Characterizing Burned Savanna Signatures from Sentinel-1 SAR Backscatter and H-Alpha Dual-Pol Decomposition: Case Study of the 2023 Bromo Fire Athar Abdurrahman Bayanuddin, Retnadi Heru Jatmiko, Nur Muhammad Farda
Remote Sensing Graduate Study Program, Faculty of Geography, Universitas Gadjah Mada, Indonesia.
Directorate of Laboratory Management, Research Facilities, and Science and Technology Park, National Research and Innovation Agency (BRIN), Indonesia.
Department of Geographic Information Science, Faculty of Geography, Universitas Gadjah Mada, Indonesia
Abstract
Forest and land fires in Indonesia have increasingly shifted toward Eastern Indonesia, significantly impacting extensive savanna ecosystems. Synthetic Aperture Radar (SAR) imagery offers promise as a complementary or alternative approach for burned area mapping, yet its application in Indonesian savannas remains limited. This study investigates changes in backscatter and polarimetric decomposition (H-Alpha) parameters over burned savanna areas, using pre- and post-fire Sentinel-1 C-band data from the 2023 Bromo fire. Backscatter (VV, VH) and H-Alpha decomposition values were extracted from samples representing burned low-vegetation and tree-dominated areas. Change values (delta (d)) were calculated and assessed for statistical significance using a two-tailed Wilcoxon signed-rank test. The influence of slope-relative orientation and pre-fire Enhanced Vegetation Index (EVI) on these changes was also examined. Results show statistically significant changes in both backscatter and H-Alpha parameters for burned areas. In low-vegetation areas, Entropy (H) (d median = −-0.0049, p < 0.05), Alpha (d median = −-0.3841 degrees, p < 0.05), and VV and VH backscatter (d median = −-0.1708 dB and 0.3305 dB, respectively, p < 0.05) all changed significantly. In tree-dominated areas, Alpha (d median = −-1.1986 degrees, p < 0.05) and VH backscatter (d median = −-1.0518 dB, p < 0.05) showed strong declines, while VV backscatter changes were not significant. Both topography and pre-fire EVI influenced the magnitude of changes, with distinct patterns across vegetation types-particularly a decreasing trend in delta H and delta Alpha with increasing pre-fire EVI in tree-covered areas. This study confirms the capability of Sentinel-1 SAR imagery to detect and characterize burn scars in savanna landscapes, revealing distinct post-fire signatures for different vegetation types. These findings provide a foundation for enhancing fire-mapping algorithms tailored to tropical savannas, with particular relevance to Eastern Indonesia.
