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Posted by: Bjorn Jonsson Apr 11 2008, 01:11 AM

I now have a crude DEM of Mimas' Herschel crater created from a stereo pair. The DEM is relatively crude, both because the source images used are relatively distant and because the difference in viewing geometry wasn't very big - I couldn't use images where the difference was greater because in that case the difference in illumination became too big.

First a section of the DEM:

Many of the small scale details are noise and not real features. This version of the DEM has been heavily processed to remove noise, spurious 'contours' and to smooth it.

The central peak seems to rise 8-10 km above the creater floor. This is a bit difficult to estimate accurately, if I do not smooth the DEM the estimated height rises a bit. The crater floor may be too deep SE of the peak and/or the peak to high. The reason for this is that when I render the DEM the peak's shadow becomes a bit longer than in the images I used to create the DEM. The crater seems to be about 10-12 km deep except for a small, deeper area SE of the central peak. Again, this may be inaccurate.

This is an animation showing Herschel and the central peak:

 mimas_herschel_new.avi ( 1.17MB ) : 508


Some inaccuracies are evident, for example the shadows in the texture map draped over the DEM do not match the DEM perfectly. Despite this the animation looks interesting. That thing is *huge*. And the floor is flat - it's not curved like the terrain surrounding the crater. The field of view is 40 degrees and the altitude above Mimas' surface is 200 km.

A sample frame from the animation:



Now I'm trying to create another DEM of Herschel from the recently released PDS data. I then want to compare that DEM to this one to get an accuracy estimate. Creating this new DEM is turning out to be difficult because Herschel is lit from almost directly above. Thus there are almost no shadows and matching features is difficult. However, Cassini should be able to image Herschel at far higher resolution than ever before during a 9500 km flyby late in its extended mission.

Posted by: dilo Apr 11 2008, 05:44 AM

Very nice animation, Bjorn!

Posted by: djellison Apr 11 2008, 07:19 AM

It's no good - we're going to have to change your name to Randy Kirk Home Edition.

GREAT stuff.

Doug