Measurement of Directional Ocean Wave Spectra from Fixed Platforms

Various instrument systems providing measurements which can be analyzed to estimate the directional ocean wave spectral density are reviewed. These include (a) electromagnetic current meters with wave staff, and (b) a wave staff with satellite bottom pressure sensors. In addition, general mathematical procedures are presented for arbitrary space arrays of measuring devices. Eigenvector procedures are introduced to remove equation redundancy. Choices of directional spreading functions, including a new four-parameter formula, for modelling the output of the analysis of wave sensor data are outlined. Data was constructed to have about the same scatter as real measurements and used to illustrate the analysis, presentation, and problems in interpretation of directional spectra estimates. Such topics as directional resolution and estimate stability, as they relate to length of record, digitization increment, and other similar details of data collection are discussed.