The processing within 3D/4D-Var of satellite data follows the general layout presented in Sections 2.4 and 2.5 of Chapter 2 `3D variational assimilation' . The same vertical interpolation routines as in Chapter 5 `Conventional observational constraints' are used whenever possible. The main difference in the organization is that the radiative transfer code, RTTOV-5 (Saunders and Matricardi 1998), currently requires the model profiles to be interpolated to 43 fixed pressure levels from 1013.25 hPa to 0.1 hPa on which the radiative transfer coefficients are determined.

The current operational configuration uses TOVS radiances (Andersson et al. 1994), SCAT ambiguous surface winds (Stoffelen and Anderson, 1997), SSM/I total column water vapour and wind speed (Gerard and Saunders, 1999; Phalippou, 1996; Phalippou and Gérard, 1996) and SATOB cloud motion winds of various types (Tomassini et al. 1997). Operators also exist for SATEM thicknesses and PWC (Kelly and Pailleux, 1988; Kelly et al. 1991), and radiances from geostationary satellites. Cloud motion winds (SATOBs) are used just like any other upper level wind observations (Chapter 5 `Conventional observational constraints' ) and will not be discussed any further.

At the introduction of 21r1 (May 1999) we move from the use of RTOVS cloud-cleared radiances to 1C, or `raw', radiances, which do not require the 1D-Var retrieval step.

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20.03.2002

DATA ASSIMILATION

IFS documentation Front Page

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6.1 Introduction