Heave Compensation

Heave compensation is the correction for vertical motion of the survey platform so that soundings refer to a stable vertical datum rather than the rising and falling hull. A motion reference unit or inertial sensor measures heave, the vertical displacement caused by waves, and that value is subtracted from each ping in real time and in post-processing. Roll, pitch, and induced heave at the transducer offset are corrected with it. Uncompensated heave injects a wave-period error into the seabed surface that crossover analysis exposes. Reliable heave correction is required to hold the vertical uncertainty inside an IHO S-44 order, especially for shallow Special and Exclusive surveys.