L-band SAR sensitivity to prescribed burning effects in eucalypt forests of Western Australia

Abstract

Prescribed burning is a technique applied to control fire risk, and it has been used in the forests of Western Australia since the 1960s. Synthetic Aperture Radar (SAR) data are sensitive to vegetation structural changes and may detect changes in understory vegetation particularly when the upper forest canopy remains largely unaffected, as it is often the case for prescribed burns. In this study, the ability of the Radar Burn Ratio (RBR), a SAR index that measures the degree of change between pre- and post-event radar backscatter, to appraise fire efficiency in prescribed burns was assessed. Data acquired by the L-band PALSAR-2 sensor, onboard the ALOS-2 satellite, were analysed to study the relationship between radar backscatter coefficient and prescribed burns carried out in eucalypt forests in Western Australia. A previously proposed framework was adapted to evaluate burn impacts in different environmental conditions (dry, wet and mean) using HV and HH polarizations as well as the RFDI (Radar Forest Degradation Index). A linear relationship between RBR and fire severity was found for HV polarization and RFDI confirming previous results observed for wildfires. RBRHV in dry environmental conditions yielded the most accurate estimates of fire impact (OA = 77.8 %; k = 0.67). RBRHH showed higher ability to differentiate between severity classes in wet conditions while the RBRRFDI showed an intermediate behavior. HH polarization and RFDI showed special ability for burn area detection in wet conditions. The results showed that it is possible to estimate the impact of prescribed burns using SAR data. As such, SAR data could contribute and assess the effectiveness of fire policy in Western Australia and similar environments.