chapter 11, Longwave Infrared pBRDF Principles

Excerpt

To simplify the discussion of polarization concepts, we have for the most part avoided consideration of the emissive region of the EM spectrum. This chapter and the next specifically address the emissive region. In this chapter, we begin with a short review of some of the measurement and applications work involving polarimetric sensing in the thermal infrared. We then explain the fundamental concepts related to pBRDF models in the emissive region of the spectrum.

In the thermal infrared, we have two potential sources of polarized energy. The first is reflected energy, which will have behavioral phenomena similar to those in the VNIR-SWIR and are discussed in Chapters 2 through 10. The second involves the polarization state of the emitted energy. The final polarization state will depend on the degree of polarization due to each of these components and their relative magnitude. To begin this review we will briefly examine some of the literature describing measurements of the polarimetric emission from surfaces, as well as some papers that motivate consideration of the thermal infrared for polarimetric sensing.

11.1 Background on Polarimetric Remote Sensing in the Thermal Infrared

Although rare, polarimetric IR imaging-related topics have received some attention in the literature over the past 20 years. The experimental and theoretical work in polarimetric IR spans a range of applications, including but not limited to: astronomy, observations of space objects, characterization of polarized material emissivity, target cueing, and decoy discrimination. We will review a small sample of this work to introduce some of the principles and issues associated with sensing in this spectral region.

Jordan and Lewis (1994) describe experimental measurements of the emission polarization from glass and aluminum. Their work focused primarily on the wavelength region of 10 to 11 μm, dictated by their optical coatings and detector spectral response.