DANISH METEOROLOGICAL INSTITUTE SCIENTIFIC REPORT 01-02 Radioholographic methods for processing radio occultation data in multipath regions

Multipath propagation in the lower troposphere plays a very important role in forming the structure of radio signals used for radio occultations. Processing radio occultation data in multipath regions requires the solution of the problem of the reconstruction of the ray structure of a wave eld. Two methods were formerly suggested for processing multipath data: back-propagation and radio-optic (radio-holographic or sliding-spectral) method. In the rst section of this report we analyzed the two methods and their restrictions. Back-propagation method does not work in the presense of complicated caustic structures. The radio-optic method results in signi cant errors in sub-caustic zones. In the second section we suggest a combination of these methods. It uses the spectral analysis of both measured and back-propagated eld and the computation of the averaged spatial spectra. It is shown that the e ects of caustic are suppressed in the averaged spectra, which allows for the reconstruction of refraction angles. In the third section we suggest a new method of the reconstruction of the ray structure of a wave eld. The method is based on the theory of canonical transforms and Fourier integral operators. It allows for a very accurate reconstruction of unique pro les of refraction angles. All the methods are validated in numerical simulations based on global eld from analyses of European Centre for Medium-Range Weather Forecast. 1 Comparative analysis of radioholographic methods of processing radio occultation data