 Artist's interpretation of the OSTM/Jason-2 satellite | |
| Names | Jason-2 Ocean Surface Topography Mission OSTM |
|---|---|
| Mission type | Oceanography mission |
| Operator | NASA,NOAA,CNES,EUMETSAT |
| COSPAR ID | 2008-032A |
| SATCATno. | 33105 |
| Website | Ocean Surface Topography from Space |
| Mission duration | 3 years (planned) 11 years, 3 months, 18 days (achieved) |
| Spacecraft properties | |
| Bus | Proteus |
| Manufacturer | Thales Alenia Space |
| Launch mass | 510 kg (1,120 lb) |
| Power | 500 watts |
| Start of mission | |
| Launch date | 20 June 2008, 07:46:25UTC |
| Rocket | Delta II 7320-10C (Delta D334) |
| Launch site | Vandenberg,SLC-2W |
| Contractor | United Launch Alliance |
| End of mission | |
| Deactivated | 9 October 2019 |
| Orbital parameters | |
| Reference system | Geocentric orbit |
| Regime | Low Earth orbit |
| Altitude | 1,336 km (830 mi) |
| Inclination | 66.00° |
| Period | 112.00 minutes |
OSTM/Jason-2, orOcean Surface Topography Mission/Jason-2 satellite,[1] was an internationalEarth observationsatellite altimeter joint mission forsea surface height measurements betweenNASA andCNES. It was the third satellite in a series started in 1992 by the NASA/CNESTOPEX/Poseidon mission[2] and continued by the NASA/CNESJason-1 mission launched in 2001.[3]
Like its two predecessors, OSTM/Jason-2 used high-precision oceanaltimetry to measure the distance between the satellite and the ocean surface to within a few centimeters. These very accurate observations of variations in sea surface height — also known asocean topography — provide information about globalsea level, the speed and direction ofocean currents, and heat stored in the ocean.
Jason-2 was built byThales Alenia Space using aProteus platform, under a contract from CNES, as well as the main Jason-2 instrument, the Poseidon-3 altimeter (successor to the Poseidon and Poseidon 2 altimeter on-board TOPEX/Poseidon andJason-1). Scientists consider the 15-plus-yearclimate data record that this mission extended to be critical to understanding how ocean circulation is linked to globalclimate change.
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OSTM/Jason-2 was launched on 20 June 2008, at 07:46UTC, fromSpace Launch Complex 2W atVandenberg Air Force Base inCalifornia, by aDelta II 7320 rocket.[4] The spacecraft separated from the rocket 55 minutes later.[5]
It was placed in a 1,336 km (830 mi) circular, non-Sun-synchronousorbit at an inclination of 66.0° to Earth'sequator, allowing it to monitor 95% of Earth's ice-free ocean every 10 days. Jason-1 was moved to the opposite side of Earth from Jason-2 and now flies over the same region of the ocean that Jason-2 flew over five days earlier.[6] Jason-1's ground tracks fall midway between those of Jason-2, which are about 315 km (196 mi) apart at the equator. This interleaved tandem mission provided twice the number of measurements of the ocean's surface, bringing smaller features such as ocean eddies into view. The tandem mission also helped pave the way for a future ocean altimeter mission that would collect much more detailed data with its single instrument than the two Jason satellites did together.
With OSTM/Jason-2, ocean altimetry made the transition from research into operational mode. Responsibility for collecting these measurements moved from the space agencies to the world's weather and climate forecasting agencies, which use them for short-range, seasonal, and long-range weather and climate forecasting.[7]
"Spaceborne radar altimeters have proven to be superb tools for mapping ocean-surface topography, the hills and valleys of the sea surface. These instruments send a microwave pulse to the ocean's surface and time how long it takes to return. Amicrowave radiometer corrects any delay that may be caused bywater vapor in theatmosphere. Other corrections are also required to account for the influence of electrons in theionosphere and the dry air mass of the atmosphere. Combining these data with the precise location of the spacecraft makes it possible to determine sea-surface height to within a few centimetres (about one inch). The strength and shape of the returning signal also provides information on wind speed and the height of ocean waves. These data are used in ocean models to calculate the speed and direction ofocean currents and the amount and location of heat stored in the ocean, which, in turn, reveals globalclimate variations".[8]
Another payload aboard Jason-2 is the T2L2 (Time Transfer by Laser Link) instrument. T2L2 is used to synchronize atomic clocks at ground stations, and to calibrate the on-board clock of the Jason-2 DORIS instrument. On 6 November 2008,CNES reported the T2L2 instrument was working well.[9]
OSTM/Jason-2 was a joint effort by four organizations.[10] The mission participants were:
CNES provided the spacecraft, NASA and CNES jointly provided the payload instruments, and NASA's Launch Services Program at theKennedy Space Center was responsible for the launch management and countdown operations. After completing the on-orbit commissioning of the spacecraft, CNES handed over operation and control of the spacecraft to NOAA in October 2008.[11]
CNES processed, distributed, and archived the research-quality data products that became available in 2009. EUMETSAT processed and distributed operational data received by its ground station to users in Europe and archived that data. NOAA processed and distributed operational data received by its ground stations to non-European users and archived that data along with the CNES data products. NOAA and EUMETSAT both generated near-real-time data products and distributed them to users.
NASA evaluated the performance of the following instruments: the Advanced Microwave Radiometer (AMR), the Global Positioning System payload, and the Laser Retroreflector Assembly (LRA). NASA and CNES also validated scientific data products together. NASA'sJet Propulsion Laboratory inPasadena, California, managed the mission for NASA'sScience Mission Directorate inWashington, D.C.
The two previous altimetry missions,TOPEX/Poseidon andJason-1, led to major advances in the science ofphysical oceanography and in climate studies.[12] Their 15-year data record of ocean surface topography provided the first opportunity to observe and understand the global change of ocean circulation and sea level. Their results improved scientific understanding of the role of the ocean in climate change and improved weather and climate predictions. Data from these missions were used to improve ocean models, forecast hurricane intensity, and identify and track large ocean/atmosphere phenomena such asEl Niño andLa Niña. The data was also used in daily applications as diverse as routing ships, improving the safety and efficiency of offshore industry operations, managing fisheries and tracking marine mammals.
Some of the areas in which TOPEX/Poseidon and Jason-1 have made major contributions,[13] and to which OSTM/Jason-2 continued to add, are:
The missions revealed the surprising variability of the ocean, how much it changes fromseason to season, year to year, decade to decade and on even longer time scales. They ended the traditional notion of a quasi-steady, large-scale pattern of global ocean circulation by proving that the ocean is changing rapidly on all scales, from huge features such as El Nino and La Nina, which can cover the entire equatorial Pacific, to tinyeddies swirling off the largeGulf Stream in theAtlantic Ocean.
Measurements by TOPEX/Poseidon and Jason-1 show that mean sea level has been rising by about 3 mm (0.12 inches) a year since 1993. This is about twice the estimates from tide gauges for the previous century, indicating a possible recent acceleration in the rate of sea level rise. The data record from these altimetry missions has given scientists important insights into how global sea level is affected by natural climate variability, as well as by human activities.
TOPEX/Poseidon and Jason-1 made clear the importance of planetary-scalewaves, such asRossby andKelvin waves. Thousands of kilometres wide, these waves are driven bywind under the influence of Earth's rotation and are important mechanisms for transmitting climate signals across the large ocean basins. At high latitudes, they travel twice as fast as scientists believed previously, showing the ocean responds much more quickly to climate changes than was known before these missions.
The precise measurements of TOPEX/Poseidon's and Jason-1 have brought knowledge of oceantides to an unprecedented level. The change of water level due to tidal motion in the deep ocean is known everywhere on the globe to within 2.5 centimetres (one inch). This new knowledge has revised notions about how tides dissipate. Instead of losing all their energy over shallow seas near the coasts, as previously believed, about one third of tidal energy is actually lost to thedeep ocean. There, the energy is consumed bymixing water of different properties, a fundamental mechanism in the physics governing the general circulation of the ocean.
TOPEX/Poseidon and Jason-1 observations provided the first global data for improving the performance of the numerical ocean models that are a key component of climate prediction models.
Validated data products in support of improved weather, climate and ocean forecasts were distributed to the public within a few hours of observation. Beginning in 2009, other data products for climate research were made available a few days to a few weeks after observations were taken by the satellite. Altimetry data have a wide variety of uses from basic scientific research on climate to ship routing. Applications include:
The OSTM/Jason-2 mission concluded on 1 October 2019, after NASA and its mission partners made the decision to decommission the spacecraft upon discovering significant recent deterioration of the spacecraft's power systems.[14] The decommissioning of the satellite took some days; the final decommissioning activities on the satellite ended 9 October 2019, with the satellite rendered fully inactive.[15] Because Jason-2 is orbiting at an altitude of over 1,300 km (810 mi), NASA estimates that it will remain in orbit for at least 500 to 1,000 years after decommissioning.[15]
The fourth spacecraft to be part of the Ocean Surface Topography Mission isJason-3. Like its predecessors, the primary instrument aboard Jason-3 is aradar altimeter. Additional instruments include:[16]
Jason-3 launched fromVandenberg Air Force Base on board aSpaceXFalcon 9 v1.1launch vehicle in 2016.[17] The satellite was shipped toVandenberg Air Force Base on 18 June 2015,[18] and after delays due to a June 2015 Falcon 9 launch failure, the mission was launched 17 January 2016 at 18:42:18 UTC.[19][20]
The technologies and data-sets pioneered by Jason-1, OSTM/Jason-2, and Jason-3, will be continued through theSentinel-6/Jason-CS satellites, planned for launch in 2020 and 2025.[14]
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