Viking Orbiter Image Viewer

Software for Viking Orbiter TV experiment.

Program VikingOrbiterView is created for Viking Orbiter Raw Image Archive on CD-ROM (PDS). Data set id: NSSDC ID PSPA-00073. Other id: 75-075A-01c, 75-075A-01d, 75-083A-01a, 75-083A-01b. The Viking Orbiter images are arranged on the CD's in chronological order for each Orbiter, grouped by orbit number. There are 32 CD's with Viking 1 Orbiter images (VO_1001 to VO_1032) holding over 34,200 frames and 14 CD's for Viking 2 (VO_1051 to VO_1064) with over 15,600 images.

These CD-ROMs contain raw images taken by the Visual Imaging Subsystems (VIS) on NASA's twin Viking Orbiter spacecraft to Mars. These images are copies of the Experiment Data Record (EDR) images. No processing has been performed on the EDR image data. Thus, processing to perform radiometric and geometric calibration, removal of noise, and interpolation of missing data may be required to interpret the images.

The EDR image data are stored on CD-ROM in a compressed format that allows exact reconstruction of the original images. The average Viking Orbiter image is compressed by a factor of about 3.5. 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 First-Difference Huffman encoding algorithm.

This data set is available:
from National Space Science Data Center (NSSDC)
http://nssdc.gsfc.nasa.gov/
online on CD or DVD in a jukebox at the PDS Central Node.
http://www-pdsimage.jpl.nasa.gov/PDS/public/resources/cd_viking.html#vkoEDR
or on PDS online data volumes
http://pds-imaging.jpl.nasa.gov/Admin/resources/cd_viking.html#vkoEDR

VikingOrbiterView is a Windows viewer for this data set.

Example 1.
Viking Orbiter 1 - Marineris Vallis.

Program options

Auto Despeckle
Auto Contrast Stretch
Auto Flip Vertically
Auto Rotate
Auto Invert Display
Auto Missing Lines Removal
Auto Minimize 1 ( 50% original image )
Auto Scan - scan pause options (2,3,4,5 seconds)

Example 2.
Viking Orbiter 1 - Tharsis volcanoes.

Buttons

Next and Previous image buttons
Scan Forward button
Scan Backword button
Scan Stop button
Restore Original Image button
Despeckle on/off button
Contrast Stretch on/off button
Flip Vertically on/off button
Rotate on/off button
Invert Display on/off button
Missing Lines Removal on/off button
Minimize 50% on/off button
Brightness up/down buttons
Contrast up/down buttons
Info Image button

Additional options

Save as BMP
Print Setup
Print

Viking Orbiter mission overview.
Viking Mission consisted of four spacecraft: two identical orbiters and two identical landers. Viking spacecraft were launched from Cape Canaveral - Viking 1 on August 20, 1975, and Viking 2 on September 9, 1975. The spacecraft spent nearly a year cruising to Mars. Viking 1 reached Mars orbit June 19, 1976, Viking 2 began orbiting Mars August 7,1976. The Viking Orbiter spacecraft operated in orbit around Mars from 1976 until 1980. The overall Viking mission was divided into a number of misssion phases with specific objectives.

Primary Mission - from orbital insertion until November 1976. The main objective in this phase was to collect data in support of landing selection
Extended Mission - from November 1976 through May 1978
Continuation Mission - from May 1978 through February 1979
Survey Mission - from July 1979 until July 1980 (only Viking Orbiter 1). Survey mission was designed to obtain contignous high resolution coverage of the Martian cratered terrain.

Scan platform with Visual Imaging Subsystem

Visual Imaging Subsystem.

Each Viking Orbiter was equipped with two identical vidicon cameras, called the Visual Imaging Subsystem. Each VIS camera consisted of a telescope, a slow scan vidicon, a filter wheel and associated electronics. The angular field of view of camera as defined by the reseau pattern was 1.51 by 1.69 degrees. A digital image was generated by scanning the vidicon face plate. The signal at each location (pixel) was digitized as 7-bit number and converted to 8-bit number by multiplying by 2. A full-resolution, uncompressed Viking image consist of an array of 1056 lines with 1204 samples in per line. Each VIS camera contained a filter wheel with five color filters and a clear position (no filter).
The filter bandwidith are approximately:

blue - from 0.35 to 0.53 micrometers
minus-blue - from 0.48 to 0.70 micrometers
violet - from 0.35 to 0.47 micrometers
clear - from 0.35 to 0.70 micrometers
green - from 0.50 to 0.60 micrometers
red - from 0.55 to 0.70 micrometers

Viking Orbiter data decompression method
A compressed image file is composed of variable-length records defined according to the ISO-9660 standard. Each variable length record starts with a record length indicator, stored as 16-bit integer, followed by the number of bytes indicated in the record length indicator.

Compressed Viking Orbiter image structure:

PDS label area
Image Histogram
Encoding Histogram
Engineering Table
Line Header Table
Image Object

The Image Object contains 1056 variable-length records; each represents a single line. The compressed lines have varying lengths because the compression factor for each line is different. The first byte of a compressed line is original value of the first sample in the line. The rest of record contains the Huffman coded bits of first-difference value.

Steps for image decompression:

Encoding Histogram and Image Object localization
First-difference Encoding Histogram extraction
Huffman tree creation using Encoding Histogram
Extraction and restoration of Image Object lines using Huffman tree

Important information: Each item of encoding histogram is a 32-bit VAX integer. Bytes are written from right to left.

Huffman Tree.
The Huffman coding technique creates variable length bit strings to represent each value. The most frequently occuring values (in this case first-difference values) will consist of very short bit strings, and the less frequently occuring values will of longer bit strings. The first element of the Viking Orbiter image encoding histogram contains the number of pixels with a first difference value of -255. The last element contains the number of pixels with first-difference value 255. Encoding histogram contain total 511 items.

Huffman tree example.
Suppose we know that the frequency of occurrance for six item A-3, B-4, C-9, D-10, E-11, F-17
To build the Huffman tree, we sort the frequencies into increasing order (3, 4, 9, 10, 11, 17). Then we choose the two smallest values, 3 and 4, and construct a binary tree with labeled edges. Next, we replace the two smallest values 3 and 4 with their sum, getting a new sequence, (7, 9, 10, 11, 17). We again take the two smallest values, 7 and 9 and construct a labeled binary tree. We now have the frequencies (16, 10, 11, 17) which must be sorted into (10, 11, 16, 17) and the two lowest are selected once again.

Decompression involves re-building the Huffman tree from a stored frequency table, and converting its bit streams into characters. You read the file a bit at a time. Beginning at the root node in the Huffman Tree and depending on the value of the bit, you take the right or left branch of the tree and then return to read another bit. When the node you select is a leaf (it has no right and left child nodes) you write its character value to the decompressed file and go back to the root node for the next bit.
In this example: 0 - right branch 1 - left branch
A (probability 3/54) - 0111, B (probability 4/54) - 0110, C (probability 9/54) - 010,
D (probability 10/54) - 11, E (probability 11/54) - 10, F (probability 17/54) - 00

Noise filtering.
Many Viking Orbiter images are missing data and contain some amount of noise. 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.

Original image (contrast stretched)

Full size (502 KB)

Image filtered by VikingOrbiterView

Full size ( 180 KB)

A common pattern of missing data is 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.

Original image

Full size (231 KB)

Image filtered by VikingOrbiterView

Full size ( 245 KB)

If the amount of mising data and noise is large, noise removal may be needed to make the image viewable.

Viking Orbiter 1 and 2 processed image gallery
Example 3.
Heavily cratered terrain.

Oblique view obtained by Viking Orbiter 1 showing the heavily cratered terrain. Heavily cratered terrain occurs mostly in the southern hemisphere. Horizon in the background shows haze layers 24-40 km high, thought to be crystals of carbon dioxide.
Viking Orbiter frame F101A32.

Full size (231 KB)

Example 4.

Cratered upland.

Cratered southern upland - scene typical at latitudes above about 30 degrees. The rims of many large craters are rounded and softened.
Viking Orbiter frame F093A47.

Full size (282 KB)

Example 5.

View of the martian moon, Phobos.

View of the martian moon, Phobos, showing grooved and cratered surface. The albedo, spectral reflectance and low density of both martian moons suggest that they have a composition similar to carbonaceus chondrites.
Viking Orbiter frame F250A68.

Full size (121 KB)

See also :

Mariner 10 Image Browser and Reconstructor