THE DELAY DOPPLER RADAR ALTIMETER

The key innovation in the delay/Doppler radar altimeter is delay compe nsation, analogous to range curvature correction in a burst-mode synth etic aperture radar (SAR), Following delay compensation, height estima tes are sorted by Doppler frequency, and integrated in parallel, More, equivalent looks are accumulated than in a conventional altimeter, The relatively small along-track footprint size is a constant of the syst em, typically on the order of 250 m for a Ku-band altimeter, The flat- surface response is an impulse rather than the more familiar step func tion produced by conventional satellite radar altimeters. The radar eq uation for the delay/Doppler radar altimeter has an h(-5/2)(c tau)(1/2 ) dependence on height h and compressed pulse length tau, which is mor e efficient than the corresponding h(-3)c tau factor for a pulse-limit ed altimeter, The radiometric response obtained by the new approach wo uld be 10 dB stronger than that of the TOPEX/Poseidon altimeter, for e xample, if the same hardware were used in the delay/Doppler altimeter mode, This new technique leads to a smaller instrument that requires l ess power, yet performs better than a conventional radar altimeter, Th e concept represents a new generation of altimeter for earth observati on, with particular suitability for coastal ocean regions and polar ic e sheets as well as open oceans.