The effect of surface fire in Savannah systems in the Kruger National Park (KNP), South Africa, on the backscatter of C-band sentinel-1 images
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Abstract
Savannahs are mixed woody-grass communities where low-intensity surface fires are
common, a ecting mostly the grass layer and rarely damaging trees. We investigated the e ect of
surface fires in a savannah system in the Kruger National Park, South Africa, on the backscatter of
synthetic aperture radar (SAR) C-band Sentinel-1A images. Pre-fire and post-fire dual polarized
(VH, VV) C-band backscatter values were examined for 30 burn events. For all events, a systematic
backscatter decrease from pre-fire to post-fire conditions was observed, with mean backscatter
decreases of 1.61 dB and 0.99 dB for VH and VV, respectively. A total of 90% and 75% of the burn
events showed a decrease in VH and VV backscatter greater than 0.43 dB, the overall absolute
radiometric of Sentinel-1A products. The VH data were, overall, 1.7 times more sensitive to surface
fire e ects than the VV data. C-band data are likely sensitive to a reduction in grass biomass typical
of surface fires, as well as in grass/soil moisture levels. Early season fires had higher backscatter
decreases due to greater early season moisture conditions. For region with more than 30% woody
cover, the e ect of fire on the C-band backscatter was reduced. Denser woody communities tend
to produce lower grass fuel load and less intense surface fires, and limit the penetration of C-band
microwaves to the ground where most savannah fires and associated e ects occur. This research
provides evidence that C-band space-borne SAR is sensitive to the e ects of surface-level fires in
southern African savannahs. The unique availability of frequent and spatially detailed C-band data
from the Sentinel-1 SAR constellation provide new opportunities for burned area mapping and
systematic monitoring in savannahs systems, for instance, for fine-scale fire propagation studies.
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Keywords
Fire, Burned area, Mapping, Sentinel-1, African savannahs, Kruger National Park (KNP)
Sustainable Development Goals
Citation
Mathieu, R., Main, R., Roy, D.P. et al. 2019, 'The effect of surface fire in Savannah systems in the Kruger National Park (KNP), South Africa, on the backscatter of C-band sentinel-1 images', Fire, vol. 2, art. 37, pp. 1-24.