Hyperspectral and Polarimetric Fire Emission Characterization from the NASA ER-2 Aircraft

Biomass burning (BB) is a significant air pollution source, and BB emissions are composed of a complex mixture of gases and particles that may directly and indirectly affect both air quality and climate. As the size and frequency of landscape fires and their potential effects on human populations grow, a more comprehensive understanding of the fundamental coupling of weather, fuels, and BB emissions becomes essential. There is a critical need for high-resolution, large-scale, observational constraints on end-to-end fire processes from available fuels through fuel consumption, to emissions and plume development in order to predict the dispersion of BB pollutants.

Remote sensing from NASA’s ER-2 high-altitude research aircraft can provide large-scale, high-resolution observations of fuel maps, fire intensity, plume rise, pollutants/smoke characteristics, and area burned. The Hyperspectral Thermal Emission Spectrometer (HyTES), recently integrated on the ER-2, produces a wide-swath thermal infrared (TIR) image with high spectral (256 bands from 7.5 to 12 μm) and spatial resolution (34 m from the altitude of the ER-2). The Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) acquires multiangular observations over a ±67◦ along-track range in eight (355, 380, 445, 470, 555, 660, 865, 935 nm) radiometric and three (470, 660, and 865 nm) polarimetric bands with 10 m resolution from the ER-2. Using data from recent field campaigns including SEAC⁴RS and IMPACT-PM, we will demonstrate how hyperspectral and multi-angle, spectropolarimetric remote sensing imagery can be used to constrain gaseous emissions and particulate composition of smoke.

We evaluate the capabilities of HyTES to quantify surface and atmospheric temperature in the vicinity of the fire, and the amounts of ammonia (NH₃) and methane (CH₄) gaseous emissions downwind. We found that the amount of ammonia emitted by fires can be comparable to those emitted from local power plants. AirMSPI data were used to assess the relative contribution of organics, non-organic, and black carbon particles to the total airborne particle emissions, constrained by simultaneous, in situ, aerosol measurements from the Aerosol Mass Spectrometer (AMS), a Scanning Mobility Path Sizer (SMPS), and a Single Particle Soot Photometer (SP-2) flying in coordination on the CIRPAS Twin Otter aircraft. Because TIR spectrometers rely on the thermal emission and thermal contrast between the ground and the target gas, such measurements are less affected by particulate scattering from the smoke. This suggests the potential for joint analysis of the particulate and gaseous emissions within the same BB plume with the HyTES and AirMSPI instruments flying together on the ER-2 platform.