Rotation about the athwartships axis, measured by the motion sensor and applied to place each ping along track. Pitch errors move soundings forward or aft by roughly depth times the angle error, so features appear in different places on reciprocal lines. Pitch bias is resolved in the patch test by running reciprocal lines at the same speed over a slope or a distinct feature.
Pitch bias pushes the wreck 3 metres forward on every line, sort it before we start developing.
Also heard as
- pitch angle
Related terms
Roll
Rotation of a vessel about its fore-and-aft axis, measured to correct the angle of every sonar beam.
Heave
The vertical up-and-down motion of a vessel caused by waves, measured and removed from sonar depths.
Patch test
A set of calibration lines over flat ground and slopes that measures sonar alignment biases and timing error.
MRU
Motion reference unit: the sensor that measures a vessel's roll, pitch and heave to correct sonar data.