Radioholographic analysis of radio occultation data in multipath zones

Numerical simulations of radio occultation experiments indicate that the effect of multipath propagation and diffraction must play a very significant role in the lower troposphere. Two methods of processing radio occultation data in the multipath zone were previously discussed: the radioholographic (radio-optics) method and the back propagation method. Both methods, however, have their restriction. The radio-optics method cannot accurately take into account the effects of diffraction in subcaustic zones. The back propagation method does not work for complicated caustic structures. In this paper we describe a combined method. The radio-optics analysis is applied both for the radio occultation data measured along the low Earth orbiter orbit and for the back propagated data. The computed spatial spectra are then averaged. This allows one to get rid of diffraction effects in subcaustic zones to a significant extent. The method is validated in numerical simulations on the material of global fields of atmospheric variables from analyses of the European Centre for Medium-Range Weather Forecasts. An example of processing a real GPS/MET occultation is given.