BASIC PRINCIPLES OF SAR POLARIMETRY
The field of synthetic aperture radar changed dramatically in the early 1980s with the introduction of advance radar techniques, such as polarimetry and interferometry. While both of these techniques had been demonstrated much earlier, radar polarimetry only became an operational research tool with the introduction of the NASA/JPL Airborne Synthetic Aperture Radar (AIRSAR) system in the early 1980s. Radar polarimetry was proven from space with the two Spaceborne Imaging Radar C-band and X-band (SIR-C/X) SAR flights on board the space shuttle Endeavour in April and October 1994. In this chapter, we describe the basic principles of SAR polarimetry and, thereby, provide tools necessary to understand SAR polarimetry applications, such as land classification.
2.1 POLARIZATION OF ELECTROMAGNETIC WAVES
In SAR polarimetry, information is transmitted from an object to a sensor by electromagnetic waves. The information could be encoded in the frequency content, intensity, or polarization of the electromagnetic wave. The electromagnetic waves propagate at the velocity of light from the object directly through free space or indirectly by reflection, scattering, and radiation to the sensor. The interaction of electromagnetic waves with natural surfaces and atmospheres is strongly dependent on the frequency of the waves.
An electromagnetic wave consists of coupled electric and magnetic force fields. In free space, these two fields are at right angles ...