Advances in BRDF field measurement: New principle and instrument

The advances in the capabilities of sensors and methods used for remote sensing the earth call for taking into account angular effects. The effect is described through the ¿bidirectional reflectance distribution function¿ (BRDF). For most applications BRDF models are used. To validate such models and for in-flight calibration purposes the measurement of BRDF of natural surfaces is necessary. Most of the methods used to measure angular reflection properties in the past had to use interpolation or smoothing algorithms in the data processing. These computations influence the resulting BRDF. We present the instrument GRADIS (Ground Reflectance Angular Distribution Investigation System) which avoids this problem by using a new principle for acquiring the data. Several measurement campaigns were conducted for basic measurements of different surfaces and for calibration measurements of airborne instruments.