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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 4, issue 10 | Copyright

Special issue: Observing atmosphere and climate with occultation techniques...

Atmos. Meas. Tech., 4, 2065-2071, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 04 Oct 2011

Research article | 04 Oct 2011

Processing and validation of refractivity from GRAS radio occultation data

K. B. Lauritsen1, S. Syndergaard1, H. Gleisner1, M. E. Gorbunov2, F. Rubek1, M. B. Sørensen1, and H. Wilhelmsen1 K. B. Lauritsen et al.
  • 1Danish Meteorological Institute, 2100 Copenhagen, Denmark
  • 2A. M. Obukhov Institute for Atmospheric Physics, Moscow, Russia

Abstract. We discuss the processing of GRAS radio occultation (RO) data done at the GRAS Satellite Application Facility. The input data consists of operational near-real time bending angles from December 2010 from the Metop-A satellite operated by EUMETSAT. The data are processed by an Abel inversion algorithm in combination with statistical optimization based on a two-parameter fit to an MSIS climatology. We compare retrieved refractivity to analyses from ECMWF. It is found that for global averages, the mean differences to ECMWF analyses are smaller than 0.2% below 30 km (except near the surface), with standard deviations around 0.5% for altitudes between 8 and 25 km. The current processing is limited by several factors, which are discussed. In particular, the penetration depth for rising occultations is generally poor, which is related to the tracking of the L2 signal. Extrapolation of the difference between the L1 and L2 signals below the altitude where L2 is lost is possible and would generally allow deeper penetration of retrieved refractivity profiles into the lower troposphere.

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