The process uses high resolution Sentinel-2 satellite imagery downloaded weekly from the European Space Agency. This imagery is processed automaticaly to produce high-resolution satellite image visualisations highligting burnt areas. Two primary burnt area image types are produced each week. These weekly images will be served via a web map service (WMS) that allows internet to the updated imagery.
- A single natural colour image for the latest week. These ‘natural’ colour images provide a reference for identifying landscape features and burnt areas.
- Imagery created using a middle infrared burn ratio (MIBR) algorithim specifically designed to highlight fire. These (MIBR) images are subtracted from each other each week. This “difference imaging” technique further highlights burnt areas each week.
The MIBR difference images form a basis for automated ‘segmentation’ burnt area mapping. The ‘segmentation’ processes automatically creates polygons around burnt areas. These need to be manually edited to reduce mapping errors. The manually editing process is to be conducted using QGIS. QGIS is free open source GIS software that has sophisticated functionality to support the viuslisation and editing of the
The process described above are represented in the schematic below.
An example of Sentinel-2 satellite imagery of the Darwin region in the ‘natural colour’ format is shown below.
The same area using MIBR difference images to highight burnt areas. Burnt areas shown in red.
The image is zoomed in to Darwin rural area with red burnt areas clearly visiable, however there are some poygons which are not mapping fire that need to be deleted. Examples of these are highlghted by white boxes in the image below. Some polygons are falsely highlight unburnt areas as in the middle of the image whilst others seem to be highlighting drying wetlands as in the top of the image. A visual interpretation and local knowledge needs to be applied when editing the burnt area mapping to create the most accurate result.
The mapping area cover by this project is split into five tiles as shown in the map below. Tile subsets are used to reduce the file size and processing time for each area.
All of the Darwin region is covered by a single Sentinel satellite overpass. The overpass days for 2021 will be as shown below:
The Katherine map area is covered by a deifferent Sentinel-2 over pass that is always three days behind or two days ahead of the Darwin overpass. For eample the first overpass for Katherine will be.
So The polygon segements required for mapping will be stored on a server in in a folder structure similar to that shown below.
The final mapping after editing in QGIS is uploaded directly to the NAFI server from where is will will be available to all NAFI users.
The imagery is also available directly on the NAFI mobile app for use in the field.
More information about accessing and using the mobile app can be accessed here:
A key component to the implementation of this project is capacity builing amongst NTG staff to conduct the burnt area mapping using the methd described in QGIS.
General introductory training is available here:
For a tutorial on the how to map burnt areas using the system described above in QGIS click the link below: