Optical sensor package for multiangle measurements of surface reflectance

The Remote Sensing Group of the Optical Sciences Center at the University of Arizona has performed the vicarious calibration of satellite sensors since the 1980s. Ground-based measurements of atmospheric and surface properties, including the surface bidirectional reflectance distribution function (BRDF), are conducted during a satellite or airborne sensor overpass and the at-sensor radiance is calculated using these properties as input to a radiative transfer code. Recently, the Remote Sensing Group has investigated an imaging radiometer based on an astronomical-grade 1024 × 1024-pixel silicon CCD array that was developed and calibrated for ground-based measurements of BRDF. The results of that study have been used to examine the feasibility of a lightweight instrument package for measurements of surface BRDF based on a combination of nonimaging radiometers and inexpensive digital cameras. The current work presents a preliminary design of such a system including specifications for ground-based operations of the system to characterize the BRDF of test sites used by the Remote Sensing Group. Also included is a preliminary evaluation of a Nikon 990 digital camera coupled with a 1.7-mm focal length fisheye lens to determine the level of accuracy that can be obtained in surface BRDF.