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The purpose of this letter is to show that the azimuth scanning mode of a synthetic aperture radar can be applied to deriving ocean wave spectra and determining the wave propagation direction for the first time, which reveals its enormous potential and great future in ocean observation. The improved Doppler beam sharpening imaging algorithm is used to produce a sequence of individual subimages of ocean waves in the same scan region from different aspect angles with a high revisit rate. These subimages have an inherent property that they are formed at different discretely delayed times. Therefore, wave propagation direction can be determined from a pair of wave images in different scans. Several different methods are applied to the real airborne radar wave data, including the methods of scan sum (taking the standard Fourier spectrum of the scan-summed image), spectral sum, spectral phase shift, and cross-correlation function of subimages. The processing results demonstrate the effectiveness of the algorithms.

A novel ship wake constant false alarm rate (CFAR) detection algorithm is proposed. The algorithm first detects all the ships and replaces the pixels' gray value of the detected ship with the gray mean value. Then, with the ship target's geometric center as the center, a square image with a certain length is got, and the image is subdivided into four subimages, where the gray intensity contrast of the wake to clutter in the subimage is enhanced. Normalized Hough transform is applied on every subimage, and the probability distribution function in the Hough domain of each subimage is modeled, which can be used for CFAR detection. Finally, the detection results of the subimages are fused to get the final detection. Using our algorithm, the signal-to-clutter ratio of the wake to clutter is enhanced, the ship's navigation direction can be extracted easily, and most importantly, CFAR detection is realized.