A cross-track oscillation that rocks in step with the vessel's motion, visible as seesawing swath edges on flat seabed. Typical causes are a small roll bias, a timing offset between attitude and sonar, or a misaligned motion sensor. Comparing the residual pattern with the recorded roll, pitch and heave, an approach known as wobble analysis, points to which sensor or offset is wrong.
Outer beams have a wobble that tracks the roll exactly, the attitude timing must be out.
Also heard as
- motion artefact
- roll artefact
Related terms
Roll
Rotation of a vessel about its fore-and-aft axis, measured to correct the angle of every sonar beam.
Latency
A time delay between when a sensor measures something and when that measurement gets its time stamp.
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.