skinnee wrote:
Thanks Matt - the side scan water column feature worked well, does this affect GPS locations at all , ie fo underwater tree positions change when i hide the black holes from the water column
Lateral offsets for objects in sidescan are calculated using simple trigonometry so yes, the positions will change slightly as the depth underneath the boat is changed. As an example, something showing at a raw sonar range of 20m will be shown 19.36 from the boat at a depth of 5m and 19.22m from the boat at a depth of 5.5m. So the change is relatively small, especially at higher ranges (and a 0.5m adjustment is quite a large one). You need to remember though that all sidescan offsets are approximations, and all rely on the (often/usually false) assumption that the surrounding terrain is flat, with the same depth as directly underneath the boat. In this context, changing the depth slightly to remove the water column is not going to reduce the overall quality of sidescan mosaics and should in fact improve them given that visible water column is an indication of a recorded depth that doesn't match the recorded sonar exactly.