CS, mm43, and perhaps swordfish41,
With all due respect, I think you may be trying to read too much into a few low resolution blips in a sonar image. The dark spot does look like a shadow, but if it is, we should do the math for it.
Using the provided scale:
The eastern target is 360m from the (eastern) vehicle track.
The length of the shadow is 11-13m long.
The vehicle is typically flown at 10% of the maximum range setting of the sonar (10% gives a good compromise between pronounced shadows and not letting the grazing angle on the seabed get too shallow for receiving good back scatter). For the 600m range used here, the altitude of the vehicle is about 60m.
That puts the target 6 times as far from the vehicle as its altitude. Thus the shadow is 6 times longer than the height of the object casting it. So the object is standing about 2m above the sea floor. Does that match your other assumptions? (I see from our intersecting posts that mm43 is wondering, too.)
Last edited by auv-ee; 15th Apr 2011 at 00:47.