Retrieval of biomass combustion rates and totals from fire radiative power observations: FRP derivation and calibration relationships between biomass consumption and fire radiative energy release

TLDR

Wildfire aerosol and trace gas emissions are typically derived from biomass combustion estimates, and the radiative component of burning fuel can be measured by remote sensing, offering potential to infer biomass consumption from spaceborne fire radiative energy. The study aims to develop and validate calibration relationships between fire radiative power and fuel consumption using spaceborne sensors that can derive FRP from subpixel fires with one or two spectral channels. The authors conduct a sensitivity analysis and experimental fires to investigate the feasibility of deriving FRP from subpixel observations and establishing calibration relationships. Experimental work shows that FRP estimates from hyperspectral and MIR radiance agree, with fires radiating about 14 % of their theoretical heat yield detectable by a nadir‑viewing MIR imager; the relationship between FRE and fuel mass combusted is linear (r² = 0.98) and FRP correlates strongly with combustion rate (r² = 0.90), indicating that FRE assessment can enhance burned‑area based fuel consumption and emissions estimates.

Abstract

Estimates of wildfire aerosol and trace gas emissions are most commonly derived from assessments of biomass combusted. The radiative component of the energy liberated by burning fuel can be measured by remote sensing, and spaceborne fire radiative energy (FRE) measures can potentially provide detailed information on the amount and rate of biomass consumption over large areas. To implement the approach, spaceborne sensors must be able to derive fire radiative power (FRP) estimates from subpixel fires using observations in just one or two spectral channels, and calibration relationships between radiated energy and fuel consumption must be developed and validated. This paper presents results from a sensitivity analysis and from experimental fires conducted to investigate these issues. Within their methodological limits, the experimental work shows that FRP assessments made via independent hyperspectral and MIR radiance approaches in fact show good agreement, and fires are calculated to radiate 14 ± 3% [mean ± 1S.D.] of their theoretically available heat yield in a form capable of direct assessment by a nadir‐viewing MIR imager. The relationship between FRE and fuel mass combusted is linear and highly significant ( r 2 = 0.98, n = 29, p < 0.0001), and FRP is well related to combustion rate ( r 2 = 0.90, n = 178, p < 0.0001), though radiation from the still‐hot fuel bed can sometimes contribute significant FRP from areas where combustion has ceased. We conclude that FRE assessment offers a powerful tool for supplementing existing burned‐area based fuel consumption measures, and thus shows significant promise for enhancing pyrogenic trace gas and aerosol emissions estimates.