Instrument for retrieval of BRDF data for vicarious calibration

The University of Arizona´s Remote Sensing Group has performed vicarious calibrations of satellite and airborne sensors since the mid-1980s. Improvements of the accuracy of these techniques requires that the bi-directional reflectance of the test sites be characterized. The Remote Sensing Group has developed a four-band, imaging radiometer based on a two-dimensional CCD array and 8-mm fisheye lens for the retrieval of bidirectional reflectance. This paper describes the design of this radiometer and the methods used to calibrate the system. The calibration is based upon measurements of a 40-inch spherical integrating source and we describe a method to separate the spatial inhomogeneity of the source from that of the CCD array. Early data collected with this instrument of test sites at White Sands Missile Range and Lunar Lake Playa are presented and show good agreement with previous data collected at these or similar sites