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Originally Posted by craterchains
Hope everyone has the idea now that when looking at these photos one has to take into consideration what other factors may be causing what appears to be changes on Mars between these photos. That being all stated and presented now brings us to the actual examination of the photographs content.
Examine the area C-7 for changes and comment on what you note.
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As I have already said, the THEMIS image you cite is a shaded relief map, showing NO SURFACE REFLECTANCE FEATURES. The area may be varied in the spectral wavelenths of the Viking image but have little topographic variablility, or that variablility might not show on the shaded relief map due to the chosen light direction or perhaps the elevation post spacing in that area. You would have to compare VISIBLE reflectance data (in similar wavelengths) from MGS or Odyssey with the Viking image. NOT a shaded relief map.
The same site as the OP THEMIS map has the option to switch to an albedo map, but I'd advise against using this as well, since we don't know if the spectral range of the Viking imagery matches what was used for albedo calculations in the THEMIS map.
CJSF