Intensity modulation in SAR images of internal waves

Abstract

During the SAR Signature Experiment1 (SARSEX), conducted in 1984 in the New York Bight off the eastern coast of the United States, synthetic aperture radar (SAR) images of the ocean surface and concurrent ground-truth measurements were collected in order to test quantitatively various imaging theories. These theories2–4 predict that the intensity modulations observed in SAR images of internal waves are produced by variations in the small-scale surface roughness induced by spatial variations in the internal-wave surface current field. Analysis of the SARSEX data indicates that the imaging theories can explain the observed modulation for L-band (∼24-cm) SAR wavelengths, but under-predict by almost an order of magnitude the observed X-band (∼3.2-cm) modulation. To explain this latter discrepancy, we hypothesize a two-step mechanism in which the observed X-band modulation results from additional small-scale roughness produced by the strong perturbation of the metre-scale surface waves by the internal wave current field.