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Chapter 12:
LWIR pBRDF Measurements and Modeling
This chapter builds on the thermal infrared principles introduced in Chapter 11 and parallels the simple measurements and synthetic scene modeling approach for reflective imaging polarimetry presented in Chapter 10. In Chapter 11, we introduced thermal infrared pBRDF models and the parameters they depend on. In this chapter we will look at one simple method using field measurements to calibrate pBRDF models. This method was selected based on the author's familiarity with it, for consistency with the pBRDF models presented in Chapter 11, and for its use in the scene simulation modeling presented in Sec. 12.2. 12.1 Measurement of Polarized Emissivity and pBRDF Estimation This section describes a simple field procedure for measuring pBRDF values and ways to use these measurements to calibrate pBRDF models. The approach draws on Gartley et al. (2007) and Gartley (2007). 12.1.1 Measurement approach Before making polarized emissivity measurements and generating infrared Stokes image sets, it makes good sense to first understand the key radiometric terms involved in the radiance reaching the front of an IR polarimeter. A system design must be developed that pays careful attention to the environmental conditions as well as to hardware constraints. The images collected and the algorithms utilized to extract thermal emissivity from them will utilize the radiometric terms and the key design points presented in this section. Consider a generic infrared camera equipped with a linear polarizer having rotation capability. Let the rotation angle of the polarizer be designated by an orientation angle α. Let us also assume that the target-to-camera path transmission loss is negligible.
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