DMSP-OLS estimation of tropical forest area impacted by surface fires in Roraima, Brazil: 1995 versus 1998

A procedure has been developed to locate and estimate the area of heavy forest burning based on the frequency of DMSP-OLS (US Air Force Defense Meteorological Satellite Program Operational Linescan System) fire detection from time series of observations across the fire season. A calibration was developed for Roraima, Brazil, using Landsat Thematic Mapper (TM) data acquired near the end of the 1998 burn season and analysed to identify unburnt, partially burnt and heavily burnt forest areas. A fire detection frequency threshold of five nights was used to map heavily burnt forest using the 3 months of DMSP-OLS observations. The threshold of five fire detections, which could occur anytime during the 3-month time period, was selected to constrain errors of commission involving unburnt forest to 10% of the total area for unburnt forest in the calibration area. At this threshold setting the DMSP-OLS estimate of heavily burnt forest area covered 79% of the Landsat measured area. It was found that 77% of the 1998 heavily burnt forest area was outside of the state's protected areas (national parks, reserves, indigenous areas). Two of the protected areas sustained a substantial increase in heavily burnt forest in 1998 relative to 1995 (Reserva Biologica Mucajai and Parque Indigena Yanomami). The 1998 forest burning in these two areas was concentrated in their eastern-most sections. The core of the Yanomami area did not sustain extensive burning in 1998. Protected areas in the north-eastern section of the state, where forests are mixed with cerrado, had moderate increases in heavily burnt forest in 1998. Other protected areas were largely free of the heavy forest burning, which was concentrated to the west of the state's primary cerrado zone.