The Vegetation Structure Perpendicular Index for Wildfire Severity and Forest Recovery Monitoring

The intensity of a wildfire depends in large part on the fuel available to the fire, including surface bark, leaf litter, and over- and understorey vegetation. The amount and configuration of these fuels are affected by cycles of destruction during fires and slow regrowth. Current fuel amounts, required for predictions of future fires, are therefore difficult to quantify as past fire history and fuel recovery must be taken into account. Most fire services rely on visual inspections of forest recovery, however, these are often subjective and very labour-intensive. Remote sensing offers an automated alternative with the potential for rapidly assessing fuel state over large areas allowing for continuous monitoring over time. This paper describes a new index for measuring temporal fuel state, called the Vegetation Structure Perpendicular Index (VSPI). The index provides an alternative to the Normalized Burn Ratio (NBR), which is prone to potentially large uncertainties due to large levels of seasonal dynamics. The VSPI estimates a vertically integrated burn severity and ecosystem recovery measurement for forested areas. The method is applied in this paper to a fire in Western Australia, the 2005 Perth Hills fire to demonstrate the capabilities and benefits of this new index. For this fire the VSPI provides a better estimate of fire severity and shows fuel disturbance levels for two years longer than the NBR, providing an improved estimation for post-fire vegetation recovery and vegetation condition assessment suitable for fire predictions.