As discussed in Chapter 5, scattering in the far zone is unique in that the scattered field always evolves into a simple outgoing spherical wave, irrespective of the physical nature of the scatterer. It should therefore be important, as well as instructive, to analyze how the general concepts introduced in Chapters 7–12 apply to this simplest type of electromagnetic scattering. Indeed, electromagnetic scattering in the far zone of an object was previously described in terms of the incident and scattered fields related by the amplitude scattering matrix, that is, in terms of typically unobservable quantities. The aim of this chapter is to describe FFS in terms of quantities directly measurable with a WCR and/or directly quantifying the electromagnetic energy budget of a inite volume element enclosing the scattering object.

We will begin by considering the simplest case of monochromatic scattering by a fixed object imbedded in a lossless homogeneous medium and then generalize the results by allowing the incident field to be a polychromatic parallel beam and the object to change randomly in time. The main results of this chapter will be straightforward mathematical corollaries of the total field in the far zone being a superposition of plane and spherical wavefronts. Unlike the more complex case of near-field scattering by a large multi-particle group, the relative mathematical simplicity of FFS will allow us to bypass the computation of the PST and work directly with the Poynting vector and the Stokes parameters.