Evaluation of the Processing of Radio Occultation Signals by Reconstruction of the Real Signals

The processing of radio occultation signals has the purpose of extracting the bending angle as function of the impact parameter so that a following Abel transform gives the refractivity profile of the atmosphere. The radio occultation signal is the detected electromagnetic field from a remote transmitter (a GPS satellite). Various processing techniques can be used to retrieve the bending angle. The Full Spectrum Inversion (FSI) method relies on geometrical optics and will produce the actual bending angle as function of the impact parameter, if it can be assumed that the refractivity is spherically symmetric around the Earth and the geometrical optical description of the propagating electromagnetic field is correct. The inverse problem, construction of the electromagnetic field from knowledge of the refractivity profile (or the bending angle) and the path of the receiving and transmitting antennas can also be solved in the framework of geometrical optics. This opens a way to evaluate the quality of actual occultation measurements both with respect to the computational algorithms and the assumptions of spherical symmetry. When the refractivity profile has been measured from an occultation signal, this profile together with information about the satellites’ path can be used to generate a simulated signal, which can be compared with the original signal. Processing of real data is shown here and the results are discussed.