Retrieval of biomass combustion rates and totals from fire radiative power observations: Application to southern Africa using geostationary SEVIRI imagery

摘要

Southern African wildfires are a globally significant source of trace gases and aerosols. Estimates of southern African wildfire fuel consumption have varied from hundreds to thousands of teragrams (Tg), and better-constrained estimates are required to properly assess the effects of the pollutant emissions. A new approach for providing such estimates is via remote sensing observations of fire radiative power (FRP), a variable proportional to the rate of fuel consumption. The launch of the SEVIRI radiometer onboard the geostationary Meteosat-8 platform presents a unique opportunity to monitor FRP at 15-min intervals, allowing analysis of the complete diurnal cycle of biomass burning and calculation of the total fire radiative energy. Here we present the first FRP retrievals from SEVIRI and compare them to those derived from near-coincident MODIS overpasses. Strong agreement is achieved on a per-fire basis (r(2) = 0.83, n = 139, p <0.0001), although at the regional scale SEVIRI typically underestimates FRP with respect to MODIS due primarily to its inability to confidently detect fire pixels with FRP <similar to 100 MW. Using relationships developed during ground-based experiments, SEVIRI-derived FRP measures are converted into estimates of the rate and total quantity of biomass combusted in southern Africa. During a 4.5 day monitoring period, and based on only the observed FRP recorded by SEVIRI, we infer that as a minimum estimate, peak combustion rates reached 50 tons/s and a total of 3.2 Tg of fuel was burnt in southern Africa. While provisional, we calculate that these figures maybe potentially increased upward by a factor of similar to 3 to account for atmospheric absorption of the upwelling radiation and for fires that were potentially cloud covered or too weakly emitting to be detected by the geostationary imager. The new tool of SEVIRI-derived FRP provides an insight into biomass burning on the African continent at a hitherto unobtainable temporal frequency, highly suited to the linking of pollutant emissions estimates to models of atmospheric transport