DIRECTIONAL REFLECTANCE CHARACTERIZATION FACILITY AND MEASUREMENT METHODOLOGY

A precision reflectance characterization facility, constructed specifi cally for the measurement of the bidirectional reflectance properties of Spectralon panels planned for use as in-flight calibrators on the N ASA Multiangle Imaging Spectroradiometer (MISR) instrument is describe d. The incident linearly polarized radiation is provided at three lase r wavelengths: 442, 632.8, and 859.9 nm. Each beam is collimated when incident on the Spectralon. The illuminated area of the panel is viewe d with a silicon photodetector that revolves around the panel (360 deg rees) on a 30-cm boom extending from a common rotational axis. The ref lected radiance detector signal is ratioed with the signal from a refe rence detector to the effect of amplitude instabilities in the laser s ources. This and other measures adopted to reduce noise have resulted in a bidirectional reflection function (BRF) calibration facility with a measurement precision with regard to a BRF measurement of +/-0.002 at the 1 sigma confidence level. The Spectralon test piece panel is he ld in a computer-controlled three-axis rotational assembly capable of a full 360 degrees rotation in the horizontal plane and 90 degrees in the vertical. The angular positioning system has repeatability and res olution of 0.001 degrees. Design details and an outline of the measure ment methodology are presented. (C) 1996 Optical Society of America