Detection and monitoring of African vegetation fires using MSG-SEVIRI imagery
Amraoui M., DaCamara C.C., Pereira J.M.C.
Remote Sensing of the Environment
An operational procedure is presented that allows detecting active fires based on information from Meteosat-8/SEVIRI over Africa. The procedure takes advantage of the temporal resolution of SEVIRI (one image every 15 min), and relies on information from SEVIRI channels (namely 0.6, 0.8, 3.9, 10.8 and 12.0 mu m) together with information on illumination angles. The method is based on heritage from contextual algorithms designed for polar, sun-synchronous instruments, namely NOAA/AVHRR and MODIS/TERRA-AQUA. A potential fire pixel is compared with the neighboring ones and the decision is made based on relative thresholds as derived from the pixels in the neighborhood. An overview is provided of results obtained for January and July 2007, respectively over Northern Africa (NAfr) and Southern Africa (SAfr), paying special attention to the spatial and temporal distribution of active fires. In both NAfr and SAfr, two types of vegetation clearly dominate in terms of fire activity, namely tree-covered areas, containing 40% of total fires observed, and shrub-covered areas, with 25% (19%) of total fires in NAfr (SAfr). However, marked differences were also to be found between the two regions; more than two-thirds (70%) of fires in SAfr were observed in land cover classes dominated by trees but the proportion is much lower (40%) in the case of NAfr. The duration of active fires in both regions tends to follow two-parameter generalized Pareto distributions, with both the scale and the shape parameters presenting very similar values for NAfr and SAfr. An assessment of the robustness of the algorithm, consistency of results and added value of the product was made by studying the daily cycle of fire activity over two regions located in northern and southern hemisphere Africa and by means of systematic comparisons against fire incidence reported in previous works and against hot spots extracted from the global daily active fire product developed by the MODIS Fire Team. The observed fire incidence by land cover class compares well with the results reported in previous works and it is shown that there is an overall coherence between results obtained from SEVIRI and MODIS when adequate spatial and temporal scales are chosen when performing the comparison. Data from MODIS and SEVIRI may be viewed as complementary, the latter having the added value of providing a much finer temporal resolution that allows uncovering certain aspects of fire behavior, namely the characterization of daily fire cycles.