14. Radio Wave Scattering from the Ionosphere

Abstract

Publisher Summary This chapter describes the radio wave scattering from the ionosphere. The chapter focuses on the outdoor plasmas. Radar scattering measurements made from the ground at frequencies of 50 MHz or higher, frequencies far above the maximum value of the plasma frequency found in the ionosphere are discussed. At such frequencies most of the transmitted energy passes through the ionosphere and is lost; only a small fraction is scattered back to the receiver from small fluctuations in the electron density. As a result, high power transmitters and sensitive receiving equipment and sophisticated data analysis techniques must be used. The chapter discuses incoherent (or Thomson) scatter; it involves scattering from random thermal fluctuations in the plasma density. The chapter also describes scattering from ion-acoustic waves generated by a type of two-stream instability that is encountered in certain regions of the ionosphere. Some general features of all scatter measurements are discussed. Incoherent scatter and the much stronger scattering from unstable regions are examined. The incoherent scatter experiments have shown remarkable quantitative agreement with theory. A very wide range of observations are explained by the linearized kinetic theory.