Wave Optics Algorithms for Processing Radio Occultation Data in the Lower Troposphere: A Review and Synthesis

Abstract

Wave optics algorithms are applied for processing radio occultation data, especially in the lower troposphere in order to reconstruct the geometric optical ray structure of the wave field. Wave field diffracted by strong inhomogeneities in the lower troposphere and by long propagation distance from the planet limb to the space-borne receiver has a complicated structure. Its amplitude and phase are determined by multiple interfering rays and diffraction effects on caustics. There are two groups of the methods of the interpretation of radio occultation data. The first group (radio holographic technique) uses short term Fourier analysis of the wave field multiplied by the reference signal, in small sliding apertures. The maxima of local spectra localize rays. The second group uses a global Fourier Integral Operator, which transform the wave field to a single-ray representation. These method include back propagation and canonical transform methods. Refraction angles are then computed from the phase of the transformed wave field. The both groups of the methods are complementary to each other. Short term Fourier analysis is convenient for data visualization and identification of different kinds of problems in the data. The analysis based on Fourier Integral Operators is facilitated for operational data processing. We show examples of processing simulated radio occultation data using the radio holographic and canonical transform techniques.