Tjoritja (West MacDonnell Ranges) National Park

2023 Bushfire Analysis using ProRaster Scientific

In March 2023 a large uncontrolled bushfire burned through much of the Tjoritja (West MacDonnell Ranges) National Park. The park is located in Central Australia to the west of Alice Springs and is a popular outback tourist destination. In addition to visiting the waterholes, gorges, and mountain ranges, tourists now come to walk the Larapinta Trail, a multi-day walk through the rugged and scenic heart of Australia.

I used ProRaster Scientific to track the evolution of this fire and to measure the total area burned. Although the focus was on the damage done to the National Park, the fire also burned through a significant amount of land, probably grazing country, on the boundaries of the park.

You will find a video describing the analysis at the bottom of the page, or on YouTube.

I start by acquiring Landsat 8 and Landsat 9 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 before the fire to mid-winter after the fire, approximately five 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.

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 NBRT1 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 0.45 where all values less than this represent burnt ground. Using this cut-off value I can then build an appropriate color table (incorporating a color map) that I can use to visualise the fire scar. In the Product Editor, I also use a raster masking operation to remove cloud-affected pixels, and a raster calculator operation to remove all (unburnt) pixels with values greater than 0.45.

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 a few moments, I have detailed summary and distribution statistics for the fire scar over all of the time events in the scene sequence. From this, I conclude that the total burnt area is about 140000 hectares.