Atmospheric correction for global mapping spectroscopy: ATREM advances for the HyspIRI preparatory campaign

Orbital imaging spectrometers, such as the proposed Hyperspectral Infrared Imager (HyspIRI) mission, will provide global, multi-year Visible Shortwave Infrared (VSWIR) reflectance maps. Monitoring the Earth's surface at high spectral resolution will advance our understanding of changing ecosystems and land use. These applications depend on reliable correction of atmospheric scattering and absorption. The HyspIRI Preparatory Campaign is an airborne precursor mission comprised of multiple flights by the “classic” Airborne Visible Infrared Imaging Spectrometer (AVIRIS-C) over a wide geographic area. This article describes the atmospheric correction that we have implemented for the campaign. We first present the theoretical basis of our approach, which is grounded in the ATmospheric REMoval (ATREM) algorithm. We then describe new enhancements including retrieval of pressure altitude, which improves accuracy over widely varying topography, and joint retrieval of optical absorption for three phases of water (vapor, liquid, and ice), which improves accuracy over vegetated areas. Reflectance is validated using ground spectra acquired across a wide range of targets and elevations. Finally, we use the algorithm to map vapor, liquid, and ice phases of water over 6 months across a 14,000 km2 region of California.