THE DEVELOPMENTS OF A METHOD FOR ESTIMATING DIRECTIONAL WAVE SPECTRUM FROM SPARSE ARRAYS (FOURIER, TRANSFORM)

Directional spectra for ocean surface waves have in the past been estimated from sparse arrays of wave elevation sensors, from the wave elevation and wave slope measurements obtained from a single pitch-roll wave buoy, and from stereophotographs of a segment of the ocean surface. For the research reported here, a sparse array of pitch-roll buoys is considered. An Improved Direct Fourier Transform (IDFT) method has been developed to use the data derived from an array of three pitch-roll buoys to estimate the fourier coefficients of the directional wave spectrum.; A numerical simulation of the wave data which would be obtained from an array of three pitch-roll buoys for a specified input wave spectrum showed that the IDFT method would provide estimates of the first 11 Fourier coefficients. In comparison, a single pitch-roll bouy provides only the first 5 Fourier coefficients.; The resolving power of the array of three pitch-roll buoys was also investigated by numerical simulations. There are two aspects of resolving power. First, the analysis of the data from the array must provide the predominant direction without ambiguity of the waves within the frequency range of significant wave energy. Second, the resolving power can be defined as the range of wavelengths, (lamda), which can be detected by an array with a characteristic sensor spacing, r. One measure of resolving power is the range of the ratio, r/(lamda).; An array of pitch-roll buoys at the vertices of an equilateral triangle with buoy spacing equal to 0.44 of the wavelength for which the wave energy is a maximum proved to be an optimal array design. For this array, the range of r/(lamda) was found to be from 0.2 to 2.1.