Detection of Burned Areas in Southern African Savannahs Using Time Series of C-Band Sentinel-1 Data

Abstract

This paper investigated the potential of multi-temporal Synthetic Aperture Radar (SAR) Sentinel-1 data for detecting burned areas in southern African deciduous savannahs. Prior to Sentinel-1, low cost, frequent, global coverage of C-band SAR data with a high level of spatial detail (<1 ha) were not available. The study took place in the Kruger National Park (KNP), South Africa (SA). Pre-fire and post-fire Sentinel-1 dual polarized (VH, VV) C-band backscatter values for 30 burn events recorded by a 500-m MODIS burned area dataset in 2015 were examined. For all burned areas, a systematic backscatter decrease from pre-fire to post-fire conditions was observed. The burned areas exhibited a mean backscatter decrease of 1.85 dB and 1.12 dB, and 93% and 83% of the fire events had backscatter decreases greater than the Sentinel-1 0.38 dB radiometric accuracy, for VH and VV respectively. The decrease in backscatter was hypothesised as being due to a reduction in grass biomass and grass/soil moisture levels post-fire. This research provides evidence that burned areas can be detected by C-band space borne SAR in southern African savannahs.