Use of MODIS-derived Fire Radiative Energy to Estimate Smoke Aerosol Emissions over Different Ecosystems

Biomass burning is the main source of smoke aerosols and certain trace gases in the atmosphere. However, estimates of the rates of biomass consumption and emission of aerosols and trace gases from fires have not attained adequate reliability thus far. Traditional methods for deriving emission rates employ the use of emission factors Ex (in g of species x per kg of biomass burned), which are difficult to measure from satellites. The era of continuous environmental monitoring from space was ushered in a few decades ago. Nevertheless, fire characterization was not a major consideration in the design of the early satellite-borne remote sensing instruments, such as AVHRR. Therefore, although they are able to provide fire location information, they are not adequately sensitive to variations in fire strength or size, because their thermal bands used for fire detection saturate at the lower end of fire radiative temperature range. As such, hitherto, satellite-based emission estimates employ proxy techniques using satellite derived fire pixel counts (which do not express the fire strength or rate of biomass consumption) or burned areas (which can only be obtained after the fire is over). The MODIS sensors, recently launched into orbit aboard EOS Terra (1999) and Aqua (2002) satellites, have a much higher saturation level and, not only detect the fire locations 4 times daily, but also use their 4 micron channel temperatures to measure the at-satellite fire radiative energy (which is a measure of the fire strength). Also, MODIS measures the optical thickness of smoke and other aerosols. Preliminary analysis shows appreciable correlation between the MODIS-derived rates of emission of fire radiative energy and smoke over different regions across the globe. These relationships hold great promise for deriving emission coefficients, which can be used for estimating smoke aerosol emissions from MODIS active fire products. This procedure has the potential to provide more accurate emission estimates in near real-time, thereby broadening opportunities for various active fire disaster management applications such as alerts, evacuation and, smoke dispersion forecasting.