Unfolding of Radio Occultation Multipath Behavior Using Phase Models

Abstract

We have analyzed radio occultation simulations containing atmospheric multipath behavior. In the case where the medium and the satellite orbits are spherically symmetric the multipath behavior can be unfolded by a Fourier transform of the measured signal. However, small deviations from circular orbits may imply that the multipath behavior cannot be completely unfolded due to the fact that a given instantaneous frequency may occur at more than one time instant. In order to resolve the multipath behavior for realistic satellite orbits, we use the full-spectrum inversion approach and modify the measured signal by a phase model before carrying out a Fourier transform. For certain models, which depend on the measured phase of the simulated signal, we find that multipath behavior can be successfully unfolded. Even very strong multipath behavior, leading to critical refraction, can in some cases also be handled. The combined effect of applying a model and a Fourier transform can be viewed as a specific type of a canonical transform.