A Slant-range Estimation Method Based on Waveforms of Near-nadir Altimeter

Spaceborne radar altimeter is one of the most important instruments for measuring the ocean dynamic environment. The new generation of altimeter that works in near-nadir interferometry mode retrieves the sea surface height from the interferometric phase instead of the power waveform, which the nadir-looking altimeter uses for sea surface height re-tracking. However, the precise slant-range information also exists in the near-nadir-looking waveforms, which has been ignored so far. This paper proposes a precise slant-range estimation method based on near-nadir power waveforms. Since an analytical waveform model can hardly be established due to the asymmetrical measurement geometry, a large number of near-nadir looking power waveforms are simulated based on a semi-physical model, and a series of empirical analytical models of different looking angles are established based on waveform fitting. Statistical results show that the precision of the proposed method is better than 8cm for the typical near-nadir looking angle range below 4°.