Remote sensing of biomass burning in the tropics

A new method has been developed for the global assessment of trace gases and particulates emission from tropical biomass burning. The method is based on remote sensing of one emitted product: particulates. It uses daily meteorological satellite data with resolution of 1 km 2 . The visible (0.63 μm) and near‐infrared (0.84 μm) bands are used to determine the mass of particulates in the emitted smoke and to estimate the relative contribution of flaming and smoldering fires to the resulting smoke. The mid‐IR (3.5–3.9 μm) and the thermal infrared (10.5–11.4 μm) bands are used to detect and count fires in order to integrate the smoke result with the whole season and for the whole area of interest. The thermal channels are sensitive enough to detect flaming fires as small as 10 m×10 m and smoldering fires as small as 30 m×30 m. The detected mass of emitted particulates is converted into a mass of emitted trace gases using published relations between the emitted particulates and trace gases for the flaming and smoldering phases. The technique can be applied to regions where intensive biomass burning takes place. It is capable of monitoring the extent of current biomass burning, discovering new deforestation frontiers (unknown otherwise), and estimating quantitative contribution of biomass burning to changes in atmospheric composition. The method has been applied to a limited area where substantial deforestation has taken place. Analysis of the 1987 burning season shows that in Brazil (in a limited area between 6.5°–15.5°S and 55°–67°W) during the 3 months of the dry season (July 1 to September 30) there are up to 8000 fires a day (observed from space) each contributing 4500 t of CO 2 , 750 t of CO, and 26 t of CH 4 to the atmosphere. During the dry season of 1987, it is estimated that 240,000 fires were burning in this area resulting in the emission of 1×10 13 g of particulates, 7×10 12 g of CH 4 , 2×10 14 g of CO, and 1×10 15 g of CO 2 . A comparison to estimates of global emissions is also given.