7th Workshop on Forest Fire Management - EARSeL, European ...

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IV - BURNED LAND MAPPING, FIRE SEVERITY DETERMINATION, AND VEGETATION RECOVERY ASSESSMENT
images based analysis are assumed to be minimal and are not considered in
most studies using the dNBR. Therefore the focus of this research is to
evaluate illumination effects and to propose a topographic correction
approach to become a more reliable dNBR fire severity assessment.
2 - Methods
2.1 - Study area and data-preprocessing
The study area is situated at the Peloponnese (Greece). Large wildfires
stroke the Peloponnese in the 2007 summer. The pre-fire image dates from
23/07/2006, whereas the post-fire image was acquired at 28/09/2007. The
images were subjected to geometric, radiometric and atmospheric correction
(Chavez, 1996).
2.2 - dNBR optimality
For evaluating the optimality of the bi-temporal change detection the TM4-
TM7 bi-spectral space was considered. A displacement from unburned (U)
to optimally (O) sensed burned is illustrated in figure 1. Perturbing factors
decrease the performance of the index. The magnitude of change to which
the index is insensitive is equal to the Euclidian distance. Thus the
observed displacement vector UB can be decomposed in the sum of the vectors
UO and OB, hence, following the expression of Roy et al. (2006) the
index optimality is defined as:
⎟OB⎥
optimality = 1 - --------------- (2)
⎟UB⎥
Figure 1 - Example pre/post-fire trajectory
of a pixel in the TM4-TM7 feature
space.