Voyager 1 Narrow Angle Camera Description

Index

Instrument Information

      Instrument Id                  : ISSN      Instrument Host Id             : VG1      Pi Pds User Id                 : BASMITH      Naif Data Set Id               : UNK      Instrument Name                : IMAGING SCIENCE SUBSYSTEM -                                         NARROW ANGLE      Instrument Type                : VIDICON CAMERA      Build Date                     : 1976-12-17      Instrument Mass                : 22.060000      Instrument Length              : 0.980000      Instrument Width               : 0.250000      Instrument Height              : 0.250000      Instrument Serial Number       : SN07      Instrument Manufacturer Name   : JET PROPULSION LABORATORY

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Instrument Description

The Voyager Imaging Science Subsystem (ISS) is a modified version of the slowscan vidicon camera designs that were used in the earlier Mariner flights. Thesystem consists of two cameras, a high resolution Narrow Angle (NA) camera anda lower resolution, more sensitive Wide Angle (WA) camera. Unlike the other onboard instruments, operation of the cameras is not autonomous, but iscontrolled by an imaging parameter table residing in one of the spacecraftcomputers, the Flight Data Subsystem (FDS) (Science and Mission SystemsHandbook, 1987, JPL D-498, an internal JPL document available from the JPLvellum files).

The original mission was to Jupiter and Saturn. Voyager surpassed expectationsand went on to encounter Uranus and Neptune. As the Voyager mission progressedthe objects photographed were further from the sun so they appear more fainteven though longer exposures were used. As the Voyager spacecrafts’ distancefrom the Earth increases, the telecommunications capability at each encounterdecreases. The difference in capabilities from the Jupiter and Saturnencounters and that at Uranus and Neptune was considerable. The reducedtelecommunications capability limits the number of data modes that imaging canuse. Because of the diminished brightness of the objects being photographed,longer exposure times were used, many beyond the stated maximum of 15.360seconds. Longer exposure times were all 48-second increments added to themaximum. In addition, the camera was slewed in order to avoid smeared imaging.The light flood state (on/off) was independent of the instrument mode.

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Science Objectives

The overall objective of this experiment is exploratory reconnaissance ofJupiter, Saturn, Uranus, Neptune and their satellites and rings. Suchreconnaissance, at resolutions and phase angles unobtainable from Earth,provides much new data relevant to the atmospheric and/or surface propertiesof these bodies. The experiment also has the following specific objectives:observe and characterize global circulation and meteorology; determine thehorizontal and vertical structure of visible clouds; characterize the natureof any colored material which may be in clouds.

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Operational Considerations

To make full scientific use of the imaging collection, it is necessary tounderstand the radiometric and geometric characteristics of the camera systemand perform corrections to the data.

Each Voyager camera is unique in terms of its calibrated characteristics. Eachhas intrinsic shading (spatially non-uniform output DNs from flat fieldtarget) and exhibits barrel distortions typical of TV cameras flown onprevious planetary missions. Because of these characteristics, the cameraswere calibrated before launch. The response of the pixels to known targets,illumination, exposures, etc. was measured and Calibration Files weregenerated to remove radiometric an geometric distortions from the flightimages. These Calibration Files and detailed information on their use areavailable through the Imaging Node.

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Calibration Description

The calibration program for the Voyager television cameras consisted of threeparts: (1) component calibrations (‘Voyager Imaging Science SubsystemCalibration Report’ July 31, 1978, M. Benesh and P. Jepsen, D618-802); (2)subsystem calibrations; and, (3) system calibrations. Component calibrationswere carried out prior to camera assembly. Important measurements includespectral transmittance of the lens and filters, actual exposure times andshading characteristics of the shutter, and pertinent electro-opticalproperties of the vidicon. After the optics and sensor were assembled it waspossible to run calibrations at the camera, or subsystem, level. Particularactivities accomplished during this period included radiometric calibrations,focal length measurement, determination of the modulation transfer function,measurement of the geometric distortion, and calibrations required for colorreconstruction. System calibrations were conducted after the cameras wereinstalled on the spacecraft. Important tasks included measurement of theField-Of-View (FOV) alignment and verification of the flat-field lighttransfer characteristics. Noise measurements were also made at the systemlevel.

A method for in-flight verification of the radiometric calibrations that wererun on the ground is employed on the Narrow-Angle optics. It is very similarto the scheme used on the Wide-Angle optics except that eight lamps arerequired. They are located just within the Field-Of-View around the peripheryof the telescope aperture. By either pulsing the lamps or leaving them on andvarying the shutter exposure time a transfer curve may also be generated byusing the calibration plaque. The method is identical to that described forthe wide-angle optics. However, calibration data was collected but no newcalibration files were generated during the Jupiter, Saturn, or Uranusencounters or their related cruise periods.

Although the INSTRUMENT_PARAMETER_NAME has been provided as Radiance, theVoyager Experiment Data Record (EDR) data set has not been radiometricallycorrected, and thus images do not represent radiance units. In order toconvert an image from Data Number (DN) to radiance units, the image must becalibrated. Radiometric calibration files, and selected radiometricallycorrected images are available through the Imaging Node.

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Field Of View (FOV)

      Total Fovs                     : 1      Sample Bits                    : 8

FOV (Field Of View) Shape ‘SQUARE’

      Section Id                     : ISSN      Fovs                           : 1      Horizontal Pixel Fov           : 0.000530      Vertical Pixel Fov             : 0.000530      Horizontal Fov                 : 0.424000      Vertical Fov                   : 0.424000

Parameters

Radiance is the amount of energy per time per projected area per steradian.

      Instrument Parameter Name      : RADIANCE      Sampling Parameter Name        : PIXEL      Instrument Parameter Unit      : DIMENSIONLESS      Noise Level                    : UNK

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Instrument Detector

      Detector Type                  : VIDICON      Detector Aspect Ratio          : 1.000000      Minimum Wavelength             : 0.280000      Maximum Wavelength             : 0.640000      Nominal Operating Temperature  : 282.000000

The sensor used in the Voyager Imaging Science Subsystem (ISS) camera systemis a 25-mm diameter magnetic deflection vidicon (number B41-003, GeneralElectro-dynamics Co.). The vidicon storage surface (target) is seleniumsulphur and can store a high resolution (1500 TV lines) picture for over 100 sat room temperature. The active image area on the target is 11.14 x 11.14 mm.Each frame consists of 800 lines with 800 picture elements (pixels) per line,i.e., 1 pixel =14 microns. One frame requires 48 s for electronic readout. Inaddition to the normal frame readout of 48 s (1:1), four extended frame-timemodes of 2:1, 3:1, 5:1, and 10:1 are available by command. Following readout,light flooding is used to remove any residual image that might remain from theprevious frame. At the end of light flooding, 14 erase frames are used tostabilize and prepare the vidicon target for the next exposure sequence (VGRISS Calibration Report, 1978, an internal JPL document available from JPLvellum files).

Sensitivity

Calibration experiments show the gain map indicating higher sensitivity towardthe top of the frame in a radial manner. Dark-current ratio results indicate amean within plus-or-minus 3% of the true linearity of the light transferfunction. The required accuracy of the light transfer functions was plus-or-minus 5% of half-scale signal averaged over any randomly selected area of 10contiguous pixels. This requirement was consistently met for all ISS flightcameras. The radiance of the used light cannons was supposed to be plus-or-minus 5% or better of the level to produce a half-scale signal. This criterionwas also met. It is not clear whether the color spatial dependence is due tothe vidicon, or whether the filters have varying transmissions. In the lattercase, the ratios would be independent of light level; and this has beenobserved to be the case for all flight cameras. Moreover, vidicons have notshown scale variations of this magnitude in the past, so that it is easier tobelieve that they are due to the spectral filters rather than to the vidicons.The color sensitivity is sufficient to require a separate decalibration filefor each spectral filter, which has been done, but not gross enough to causeconcern about the quality of the image itself (VGR ISS Calibration Report,1978, an internal JPL document available from JPL vellum files).

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Instrument Electronics

The Imaging Science Subsystem (ISS) electronics consist of the vidicon supportcircuits and the signal chain. The vidicon support circuits are the verticaland horizontal sweep circuits, and the various power supplies for the vidiconfilament, and the focus and alignment coils. The signal chain consists of theanalog signal amplifiers, bandpass filters, and an eight bit analog-to-digitalconverter. The digital output is sent to the Flight Data Subsystem (FDS) forediting.

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Filters

Spectral measurements at the manufacturer were taken on Beckman spectro-photometers, and verifications at Jet Propulsion Laboratory (JPL) were madewith a Cary 14 spectro-photometer. Each test scan was run from 2000 to 7000Angstroms to check for eventual leaks outside the passband (VGR ISSCalibration Report, 1978, an internal JPL document available from JPL vellumfiles). For spectral information on each filter, see Danielson, E. G., et al.Radiometric Performance of the Voyager Cameras, JGR, v. 86, Sept. 1981.

Instrument Filter ‘0 - CLEAR’

      Filter Name                    : CLEAR      Filter Type                    : ABSORPTION      Minimum Wavelength             : 0.280000      Maximum Wavelength             : 0.640000      Center Filter Wavelength       : 0.460000

Optics/filter response plots and data

Instrument Filter ‘1 - VIOLET’

      Filter Name                    : VIOLET      Filter Type                    : INTERFERENCE      Minimum Wavelength             : 0.350000      Maximum Wavelength             : 0.450000      Center Filter Wavelength       : 0.400000

Optics/filter response plots and data

Instrument Filter ‘2 - BLUE’

      Filter Name                    : BLUE      Filter Type                    : INTERFERENCE      Minimum Wavelength             : 0.430000      Maximum Wavelength             : 0.530000      Center Filter Wavelength       : 0.480000

Optics/filter response plots and data

Instrument Filter ‘3 - ORANGE’

      Filter Name                    : ORANGE      Filter Type                    : INTERFERENCE      Minimum Wavelength             : 0.590000      Maximum Wavelength             : 0.640000      Center Filter Wavelength       : 0.615000

Optics/filter response plots and data

Instrument Filter ‘4 - CLEAR’

      Filter Name                    : CLEAR      Filter Type                    : ABSORPTION      Minimum Wavelength             : 0.280000      Maximum Wavelength             : 0.640000      Center Filter Wavelength       : 0.460000

Optics/filter response plots and data

Instrument Filter ‘5 - GREEN’

      Filter Name                    : GREEN      Filter Type                    : INTERFERENCE      Minimum Wavelength             : 0.530000      Maximum Wavelength             : 0.640000      Center Filter Wavelength       : 0.585000

Optics/filter response plots and data

Instrument Filter ‘6 - GREEN’

      Filter Name                    : GREEN      Filter Type                    : INTERFERENCE      Minimum Wavelength             : 0.530000      Maximum Wavelength             : 0.640000      Center Filter Wavelength       : 0.585000

Optics/filter response plots and data

Instrument Filter ‘7 - ULTRAVIOLET’

      Filter Name                    : ULTRAVIOLET      Filter Type                    : INTERFERENCE      Minimum Wavelength             : 0.280000      Maximum Wavelength             : 0.370000      Center Filter Wavelength       : 0.325000

Optics/filter response plots and data

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Instrument Optics ‘ISS-NA’

      Telescope Diameter             : 0.176500      Telescope F Number             : 8.500000      Telescope Focal Length         : 1.502380      Telescope Resolution           : 0.000018      Telescope Serial Number        : NAO-05      Telescope T Number             : 12.110000      Telescope T Number Error       : 0.110000      Telescope Transmittance        : 0.600000

The Narrow-Angle camera optics is a 1500mm diameter focal length all-spherical, catadioptric cassegrain telescope (a modified MVM 1973 design)consisting of five elements plus an additional dust lens located between theshutter and the vidicon. The f stop number is 8.5. (VGR ISS CalibrationReport, 1978, an internal JPL document available from JPL vellum files).

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Instrument Operational Modes

Instrument Mode ‘IM2’

      Data Path Type                 : RECORDED DATA PLAYBACK      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 1:1, full frame image, 800 pix/line (Jupiterand Saturn)

Instrument Mode ‘IM3’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 1:1, full frame, 800 pix/line (Jupiter andSaturn)

Instrument Mode ‘IM4’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 1:1, centered frame, 608 pix/line (Jupiter andSaturn)

Instrument Mode ‘IM5’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 2:1, Top read out in frame #1, bottom read outin frame #2, 800 pix/line (Jupiter and Saturn)

Instrument Mode ‘IM6’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 1:1, centered frame, 440 pix/line (Jupiter andSaturn)

Instrument Mode ‘IM7’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 3:1, full frame, 800 pix/line (Jupiter andSaturn)

Instrument Mode ‘IM8’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 1:1, centered frame, 272 pix/line (Jupiter andSaturn)

Instrument Mode ‘IM9’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 3:1, centered, approx. 480 pix/line (Jupiterand Saturn)

Instrument Mode ‘IM10’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 1:1, centered frame, approx. 160 pix/line(Jupiter and Saturn)

Instrument Mode ‘IM11’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 5:1, centered frame, 800 pix/line (Jupiter andSaturn)

Instrument Mode ‘IM12’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 5:1, centered frame, approx. 440 pix/line(Jupiter and Saturn)

Instrument Mode ‘IM13’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 10:1, centered frame, 800 pix/line (Jupiterand Saturn)

Instrument Mode ‘IM14’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 1:1, centered frame, approx. 80 pix/line(Jupiter and Saturn)

Instrument Mode ‘IM15’

      Data Path Type                 : REALTIME      Gain Mode Id                   : LOW      Instrument Power Consumption   : 14.000000

Scan rate (minor frame:line) is 2:1, centered frame, top read out in frame #1,bottom read out in frame #2, 800 pix/line (Jupiter and Saturn)

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Scan Platform

      Cone Offset Angle              : 0.000000      Cross Cone Offset Angle        : 0.000000      Twist Offset Angle             : 0.000000

The measurements recorded below are the coordinates representing the center ofthe Wide Angle Field-Of-View (FOV) in relation to the center of the NarrowAngle FOV. As of 5/26/88 the Voyager 2 scan platform offset values wereupdated and the removal of all extraneous offset values for VG1 and VG2accomplished. Only the most recently input values remain in the database foreach spacecraft. These values are effective for all periods of data inclusivefrom launch to present. (June 7, 1989).

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