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

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II - VALIDATION OF RS PRODUCTS FOR FIRE MANAGEMENT
In this work we compare eight different spectral indices from the bibliography,
obtained from MODIS sensor on board Terra satellite, as fire risk indicators
in the Galicia region.
2 - Study site and materials
The study site in this work is the Galicia region placed at the Northwest of
Spain. About the 70% of the Galician territory is occupied by forest areas.
Despite its humid and rainy climate, Galicia is the Spanish region with the
largest number of forest fires.
The organisms for the management of fire prediction and extinction tasks
use a grid as a basis dividing Galicia in 360 10-km side squares (UTM 29).
Also, historic fire data are provided at the same spatial resolution.
Therefore, information on vegetation stage has been adapted to this spatial
resolution, using the same grid. As seen in Sánchez et al. (2009), the
huge majority of fire events take place from February to October. Thus, the
analysis is constrained to this period. The temporal resolution chosen is 16
days, as the vegetation stage does not change significantly within this twoweek
period. The vegetation information is obtained from the products
MOD09 A1 and MOD13 Q1 provided by the MODIS service.
3 - Methodology
3.1 - Pre-processing of the MODIS images
In this work we use images from the MOD09 A1 product, (8 days temporal
resolution and 500 m spatial resolution), as well as images from the MOD13
Q1 product (16 days temporal resolution and 250 m spatial resolution).
Within a satellite scene, there can be pixels with wrong values due to the
presence of clouds or because of some problem with the detector. Therefore
it is essential to perform a filtering process. We use the information contained
in the quality band of each product and information of the Corine
Land Cover for the filtering process. Afterwards, we carry out a filling. Then
we make a composition of two consecutive images in order to obtain one
image each 16 days. Finally we apply the 10x10 km grid and calculate a
value for each cell.
3.2 - Relation between fire frequency and the index variations
The spectral indices chosen for the present study are: NDVI (Rouse et al.,
1974), SAVI (Huete, 1988), NDII (Hunt and Rock, 1989), GEMI (Pinty and
Verstraete, 1992), NDWI (Gao, 1996), VARI (Gitelson et al., 2002), EVI
(Huete et al., 2002) and GVMI (Ceccato et al., 2002). This selection is