Double‐passage radar cross section enhancements

Abstract

Transionospheric radar measurements reported by Knepp and Houpis (1991) verify the backscatter enhancement known to be associated with the double‐passage problem. Knepp and Reinking (1989) showed, moreover, that the enhancement is proportional to the intensity scintillation index on the one‐way path. While this result is easily derived, it is more difficult to characterize the complete angular distribution of backscattered waves of which the radar measurement represents one component. In this paper we develop a simple product expression for the backscattered spectrum from an incident plane wave. The spectrum of backscattered waves from a point source is then derived by transformation of the plane‐wave result. Motivated by a discussion in a recent paper by Fremouw and Ishimaru (1992), we show that both reciprocity and energy conservation are preserved in our wave‐space formulation, which is essentially exact. We also discuss the method of computing the scattering functions and the fourth‐order moments that appear in our results; however, the general expressions are the principal results of this paper.

Average received signal power after two‐way propagation through ionized turbulence

“…The first consist of limiting analytic cases such that either space-, time-, or frequency-selective effects are dominant. These results agree with and extend previous calculations for aperture averaging [Knepp, 1985] and for the two-way enhancement in average power [Knepp and Houpis, 1991;Fremouw and Ishimaru, 1992;Rino, 1994].…”