POLARIMETRIC ANALYSIS AND MODELING OF MULTIFREQUENCY SAR SIGNATURES FROM GULF-STREAM FRONTS

Using airborne synthetic aperture radar data from the 1990 Gulf Stream Experiment, this paper investigates the polarization and wavelength d ependence of radar signatures for narrow fronts with converging hows o ccurring within the Gulf Stream. The signal-to-background ratios of th e cross-polarization backscatter return from a convergent front were f ound much higher than those of copolarization returns, when the flight path is crossing the front. However, a second convergent front, image d at 45 degrees, showed that the signal-to-background ratios are nearl y equal for co- and cross-polarizations. A polarimetric procedure, whi ch has been successfully used to measure terrain slopes and to generat e elevation maps, is applied to the convergent front to explain the po larization and imaging geometry dependence of these radar responses. A theoretical modeling of radar modulation using an ocean wave model an d a composite-Bragg scattering model, which incorporates the effect of breaking waves, was developed. Calculations with the model agree reas onable well with the radar measurements at various polarizations for t hree radar frequencies: P-band (68 cm in wavelength), L-hand (24 cm), and C-band (5.7 cm).