Evaluating commercial tablet screens for use as portable spectral radiance calibration assessment sources, specifically in support of field-deployed ground viewing radiometers

The University of Arizona Remote Sensing Group (RSG) began outfitting the radiometric calibration test site (RadCaTS) at Railroad Valley Nevada in 2004 for automated vicarious calibration of Earth-observing sensors. RadCaTS was upgraded to use RSG custom 8-band ground viewing radiometers (GVRs) beginning in 2011, several of which are currently deployed providing an average reflectance for the test site. GVRs are also beginning to be deployed at other field sites for both vicarious calibration and reflectance product validation. The measurement of ground reflectance is the most critical component toward both of these goals. In order to ensure the quality of these measurements, RSG has been exploring more efficient and accurate methods of on-site calibration evaluation. We will present experimental methods and results testing commercial tablet screens as portable calibration sources. Recent work in medical fields have shown encouraging results for stability of tablet display luminance both short and long term. We assess them in spectral radiance using NIST-traceable methods and transfer radiometers, particularly the Calibration Test Site SI-Traceable Transfer Radiometer (CaTSSITTR). CaTSSITTR will also continue to play an integral role in the on-site deployment of this or any source, providing radiance calibration at time of use. Current on-site calibration methods (sun-illuminated sources) rely on stable, preferably clear sky conditions and require personnel involvement at each radiometer. While spectrally limited, a tablet source method may be able to help monitor some spectral bands more often and in any dry weather conditions.