A Variational Adjoint Approach on Wide-Angle Parabolic Equation for Refractivity Inversion

Abstract

Radar systems performance under anomalous propagation conditions can be predicted if the atmosphere is properly known. This article introduces a tomographic approach to estimate refractivity in the troposphere with an adjoint-based inversion method. A new adjoint model is developed for the 2-D wide-angle parabolic equation using a variational adjoint approach, to invert refractivity from phaseless data measured with an array of radio receivers in an open-sea environment. The obtained adjoint model is validated considering propagation through a range-independent medium over a flat perfectly-electric-conducting 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.