CoAuthors

Luciana Fenoglio-Marc (TU Darmstadt, Germany); Salvatore Dinardo (SERCO, ESA/ESRIN, Italy); Scharroo Remko (EUMETSAT, Germany); Matthias Becker (TU Darmstadt, Germany)

Since the start of the Cryosat-2 mission SAR Altimetry contributes through a higher signal to noise ratio and a better along track spatial resolution to a better understanding of the oceanic processes. Unfortunately, to achieve an analytical solution for the retrieval of geophysical parameters from the radar echo, the Point Target Response (PTR) in the time/frequency domain has to be approximated by Gaussian bell-curves. This approach leads to errors in the estimated parameters, particularly in Significant Wave Height (SWH).
In an alternative method, which allows to use the correct PTR in the convolution of Delay/Doppler Altimetry waveforms, the Flat Sea Surface Response (FSSR) is calculated analytically and the convolution with the PTR and the Probability Density Function (PDF) of the sea surface is computed numerically.

In this work a close form solution without special functions and infinite sums of SAR Altimetry waveforms is developed in the frequency/time domain by calculating analytically the two-dimensional Fourier Transform of the Convolution term. The corresponding signal in the time/frequency domain can then be computed fast and easily with a two-dimensional fast inverse Fourier transform. Furthermore a Retracking algorithm is developed from this functional model.
Estimable parameters are the amplitude, epoch, SWH, sea surface mean square slope, mispointing angles, and wave skewness.
Finally the algorithm is validated in the German Bight by comparison with in-situ data and the results from ESRIN/SAR and RADS/PLRM solutions.