Wooroloo, Western Australia
2021 Bushfire Analysis using ProRaster Scientific
In February 2021 a fast-moving bushfire burned from Wooroloo in the foothills to the east of Perth, west for 26 kilometres right to the edge of Greater Perth. The Wooroloo fire destroyed at least 86 houses and two fire trucks.
I used ProRaster Scientific to identify the boundary of this fire and to measure the total area burned.
You will find a video describing the analysis at the bottom of the page, or on YouTube.
I start by acquiring Landsat 8 scenes from Earth Explorer. In this case, I acquire Level 2 scenes that have multispectral bands corrected to Surface Reflectance SR (otherwise known as Bottom of Atmosphere BOA). The coverage extends from immediately before the fire to 18 months later.
From the Scene Assembly Virtual Rasters for these scenes, I build a Scene Sequence Product. This virtual raster contains all of the spectral and ancillary data from each of the scenes and adds a time dimension so that coverage is not just spatial, but temporal. I use the “Fire Scar” RGB band combination to render this raster and demonstrate how to adjust the data transform for the RGB components to improve the differentiation of the fire scar from the unburnt country surrounding (and within) it. In this video, I explain in some detail how to perform these steps.
One of the great advantages of ProRaster Scientific is that you can experiment freely with Spectral Index computations without incurring processing or storage cost. I visually compare all of the indexes related to fire scar delineation and come to the conclusion that the BAI index best maps the extent of this particular fire.
I then use the cell value reporting tool to determine the cut-off value between burnt ground and unburnt ground. In this case, I place the value at 40 where all values greater than this represent burnt ground. In the Product Editor, I use a raster calculator operation to remove all (unburnt) pixels with values less than 40.
Not shown in the video, I export the fire scar raster to a located image which I can then display in MapInfo. I then create a polygon in MapInfo that roughly encompasses the fire boundary.
I can then apply the clipping polygon to the processing chain and finally compute statistics. In this video, I explain the statistics in some detail. From this, I conclude that the total burnt area is about 8300 hectares.