Ground Facility for Vicarious Calibration of Skyborne Sensors

An automated ground facility, for vicarious radiometric calibration of airborne and spaceborne sensors of visible and infrared light has been established. In the term “vicarious calibration,” “vicarious” is used in the sense of “in place of another,” signifying “in place of laboratory calibration.” Vicarious calibration involves the use of ground truth in the form of measurements by ground-viewing radiometers, a Sun- viewing photometer, and meteorological instruments positioned in a ground target area. Typically, the target is a dry lakebed or other relatively homogeneous area. (The value of a relatively homogeneous target is that it minimizes effects of errors of registration between the target and the fields of view of sensors.) The measurement data are processed by a radiative- transfer computer code to estimate spectral radiances at the position of a sensor known to be overhead at the time of the measurements. These radiances can be compared with the sensor readings to calibrate the sensor.