ULGS II: A High-Performance Field and Laboratory Spectrogoniometer for Measuring Hyperspectral Bidirectional Reflectance Characteristics

The derivation of the bidirectional reflectance distribution function (BRDF) from Earth surface features provides vital data for improved remote estimation of Earth surface features and properties. The angular component of a reflectance signature represents a valuable source of information that has largely been ignored due to the lack of empirical data. BRDF data products are now readily available from a variety of remote sensing platforms, and these require extensive field validation to ensure data quality and validity. This paper presents a high-performance, low-cost, and computer-controlled goniometer system capable of sampling surface BRDF and demonstrates several example applications. The system introduces a number of technological advances, including real-time reflectance calibration, programmable sampling schemes, zero target interference structure, and ease of portability. Using this instrument, BRDF estimates were gathered from a variety of agricultural crops in field and laboratory settings, with performance gains of four times the speed of current designs. This system can provide very fast acquisition of a BRDF estimate, depending on the desired angular resolution. Initial experiments demonstrate that this new style of hyperspectral goniometer is a significant advance over previous designs, with respect to scan capabilities, angular resolution, calibration, and portability.