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Ground-monitor radiometer system for vicarious calibration

The Remote Sensing Group at the University of Arizona has been active in the vicarious calibration of numerous sensors through the use of ground-based test sites. Application of these approaches has been limited in the past by the fact that ground-based personnel must be present at the time of the sensor overpass. This work presents the design and implementation of a set of ground-based, ground-viewing radiometers that are deployed without the need for on-site personnel. The radiometers are based on LED detectors allowing them to be robust and inexpensive and combining the results of these measurements with known calibration of the sensors and a suitable surface BRDF model, allows the surface spectral reflectance of the test site to be determined for the sensor overpass. The at-sensor radiance can be predicted via a radiative transfer code using atmospheric data from a fully-automated solar radiometer. Early results from this approach are presented for the Landsat ETM+ and Terra and Aqua MODIS sensors. These results show that errors are currently larger for this method than those with ground-based personnel, but the increased number of calibration opportunities should improve the overall understanding of the sensor calibration.