Remote measurement of energy and carbon flux from wildfires in Brazil

Temperature, intensity, spread, and dimensions of fires burning in tropical savanna and slashed tropical forest in central Brazil were measured for the first time by remote sensing with an infrared imaging spectrometer that was designed to accommodate the high radiances of wildland fires. Furthermore, the first in situ airborne measurements of sensible heat and carbon fluxes in fire plumes were combined with remote measurements of flame properties to provide consistent remote-sensing-based estimators of these fluxes. These estimators provide a means to determine rates of fuel consumption and carbon emission to the atmosphere by wildland fires as required for assessments of fire impacts on regional air pollution or global emissions of greenhouse gases. Observed fires developed complex fire-line geometry and thermal structure, even as average whole-fire temperatures varied little. Flame temperatures sometimes exceeded 1600 K along the leading edge of actively spreading fire lines, yet >90% of the radiant energy from observed fires was associated with temperatures of 830-1440 K. Fire in a partially slashed forest encompassed a high-intensity flaming front and a trailing reach of residual combustion extending 400 m. Fire fronts in tropical savanna typically formed with little depth and a high proportion of their radiant flux density associated with high temperatures due to low levels of residual combustion. Measured fires had such low and variable radiance compared with that of a blackbody of comparable temperature as to preclude the use of fire radiance at a single wavelength as a measure of fire intensity or temperature. One-half of the radiant flux density from a measured savanna fire was associated with values of a combined emissivity-fractional-area parameter <0.091 m(2)/m(2); for a slash fire this fraction was associated with values <0.37 m(2)/m(2). Observations reported here show wildland fires to be so complex and dynamic as to require frequent high-resolution measurements over their course and duration in order to specify their effects in the environment; an understanding of global fire impacts may require such measurements over a large sample of individual fires.