Deficiences of the Forward and Backscatter Alignment Conventions in Bistatic Radar Polarimetry

Abstract

This contribution presented in the Ernst Lüneburg Memorial Session is concerned with the proper formulation of the electromagnetic wave scattering problem from coherent point targets in the general bi-static case which depends on the introduction of the proper coordinate systems. Deficiencies of often used ‘Forward Scattering Alignment (FSA)’ and the ‘Back Scatter Alignment (BSA)’ conventions are pointed out and we attempt to modify these concepts by explicitly introducing the time reversal operation, as proposed by Ernst Lüneburg. Coordinate systems are used to realize and concretize operator-valued field relations formulated in abstract vector spaces in terms of vectors and matrices in finite-dimensional complex linear vector spaces. Great care must be exercise in choosing the correct coordinate systems and conventions in such a way that the formulations allow a direct application of well-established mathematical theorems to the physical world of the various scattering scenarios. This applies in particular to the formulation of scatter problems using the conventional FSA and the BSA conventions in general bi-static radar polarimetry. This suggestion is also connected with the attempt to recombine the traditional formulations via the radar equation and via the voltage equation, considered to be the two independent cornerstones of radar polarimetry, on an equally cohesive footing. The role of symmetry and coordinate systems in bistatic scattering from random media, and the contribution of Ernst Lüneburg to this field is thoroughly addressed, which was one of the principal research areas Ernst Lüneburg was particular engaged in during his last years.