Radar characterization of ship wake signatures and ambient ocean clutter features

Matched filters based on empirical wake-signature models were applied to SIR-B SAR (Shuttle Imaging Radar-B synthetic-aperture radar) images and produced peak SNR (signal-to-noise ratio) values of 17-21 dB, demonstrating that wake signatures can be successfully exploited for ship detection. A battery (~100) of filters can determine the ship direction to within several degrees. Empirical wake signature models were also tested in a wake orientation algorithm that calculates the angular cross-correlation between the power spectrum of the model and that of a SAR image. The algorithm correctly determines wake angles (with 180° ambiguity) with SNR values comparable to the matched filter. Data from a land-based, X-band, coherent real-aperture radar (which overlooks the ocean) were processed to obtain ocean surface Doppler velocities as a function of range and time. Line-of-sight orbital currents of ocean waves are easily detected, and the power in the velocity-field spectrum is concentrated on the dispersion curve for free-surface gravity waves. Cuts taken along this curve produce quantitative wave spectra for the study of ocean surface features and ship-induced wake modifications of the surface