COMPOSITING CRITERIA FOR BURNED AREA ASSESSMENT USING MULTITEMPORAL LOW-RESOLUTION SATELLITE DATA

Five different multitemporal image compositing criteria were compared for the specific aim of monitoring burned areas using AVHRR-GAC 5 km d ata. Two of them were based on a classical maximum value technique: ma ximum value composite of NDVI (MVCN) and of surface temperature (MVCTS ). Three others were based on a minimum value technique: minimum value composite of Channel 1 (M(i)VCB1), of Channel 2 (M(i)VCB2) and of alb edo (M(1)VCA). The compositing period used was 1 week, and four output channels suitable for identifying burned areas were generated: AVHRR Channel 2 (Ch2), normalized difference vegetation index (NDVI), surfac e temperature (T-S), and global environment monitoring index (GEMI). T he different compositing criteria were assessed based on their ability to retain burned areas and also on their choice of close to nadir pix els. The separability od burned and unburned areas for each of the com positing criteria was assessed for each of the individual output chann els. The criterion that showed best results in terms of separability w as M(i)VCA followed very closely by M(1)VCB2; the MVCN criterion clear ly showed the least merit of all. An overall analysis of the satellite zenith angles showed that the M(i)VCB2 criterion selected the smalles t angles or closer to nadir pixels followed by M(i)VCA, MVCN, MVCTs, a nd M(i)VCB1. Although impossible to choose a single best compositing c riteria in absolute terms, M(i)VCA proved to be the best compromise be cause it chose near to nadir pixels and performed best in terms of sep arability between burned and unburned spectral signatures. Future work will determine how to combine different channels (e.g., GEMI, Ch2, T- s, NDVI) for burned area detection, once the M(i)VCA compositing has b een performed. (C) Elsevier Science Inc., 1998.