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1 IRIT - Institut de recherche en informatique de Toulouse 2 CLS - Collecte Localisation Satellites 3 CNES - Centre National d-Etudes Spatiales

Abstract : The concept of delay-Doppler DD altimetry DDA has been under study since the mid-1990s, aiming at reducing the measurement noise and increasing the along-track resolution in comparison with the conventional pulse-limited altimetry.
This paper introduces a new model for the mean backscattered power waveform acquired by a radar altimeter operating in synthetic aperture radar mode, as well as an associated least squares LS estimation algorithm.
As in conventional altimetry CA, the mean power can be expressed as the convolution of three terms: the flat surface impulse response FSIR, the probability density function of the heights of the specular scatterers, and the time-frequency point target response of the radar.
An important contribution of this paper is to derive an analytical formula for the FSIR associated with DDA.
This analytical formula is obtained for a circular antenna pattern, no mispointing, no vertical speed effect, and a uniform scattering.
The double convolution defining the mean echo power can then be computed numerically, resulting in a 2-D semi-analytical model called the DD map DDM.
This DDM depends on three altimetric parameters: the epoch, the sea surface wave height, and the amplitude.
A multi-look model is obtained by summing all the reflected echoes from the same along-track surface location of interest after applying appropriate delay compensation range migration to align the DDM on the same reference.
The second contribution of this paper concerns the estimation of the parameters associated with the multi-look semi-analytical model.
An LS approach is investigated by means of the Levenberg-Marquardt algorithm.
Simulations conducted on simulated altimetric waveforms allow the performance of the proposed estimation algorithm to be appreciated.
The analysis of Cryosat-2 waveforms shows an improvement in parameter estimation when compared to the CA.


Keywords : Altimetry Cryosat Delay-Doppler Least squares estimation Synthetic aperture radar





Autor: Abderrahim Halimi - Corinne Mailhes - Jean-Yves Tourneret - Pierre Thibault - François Boy -

Fuente: https://hal.archives-ouvertes.fr/



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