FFT-3D: For analysis of data to determine local currents and/or bathymetry, three-dimensional analysis of windows from a series of radar images are processed using FFT-3D.The code performs one dimensional FFT analysis of rows and columns of a square window and retains the output in complex format in memory. The full sequence of (in this case) 32 images is completed, after which the analysis is repeated in the time dimension to produce output in the frequency domain as individual K_xK_y spectra. For a 32-image sequence, the output frequency FFT will have 16 positive frequencies and 16 negative frequencies that contain redundant information. Below is shown an example of eight of 16 output frequencies for data collected in shallow water. The dispersion rule for shallow water is shown as white circles and for deep water as red circles in the results below. The spectral energy lies close to the shallow water dispersion circles as expected for these data that were collected at the USACE FRF pier.

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