Spectro-polarimetric BRDF determination of objects using in-scene calibration materials for polarimetric imagers. Brent Bartlett, Chabitha Devaraj, Michael Gartley, Carl Salvaggio, John R. Schott Rochester Institute of Technology, Chester F. Carlson Center for Imaging Science, Digital Imaging and Remote Sensing Laboratory, Rochester, NY, USA ABSTRACT For sensing systems that characterize the spectro-polarimetric radiance reaching the camera, the origin of the sensed phenomenology is a complex mixture of sources. While some of these sources do not contribute to the polarimetric signature, many do such as the downwelled sky polarization, the target and background p- BRDF(polarimetric bi-directional reflectance distribution function), the upwelled sky polarization, and the cam- era Mueller matrix transfer function. In this paper we investigate candidate in-scene calibration materials potentially allowing for portions of the p-BRDF to be derived for material surfaces throughout the scene. Ex- traction of target p-BRDF from the sensed spectro-polarimetric energy may result in improved target detection performance in the future. Results using both synthetic and real data are presented. Keywords: calibration, BRDF, polarimetric, measurement 1. INTRODUCTION Many polarimetric applications in remote sensing rely on using models of the p-BRDF (polarimetric bi-directional reflectance distribution function) to describe the way in which light interacts with scene materials. 1 It is not clear however which model will perform with the highest accuracy with a particular material or scene geometry. Due to this situation it is desirable to devise a collection strategy which can provide empirical data allowing portions of the p-BRDF to be extracted for different materials across varying scene geometries. This can provide valuable inputs to the various p-BRDF models allowing for greater accuracy. In particular, the downwelling radiance field can be highly linearly polarized and impart polarimetric sig- natures to the scene. A polarimetric panel cluster has been designed to allow for the calibration of spectro- polarimetric imaging systems. Using known reflectance values for diffuse materials present in the scene, both diffuse and specular portions of the p-BRDF can be retrieved for glossy materials within the same scene. The modeling environment of DIRSIG, in conjunction with MODTRAN-P, is used to model the collected scene and provide for additional input values required for the p-BRDF retrieval process. This process is demonstrated using both synthetic and real scene data. 2. BACKGROUND AND THEORY The generalized version of the bidirectional reflectance distribution function can be expressed as a ratio of the irradiance incident onto a surface versus the radiance scattered off from the surface as shown in equation 1. f brdf = dL(θ r ,φ r ; λ) dE(θ i ,φ i ; λ) (1) This relationship can also be expressed in a polarimetric Stokes parameter representation as shown in equation 2 (note that the wavelength dependence is implicit in the rest of the derivation). Further author information: E-mail: bdbpci@cis.rit.edu, Telephone: 1 585 475 5037 Polarization Science and Remote Sensing IV, edited by Joseph A. Shaw, J. Scott Tyo, Proc. of SPIE Vol. 7461, 74610T · © 2009 SPIE · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.825359 Proc. of SPIE Vol. 7461 74610T-1 Downloaded from SPIE Digital Library on 30 Sep 2009 to 129.21.58.45. Terms of Use: http://spiedl.org/terms