Intercomparison of imaging sensors using automated ground measurements

The reflectance-based method is a vicarious approach providing absolute radiometric calibration. A desire to increase the number of possible reflectance-based calibrations led the University of Arizona Remote Sensing Group (RSG) to deploy multispectral, downlooking radiometers at the RSG's Railroad Valley test site in Nevada. The radiometers are coupled with data from a sun photometer to provide the information needed for reflectance-based calibration without the need for on-site personnel. Results from these radiometers show similar uncertainties as on-site methods, and early results have led to their use with geostationary sensors, for derivation of surface bi-directional reflectance effects, and for comparisons of biases between sensors. The results show that radiometers with a single view angle are sufficient to characterize BRDF effects for Railroad Valley Playa. The results also give confidence in the automated approach as a means for cross-calibration relative to the vicarious results providing similar intercomparison results as with on-site personnel.