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Abstract

Reducing the dependency of precise orbits for altimeter missions from the Time Varying Gravity field

Mr Luca CERRI(1), Mr Alexandre COUHERT(1), Mrs Sabine HOURY(1), Mr Flavien MERCIER(1)

(1) Centre National d\'Etudes Spatiales (CNES), France

Session theme: Precision Orbit Determination

  • oral

    Abstract

    In recent years non-tidal time varying gravity has emerged as the most important contributor to the error budget of the altimeter satellites\' orbits. The modeling of these effects has evolved over subsequent generation of orbit standards from the launch of TOPEX-POSEIDON, mainly thanks to the GRACE gravimetric mission : originally neglected in early GDR solutions, linear rates in the degree 2,3,4 zonal harmonics derived from SLR-data analysis were included from 2005 (GDR-B standards); seasonal variations (annual and semi-annual) were added in GDR-C orbit standards (operational in 2008), and linear rates were extended up to degree/order 50 with the latest GDR-D standards (operational in 2012).
    GDR-D orbits behave well over the 2002-2011 time-span, as demonstrated by the clear improvement in consistency between the Envisat- and Jason-derived Sea Surface Heights. However, the linear trends derived from the time-series of GRACE geopotentials only constitute an empirical model which does not account for the underlying geophysical phenomena. We should not expect this model to propagate well into the future.
    Although to some extent this problem can be solved by reprocessing dynamic orbits with more recent models, this approach will reinforce the need for a gravimetric mission in support of an ocean topography mission in order to maintain the geographically correlated orbit errors at the same level.
    Alternatively, we can reduce the dependency from errors in the gravity model by improving the configuration of the adjusted empirical parameters. We address the problem of the solution parameterization focusing on DORIS-based orbits, as for these solutions the issue of observability is more critical than for GPS-based orbits, and as several upcoming missions (SARAL-Altika ,Jason-3) will still use a DORIS receiver as mission-critical tracking instrument.

     
    Corresponding author:

      Mr Luca Cerri
      Centre National d\'Etudes Spatiales (CNES)
      18, av Edouard Belin
      31401 Toulouse
      France
      E-mail:
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