Radiometric calibration of earth-Observing sensors using an automated test site at Railroad Valley, Nevada

The Remote Sensing Group (RSG) at the University of Arizona uses the reflectance-based approach to radiometrically calibrate airborne and spaceborne sensors in the solar-reflective regime. The Radiometric Calibration Test Site (RadCaTS) concept was developed in 2004 to increase the amount of ground-based data collected. RadCaTS provides a methodology to determine the surface reflectance for any arbitrary test site in the absence of ground personnel. It is founded on the reflectance-based approach and has successfully operated at Railroad Valley, Nevada, with a suite of instruments including nadir-viewing multispectral radiometers, a Cimel sun photometer, and a meteorological station. RadCaTS data are currently used by RSG to supplement those collected by on-site personnel. This work presents a description of the RadCaTS automated concept, including the process used to determine surface reflectance and top-ofatmosphere (TOA) spectral radiance. The instrumentation required to measure the surface and atmosphere is introduced, followed by discussions regarding their placement on the 1 km² site at Railroad Valley and their calibration. Lastly, the RadCaTS results are compared with those obtained from the Landsat7 Enhanced ThematicMapper Plus (ETM+) and Terra Moderate Resolution Imaging Spectrometer (MODIS). The average percent difference in TOA spectral radiance is 4.1% between the six bands of ETM+ and RadCaTS and 3.6% between the seven land bands of Terra MODIS and RadCaTS.