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1.1 Scope
Polarimetric Remote Sensing is a relatively new and largely undeveloped field. If we begin with a simple definition of remote sensing as the science or process associated with learning about the world without coming into physical contact with it, then, in its broadest definition, polarimetric remote sensing is just the subset of remote sensing that uses the polarized nature of electromagnetic (EM) energy to learn about the world. In order to keep this to a brief introductory text, we need to restrict our interest to a small subset of the much broader field that might be encompassed by this general definition. This section will describe the aspects of polarimetric remote sensing that we will consider here.
To begin, we will emphasize remote sensing of the earth. Many of the techniques we will present are applicable to planetary astronomy; however, we will not pursue these applications. Furthermore, we will focus on sensing the earth at geospatial scales where human activities are dominant. By this we mean that we are interested in spatial scales where objects such as agricultural fields and roads or smaller objects such as buildings and vehicles are sampled (i.e., tens of meters to fractions of meters). As we will see, human activities often change the polarization state of the EM energy reflected or emitted from the surface of the earth, so, looking at spatial scales where we can see human influence is one of the most interesting areas of potential utility for polarimetric sensing. To further limit our scope, we will focus on passive remote sensing in the visible through thermal infrared regions of the spectrum (0.4â14 μm). Polarimetric sensing using radar systems has been shown to have significant value for various applications [Elachi (1987) and Henderson and Lewis (1998)]. However, the relevant source-target-sensor physics and phenomenology are different enough from the electro-optical phenomenology that they will not be covered here. On the other hand, much of the material presented here is relevant to active sensing in the electro-optical region using polarimetric LIDAR. We choose not to include treatment of this topic only to maintain a focus on somewhat more widely accessible data.
While much of the laboratory work on polarimetric sensing has used radiometers (polarimeters), we will emphasize imaging systems.
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