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

3 - Methodology and results
MODIS reflective and active fire data for burn mapping in Colombia 229
Figure 1 - Study area: Colombia (in green), H10V08 tile (in red) and test area (in black).
All burned area estimation and mapping followed three steps: (i)
Normalized Burn Ratio (NBR) calculation using the MODIS reflectance product,
(ii) NBR threshold establishment using MODIS active fire information
and (iii) validation. Image and data processing was carried out using ENVI
4.2 and ArcGIS 9.2 software packages.
The NBR (Key and Benson, 1999) is a spectral index that integrates nearinfrared
(NIR) and shortwave-infrared (SWIR) bands, both of which register
the strongest response, albeit in opposite ways, to burning (Lentile et al.,
2006; Roldán-Zamarrón et al., 2006). The NBR is estimated using the following
equation:
NBR = (ρ swir – ρ nir )/(ρ swir + ρ nir ) (1)
NBR threshold value was established based on the best spatial correlation
between burn area as derived from the NBR image itself and MODIS active
fire locations. On the one hand, the NBR image was threshold using several
values ranging from 0.00 to 0.10, what resulted in a set of binary images.
On the other hand, active fire locations point format file were converted
into a binary image of 1km pixel size. At this point it is worth pointing out
that we only accounted for active fire locations occurred between the 1 st
of January and the 9 th of February with a higher than 60 confidence value.
The two sets of data were then compared using confusion matrices in order
to find the threshold value that better correlate the two types of data
(post-fire reflective and active fire data). The latter was tested using the