Examining Fire Radiative Power (FRP) Retrievals using Shortwave and Mid-Infrared Radiance from FIREX-AQ

Abstract:

Fire radiative power (FRP) is one of the most widely used methods for describing biomass burning events and has traditionally relied on the middle infrared (MIR). Observations of active fire, however, do not always include the MIR (e.g., Landsat/Sentinel-2). Because higher temperature wildfires also emit radiation within the short-wave infrared (SWIR) wavelengths based on the Planck function, which is often available at finer resolutions, there is a need to determine FRP using different portions of the electromagnetic spectrum. This paper represents results from a comparative analysis between 2.38 (SWIR) bands and a 4.06 (MIR) micron band from sensors flown over the Williams Flats fire in the 2019 FIREX-AQ campaign. Sensors compared included the MODIS/ASTER airborne simulator (MASTER) with 2.38 and 4.06 micron bands, the Airborne Visible / Infrared Imaging Spectrometer (AVIRIS), and Enhanced Modis Airborne Simulator (EMAS), both with 2.38 micron bands only. While saturation and reflected solar radiance were significant obstacles for cross-sensor comparison in the SWIR, we show that FRP at 2.38 microns of unsaturated pixels were similar to those from 4.06 microns, with a total FRP difference of 10%. This observation provides insight as to feasibility of utilizing the SWIR bands for biomass emission estimates, offering potential for FRP measurements from additional sensors that may not necessarily offer the traditional MIR wavelength, but have other benefits (e.g., high spatial resolution). Ultimately, validating FRP will assist atmospheric scientists in accounting for the role that biomass burning plays in resulting fire emissions, which contribute to the carbon cycle and affect climate.