This paper presents a preliminary study of a new inversion strategy combining the method of adjoint applied to the wide-angle parabolic equation and the method of splitstep wavelet for tropospheric refractivity estimation. Our main motivation is to use a gradient based optimization method to infer atmosphere from radio-frequency data, in an effort towards a real-time accurate refractivity-from-clutter system. The proposed adjoint formulation is validated with the method of finite differences. The validation setup is developed for inversion using a tomographic approach.
Radar systems performance under anomalous propagation conditions can be predicted if the atmosphere is properly known. This paper introduces a tomographic approach to estimate refractivity in the troposphere with an adjoint-based inversion method. A new adjoint model is developed for the two-dimensional wide-angle parabolic equation using variational adjoint approach, to invert refractivity from phaseless data measured with an array of radio receivers in open-sea environment. The obtained adjoint model is validated considering propagation through range-independent medium over flat perfectly-electricconducting surface at horizontal polarization. The ill-posedness of the regarded inverse problem is shown with the optimization landscapes. The parametric study indicates the potential use of this method as a refractivity gradient retrieval system under certain circumstances.Index Terms-Refractivity inversion, inverse problem, wideangle parabolic equation, adjoint model.
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