Estimation of directional sea spectra from ship motions in sea trials

This paper compares the skill of two algorithms that enable real-time estimation of the directional wave spectra exciting a ship from its measured motions. One algorithm consists of a nonlinear optimization of a parametric or non-parametric spectral model and the other is a Kalman filter based observer. Sea trials have been conducted on an oceanographic vessel that was instrumented with a six degree of freedom fiber optic gyro, complemented with a rate gyro, several accelerometers, a dedicated GPS receiver and a bow mounted down-looking wave radar with motion compensation. The two algorithms are applied to the measured data and a discussion is provided on their skill to recover the properties of existing sea states.