ANGEO

Annales Geophysicae

ANGEO

1432-0576

Copernicus GmbH

Göttingen, Germany

10.5194/angeo-19-459-2001

Smoothing radio occultation bending angles above 40 km

Healy

S. B.

NWP Division, The Met Office, London Road, Bracknell, RG12 2SZ, UK

30 11 1999

19 4 459 468

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The 'statistically optimal' approach to smoothing bending angles derived from radio occultation (RO) measurements is outlined. This combines a measured bending angle profile with an a priori or background estimate derived from climatology, in order to obtain the most probable bending angle profile. However, the method is only optimal if the error statistics of both the measured and background profiles are known and applied accurately. In this work it is shown that correlations in the background estimate have a significant role in determining the degree of smoothing in the solution. We find that smooth profiles, consistent with the measured values, can be derived if the correlations are approximated analytically with a Gaussian, assuming a scale length of 6km. In regions where the observed and background error levels are comparable, the solutions take the general shape from the background estimate, centred on the observation data. The effects of correlated observation errors are also considered. It is shown that the quality of the temperature retrievals can be significantly affected by the choice of climatology used for background estimate. Key words. Atmosphere composition and structure (pressure, density and temperature) – Radio science (remote sensing)