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

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IV - BURNED LAND MAPPING, FIRE SEVERITY DETERMINATION, AND VEGETATION RECOVERY ASSESSMENT
Sensor TerraSAR-X Sensor ASAR
Polarization HH HV HH&HV Polarization VV HH HV HH&HV
Scene data 12.1908 Scene data 09.12.08 01.08.09 03.19.09
All pseudo-plots 0.529 0.085 0.546 0.101 0.176 0.539 0.542
Pseudo-plots grouped by local incidence angle
26°-30° 0.833 0.291 0.916 6°-10° 0.359 0.768 0.700 0.843
31°-35° 0.707 0.234 0.861 10°-15° 0.338 0.555 0.733 0.758
36°-40° 0.732 0.050 0.857 16°-20° 0.361 0.449 0.609 0.648
41°-45° 0.666 0.291 0.815 21°-25° 0.186 0.354 0.693 0.752
46°-50° 0.621 0.402 0.792 26°-30° 0.001 0.198 0.699 0.699
51°-55° 0.612 0.520 0.824 31°-35° 0.007 0.154 0.767 0.767
56°-60° 0.584 0.464 0.833 36°-40° 0.001 0.174 0.715 0.715
61-65 0.476 0.582 0.843 41-45 0.050 0.109 0.744 0.744
Table 1 - Determination coefficients explaining the agreement between dNBR and radar
backscatter at X- and C-band.
5 - Discussion
Both sensors showed similar trends of the backscatter with respect to dNBR
for co- and cross-polarized beams. Figures 1 and 2 show that for co-polarized
beams the backscattering coefficient increased with burn severity. For
X-band HH-polarization, the backscattering coefficient increased (Figure 2)
from low to medium burn severity reaching saturation for high burn severities
(i.e. dNBR 800). The HV-backscatter
decreased with the increase of burn severity at both frequencies
(Figures 1 and 2). This is explained by the larger amount of gaps in the
canopy and the increased transmissivity with the increase of burn severity.
Figure 3 shows the strong effects of the local incidence angle on the
backscatter at all SAR frequencies and polarizations. For increasing local
incidence angle decreasing trends were registered for co-polarized beams.
This decrease is the result of a decreasing proportion of direct scatter from
the ground to the total forest backscatter. Cross-polarized beams showed
increase of the backscatter coefficient with increasing local incidence angle
explained by the longer path traveled by the radar wave within the canopy.
The strength of association (i.e. R 2 ) for co-polarized beams decreased with
increasing incidence angle while the error increased (Table 1). The simultaneous
use of cross and co-polarized channels (HH and HV) provided the
highest R 2 coefficients and the smallest errors.