Satellite data for flood mapping in Australia
By Mazdak Ghasemi · Last checked 22 October 2026
Which satellite data is best for mapping a flood in Australia?
Radar first. Floods usually come with cloud, and radar images the ground through rain and cloud, by day or night. Sentinel-1 is the free standard: the Copernicus Global Flood Monitoring service maps floods worldwide from it, and UN-SPIDER calls SAR-based flood mapping a standard and reliable method. Optical imagery from Sentinel-2 and Landsat adds detail when the sky clears, and LiDAR elevation supports flood modelling.
Which data to use
| Data | Resolution | Revisit | Record | Use |
|---|---|---|---|---|
| Sentinel-1 radar | 10 m pixels (5 × 20 m ground resolution) | 6 days | From April 2014 | Flood extent through cloud, day or night |
| Sentinel-2 optical | 10 m | 5 days | From June 2015 | Water extent with water indices when the sky is clear |
| Landsat 8 and 9 | 30 m | 16 days each, 8 together | From 2013 | Cloud-free scenes before and after a flood |
| Landsat 5 and 7 archives | 30 m | Archive | 1984 to 2024 | Flood history |
| DEA Water Observations | 30 m | Updated daily | From August 1986 | Where water has been seen across Australia, from Landsat |
| ELVIS LiDAR elevation | About 1 m (varies by survey) | Surveys vary | Varies by area | Terrain for flood models |
How it is done
- Take radar images of the same area from before and after the flood.
- Compare them. UN-SPIDER's recommended practice divides the after-flood image by the before-flood one and marks pixels whose change passes a threshold as potential flood.
- Leave out permanent water such as rivers and lakes, check against optical imagery when a cloud-free scene arrives, and use elevation data where depth or flow paths matter.
Limits to know
- Radar is distorted in steep terrain (layover and shadow), and buildings and dense vegetation complicate the signal.
- Wind-roughened water reduces the contrast between water and land on radar.
- Optical imagery needs a cloud-free scene, which is often unavailable during a flood.
- LiDAR may be required for formal flood mapping submissions in some jurisdictions.
Who does this in practice
- The Copernicus Global Flood Monitoring service processes all incoming Sentinel-1 data to map floods worldwide.
- UN-SPIDER publishes a recommended practice for flood mapping with Sentinel-1.
- Digital Earth Australia's Water Observations classify every Landsat pixel as wet or dry, back to August 1986.
What Terrascout returns
The real result for “Map flood extent around Lismore NSW after heavy rain” (Lismore, NSW), captured on 22 October 2026: the top 5 of 6 sources.
Radar (SAR) sources are listed first: floods usually come with cloud, and radar flood mapping is the standard method; the Copernicus Global Flood Monitoring service maps floods from Sentinel-1.
| # | Source | Type | Resolution | Cost | Fit |
|---|---|---|---|---|---|
| 1 | Sentinel-1 C-SAR | Radar | 10 m | No data fee | 95 |
| 2 | Sentinel-2 MSI | Optical | 10 m | No data fee | 96 |
| 3 | NSW Aerial Imagery | Aerial | 5 cm | No data fee | 87 |
| 4 | OpenTopography Global LiDAR | Elevation | 1 m | No data fee | 86 |
| 5 | ELVIS LiDAR DEMs | LiDAR | 1 m | No data fee | 86 |