chapter 10, Measurements and Modeling of the pBRDF of Materials

Excerpt

To this point we have focused on the underlying phenomenology that governs the formation and observation of polarimetric signatures in remotely sensed images. In this chapter we will introduce a simple method to measure the primary terms impacting linear pBRDF (Sec. 10.1) and an approach to modeling polarimetric imaging phenomenology in the reflective region (0.4–2.5 μm) of the spectrum (Sec. 10.2). Many devices and approaches have been developed to measure pBRDF and the variation in pBRDF. A variety of these are described in Chapter 6. To keep our treatment here manageable, we have chosen to present only one approach, due to its simplicity (i.e., nearly anyone could use the approach with minimum instrumentation) and the author's familiarity with the data. We have chosen to limit the discussion to the linear polarization terms, due to the small contribution from circular polarization for most passive sensing of the earth.

10.1 Polarimetric BRDF Measurement Approach

Ideally, BRDF measurements are made in a lab environment using a “point” illumination source with careful control and minimization of stray light. However, many materials such as vegetation do not lend themselves to easy indoor measurements, due to alteration of their natural state or simply because of their physical size (e.g., a tree canopy). Outdoor BRDF measurements of such materials become a necessity and, as described in Chapter 6, many approaches have been successfully employed [Deering and Leone (1986), Walthall et al. (2000), Sandmeier and Itten (1999), and Sandmeier (2000)]. Wide field-of-view (FOV) imaging systems may be used that efficiently enable the simultaneous measurement of multiple scattering angles [Czapla-Myers (2002), Han and Perlin (2003), and Dana and Wang (2004)].

10.1.1 Measurement approach

One simple approach described by Shell and Schott (2005) for measurement of background materials will be presented here.