QUOTE (titanicrivers @ Apr 23 2011, 04:00 AM)
While the SAR Topo maps show Adiri is relative high ground and the bright spots are associated with bright terrain in ISS images, they don't seem to precisely register with the linear bright ridges (presumably the highest ground) seen in the T8 SAR swath.
The T8 Swath just "missed" the lower brighter area in the blink image. But assuming a regular mountain spacing, it's likely there is another mountain "line" just beyond the southern T8 edge that would correlate with the brightened area.
The brightening effect doesn't necessarily need to correlate with elevation. Instead it might correlate with certain materials and the washing off of an overlaying "paint" on those materials. The assumption is that some materials might, but not always, correlate with elevation.
(F'r instance, on Earth, granite might make up the tops of some mountains, while in others it might be schist. But in most cases the valley floors and lowlands are neither, being made up of clays, soils, and general alluvium.)
Another possibility is that the stream bottoms have darker stuff in them. And the more dense the drainage network, the darker the overall terrain. So an elevated region without a lot of bigger channels (or higher order) might be able to brighten as dark stuff gets washed into channel bottoms. But lower down, where there are more channels (and channel bottoms) you still see the same amount of darker stuff so the brightening effect isn't so evident. In that case the brightening effect would correlate with drainage density (at a given channel size resolution), which may also correlate with material. (F'r instance, on Earth you get a much more impressive drainage density in soft clays and weak sandstone than you do in hard relatively impermeable granite or in strongly absorbing surfaces)