Wave number mapping in ocean wave spectrum estimation from marine radar data by the Polar Fourier Transform

The Polar Fourier Transform (PFT) can be used to estimate the ocean wave number spectrum. The main advantage of the PFT over the Cartesian Fourier Transform (CFT) is the ability to be applied on the native radar data without the need for the intermediate stage of scan conversion. However, by definition, the PFT may not be used to detect 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 pi/2. This mapping migrates all wave numbers to fit into the range of 0 to pi so that the PFT is required to deal with only positive wavenumbers.