Cause, effect, and correction of field spectroradiometer interchannel radiometric steps

Abstract

Field spectroradiometers are often comprised of several spectral detectors to sample the full range of reflected solar irradiance. An example of such an instrument is the Analytical Spectral Devices (ASD) full-range spectroradiometer, featuring three spectral detectors to capture spectra between 350 and 2500 nm. The resulting spectra often exhibit radiometric steps at the joints of these detectors. This study investigates the influence of external temperature and humidity on the magnitude of these steps by experiments based on a climate chamber. Relative radiometric errors at the detector borders were found to reach up to 16% for the visible and near infrared and 21% for the shortwave infrared 2 (SWIR2), whereas relative reflectance errors are target dependent, typically ranging between 2% and 6%. The derived sensor model provides a physically based explanation of the changes in radiometry due to temperature and demonstrates that all spectral bands are affected to a higher or lesser degree. The model can be used to correct for the effect of temperature on the recorded radiances. Applying the model to ASD instruments that were not tested in the climate chamber still leads to reasonable correction results with RMSE values of 0.6%.