# Survey line planning (SALMON)

Multibeam swath width W = 2 * depth * tan(half_angle).
At 60 deg half-angle (120 deg total): W = 2*d*tan(60) = 3.46*d.
So in 50 m water -> ~173 m swath. deep water = wide swath = fast. shallow = slow.

Line spacing = W * (1 - overlap). use 20% overlap for nadir gap + nav drift.
Survey speed 3 kt = 1.54 m/s. coverage rate = speed * spacing.

For a 5 km x 3 km box @ 50 m depth, 20% overlap:
  spacing ~138 m -> ~22 lines x 5 km = 110 km of line
  110000 / 1.54 = ~71400 s = ~20 h + turns. one long sortie. ok.