Lunar and Planetary Institute






 


Winds of Mars: Aeolian Activity and Landforms

Appendix


Mariner and Viking Image Nomenclature


Mariner 9 Photographs

Mariner 9 images are identified by their DAS (Data Automation Subsystem) time number. DAS time is an eight-digit integer incremented each 1.2 seconds. The DAS time at which the camera was shuttered is listed in the main data file, the SEDR (Supplementary Experiment Data Record). The final processed photographs, the RDR (Reduced Data Record) version, use a DAS number that is five counts larger than that in the SEDR, representing the DAS time of the arrival of the first line of data.

Viking Orbiter Photographs

A much simpler system is used to identify the Viking orbiter photographs. Each frame has a unique picture number with the format mmmxyy, where mmm denotes the orbit number and yy denotes the number in the photo sequence taken in that orbit. X can be A, B, or S: A denotes Viking 1 orbiter, B denotes Viking 2 orbiter, and S denotes Viking 1 orbiter for orbits greater than 999. (The Viking spacecraft were designed for only a 90-day lifetime! Both orbiters eventually ran out of altitude control gas and both landers died a natural death. VL-1 was the last to go, hanging on until November 1982, completing over 75 months of service on the surface of Mars.)

Two processed versions of Viking images are in common use, SCR2 and NGF. The raw image often lacked contrast, so the SCR2 (Shading Corrected) version stretched the image contrast to make the darkest thing in the image completely black and the brightest thing in the image completely white, with the intermediate brightness values stretched accordingly. The other common version, NGF (Non Gradient, high-pass Filtered), used what is called an asymmetric boxcar filter for image processing. Two projections were used: rectilinear (as seen by the spacecraft) and orthographic (a geometrically processed image of the scene as it would appear from directly overhead). Viking pictures would be taken using an array of filters: clear, red, green, blue, violet, and minus-blue. Minus-blue is a filter that passes all but blue light; the other filters pass only the color indicated. Color images can be constructed by combining black-and-white images taken with different color filters, usually red, green, and blue.

For more information on Mariner 9 photographs, see Mutch et al (1976); for more on Viking orbiter photographs, see Carr (1981).

Viking Lander Photographs

The Viking lander photographs are uniquely identified by a number with the following format: abxmmm/nnnn. The mission number is designated by a = 1 for VL-1 or a = 2 for VL-2. There are two cameras on each lander, designated by the b number. The frame number is designated by the xmmm character string, with x being a letter and mmm being a number. The framing sequence, regardless of the camera used, starts at AOOO and counts sequentially to A255, then the next frame is BOOO and so on. The nnnn number is the sol on which the photograph was taken.

Viking Lander Images Processed at Washington University in St. Louis

The high-resolution, color-enhanced slides of the martian surface (slides #27, #28, and #30) were made by combining high-resolution black-and-white images with lower-resolution three-channel (red, green, and blue) images. Care was taken in image selection to ensure similar illumination geometry between images.

The color triplets were processed as follows. The first step was to remove random noise spikes from the image, then expand them in size by a factor of three to match the high-resolution frame scale. The three-channel image was then converted into intensity, hue, and saturation images (see a basic text on image processing for a more detailed explanation of the processing described in this Appendix). In this usage, hue is the peak wavelength, intensity is the amount of energy at that wavelength, and saturation is a measure of how much energy is received at wavelengths near the peak value. The high-resolution images were substituted for the intensity image derived from the color triplet and subjected to a linear contrast enhancement (similar to the SCR2 stretch for Viking orbiter photographs). Linear contrast enhancement was performed on the saturation image and a piecewise contrast enhancement was performed on the hue image. The last step was to convert back into red, green, and blue images and to generate a color composite image. The resulting image provides a detailed color portrayal of the surface, and one in which colors can be enhanced to show variations from place to place.

The designated slides in this set were produced at the Earth and Planetary Remote Sensing Laboratory, Department of Earth and Planetary Sciences, McDonnell Center for the Space Sciences, Washington University, St. Louis, headed by Dr. Raymond Arvidson. They were generously made available by Mary Ann Dale-Bannister. My thanks to all involved in their preparation.


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