Characterizing Vicarious Calibration Test Sites using Imaging Spectroscopy

Data from Earth-observing imaging spectrometers installed on the International Space Station (ISS) platform provide opportunities to use fine spectral information about the Earth with various imaging angles and conditions. The results here are based on hyperspectral scenes captured by the Earth Surface Mineral Dust Source Investigation (EMIT) and the DLR Earth Sensing Imaging Spectrometer (DESIS). Intercomparison of EMIT and DESIS from the same platform provides many opportunities for coincident views of various surface types and atmospheric conditions. Here, we focus on observations of the radiometric calibration sites with automated SI-tractable surface-characterization instruments of the Radiometric Calibration Network (RadCalNet) and conduct comparative analyses of EMIT and DESIS. We validate the data by comparing them to measurements from RadCalNet sites as a quantitative inter-calibration approach. The results of this study show the utility of RadCalNet for the harmonization of hyperspectral instruments. In addition, the approach here makes use of the precessing orbit of the ISS enables observations under similar sensor/sun angles for varying sun/sensor angles over short time periods, limiting the effect of sensor or site changes and highlighting directionality dependencies of the surface reflectance and corresponding atmospheric conditions. The intercomparison methodology discussed here can eventually be used for calibration and validation of hyperspectral instruments of the Surface Biology and Geology (SBG) and Copernicus Hyperspectral Imaging Mission for the Environment (CHIME).