Total horizontal uncertainty covers everything that misplaces a sounding on the seabed: GNSS position error, heading error, lever-arm mistakes, timing offsets and beam pointing errors that grow with depth and beam angle. Limits run from 1 m for Exclusive Order to 20 m plus 10 percent of depth for Order 2. A heading bias that is trivial at nadir can push outer-beam soundings out of tolerance in deep water.
THU is fine at nadir but the yaw bias walks the outer beams out a metre and a half at 40 metres.
Also heard as
- total horizontal uncertainty
Related terms
TPU
Total propagated uncertainty: the combined estimate of how far each sounding could be from the truth, at 95 percent confidence.
TVU
Total vertical uncertainty: the depth part of a sounding's uncertainty, judged against a depth-dependent limit.
GNSS
Global navigation satellite systems: satellite positioning such as GPS, GLONASS, Galileo and BeiDou, used together.
Patch test
A set of calibration lines over flat ground and slopes that measures sonar alignment biases and timing error.