Spectral Wave Data Analysis

Spectral analysis identifies the distribution of wave energy in terms of frequency and direction, for which the AIM wave buoy sensor has a number of options.

Non-directional analysis generates a standard wave spectrum based on the heave motion of the buoy. Directional spectral analysis is achieved by analysing the secondary motion parameters coupled together with buoy heading measurement. For a ‘surface following’ buoy, this normally entails using the buoy pitch and roll data as a measure of surface slope and correlating this with buoy heave. For example, with a buoy at the crest or trough of a wave, the pitch measurement will be zero. In between crest and trough, the buoy would take up a pitch attitude consistent with the wave steepness. The lateral shape of the waves is identified by the roll measurement. Taking heave roll and pitch together allows the calculation of the directional wave spectrum, identified by mean direction and directional spread at a range of frequencies. Alternative means of presentation are also possible, for example the first 5 directional Fourier coefficients as a function of frequency.

This Heave/Roll/Pitch combination as for directional measurement is traditional and typically employed  for buoys with ‘discuss’ hull forms, but which is not necessarily appropriate for other hull forms, and in particular for larger buoys where pitch and roll response is inhibited by hull form and/or mooring arrangements. To increase the range of options therefore, the AIM sensor also allows for calculation of the directional spectrum from other combinations, such as heave with surge and sway measurements (this as typically employed by GPS buoys). Basically a number of combinations are supported between the buoy vertical and lateral motions.

Non Directional Analysis,resolution 0.00195Hz

Omni Directional Spectral Amplitude/Ordinate

Directional Analysis, resolution 0.00195 Hz

Directional Energy Spectrum Amplitude/Ordinate

Directional Energy Spectrum Mean Direction

Directional Energy Spectrum Directional Spread

Directional Energy Spectrum First 5 Fourier Coefficients

Overall Directional Properties

Wave Direction

Directional Spread