Directional wave spectrum estimation by synthetic aperture radar altimeter

The radar cross section (RCS) of sea surface measured by a radar altimeter is dominated by specular reflection. There are two factors affecting the normalized RCS of this type of target: one is the mean surface slope; the other is the radar look angle. For nadir looking altimeter, a long wave length wave has the effect of changing the local incident angle of the coming electromagnetic waves. The authors investigate the possibility of using synthetic aperture radar altimeter for estimation of directional wave spectrum. Synthetic aperture processing inherently can give a high spatial resolution in the along track direction by combining of several pulses. Then by appropriate sampling within each pulse they can sample the sea surface at high resolution in the across-track direction. They study this novel process by using computer simulation. They simulate the image got by synthetic aperture radar altimeter. The resolution achieved by SAR altimeter in the simulation is about 25 m×25 m. The results show they can estimate the directional wave spectrum but with an ambiguity in wave direction