sources combined to operate together for a specific purpose
• source levelthe amount of sound radiated by a sound source. It is defined as the intensity of the radiated sound at a distance of 1 meter from the source, where intensity is the amount of soundpower transmitted through a unit area in a specified direction. Source level is given as a relativeintensity in units named decibels (dB). In underwater sound,(...)
• Southern California Offshore Range (SCORE)a state-of-the-art facility that provides training and testing services to the U.S. Navy’s Pacific Fleet. The underwater tracking range is located west of San Clemente Island, CA, and consists of 84 bottom-mounted hydrophones that provide a coverage area of approximately 660 square nautical miles. Similar to AUTEC, a Marine Mammal(...)
• southern right whaleEubalaena australis
• Sparkera sound source that uses an electric spark to generate a broadband signal.
• spatial resolutionthe minimum difference or distance between two measured or computed values or objects that can be distinguished. It defines the limit of accuracy for a technique.
• spatulatehaving a narrow base and a broad body (spade-shaped).
• spawningto produce, release, or deposit eggs for reproduction
• specific acoustic impedancethe ratio of acousticpressure to the associated particle speed in a medium.
• spectralthe frequency composition of sound.
• spectral characteristicsthefrequency components of an acousticsignal
• spectrograma graphic presentation of a sound. A spectrogram plots the frequency vs. time and represents the different intensity of the frequencies with different colors. It is similar to a contour map orbathymetric map where the different colors represent different water depths. Also called a sonogram
• spectruma catalog of the amplitude of a signal as a function of frequency orpitch, with graphics showing low frequencies on the left of the x-axis and highfrequencies on the right.
• sperm whalePhyseter macrocephalus
• spermaceti organan elongated connective tissue sac in the forehead of the sperm whale that contains a waxy fluid called spermaceti
• spherical spreadingenergy spreading out from asound source in the shape of a sphere; the power is radiated equally in all directions from the sound source
• spinner dolphinStenella longirostris
• Spiny LobsterPalinurus elephas
• spratSprattus sprattus
• spreading lossa decrease in the intensity of a wave as it spreads out from a source
• spy-hoppinga common whale activity in which they lift their heads above the surface of the water and observe what is happening on the surface. Whales will often spin around in order to observe in all directions.
• squidmollusks of the family Cephalopoda that are a favorite food of the sperm whale
• standard deviationan estimate of the variability of a set of measurements about themean value; it is calculated by computing the square root of thevariance.
• standard deviation of the meanan estimate of the variability of the mean value computed from a specific set of measurements; it is calculated by dividing thestandard deviation of the measurements by the square root of the number of measurements; also often called the standard error of the mean.
• startle responsea largely involuntary, defensive response to a sudden and/or threatening stimuli, such as a flash of light, a sudden  movement, or loud noise.  In fishes, this behavior is often displayed as a sudden bending of the body, and is a characteristic escape response.    
• static diffusionwhen particles move from a region of higher concentration to a region of lower concentration
• statistically significantfindings of an experiment or study that have a low probability of being due to chance alone
• statisticsmathematical analysis that is used to explain and compare numerical data. This analysis helps make broader generalizations about a population from a smaller number of specific observations.
• statocysta sac-like structure containing a mineralized mass (statolith) in association with numerous sensory cells.
• stepsa break or irregular change infrequency of a whistle.
• stereoshort for stereophonic: a sound-reproduction system that uses two or more separate channels to give a more natural distribution of sound.
• stereocilialong, flexible hair-like structures that occur as a brush border on the surface of some membranes
• stereociliary bundlesgroups of hair-like projections on the upper surface of a hair cell. When stereocila bend, they trigger a release of chemicals that initiates the electrical signal (neural impulse) that is carried to and processed by the brain.
• stereotypedfixed or settled in form.
• stewardshipthe conducting, supervising, or managing of something, especially, the careful and responsible management of something entrusted to one's care.
• strandingan event where an aquatic animal, especially a marine mammal, lands on a beach or becomes stuck in shallow water, is dead or sometimes alive, and probably in distress.
• stratificationseparation of water layers based on strong density differences
• streaked gurnardsTrigloporus lastoviza
• streamersa long (2000-6000 m) string ofhydrophones typically used with air-gun arrays
• stresswhen an optimal steady state is threatened by internal and/or external forces, and is counteracted by a physiological or biological response (to maintain/establish equilibrium).
• stress responsethe natural coping mechanism that allows the body to deal with stressful events. A group of physiological and behavioral processes enable an animal to adapt to changes in their environment.
• stressoranything that causes the body to respond by releasing stress hormones.
• stridulationto produce a sound by rubbing two body parts together. Some fish make a shrill creaking noise by rubbing together bodily structures, especially skeletal parts.
• striped cusk eelOphidion marginatum
• striped dolphinStenella coeruleoalba
• stripersMorone saxatilis
• sub-arcticrelating to the region immediately south of the Arctic Circle.
• subduction zonesplaces where twotectonic plates move toward each other, and one plate plunges beneath the other plate. Often ocean crust is subducting beneath continental crust
• submarineunderwater
• submarine canyonnarrow, steep-sided valleys on the seafloor.
• subsonica frequency that is below the audible range
• substratethe surface ormedium on which an organism lives or grows, or the material on the bottom of the ocean.
• substratum (substrate)the surface that an organism grows on or is attached to
• supersaturatedmore highly concentrated than is normally possible under given conditions of temperature and pressure
• surf zoneThe zone within whichwaves approaching the coastline start breaking; also called the breaker zone.
• surface reverberationsoundscattering that occurs on or at the sea surface
• surface wavea sound wave (or seismic wave) that travels only at an interface boundary
• Surveillance Towed Array Sensor System (SURTASS)a passive sonar system used to listen for noises produced by submarines. The system consists of a long string of underwater hydrophones that are towed behind a ship and pick up sounds in the ocean.
• SUS (Signal, Underwater Sound)anexplosive sound source used by the U.S. Navy that consists of 0.82-kg (1.8-lb) ofTNT explosive material.
• swathan area shaped like a broad strip.
• Swift scallopChlamys swifti
• swim bladdera gas filled organ that is primarily used for buoyancy control but is also important for hearing in some fishes.
• swim bladder (also called an air bladder)an expandable, gas-filled sac that helps fish maintain buoyancy in the water. This organ is also important for hearing in some species of fish.
• symbiotichaving an interdependent relationship that benefits both parties involved.
• synapsea junction between a nerve cell and another nerve cell or a nerve fiber or a sensory receptor
• synthetic-aperture sonarSynthetic-aperturesonars combine a number of acoustic pings to form an image with much higher along-track resolution than conventional sonars.
• t-testa statistic that compares the sample means with the standard deviations of thesample means to determine whether the two sample means are statistically different.
• target strengththe amount of sound reflected back toward a sonar by a target.
• tectonicrelating to the deformation of the earth's crust
• tectorial membranea membrane that covers the surface of the organ of Corti in the cochlea of the inner ear
• telemetrymeasuring and transmitting data from a remote location
• temperaturea measure of the atomic and molecular vibration in a substance, in degrees. The response of a solid, liquid, or gas to the input or removal of heat energy.
• temporary threshold shift (TTS)a temporary increase in the threshold of hearing (minimumintensity needed to hear a sound) at a specific frequency that returns to its pre-exposure level over time
• terrestrialsomething that lives on land as opposed to in the water. Some animals, such as sea lions spend time both on land and in the water, they are considered to be bothterrestrial and marine.
• Terrigenousderived from land,  referring to weathered rock grains and minerals
• territoriality/territorialbehavior in which an organism, for example a fish, defends its home
• Tertiary waveseismic energy that has been converted into acoustic energy in the ocean. Also known as aT-wave"."""
• Tertiary waveseismic energy that has been converted into acoustic energy in the ocean. Also a T-wave.
• testthe outer skeleton of a sea urchin. It is made up of plates that encircle the sea urchin. Spines of the sea urchin grow from thetest.
• Thalassiaa broad-bladed seagrass occurring in shallow tropical and subtropical estuaries and nearshore marine waters
• theorya hypothesis or group of hypotheses that have been consistently validated through scientific observations or experiments. Geology'stheory of plate tectonics is an example of a well-documented and widely accepted theory.
• thermoclinea layer of water in an ocean or certain lakes, that separates warmer surface water from colder deep water.Temperature rapidly changes with depth in this region of the water column.
• thermometrythe measurement of temperature
• thick-billed murre Uria lomvia
• threatenedany species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range (as defined in the U.S. Endangered Species Act).
• threshold of hearingthe minimum intensity at which a sound of a specificfrequency is reliably detected in absolute quiet conditions. The intensity level varies with frequency. Also called hearing thresholds.
• threshold of paintheintensity level where sound is physically painful. Usually at 115-130 dB.
• threshold shiftan increase (worsening) in thethreshold of hearing for an ear at a specified frequency
• tidewater glaciersvalley glaciers that flow all the way down to the ocean.
• tiger sharkGaleocerdo cuvier
• TNTtrinitrotoluene; a chemical compound used as an explosive material.
• toadfishopsanus tau
• tonala sound consisting of a singlefrequency.
• tone pipsacoustic stimuli that are presented as single frequency, pure tone(s).
• tonotopic organizationto be organized by frequency.
• tonotopically organizedfrequency-dependentresonance, in which the basilar membrane vibrates more near the base with high frequencies, while lower frequencies cause the membrane to vibrate most towards the apex.
• towfishan instrument, such as a side scansonar, that is towed behind a ship
• tracheaa large membranous tube reinforced by rings of cartilage, extending from the larynx to the bronchial tubes and conveying air to and from the lungs; the windpipe.
• transducera device that converts energy from one form to another. In acoustics, it is often converting between mechanical energy (motion) and acoustic energy, or electrical energy and acoustic energy.
• transmission lossthe decrease in acoustic intensity (due to spreading and/or attenuation) as an underwater soundwavepropagates outwards from a source.
• transmitteran instrument that sends out slectrical signals
• transpondera device for receiving an acousticsignal and automatically transmitting a unique return signal in response. Transponders are often used to show the location of something.
• transverse wavea disturbance in which the particles vibrate up-and-down and the energy moves left-and-right
• triangulationmethod for determining the location of a target of interest. Three distances from three known points are measured, and from these distances, a unique point of intersection can determined (this calculation is usually performed by computers).  The point of intersection indicates the target's location.
• trilla fluttering sound that alternates rapidly with another note
• trophic levela particular step or position within a food chain, food web, or ecological pyramid where a group of organisms exist.
• tropical cyclonea rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. These intense circular storms originate over warm tropical oceans.
• tsunamiatsunami is a series of ocean waves generated by sudden displacements in the sea floor, landslides, or volcanic activity. In the deep ocean, the tsunami wave may only be a few inches high at the sea surface. When a tsunamiwave comes ashore it will increase in height and can become a fast moving wall of water several meters high.
• tuberclea small rounded projection.
• tuned airgun arraymultiple airguns of different, carefully selected volumes that are fired at the same time.
• turbiditythe measure of relative clarity of a liquid. It is an optical characteristic of water and is a measurement of the amount of light that is scattered by material in the water when a light is shined through the water sample.Turbidity makes water cloudy or opaque. The higher the intensity of scattered light, the higher the turbidity. Material(...)
• tympanic membrane or eardruma membrane that separates the outer ear from the middle ear. The eardrum vibrates in response to sound waves and passes the vibrations on to the bones of themiddle ear.
• Type I Erroran error when one concludes that there is a real difference between two means when, in fact, there is not; also called a false positive error.
• Type II Erroran error when one concludes that there is not a real difference between two means when, in fact, there is a difference; also called a false negative error.
• ultrasonicsound waves that have afrequency that is higher than what humans can hear (i.e. greater than 20,000 Hz). Bats and dolphins use these high frequency sounds for communication and navigation.
• ultrasound signalsound vibrations that havefrequencies above the range of human hearing
• underwater dBthe relative unit used to specify theintensity of an underwater sound. The phraseunderwater dB is used on DOSITS to indicatedecibels computed usingroot-mean-square (rms) pressure unless otherwise indicated. Underwater dB are referenced to a pressure of 1 microPascal (µPa), which is abbreviated as dB re 1 µPa. To be able to compare(...)
• underwater soundscapecharacterization of the ambient sound in terms of its spatial, temporal, and frequency attributes, and the types of sources contributing to the sound field (ISO Technical Committee on Acoustics, Underwater Acoustics Subcommittee, ISO 18405:2017).Underwater soundscape is sometimes used synonymously with acoustic environment (or ambient(...)
• upsweepa signal that increases infrequency over time.
• utriclethe larger of the two fluid-filled cavities forming part of the inner ear (the other being the sacculus).
• vacuuma space from which all gas and other matter has been removed
• vaquitaPhocoena sinus
• variancean estimate of the variability of a set of measurements about themean value; it is calculated by subtracting the mean from each of the measurements, squaring the differences, adding all of the squared differences together, and dividing by one less than the total number of measurements; the square root of the variance is the standard deviation.
• vectora quantity, such as avelocity or force, that has both magnitude and direction.
• velocitythe linear speed of an object in a specified direction.
• ventralof, pertaining to, or situated at the back or upper side.
• vertebratehaving vertebrae or having a backbone or spinal column. Fish and humans are examples of vertebrates.
• vertical migrationa pattern of movement that some marine organisms undertake each day. Usually organisms move to shallow waters at night and return to deeper waters during the day.
• vestibular systema fluid-filled maze of canals and chambers inside theinner ear that helps maintain orientation and balance.
• viscositya molecule'sresistance to motion
• vital ratesfactors that determine the abundance or density of apopulation, including birth rate, death rate, emigration, age structure, and sex ratios. These factors influence population dynamics and allow scientists and managers to track population demographics through time.
• vocal cordssmall bands of tissue within the larynx that vibrate (when air passes over them) to produce the sound.
• vocal fold ligamentconnective tissue that strengthens the vocal folds via stiffness and support
• vocal learningthe modification of an animal’s vocalization(s) based on acoustic signals in its environment, such as vocalizations by conspecifics.
• vocalizationsounds intentionally produced by animals that may be used for communication, navigation, and feeding. In humans, air is moved from the lungs and across the vocal folds (also known asvocal cords). The vibration of the vocal folds produce sounds that are formed into words and other vocal communication signals. We do not know how sound is(...)
• volume reverberationsound scattering caused by interactions with marine life, inanimate matter, andinhomogeneities in the water
• vulnerablesusceptible to being hurt or damaged.
• wakethe track ofwaves left by a ship or other solid object moving through the water.  It is caused by the flow of the fluid around the body.
• walleye pollockGadus chalcogrammus (also known as Alaska pollock)
• walrusOdobenus rosmarus
• wavedisturbance caused by the movement of energy through a medium
• wave fronta surface consisting of all points on a wave at the same position in a wavecycle.
• waveforma waveform presents the sound in a graph as positive and negativepressure on a relative scale (often from -1 to 1) through time. The relative pressure is related to the intensity of the sound.
• waveguidea structure that guideswaves by restricting the wave movement in one or more dimensions resulting in efficient transmission of the wave. For example, the SOFAR channel is awaveguide in the ocean.
• wavelengththe length of one cycle of awave (one crest and one trough)
• Weberian ossiclesa series of bones which connect the swim bladder to the inner ear and carry vibrations between to the two, aiding in hearing.
• weddell sealLeptonychotes weddelli
• whistlesnarrow-band, tonal sounds produced by many toothed whales for communication purposes. Whistles are frequency-modulated, which means the pitch of the sound changes over time.
• white-beaked dolphinLagenorhynchus albirostris
• white noisea heterogeneous mixture of sound waves extending over a wide frequency range (but equal intensities).
• white-sided dolphinLagenorhynchus spp.
• Yangtze finless porpoiseNeophocaena phocaenoides
• yawa shipyaw motion is rotation about a vertical axis through the ship or left to right turning of the ship.
• Yellow perchPerca flavescens
• yellowtail rockfishSebastes flavidus
• zooplanktonmicroscopic animals, such ascrustaceans and fish larvae, that drift in the water column.