Data Set Overview : After the digital data were transmitted to Earth and received at the Jet Propulsion Laboratory, they were subject to a variety of processes to produce the final digital tapes and photoproducts. The first step was to strip out all the non-video data and produce a System Data Record (SDR). This was compiled into video format, and an Experiment Data Record (EDR) was produced. The EDR data consist of unprocessed (raw) instrument data. Substantial processing is required to reconstruct each image owing to the unique manner in which data were transmitted to earth. Images were initially recorded on 7-track magnetic tape recorders on the spacecraft. Each raw data frame retrieved from the tracking station thus contains every seventh pixel arranged in either increasing or decreasing order. Image data reconstructed from these raw data frames by the Mission Test Imaging System (MTIS) form the EDR digital archive tape.  The Orbiter Visual Imaging Subsystem (VIS) consists of two high-resolution, slow-scan television framing cameras, each with a telescope having 475-mm focal length and a 37-mm-diameter vidicon, the central region of which is scanned with a raster format of 1056 lines by 1182 samples. Each field of view is 1.54 deg. X 1.69 deg., and each picture element subtends 24.8 microradians. The optic axes are offset by 1.38 deg. so that the fields overlap slightly. The cameras are shuttered and read out alternately, providing a single contiguous digital data stream, the interval between pictures (one frame time) being 4.48 s. This interval determine the basic timing of the other two science instruments as well. Each camera has five color filters and one clear 'filter'.  The objectives of the Viking Orbiter imaging investigation were to characterize potential landing sites in sufficient detail to support the site choice topographic, photometric, and colorimetric characteristics of the surface features (volcanos, canyons, channels, faults, polar cap formations, etc.) that have been discovered by Mariner 9 to improve our knowledge of the geologic evolution of Mars document changes in cloud structure, polar caps, polar hoods, and in the contrast of the surface features observe the vertical structure of the atmosphere.  The orbiter photographed 100% of Mars at a resolution of at least 260 meters per pixel, 84% at 240 meters per pixel, 60% at 220 meters per pixel, 44% at 200 meters per pixel, 30% at 180 meters per pixel, 17% at 160 meters per pixel, 6% at 140 meters per pixel, 5% at 100 - 60 meters per pixel, and less than 1% at 30 meters per pixel.  The Planetary Conversion Task rerecorded JPL's digital archive of planetary images (EDR) onto 9-track 12in tape reels at 6250 bpi with 32,000 bytes per block (VSFEDR format). The VSFEDR format consists of a VICAR standard header label, mission dependent VICAR labels, the digital image lines (1056 lines with 1204 pixels per line), engineering data (396 bytes) appended to each line, and mission dependent EDR header record. Pixel values are stored as 8-bit integers with a range of 0 to 254. The values represented on the EDR tape are actually two times the value received in the telemetry stream. Because of the nature of the recording and playback system, strings of missing bits appear as vertical bars at 7-pixel intervals. Missing pixels are set to zero in the EDR tape. Further details describing this format and tape contents will be supplied with the tape.  Additional mission products are also available. These include systematic photoproducts and Supplementary Experimental Data Record (SEDR). Systematic processing of the EDR to clean up and enhance the images produced a shading-corrected and contrast enhanced version called the SCR-2 and two filtered versions, orthographic and rectilinear, called the NGF. The geometric data were compiled into the SEDR.   Processing Level Id : 2 Software Flag : N Processing Start Time : 1976   Parameters :  Description ----------- Data Number is an integer expressing the digital value of an experiment's telemetry data.  Sampling Parameter Name : PIXEL Data Set Parameter Name : DATA NUMBER Data Set Parameter Unit : DIMENSIONLESS Noise Level : UNK   Source Instrument Parameters : Instrument Host ID : VO1 Data Set Parameter Name : DATA NUMBER Instrument Parameter Name : RADIANCE Important Instrument Parameters : 1  Instrument Host ID : VO2 Data Set Parameter Name : DATA NUMBER Instrument Parameter Name : RADIANCE Important Instrument Parameters : 1   Processing :  Processing History ------------------ Source Data Set ID : P30 CARDS Software : VISRAP (MTIS SOFTWARE) Product Data Set ID : VO1/VO2-M-VIS-2-EDR-V1.0  Source Data Set ID : SYSTEM DATA RECORD (SDR) Software : VISRAP (MTIS SOFTWARE) Product Data Set ID : VO1/VO2-M-VIS-2-EDR-V1.0   Software 'VISRAP' ----------------- Software Name : VISRAP (MTIS SOFTWARE) Software Type : N/A Software Release Date : 1976 Node ID : PIN Cognizant Engineer : RICH BENSON Software Access Description : N/A

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