Mapping the Mgarr Valley Grass Fire

A grassfire swept through parts of Mgarr valley on June 8th 2025. We can use remote sensing to help map the location and scale of the fire.

The most classical way to do this is to compare two satellite images, one before the fire and another after. Earth observation satellites like Sentinel-2 capture a wide range of spectral bands beyond the standard visible (red, green, blue) channels. The two which are most useful for us are near-infrared and shortwave-infrared.

The reason for this is that vegetation and burned areas have markedly different behaviours in both these bands: Healthy vegetation has high NIR and low SWIR, while ash and scorched soil have low NIR and high SWIR.

We can construct a ratio of this:

NBR = (NIR - SWIR) / (NIR + SWIR)

And calculate the change by subtracting the pre event NBR from the post event NBR.

This is visualised as a layer below (which can be toggled over a post fire image).

The other important part of this pipeline is that traditional Sentinel 2 imagery does not have this fine resolution: the images were up-sampled using Sentinel-2 Deep Resolution 3.0.