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Analysis of the relationship between spatial pattern and spectral detectability of areas burned in southern Africa using satellite data
Authors:A. C. L. Sá  J. M. C. Pereira  R. H. Gardner
Affiliation:1. Department of Forestry , Instituto Superior de Agronomia , Tapada da Ajuda, 1349‐017 Lisbon, Portugal anasa@isa.utl.pt;3. Department of Forestry , Instituto Superior de Agronomia , Tapada da Ajuda, 1349‐017 Lisbon, Portugal;4. University of Maryland Center for Environmental Science , Appalachian Laboratory , 301 Braddock Rd, Frostburg, MD 21532, USA
Abstract:Fires in Africa affect atmospheric emissions and carbon sequestration, landscape patterns, and regional and global climatic conditions. Studies of these effects require accurate estimation of the extent of measurable fire events. The goal of this study was to assess the influence of burned area spatial patterns on the spectral detectability of burned areas. Six Landsat‐7 ETM+ images from the southern Africa were used for burned area mapping and spatial pattern analysis, while contemporaneous MODIS 500 m spatial resolution images were used to measure the spectral detectability of burned areas. Using a 15 by 15 km sample quadrats analysis, we showed that above a burned area proportion threshold of approximately 0.5 the spectral detectability of burned areas increase due to the decrease in the number of mixed pixels. This was spatially related to the coalescence of burned patches and the decrease in the total burned area perimeter. Simple burned area shapes were found at the Botswana site, where the absence of tree cover and the presence of bright surfaces (soil and dry grass) enhanced the spectral contrast of the burned surfaces, thus enabling better estimates of burned area extent. At the Zambia and Congo sites, landscape fragmentation due to human activity and the presence of a tree vegetation layer, respectively, contribute to the presence of small burned area patches, which may remain undetectable using moderate spatial resolution satellite imagery, leading to less accurate burned area extent estimates.
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