Remote Imaging Spectroscopy of Earth's Surface in UV to Thermal Wavelengths

Abstract:

Passive remote optical spectroscopy of terrestrial ecosystems falls into one of two categories: UV, Visible and ShortWave InfraRed (VSWIR) methods that use reflected solar illumination, and Thermal InfraRed (TIR) methods that use thermal radiation of the Earth's surface. Both rely on inversion algorithms that estimate surface reflectance properties, temperature and atmospheric effects. To date, however, the two regimes have used widely different inversion approaches. Here we present the first methods for simultaneous inversion of the entire downlooking radiance spectrum from UV to the Thermal Infrared. Maximum A Posteriori estimation determines the surface and atmosphere state that is most consistent with measured radiance across the entire range. We analyze retrieval properties in simulation, finding that the complementary information provides accuracy advantages for atmospheric correction, surface emissivity and temperature estimation. We then demonstrate the method on coincident data from The Next Generation Airborne Visible Infrared Imaging Spectrometer (AVIRIS-NG) operating in the VSWIR range, and the Hyperspectral Thermal Emission Spectrometer (HyTES) in the TIR range, during flights on NASA's high-altitude ER-2 aircraft. As a test of the retrieval’s fidelity, we further make comparisons against multiple in situ measurements for surface reflectivity / emissivity, temperature and atmospheric state. Simultaneous maps of surface temperature along with reflectance properties spanning 0.4 to 12 microns can significantly advance studies in terrestrial ecosystems, geologic composition, agricultural lands, and urban areas.