# Automatic Methodology for Forest Fire Mapping with SuperDove Imagery
## 3 Results
### Selected Vegetation Index  
The preliminary phase involves the collection and analysis of the data set for vegetation indices. These indices are likely to provide detailed information on the state of the land cover and, therefore, the difference between pre- and post-fire values could be used as an indicator of the state of the land cover. To test this, pixel-by-pixel differences were computed between the vegetation indices detailed in Table 2 for each pair of pre- and post-fire images. Finally, the average of the pixel values within the measured area was calculated using the fire delimitation vector mask provided by the CEMS.  
Figure 4 shows the results of the average differences between vegetation indices in the images. At first glance, it seems to indicate that the greatest differences are obtained with the MSR and SR indices and that, therefore, these would be the ideal indices for delimiting burned areas.  
Figure 4: Average differences between vegetation indices in pre- and post-fire images.  
Figure 3: Processing of the DEM.  
However, if the pre- and post-fire differences in the different indices that appear in Figure 5 are observed in detail and, especially, if they are compared with the delimitation mask of the burned area provided by the CEMS (Figure 5a), the information presented the MSR and SR indices (Figures 5f and 5i, respectively) makes the process of obtaining a burned-area mask difficult. This degraded performance is probably due to the definition of these indices (Table 2), in addition to the spectral responses involved in their calculation in the case of changes in vegetation status.  
Figure 5: Difference between pre- and post-fire images for different vegetation indices in north Attica area: (**a**) fire delimitation mask provided by CEMS, (**b**) EVI, (**c**) GEMI, (**d**) GNDVI1, (**e**) GNDVI2, (**f**) MSR, (**g**) NDVI, (**h**) SAVI, (**i**) SR, (**j**) WDRVI, and (**k**) YNDVI.  
Similarly, a visual inspection of the variation in other vegetation indices, such as EVI, SAVI, and GEMI (Figure 5b, Figure 5e, and Figure 5h, respectively), allows the identification of various areas where changes in vegetation are detected that do not correspond to the area affected by the fire. This is likely due to the sensitivity of these indices to radiometric changes between the pre- and post-fire images. Although this aspect could possibly be corrected with a better preprocessing stage, these groups of indices were discarded because the aim was to achieve a robust and simple methodology for determining the burned-area extent and severity level.  
Finally, there is a group of indices that seem to separate the burned area well from the rest of the land cover (if MSR and SR are excluded) and that are more immune to radiometric problems. Among them are the NDVI, WDRVI, and YNDVI (Figure 5g, Figure 5j, and Figure 5k, respectively). For the final automatic detection of burned areas, the first and last indices were used because they always appeared among those with the greatest average difference detected in the four study areas (see Figure 4). Although the inclusion of the WDRVI was tested in the following processing stages, the results did not vary substantially.