Originally Posted by Peter-1959
... in other words to find a trace, while the towed sidescan sonar, and the preprogrammed auv are in fact not descending into the deeper valleys, assuming analysis based upon existing bathymetric data alone will provide the result for those area's depicted in light blue on the latest charts in this thread ?
Or maybe something is wrong with my assumption ?
I'm not sure I understand your question. Are you asking if the sidescan sonars may have flown too high in some places? I don't think that would be a common problem, or at least the operators will know where in the search area the vehicles were not low enough.
The towed sonar provides real-time sidescan data to the operator. The sidescan provides an excellent measure of altitude in the form of the time-to-the-first-echo. The operator uses this information, or separate altimeter information, to adjust the tow-body height by paying cable in or out (or even by changing ship speed in extreme cases).
The AUV measures altitude acoustically, and for this type of mission would be programmed to fly in constant altitude mode. The only places where the altitude will be significantly in error are where the slope of the bottom exceeds the AUV's climb/descent capability. Route planning that follows the ridge lines, rather than crossing them, minimizes, but does not eliminate these places. The direction of the tracklines is the only part of the AUV programing (or towed sonar planning) that is based on previous measurements of bathymetry.
With the debris assumed to be spread over a few hundred meters, any "holiday" in the data, from either the tethered or untethered sonars, that is smaller than 100m long and wide is unlikely to contain the a/c. Larger holidays can be searched again along a different track.