Estimate of Directional Spreading Parameters of a Cosine-2s Model

For accurate and consistent estimate of the directional spreading parameter and mean wave direction of directional seas based on a cosine-2s model, a new approach is proposed, which employs a Maximum Likelihood Method (MLM) to estimate the directional spreading function and then the angular Fourier coefficients. Because a MLM is more tolerant of errors in the estimated cross spectrum than a directional Fourier transfer used in the conventional approach, the proposed approach is able to estimate the directional spreading parameters more accurately and consistently, which is examined and confirmed by applying the proposed and conventional approach, respectively, to the time series generated by numerical simulation or recorded in the field.