Statistical Properties of Directional Sea Measurements

Abstract

The statistical variability of directional sea estimates is considered. A general, but brief study in the mean and variance of the spatial coherence estimate is first presented. This function is found to be relatively unstable when it is not close to 1. A directional sea estimation procedure based on Fourier Series Expansion of the directional spectrum combined with a Maximum Entropy Condition is then described. This method is used in a numerical directional analysis test in order to demonstrate the effect on sea state estimates from the variability in the spatial coherence. Numerical sea states for this test are generated with 2049 frequencies and 100 directions per frequency. Significant statistical scatter is observed in the resulting estimated directional spectra and their parameters, in qualitative agreement with the spatial coherence statistics considered theoretically.