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Abstract

An analytical model for Doppler altimetry and its estimation algorithm

Mr Abderrahim HALIMI(1), Pr Corinne MAILHES(1), Pr Jean-Yves TOURNERET(1), Mr Francois BOY(2), Dr Nicolas PICOT(2), Dr Pierre THIBAUT(3)

(1) University of Toulouse, IRIT/INP-ENSEEIHT/TéSA, France
(2) Centre National d\'études Spatiales (CNES), France
(3) Collecte Localisation Satellite (CLS), France

Session theme: Instrument processing

  • oral

    Abstract

    The concept of delay/Doppler radar altimeter has been under study since the mid 90's, aiming at reducing the measurement noise and increasing the along-track resolution in comparison with the conventional pulse limited altimeters. This paper introduces an analytical model of the mean backscattered power waveform acquired by a radar altimeter operating in SAR mode, as well as an associated least squares estimation algorithm. As for conventional altimetry, the mean power can be expressed as the convolution of three terms: the flat sea surface response, the sea wave height probability density function and the time/frequency impulse response of the radar. An important contribution of our work has been to derive an analytical formula for the flat sea surface response associated with Doppler altimetry. The double convolution defining the mean power can then be computed numerically. The resulting single-look model depends on three parameters: the epoch, the sea surface wave height and the amplitude. A multi-look model is obtained by summing all the reflected power from the along track beam surface of interest after applying appropriate delay compensation. The second contribution of our work concerns the estimation of the parameters associated with the single and multi-look analytical Doppler models. A least squares approach is investigated by means of the Levenberg-Marquardt algorithm (which does not need computing the exact model derivatives). Simulations conducted on synthetic altimetric waveforms allow the performance of the proposed estimation algorithm to be appreciated. The proposed analytical model (and the associated estimation algorithm) are finally compared with other models developed by the Centre National d\'Etudes Spatiales (CNES) and the company Collecte Localisation Satellites (CLS) both located in Toulouse, France. The analysis of a huge number of Cryosat waveforms shows an improvement in parameter estimation when compared to the conventional LRM mode altimeter. These results are very promising.

     
    Corresponding author:

      Mr Abderrahim Halimi
      University of Toulouse, IRIT/INP-ENSEEIHT/TéSA
      2 rue Camichel, BP 7122
      31071 Toulouse
      France
      E-mail:
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