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

Some notes on spectral properties of burnt surfaces at sub-pixel level using multi-source satellite data 245
vegetation indices of the post-fire satellite images were computed. Then
the percent of cover for each type was correlated to surface reflectance values
and vegetation indices for all satellite images, and regression models
were fitted to characterize those relationships. These relationships were
implemented by overlaying a fishnet of 90 meters resolution over the LAND-
SAT and ASTER imagery and 250 meters for MODIS.
3 - Results and discussion
In the literature, the spectral channel TM4 has been proved to be the most
sensitive regarding alterations in spectral response of the burned pixels.
The second spectral channel with the highest contribution to burned area
discrimination has been reported that it is TM7. A strong decrease in
reflectance of burned areas occurs in the near-infrared part of the electromagnetic
spectrum as a result of deterioration of the leaf structure of the
vegetation layer, which reflects large amounts of the incident solar radiation.
In addition, a strong increase in reflectance of the burned areas
occurs in the mid-infrared region as a result of the decrease of the vegetation
moisture content. The replacement of the vegetation layer with charcoal
reduces the water content, which absorbs the incident radiation in this
spectral region, and consequently the burned areas present higher midinfrared
reflectance values than those of healthy vegetation.
In the graphs below it is clear that the relationship between percent of
burned and percent of vegetation with NIR and MIR ground reflectance
value as well as with NDVI values at grid cells of 90 and 250 meters resolution
of LANDSAT, ASTER and MODIS data respectively is described by a linear
model.
Figure 2 - Relationship between percent of burned and percent of vegetation with NIR and MIR
ground reflectance and NDVI at grid cells of 90 meters resolution of LANDSAT data.