Ship wake detection in synthetic aperture radar images using a combination of a wavelet correlator and Radon transform

A moving ship in a synthetic aperture radar (SAR) image produces a multiscale wake with a characteristic linear V-shaped pattern. Detection of the wake can provide substantial information about the ship, such as its size, direction, and speed of movement. In general, ship-generated wakes in SAR images are associated with high sea clutter, which causes the deterioration of detection performance. We present a hybrid method that combines the wavelet technique and the Radon transform technique to detect the ship wake. The wavelet technique is first applied to generate a set of multiscale images. An orthogonal basis function is adopted so that three high-pass images in the horizontal, vertical, and diagonal directions are generated for each resolution scale. Then a spatial correlator is applied among the moduli of different scale, where modulus images are formed from three high-pass images. The output of the correlation process is shown to be highly representative at ship wake edges. Comparisons with other methods indicate the superior performance of this approach in that not only are the wakes detected, but the V-shaped pattern is well preserved. The second stage of the method involves the application of the Radon transform technique to estimate the V opening angle from the detected ship wakes. Compared with a direct Radon transform, the greater effectiveness of the proposed scheme is demonstrated in terms of efficiency as well as reliability for ship wake detection in noisy backgrounds. (C) 2002 Society of Photo-Optical instrumentation Engineers.