Wanted to reproduce here my comments from the Mars Anomaly Research guestbook on Report 188.
Hey, in Report 188 Mr. Skipper says that the HiRISE images are raised pillow shapes instead of concave depressions. But that's wrong! And you can verify it from the page that he links to
http://hirise.lpl.arizona.edu/PSP_001446_1790
Right at the bottom of the page in the Observation Toolbox it tells you what the orientation of the sun is for both map-projected (201.5 degrees) and non-map-projected images (27.1 degrees). 0 degrees is right, 90 degrees is down, 180 degrees is left, 270 degrees is up. And the direction of sunlight is really important in visually figuring out whether you're looking at a mound or a depression. It's really easy to get wrong. Your brain is used to seeing things illuminated from the top, so it's easy for your brain to get fooled if the light is coming from the bottom. If you've ever seen a Moon photo of lots of shallow domes, you're looking at a field of craters with the illumination coming from the bottom of the photo. A really good example of how it can fool you is
In the 4th image in the report, the sunlight is coming from the lower right, not the upper left! That makes the terrain look like puffy mounds instead of scalloped depressions. It looks like that image was a closeup cropped from the NON-map-projected image at
If you look at the bottom of that image, you'll see two little craters that likely appear as domes, a sure sign that the sunlight is coming from below. The data from the toolbox corroborates this, a sun azimuth of 27 degrees is from about east-south-east. But look at the map-projected version at
In that image the sunlight is coming from 201 degrees, or about west-north-west, and the craters look like crater depressions and what appeared to be puffy mounds are now seen to actually be scalloped depressions.
I guess that Mr. Skipper just got confused between the images when figuring out what direction the illumination was coming from!
