Acquisition of Bidirectional Reflectance Factor Data with Field Goniometers

With the launch of new spaceborne sensors capable of acquiring bidirectional reflectance distribution function (BRDF) data of the earth surface, extensive ground BRDF measurements will become necessary to provide much-needed ground reference data for numerous remote sensing applications. To obtain homologous BRDF data from field goniometer devices, guidelines and recommendations are required that will allow a better comparison between BRDF data from different goniometer systems, from air- and spaceborne sensors, as well as from theoretical studies with physically based BRDF models. In this study, two examples of recent goniometer systems are given, and the quality and limits of field goniometer systems are discussed, along with detailed practical advice for the acquisition, processing, and documentation of BRDF data and ancillary information. Special emphasis is on the characterization and documentation of atmospheric and measurement surface conditions. The study also presents common shortcomings and limitations of field BRDF data, such as the influence of diffuse irradiance and changes in illumination conditions, and gives recommendations for correcting these effects from an application-oriented viewpoint.