Data Set Information
DATA_SET_NAME VO1/VO2 MARS VISUAL IMAGING SS EXPRMNT DATA RECORD V2.0
DATA_SET_ID VO1/VO2-M-VIS-2-EDR-V2.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : This data set is a digital archive of images acquired by the Viking Orbiter 1 and 2 spacecraft. The archive will include the best available Experiment Data Record (EDR) versions of images acquired by the Viking Orbiter Visual Imaging Subsystems (VIS). The archive is stored on compact read-only optical disk media (CD-ROM) for distribution. The EDR image data are stored on CD-ROM in a compressed format that allows exact reconstruction of the original image. The images were compressed in order to reduce the number of CD-ROMs required for the archive. The average Viking Orbiter image is compressed by a factor of about 3.5. Each CD-ROM in the archive also includes documentation about the organization and contents of the disk. Software is included to provide programmers with tools to decompress image files. The CD-ROM has index files containing information about all the images stored in the archive. These index files can be loaded into a database management system to help the user locate images of interest. The EDR images in this archive have not been processed in any form other than organizing the original telemetry into raster formatted files and compressing the image data using a Huffman encoding algorithm. The reason for distributing unprocessed data rather than processed versions of the images is that the calibration files and processing procedures will continue to evolve. This is due to improvements, not only in the procedures, but also in the radiometric calibration data and in the geometric information concerning spacecraft position and pointing. By providing unprocessed images, improved image processing capabilities can be reapplied to the original unprocessed data. To make full scientific use of the image collection, it is necessary to understand the radiometric and geometric properties of the Viking Orbiter imaging systems and to perform corrections to the EDR data. A number of image processing systems are available that provide radiometric and geometric corrections, display capabilities, and analysis tools for planetary images. Further information on processing Viking Orbiter image data and the necessary radiometric and geometric calibration data is available through the PDS Image Node at the U.S. Geological Survey in Flagstaff, Arizona. Processing Level Id : 2 Software Flag : N Processing Start Time : 1990-11-01 Processing Stop Time : UNK 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 : MASTER DATA RECORD (MDR) Software : UNK Product Data Set ID : VO1/VO2-M-VIS-2-EDR-V2.0 Source Data Set ID : VO1/VO2-M-VIS-2-EDR-V1.0 Software : UNK Product Data Set ID : VO1/VO2-M-VIS-2-EDR-V2.0
DATA_SET_RELEASE_DATE 1990-12-01T00:00:00.000Z
START_TIME 1976-06-22T05:59:00.046Z
STOP_TIME 1980-07-30T10:14:59.046Z
MISSION_NAME VIKING
MISSION_START_DATE 1975-08-20T12:00:00.000Z
MISSION_STOP_DATE 1983-02-01T12:00:00.000Z
TARGET_NAME MARS
DEIMOS
PHOBOS
STAR
TARGET_TYPE PLANET
SATELLITE
STAR
INSTRUMENT_HOST_ID VO1
VO2
INSTRUMENT_NAME VISUAL IMAGING SUBSYSTEM - CAMERA A
VISUAL IMAGING SUBSYSTEM - CAMERA B
INSTRUMENT_ID VISA
VISB
INSTRUMENT_TYPE CAMERA
NODE_NAME Imaging
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Overview : In the process of preparing the EDR images for inclusion in this data set, several steps were taken to insure that the best available image data and label information were archived. The primary digital data source was a collection of magnetic tapes produced by the Planetary Image Conversion Task. These tapes, also known as the Planetary Archive tapes, constitute PDS Version 1 of the Viking Orbiter image data set (PDS data set id 'VO1/VO2-M-VIS-2-EDR-V1.0'). The data on the Planetary Archive tapes were derived from EDR tapes. The quality of the image data on the Planetary Archive tapes was checked for problems such as missing lines, segments of data from other images, and mismatched images and labels. Some of the images received on Earth were not available on these Planetary Archive tapes. In addition, some Viking Orbiter images were never transferred to EDR tapes. For images with data problems and for images not available from either tape source, attempts were made to retrieve the data from the Viking Master Data Record (MDR) tapes. The accuracy of the image description keywords in the image label was verified by comparing data from several sources. These sources included the PDS Central Node image catalog, image labels on the Planetary Archive tapes, and Mission Test and Imaging System (MTIS) photoproducts. In cases where there were discrepancies among the sources, label values were chosen that occurred most frequently among the sources, maintained consistency among images within a sequence, and agreed with the VIS team planning notes. For example, a discrepancy in exposure duration for an image might be resolved by choosing the value of exposure duration for other images in the same sequence. If a discrepancy could not be resolved, that keyword was assigned the value 'UNKNOWN'. As a check on the data compression procedure, each image was decompressed and compared to the original image. The compressed image file was accepted only if the results of decompression exactly matched the original image data. Many Viking Orbiter images are missing data and contain some amount of noise. A common pattern of missing data is a series of vertical bars with zero value pixels spaced at an interval of 7 samples. The 7-sample interval results from the raw data being stored on the spacecraft and transmitted to Earth in packets that contained every seventh pixel. In addition, data for a few horizontal image lines may be missing and such lines are filled with zero values. The types of noise found in Viking Orbiter images include single-pixel random noise and several sources of coherent noise. The random noise is usually due to telemetry errors. The coherent noise arises from shuttering of the adjacent camera, filter wheel stepping, and scan platform movements. If the amount of missing data and noise is large, noise removal procedures may be needed to make the image viewable. Box filtering techniques that fill in zero values or average the bright and dark spikes of random noise are often successful at noise removal. It should be noted that the START_TIME and the STOP_TIME in the PDS catalog, with values 1976-06-22T17:59:00.469Z and 1980-07-30T22:14:59.469Z respectively, are the times associated with the version 1 data set VO1/VO2-M-VIS-2-EDR-V1.0. These times are approximately correct for the current data set but will be known more accurately only after data processing has been completed. PDS labels embedded in each image file and the index tables on the CD-ROM contain the exact times associated with each image.
CITATION_DESCRIPTION Citation TBD
ABSTRACT_TEXT This data set is a digital archive of images acquired by the Viking Orbiter 1 and 2 spacecraft. The archive will include the best available Experiment Data Record (EDR) versions of images acquired by the Viking Orbiter Visual Imaging Subsystems (VIS). The archive is stored on compact read-only optical disk media (CD-ROM) for distribution. The EDR image data are stored on CD-ROM in a compressed format that allows exact reconstruction of the original image. The images were compressed in order to reduce the number of CD-ROMs required for the archive. The average Viking Orbiter image is compressed by a factor of about 3.5. Each CD-ROM in the archive also includes documentation about the organization and contents of the disk. Software is included to provide programmers with tools to decompress image files. The CD-ROM has index files containing information about all the images stored in the archive. These index files can be loaded into a database management system to help the user locate images of interest.
PRODUCER_FULL_NAME EDWARD A. GUINNESS
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