The Application of Two-Dimensional EMD to Extracting Internal Waves in SAR Images

SAR (synthetic aperture radar) is imaged by resonant interaction between radar wave and micro scale sea-surface waves. All ocean processes that affect the distribution of micro scale wave spectrum can be found in SAR images, such as ocean wave, internal waves, mesoscale eddies, fronts, etc. Thus a SAR image of sea surface often mingles with different scale ocean processes. Internal waves are often manifested in SAR images with other signals simultaneously, such as ocean wave. In this paper, 2D-EMD (two-dimensional empirical mode decomposition) algorithm is used to extract internal wave from SAR image. This algorithm produces a fully two dimensional decomposition of a SAR image into a series of IMF (intrinsic mode functions) and residual images with the same size as the original image. By combining IMF images, internal waves and ocean waves are separated. Comparing with the wavelet analysis, one can find that the 2D-EMD is more effective. The results preliminarily show that 2D-EMD provides a significant way to extract internal wave from an aliasing SAR image.