Spectral calibrations of HICO data using atmospheric bands and radiance adjustment based on HICO and MODIS data comparisons

The Hyperspectral Imager for the Coastal Ocean (HICO™) instrument is now operating from a location on the Japanese Experiment Module-Exposed Facility (JEM-EF) on the International Space Station (ISS). HICO™ is a pushbroom sensor covering a spectral range between 0.35 and 1.08 micron with a spatial resolution of about 90 meter and a spectral sampling interval of 5.7 nanometer. The instrument is not equipped with radiometric and spectral calibration devices. Before shipping the HICO™ instrument to Japan to be launched on a Japanese HII-B rocket, spatial, spectral, and radiometric calibrations of the instrument were made in a calibration lab at the Naval Research Laboratory in Washington, DC. Based on the analysis of HICO data acquired from ISS/ we have observed that the wavelengths of the HICO channels are slightly changed in comparison with those from laboratory calibrations. We have used a spectrum matching technique [2] for adjusting wavelengths. Several atmospheric water vapor and oxygen absorption bands in the HICO data measured under the normal operation mode with a spectral sampling interval of approximately 5.7 nm are used for spectrum matching. Four extra-terrestrial solar lines in the HICO data with a spectral spacing of 1.7 nm are also used for spectrum matching. The spectrum matching technique is described in this paper. Also based on analysis of ISS HICO data, we have found that the radiances of ISS HICO data calibrated with the laboratory-based coefficients are smaller than expected by approximately 25%. We have adjusted the calibration coefficients based on comparing HICO data and MODIS data acquired over several desert areas. The vicarious calibration procedure for HICO radiometric calibrations is also described in this paper.