VL1/VL2-M-LCS-2-EDR-V1.0 Software Interface Specification

VL1/VL2 Mars Viking Lander Camera System Experiment Data Record V 1.0

Edward A. Guinness, Thomas C. Stein, Jennifer Herron
Department of Earth and Planetary Sciences
McDonnell Center for the Space Sciences
Washington University
St. Louis, Missouri 63130

Version 1.0

Table of Contents

  1. General Description
  2. Volume Description
  3. Volume and File Organization
  4. Image Access
  5. Image Browser Description


1.1. Overview

This Software Interface Specification (SIS) document contains the description of the CD-ROM archive for the Viking Lander 1 and 2 Imaging Experiment Data Record (EDR) data set.

1.2. Scope

The format and content specifications in this SIS apply to the Viking Lander Imaging EDR archive as stored on CD-ROM and produced by the Planetary Data System's Geosciences Node at Washington University.

1.3. Applicable Documents

  1. ISO 9660-1988, Information Processing - Volume and File Structure of CD-ROM for Information Exchange, April 15, 1988.
  2. NASA Reference Publication 1007, Viking Lander Imaging Investigation, Picture Catalog of Primary Mission Experiment Data Record, Robert B. Tucker, February, 1978.
  3. NASA Reference Publication 1068, Viking Lander Imaging Investigation During Extended and Continuation Automatic Missions, Volume I - Lander 1 Picture Catalog of Experiment Data Record, Kenneth L. Jones, Mary Henshaw, Christe McMenomy, Andres Robles, Paul C. Scribner, Stephen D. Wall, and Jackson W. Wilson, April, 1981.
  4. NASA Reference Publication 1068, Viking Lander Imaging Investigation During Extended and Continuation Automatic Missions, Volume II - Lander 2 Picture Catalog of Experiment Data Record, Kenneth L. Jones, Mary Henshaw, Christe McMenomy, Andres Robles, Paul C. Scribner, Stephen D. Wall, and Jackson W. Wilson, April, 1981.
  5. NASA Reference Publication 1137, Conclusion of Viking Lander Imaging Investigation, Picture Catalog of Experiment Data Record, Stephen D. Wall and Teresa C. Ashmore, March, 1985.
  6. JPL D-7669, PDS Data Preparation Workbook, Version 3.1, February 17, 1995.
  7. JPL D-7669, PDS Standards Reference, Version 3.2, July 24, 1995.
  8. JPL D-7116, Planetary Science Data Dictionary Document, Revision D, July 15, 1996.

1.4. System Compatibility

The CD-ROM is readable on UNIX, PC, and Mac systems.


2.1. ISO 9660 Compatibility

Each volume is an ISO-9660 compliant CD-ROM and may be read on any standard CD-ROM player. The CD-ROM volumes were created according to the ISO-9660 standards. However, the CD-ROM does not contain any Extended Attribute Records (XAR). As a result some VAX/VMS users may have problems accessing files on this system.

2.2. PDS Compatibility

The archive complies with the PDS procedures and standards outlined in references [6], [7], and [8].

Each Viking Lander EDR image product has an attached PDS label that describes the image. Ancillary data files have detached PDS labels.

2.3. Data Sources

When Viking Lander images were transmitted to Earth, they were subjected to a number of programs that organized the data and merged multiple playbacks to minimize errors from data transmission. Once the data were edited and converted to a VICAR format they were placed onto magnetic tape and distributed to Viking Lander Imaging team members. The PDS-formatted images in this archive were created from files stored on the Imaging Team magnetic tapes at Washington University.

2.4. Data Validation

The digital images were visually compared to photographs in references [2], [3], [4], and [5].


3.1. Directory Structure

The EDR image archive volume is an NFS-mountable volume containing the following directories: CATALOG, DOCUMENT, INDEX, CALIB, GEOM, and BROWSE. In addition, there are a series of image data directories. The BROWSE directory contains several subdirectories.

The root directory contains the following files:

AAREADME.TXT - Brief description of volume contents.
AAREADME.HTM - HTML version of the AAREADME.TXT file.
ERRATA.TXT - Description of comments and errors.
VOLDESC.CAT - Volume object definition.

The CATALOG directory contains the following files:

CATINFO.TXT - Description of files in the CATALOG directory.
<files>.CAT - Files describing the Viking mission and spacecraft, Viking Lander camera, and the EDR image data set.

The DOCUMENT directory contains the following files:

DOCINFO.TXT - Description of files in the DOCUMENT directory.
CDVOLSIS.TXT - Software Interface Specification (SIS) document.
CDVOLSIS.HTM - HTML version of the SIS document. This file.
VOLINFO.TXT - Overview of the Viking Lander mission, the Lander cameras, and the archive volume.
VOLINFO.HTM - HTML version of the VOLINFO.TXT document.

The INDEX directory contains the following files:

INDXINFO.TXT - Description of files in the INDEX directory.
INDEX.TAB - Volume index in tabular format.
INDEX.LBL - PDS label for the volume index (INDEX.TAB).
CUMINDEX.TAB - Cumulative index in tabular format.
CUMINDEX.LBL - PDS label for the cumulative index (CUMINDEX.TAB).

The CALIB directory contains the following files:

CALINFO.TXT - Description of the radiometric calibration files and procedures.
CALINFO.HTM - HTML version of the CALINFO.TXT file.
<files> - Calibration data files and detached PDS label files.

The GEOM directory contains the following files:

GEOMINFO.TXT - Description of the geometry calibration files and procedures.
GEOMINFO.HTM - HTML version of GEOMINFO.TXT document.
FIGUREx.GIF - Figures for GEOMINFO.TXT document in GIF format.

The BROWSE directory contains the following files:

INDEX.HTM - Front page of the image browser.
HTML - Directory with subdirectories for HTML pages.
|- nxxx - Directories with HTML pages for images in sequence nxxx.
|- |- lcnxxxfl.HTM - HTML pages for browse image of lcnxxx.fil. (see naming conventions below)
IMAGE - Directory with subdirectories for browse images.
|- nxxx - Directories with browse images in sequence nxxx.
|- |- lcnxxxfl.GIF - Browse image for lcnxxx.fil. (see naming conventions below)
nxxx.HTM - HTML page for directory nxxx.
DD.HTM - HTML page for data dictionary used in browser.
HELP.HTM - HTML page for browser help.
<files>.GIF - Button icons used in browser.

The NXXX directories contain the individual archive image products. An example directory is B0XX that stores images with a PRODUCT_ID in the range of B000 to B099:

lcnxxx.fil - Each image product has a unique name as described below.

l - Lander number, either 1 or 2.
c - Camera number, either 1 or 2.
n - Letter sequence from A through J for Lander 1, and from A through I for Lander 2.
xxx - Number sequence from 0 through 255.
fil - Filter name abbreviation as listed below.

RED - Red filter.
GRN - Green filter.
BLU - Blue filter.
IR3 - Near-infrared (~ 1.00 micrometers) filter.
IR2 - Near-infrared (~ 0.95 micrometers) filter.
IR1 - Near-infrared (~ 0.85 micrometers) filter.
BB1 - High resolution broadband diode with focal length of 1.9 meters.
BB2 - High resolution broadband diode with focal length of 2.7 meters.
BB3 - High resolution broadband diode with focal length of 4.5 meters.
BB4 - High resolution broadband diode with focal length of 13.3 meters.
SUN - Filter used for solar imaging.
SUR - Low resolution broadband diode.
Nxx - Internal calibration image, where xx is a two digit number.

3.2. File Formats

3.2.1. General Fixed Length Record Files

Records in a file with fixed length records are all the same length. Fixed length records do not necessarily contain embedded information to indicate the beginning or end of a record. The starting byte of any record can be calculated as follows:

     offset = (record - 1) * length

     where:    offset = byte offset from start of file
               record = desired record number
               length = length of record in bytes

Each image file on this volume is broken into logical records of fixed length. Information pertaining to the size of the record is contained in the PDS label, which is discussed in Section 3.3.2.

Tables (.TAB files) are also fixed length files. Text Files

Text files are stored as ASCII files in stream format. A stream format file can have records of varying length. The end of a record for a stream file on this volume is marked by carriage return <CR> and line feed <LF> characters to accommodate various operating systems.

Detached label files, catalog files, text files (.TXT), and HTML file (.HTM) on this volume are stored in stream format. Text files have an attached PDS label at the beginning of the file. Data Format Descriptions

The reference data unit for image data is a binary byte. Each PDS format image on this volume contains several objects with different data types. The PDS label is ASCII format, image data are 8-bit unsigned integers, and histograms are 32-bit integers with a most-significant-byte first format.

3.3. PDS Image File Format

3.3.1. Image File Structure

PDS format image files on this volume have a PDS ASCII text label at the beginning of the file. The PDS label is followed by a histogram for the image, and then followed by the image data with one image line per record. The histogram records the number of pixels at each brightness level. The PDS label and the histogram are padded with 0 valued bytes, if necessary, to maintain the fixed length record structure. Each image is 512 pixels high. The image width (hence the record size) varies from image to image.

Each section of the image file begins at a logical record boundary. The image structure is illustrated below.

             |           PDS Label          |
             |               :              |
             |  :  |        Padding         |
             |           HISTOGRAM          |
             |         :      |  Padding    |
             |             Image            |
             |          (512 lines)         |
             |               :              |
             |               :              |
             |               :              |
             |               :              |
             |               :              |
             |               :              |

             |<------- Width varies ------->|
                from image to image

3.3.2. Image Label Structure

The PDS label conforms to the requirements of the PDS Data Preparation Workbook [6] and Planetary Science Data Dictionary Document [8]. The label describes the image and its format. The label structure is keyword = value. A label example is provided below.

PDS_VERSION_ID                  = PDS3


RECORD_TYPE                     = FIXED_LENGTH
RECORD_BYTES                    = 564
FILE_RECORDS                    = 518
LABEL_RECORDS                   = 4

^HISTOGRAM                      = 5
^IMAGE                          = 7


DATA_SET_ID                     = "VL1/VL2-M-LCS-2-EDR-V1.0"
INSTRUMENT_NAME                 = CAMERA_2
PRODUCT_ID                      = "12A006-BLU"
TARGET_NAME                     = "MARS"
START_TIME                      = 1976-07-21T09:01:28Z
STOP_TIME                       = 1976-07-21T09:07:29Z
LOCAL_TIME                      = 12.36
PLANET_DAY_NUMBER               = 1
START_AZIMUTH                   =  80.0 
STOP_AZIMUTH                    = 147.5 
CENTER_ELEVATION                = -20.0 
FILTER_NAME                     = BLUE
OFFSET_NUMBER                   = 1
GAIN_NUMBER                     = 5
DETECTOR_TEMPERATURE            = 11.1
START_RESCAN_NUMBER             = 0
TOTAL_RESCAN_NUMBER             = 0
SCAN_RATE                       = 16000 
DUST_FLAG                       = TRUE
MISSING_SAMPLES                 = 1
NOTE                            = "FIRST LANDER 1 COLOR IMAGE"


OBJECT                          = HISTOGRAM
 ITEMS                          = 256
 DATA_TYPE                      = MSB_INTEGER
 ITEM_BYTES                     = 4
END_OBJECT                      = HISTOGRAM

OBJECT                          = IMAGE
 LINES                          = 512
 LINE_SAMPLES                   = 564
 SAMPLE_TYPE                    = UNSIGNED_INTEGER
 SAMPLE_BITS                    = 8
 SAMPLE_BIT_MASK                = 2#11111100#
 CHECKSUM                       = 15253232
END_OBJECT                      = IMAGE


3.3.3. Image Label Keyword Definitions

Definitions for keywords in the PDS image label are listed in this section. These definitions are based on the standard PDS data dictionary definition, but are, in some cases, customized or expanded for the specific application to the Viking Lander images.

The Viking Lander cameras were facsimile scanning systems. They had a mirror that rotated around a horizontal axis to scan about 100 degrees in elevation. They also rotated around a vertical axis to scan nearly 360 degrees of azimuth. Note that a scan line refers a vertical line of data collected at a given camera azimuth.

There are several coordinate systems used for the elevation and azimuth coordinates of Viking Lander image data. Azimuth and elevation values in the PDS labels are given in the Camera- Aligned Camera Coordinate System (CACCS) [2]. In this coordinate system, azimuths increase in the clockwise direction when viewed from above. The 0 degree azimuth reference for a camera is toward the general direction of the other camera. The 0 degree elevation reference is a plane perpendicular to the camera's azimuth rotation axis. Elevation is negative below this plane and positive above. FILE FORMAT AND LENGTH KEYWORDS

The PDS_VERSION_ID element indicates the version number of the PDS standards that apply to a data product label. The value for the Viking Lander image archive is PDS3, which indicates that version 3 of the PDS standards apply.

The RECORD_TYPE element indicates the format of records in a file. Viking Lander image files have fixed length records.

The RECORD_BYTE element indicates the number of bytes in a record.

The FILE_RECORDS element indicates the number of records, including PDS label records and data records.

The LABEL_RECORDS element indicates the number of file records that contain PDS label information. The number of data records in a file is determined by subtracting the value of LABEL_RECORDS from the value of FILE_RECORDS. POINTERS TO START RECORDS OF OBJECTS IN FILE

The ^HISTOGRAM keyword gives the starting logical record number of the histogram object.

The ^IMAGE keyword gives the starting logical record number of the image object. IMAGE DESCRIPTION KEYWORDS

The DATA_SET_ID element is a unique alphanumeric identifier for a data set. DATA_SET_ID is a combination of identifiers for the mission, target, instrument, data type, and version of the data set. In most cases the DATA_SET_ID is an abbreviation of the DATA_SET_NAME.

The SPACECRAFT_NAME element provides the full name of a spacecraft. Values for the Viking Landers are VIKING_LANDER_1 and VIKING_LANDER_2.

The INSTRUMENT_NAME element provides the full name of an instrument. Values for the Viking Lander cameras are CAMERA_1 and CAMERA_2.

The PRODUCT_ID element is a unique identifier assigned to a data product by the data product producer. For Viking Lander images, PRODUCT_ID has the form LCXSSS-FFF, where L is the lander number, C is the camera number, X is a letter (starting with A for the first images and ending with J for Lander 1 and I for Lander 2), SSS is a sequence number from 000 to 255, and FFF is a code for the filter name. Note that when the sequence number reaches 255, it was then reset to 000 and the letter was incremented. An example PRODUCT_ID is 12A001-BB1 for the first image acquired by Viking Lander 1.

The MISSION_PHASE_NAME is a commonly used identifier for a portion of time during a mission. Examples are PRIMARY MISSION and EXTENDED MISSION.

The TARGET_NAME identifies a target. The target may be a planet, satellite, ring, region, feature, asteroid, or comet. For the Viking Lander image data set, TARGET_NAME values include MARS, SUN, PHOBOS, DEIMOS, and N/A. The N/A values are associated with calibration images.

The START_TIME element provides the date and time in UTC of the beginning of an image. Format is yyyy-mm-ddThh:mm:ssZ.

The STOP_TIME element provides the date and time in UTC of the end of an image. For Viking Lander images STOP_TIME may be approximate. Format is yyyy-mm-ddThh:mm:ssZ.

The LOCAL_TIME element provides the local time of day, measured in local hours from midnight. A local hour is defined as one twenty-fourth of a local solar day. A local hour for Mars, by this definition, is longer than an hour because a Mars solar day is greater than 24 hours. Also, the value of LOCAL_TIME is given as a decimal number (NOT as hour and minutes). For Viking Lander images LOCAL_TIME is the local time at the start of the image.

The PLANET_DAY_NUMBER element indicates the number of days elapsed since the landing day (landing day is zero). This keyword is often referred to as sol number for the Viking Landers.

The START_AZIMUTH is the azimuth at which an image starts. It is given in degrees in the camera-aligned camera coordinate system.

The STOP_AZIMUTH is the azimuth at which an image stops. It is given in degrees in the camera-aligned camera coordinate system.

The CENTER_ELEVATION is the elevation at the center line of an image. Depending on the SAMPLING_PARAMETER_INTERVAL value, the camera scanned either approximately 20 degrees or 60 degrees in elevation.

The OBSERVATION_TYPE element identifies the general type of an observation. For Viking Lander images, some examples are HIGH RESOLUTION SINGLET, COLOR TRIPLET, and INFRARED TRIPLET.

The FILTER_NAME element provides the common name of the instrument filter used for a given image. Values of FILTER_NAME for Viking Lander images include: BB1, BB2, BB3, BB4, BLUE, GREEN, RED, IR1, IR2, IR3, SURVEY, and SUN.

The SAMPLING_PARAMETER_INTERVAL element identifies the spacing between data points. In this case, SAMPLING_PARAMETER_INTERVAL is the spacing between pixels of an image. Possible values for Viking Lander cameras are 0.04 and 0.12 degrees in azimuth and elevation.

The OFFSET_NUMBER indicates the offset value used in the analog to digital conversion. The offset was a constant voltage added to the measured voltage signal before digitization. Viking Lander cameras had 32 commandable offsets with equal voltage steps.

The GAIN_NUMBER indicates the gain value used in the analog to digital conversion. The gain value was a multiplicative factor used in the analog to digital conversion. There were 6 commandable gains for the Viking Lander cameras.

The DETECTOR_TEMPERATURE is the average detector temperature during the time of image acquisition. Values are given in degrees Celsius.

The START_RESCAN_NUMBER is the scan line number at which the rescan mode begins. The rescan mode consists of scanning vertically repeatedly at the same azimuth. A value of 0 for START_RESCAN_NUMBER means there was no rescan.

The TOTAL_RESCAN_NUMBER is the total number of rescan lines acquired.

SCAN_RATE is the rate at which the instrument scanned while acquiring a data frame. For Viking Lander images, the SCAN_RATE value is given in bits/second.

The DATA_PATH_TYPE element describes the telemetry path that data traversed from spacecraft to the ground. Values for Viking Lander images are RECORDED UHF LINK, REALTIME UHF LINK, RECORDED S-BAND LINK, and REALTIME S-BAND LINK

The DUST_FLAG parameter indicates whether a dust sequence was executed in association with an image. It is TRUE if a Viking Lander camera was commanded to discharge a stream of CO2 gas across the protective outer window of the camera prior to acquiring an image. It is FALSE otherwise.

The MISSING_SCAN_LINES element is the total number of scan lines missing from an image when it was received on Earth. Missing scan lines are filled with zeros in the archive image file.

The NOTE element provides miscellaneous notes or comments about a data product. The note in Viking Lander image labels indicates the reason for acquiring the image or describes the image content. HISTOGRAM OBJECT KEYWORDS

The ITEMS element defines the number of multiple occurrences of a single object, such as a column. In this case there are 256 items in the image histogram.

The DATA_TYPE element supplies the internal representation and/or mathematical properties of a value being stored. For example, MSB_INTEGER means an integer number stored in most significant byte first order.

The ITEM_BYTES element gives the size in bytes of an item within a data object. IMAGE OBJECT KEYWORDS

The LINES element is the total number of data instances along the vertical axis of an image. For Viking Lander EDR images there are always 512 lines.

The LINE_SAMPLES element is the total number of data instances along the horizontal axis of an image. The number of samples for Viking Lander images varies from image to image.

The SAMPLE_TYPE element indicates the data storage representation of sample value. For example, UNSIGNED_INTEGER is a positive integer number.

The SAMPLE_BITS element indicates the number of bits used to store one data sample value. The value is always 8 for Viking Lander EDR images.

The SAMPLE_BIT_MASK element identifies the active bits in a sample. The value 2#11111100# means that the original 6-bit data value was multiplied by 4 to generate the data value in the archive product.

The CHECKSUM element is sum of all data values in a data object.


PDS provides software for displaying PDS format images on a variety of computer platforms. The application program for image display is called NASAView, which has versions for SUN, Macintosh, and PC platforms. For some computer platforms, there is a NASAView version that will work as a Web browser helper application.

It is the intent of PDS to distribute NASAView through its Web and FTP sites. Consult the PDS Web site (http://pds.jpl.nasa.gov/) for the status of NASAView in terms of its current capabilities and availability.


The image browser system contained on this volume is a hypertext based system that provides a simple quick-look capability. It consists of a series of HTML pages including one for each image. The INDEX.HTM file in the BROWSE directory is the front page of the image browser. The front page includes a brief description of the image browser. Additional help on using the image browser can be found on the help page, which is accessible from most sections of the image browser. Each image page displays a reduced size version of the PDS format image. The browse image has also been contrast enhanced. Most of the PDS label is displayed with the browse image.

Browse images are stored in GIF format. They can be displayed outside the image browser with any image display tool that can handle GIF images.

The image browser is for the most part compliant with HTML version 2.0. However, it does use HTML tables, which may cause problems on some Web browsers.