One of the observation methods of directional wave spectra is the analysis of simultaneous wave profile records obtained with a wave gauge array. The present report examines the applicability of the maximum-likelihood-method(MLM) for directional spectral analysis of the sea waves, with numerically simulated profiles of irregular waves. For free progressive waves, the MLM reproduces the directional spectra of simulated waves quite well and is capable of resolving two wave groups superimposed each other.
　For standing waves formed in front of reflective structures, however, the existence of certain phase relation between incident and reflected wave components interferes with the resolution of directional spectra, causing a decrease in the resolving power of wave gauge array for incident and reflected waves. This poses a limitation in the detection of reflected waves by means of directional wave spectra.
　Observation of directional wave spectra was made in December 1976 in front of the south breakwater of caisson type of New Sendai Port with a line array of four
wave sensors. Analysis of the records indicates that the waves reflected by the breakwater can be recognized in a certain frequency range only and there seem to exist the wave components moving parallel to the break-water in the frequency range of 0.06 to 0.09 Hz.