Use of advanced directional wave spectra analysis methods

Frequency-dependent cross-spectral parameters for pitch-roll buoy data and parameters that describe directional wave spectra based on a directional Fo urier series are developed by the National Data Buoy Center (NDBC) and othe r organizations that collect wave data. The World Meteorological Organizati on (WMO) specifies wave data product formats in its Wave Observation (FM 65 WAVEOB) code. Other organizations, such as the US Army Corps of Engineers Field Wave Caging Program (FWGP), have similar specifications. A directiona l Fourier series has poor directional resolution compared with advanced met hods such as those based on maximum likelihood and maximum entropy. Transfo rmations are developed for applying the advanced methods and working with d irectional wave information stored in the WMO's FM 65 WAVEOB code, the FWGP 's Wave Data Analysis Standard (WDAS) format, and similar codes and formats . Using the transformations, a directional Fourier series expansion method, a Maximum Likelihood Method (MLM), and a Maximum Entropy Method (MEM) are each applied to 115 sets of NDBC directional wave data. The MEM and MLM pro vide better directional resolution, but the MEM produces artificial double peaks, There are considerable differences for the three used methods. The d eveloped transformation equations enable wave data users to apply the metho d that best suits their applications. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.