Detecting Change in Burnt Landscapes using a Terrestrial LiDAR System

A Terrestrial LiDAR system or Terrestrial Laser Scanner (TLS) was used to detect changes in burnt landscapes. Since wildfires are a common occurrence in the Australian landscape, prescribed burns are routinely carried out by land management agencies and government departments. These prescribed burns reduce the fuel load which decreases the severity of subsequent unplanned wildfires. Recent advances in LiDAR have enabled the successful measurement of complex structures in the field with both high accuracy and precision. LiDAR remote sensing has been used for estimating a wide variety of forest metrics. However, airborne LiDAR in particular has been unsuited for measuring understorey vegetation. Modern ground-based LiDAR systems can overcome some of the shortcomings of airborne LiDAR systems (sub-centimetre resolution, canopy obscuration). In this study, four plots of 10m radius were chosen within a prescribed burn area in St. Andrews, Victoria which took place in April 2012. One plot was unburnt (control) while the other three plots were given different fire treatments to simulate different fire severities. The TLS was operated from the centre of the plot and data was collected at a resolution of 10mm at a radius of 10m. Laser scans were captured pre-burn, and post-burn in week two. Data analysis was carried out at different scales (voxel and plot) and at the vertical strata comprising near-surface and surface fuel layer within 1m from the ground. Within voxels, metrics used to compute change were changes in point density and maximum z value. At the plot scale, change in volume was computed. Preliminary results demonstrate the potential of TLS to detect changes at both fine and coarse scales. Metrics such as point density are misleading because of issues around occlusion. At the plot scale, changes in volume are a good indicator of fuel consumption at the near-surface and surface fuel layer and appear to be in agreement with the different fire treatments which were given to the plots. The benefit of using a TLS is the potential for quantifying the amount of fuel consumed by a prescribed burn. TLS data can provide a quantifiable measure of post-fire effects in the understorey strata and structure of a forest. This is in contrast to current practices which rely largely on visual assessments which have some level of subjectivity and lack repeatability.