Radar altimeter gate tracking: theory and extension

The range gate tracking algorithms in the United States' satellite radar altimeters over the past 20 years all use the same waveform estimators: uniformly weighted gates. The generic algorithm is based on a nested family of range intervals, within which the average reflected power is computed. This choice of gate weighting is guided by matching the gate properties to the shape of the flat surface impulse response of the scattering surface. For the case of a conventional, pulse-limited radar altimeter, the flat surface impulse response is a step function, for which uniformly weighted gates are appropriate. In the more general case, nonuniform weights are required. This paper reviews the theory behind the gate tracking algorithm as applied to conventional altimeters and extends this basic method to the recently proposed delay/Doppler altimeter whose impulse response does not have a step-function shape. Furthermore, it is shown that the definition of the tracking gates for either type of altimeter can be modified to account for the impact of the radar antenna beampattern on the altimeter waveform.