Publications

Sounding Earth’s atmosphere by GPS radio occultation is a key objective of the Challenging Minisatellite Payload (CHAMP) satellite launched in July 2000. First results from CHAMP indicate that temperature profiles with good accuracy (about 1.5 K) and high vertical resolution can be derived from the mid-troposphere to the upper stratosphere. In the lower troposphere, however, the inversion process is frequently complicated by the occurrence of multi-path propagation rendering solutions using retrieval techniques based on single-ray propagation worthless. Recently, the canonical transform (CT) method has been introduced by one of us (M.E.G.) to solve the problem of calculating bending angle profiles within sub-caustic zones. The CT method uses the connection between geometrical and wave optics. The geometric optical rays are described by the Hamilton system in the corresponding phase space. In geometrical optics disentangling individual rays in multi-path zones can be performed by means of a canonical transform such that the projection of the ray manifold to the new geometric coordinate is unique. The corresponding asymptotic transform of the wave field to the single ray representation is then given by the Fourier integral operator associated with the canonical transform. Multiple phase screen simulation studies using refractivity profiles derived from radiosonde measurements demonstrate that the CT method accurately reproduces the true refraction angle profile. In contrast, the standard single-ray retrieval yields dry temperatures deviating by more than 10 K from the observed values. About 4000 CHAMP occultation profiles observed between 14 May and 10 June 2001 have been processed with the CT method. We present first results and compare these with corresponding profiles obtained by the standard retrieval.

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Beyerle, G.; Gorbunov, M. E.; Marquardt, C.; Reigber, C.; Schmidt, T.; Wickert, J. (2002): Inverting GPS Radio Occultation Data using the Canonical Transform Method: Results from Simulation Studies and CHAMP Observations. 27th General Assembly of the European Geophysical Society (EGS) (Nice 2002).