QUOTE (Roly @ Oct 3 2006, 08:08 AM)
This probably a really obvious question, but I'm a humble humanities student !
Is there any prospect of multiple (>2) overlapping passes for improving the characterization of particularly interesting sites; or for set of various typical terrains and features encountered across the other SAR passes? [And therefore providing an improved understanding of the single-pass data.]
Something for the extended mission perhaps? Would there be much to be gained perhaps half a dozen of the Huygens site, perhaps coupled with a lower altitude ceiling?
I don't think there's much point to having MANY passes of the same site (n>2), but there is a lot of value, potentially in having exactly n=2. That's not coincidentally why just about every advanced animal has two eyes but basically none have 3. You get stereopsis with 2, and 3 is redundant. With SAR, it's not quite stereopsis we're after, but the principle is analogous: We want to distinguish bright=rough vs. bright=sloped towards the spacecraft. Two perspectives provide the discrimination in most cases, although pathological cases could thwart that.
Unfortunately, Cassini has no chance of an extended mission that so egregiously exceeds the main mission as we've seen with the MERs. I think the best case scenario for additional RADAR passes in the extended mission will be no more than about the same number in the main mission, but that is far on the optimistic side. We might get as few as 6, even assuming that Titan is the sole target (and it will be a major one, by necessity).
Overlap of some stripes is basically unavoidable as mapping continues, so we will get at least some terrain that enjoys that level of scrutiny. However, we're not going to get to map the whole globe once, so overlap comes at the expense of "once-over" coverage. Also, targeted coverage comes at the expense of pragmatics (near-nadir pointing provides best resolution, and orbits must be designed to bring Cassini back to Titan). I think we'll end up seeing Titan covered about 25-30% (?) with a small fraction of that SAR'd twice.