### ESTIMATION OF DIRECTIONAL SPECTRUM EXPRESSED IN STANDARD FORM

#### Abstract

A standard directional spectrum is determined by a finite number of parameters included in its mathematical expression. In this paper, a theory is developed to estimate the parameters from a given data set on the basis of the maximum likelihood method. The theory is applied to estimating the parameters in the Mitsuyasu-type standard directional spectrum from data obtained by a threecomponent array. Main results of analysis of field data are 1) the peak wave direction agrees well with the mean direction defined at each wave frequency, 2) the peakedness parameter can be approximated by that estimated from the longcrestedness parameter at each wave frequency, and 3) the peakedness parameter takes its maximum at the frequency slightly lower than the peak frequency.

#### Keywords

directional spectrum; spectrum estimation

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