Comparison of methods for generation of absolute reflectance factor measurements for BRDF studies

For remote sensing applications, there is a need for knowledge concerning the reflectance properties of natural and man-made materials as a function of measurement geometry and wavelength. This information is used to determine the so-called bidirectional reflectance distribution function (BRDF). This study is intended to generate an absolute bidirectional reflectance factor for BRDF studies. This is accomplished by development of a goniospectroradiometer which can simulate any source-sensor-target geometry. The spectral range is from visible to near- infrared (2500 nm) with a spectral resolution of 10 nm. The study involves both theoretical and experimental work for calibration of BRDF by: (1) the directional hemispherical reflectance and (2) a NIST calibrated standard reflectance tile. A PTFE sample is calibrated using both methods, and a comparison test was conducted to verify the accuracy. This PTFE sample can be used as a reference standard material to transfer reflectance factor scale to all source-target-sensor geometries in the visible and infrared regions (400 nm to 2500 nm) of the spectrum