Ocean wave spectrum estimation from marine radar data using the polar fourier transform

The Polar Fourier Transform (PFT) can be used to estimate the ocean wave number spectrum from marine radar data. The main advantage of the PFT over the Cartesian Fourier Transform (CFT) is its direct applicability to the native radar data without the need for the intermediate stage of scan conversion. However, by definition, the PFT operates on positive, and not negative, wavenumbers. This leads to a problem in estimating the ocean wave spectrum which may contain negative wavenumbers. Therefore, a process of wavenumber mapping is proposed in order to circumvent this problem. In this technique, which is implemented before applying the PFT, the wave number content of the radar signal is compressed by a factor of 1/2 and shifted by π/2. This mapping migrates all wave numbers to fit into the range of 0 to π so that the PFT is required to deal with only positive wavenumbers.