ABSTRACT
This chapter focuses on the properties of polarised waves, how to describe them mathematically, and what they can tell students about a distant object. Polarimetry is one of the most challenging aspects of microwave remote sensing. The chapter attempts to capture some of the flavour and to summarise the main features — the hidden wonders of polarimetry are extensive and ominous and this chapter only touches the surface. A radar polarimeter is an instrument that not only measures the polarisation of the returned echo, but can also transmit the equivalent of a full range of polarisations. In both active and passive polarimetry, it is often worthwhile to consider polarimetric ratios. The principle behind this technique is that a polarimetric response can be characterised by a combination of idealised scatterers. In 1852 George Gabriel Stokes introduced four parameters based on such optical measurements that allow a complete description of a polarised wave.
