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 theories^2–4 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.