Directional reflectance characterization facility and measurement methodology

A precision reflectance characterization facility, constructed specifically for the measurement of the bidirectional reflectance properties of Spectralon panels planned for use as in-flight calibrators on the NASA Multiangle Imaging Spectroradiometer (MISR) instrument is described. The incident linearly polarized radiation is provided at three laser wavelengths: 442, 632.8, and 859.9 nm. Each beam is collimated when incident on the Spectralon. The illuminated area of the panel is viewed with a silicon photodetector that revolves around the panel (360 degrees) on a 30-cm boom extending from a common rotational axis. The reflected radiance detector signal is ratioed with the signal from a reference detector to the effect of amplitude instabilities in the laser sources. 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 held 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 resolution of 0.001 degrees. Design details and an outline of the measurement methodology are presented. (C) 1996 Optical Society of America