SAR Altimeter Backscattered Waveform Model
Ray, Chris1; Martin-Puig, Cristina2; Clarizia, Maria Paola3; Ruffini, Giulio4; Dinardo, Salvatore5; Gommenginger, Christine6; Benveniste, Jérôme5
1Starlab Barcelona S.L. / Saint Mary's College of California, UNITED STATES; 2isardSAT (formely at Starlab), SPAIN; 3National Oceanography Center (formely at Starlab), UNITED KINGDOM; 4Starlab Barcelona S.L., SPAIN; 5ESA/ESRIN, ITALY; 6National Oceanography Center, UNITED KINGDOM

In the framework of the SAMOSA (Synthetic Aperture Radar Altimetry MOde Studies and Applications) project (ESA/ESRIN STSE funded) Starlab Barcelona S.L. was responsible for the theoretical model derivation of the SAR altimeter backscattered waveform model. This activity was of need provided that the backscatter echo from a SAR altimeter no longer resembles the Brown model [Ref. 1] and in order to apply waveform fitting re-tracking techniques, like in conventional altimetry, it was required to derivate a new theoretical model adapted to the nature of the new altimetric mode. This model is at present the Sentinel-3 L2 ocean model to be used for fitting Level 1B SAR waveforms for the retrieval of geophysical data [Ref. 2].

A closed-form theoretical expression of the SAR altimeter waveform backscattered from the Ocean was derived. The model, being expressed in terms of parameter-less functions, allows for efficient computation of the waveform, and a clear understanding of how the various sea state conditions and radar parameters affect the waveform. The model is mathematical simple and accurate for a variety of geometrical configurations and sea conditions.

This paper aims at describing in detail the potentialities of the SAMOSA model for its exploitation in the study of Ocean surfaces. Furthermore, we will provide an overview of our experiences in retracking CryoSat-2 real data, including examples of the SAMOSA model exploitation for the derivation of geophysical parameters.

[Ref. 1] Brown, G.S., The Average Impulse Response of a Rough Surface and Its Applications IEEE Trans. Antennas Propag., 
vol. AP-25, pp. 67-74, Jan.1977.

[Ref. 2] Surface Topography Mission (STM) SRAL/MWR L2 Algorithms Definition, Accuracy and Specification. ESA doc ref S3PAD-RS-CLS-SD03-00017. June 2011.