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 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-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.