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

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IV - BURNED LAND MAPPING, FIRE SEVERITY DETERMINATION, AND VEGETATION RECOVERY ASSESSMENT
est, extending on about 14.000 ha of homogeneous, even aged Pinus
halepensis L., has been affected by recurrent fires during the last decades.
Two fires -Zuera95 and Zuera08- were studied.
The SAR dataset consisted of VV polarized images acquired by the European
Remote Sensing 1 and 2 (ERS-1/2), HH polarized images acquired by
Environment Satellite Advanced SAR (ASAR) and dual-polarized images (HH
& HV) acquired by TerraSAR-X (TSX). SAR pre-processing step consisted in
improvement of orbital state vectors and co-registration of the scenes from
the same sensor and track. The coherence was estimated from the differential
interferogram using an estimator with an adaptive window size
(Wegmüller et al., 1998). ERS and ASAR data were processed using 1*5
looks in range and azimuth while for TSX inteferograms 8*5 looks were
used. Post processing consisted of image geocoding of the coherence products
to UTM 30 coordinate system. The higher resolution TSX scenes were
geocoded to 10 m pixel spacing. For the C-band sensors the scenes were
geocoded to 25 m. Two pairs of Landat TM images were also acquired to
derive optical based estimates of burn severity.
3 - Methods
Evaluation of the coherence response over burned areas was carried out
using descriptive statistics. Determination coefficients (R 2 ) were used to
evaluate the potential of interferometric coherence for burn severity estimation.
To minimize the effects of topography on backscattered energy statistic
analyses were carried out by 5º groups of local incidence angle. Due
to the limited number of reference plots where burn severity was assessed
in situ (Tanase et al., 2009a) the study was carried out using a set of pseudo-plots
based on optical estimates of burn severity. The pseudo-plots were
generated by averaging pixels of similar dNBR for the same local incidence
angle rounded to unity. The consistency between field plots assed using
Composition Burn Index (CBI), and remotely sensed (dNBR) estimates of
burn severity was previously evaluated for Zuera08 area (Tanase et al.,
2009a). For the lower spatial resolution imagery (ERS and ASAR) pseudoplots
including 9 pixels were selected while for the higher resolution
TerraSAR-X data pseudo-plots including 25 pixels seemed appropriate
(Tanase et al., 2009c).
4 - Results
Scatter plot of coherence as a function of burn severity is presented in
Figure 1 for flat areas. The plot on the left shows 1-day ERS coherence (C-
VV) for the Zuera95 site and the 35-days ENVISAT ASAR coherence (C-HH)
for the Zuera08 site. The plot on the right in Figure 1 shows the coherence
of a TerraSAR-X image pair for HH- and HV-polarization for Zuera08 burn.