Flood Mapping and Monitoring Using Synthetic Aperture Radar

Synthetic Aperture Radar (SAR) has transformed the monitoring of flood events by providing high-resolution, all-weather and day-night imagery capable of detecting inundation beneath cloud cover. Flood mapping with SAR exploits rapid changes in backscatter—water surfaces generally produce a strong contrast with land—enabling precise delineation of flood extents. Advances in multi-temporal analysis, polarimetric observations and automated classification have improved the accuracy and speed of inundation mapping. Integration with optical sensors and hydrodynamic models enhances situational awareness, while machine-learning techniques facilitate robust detection in complex environments such as vegetated floodplains and urban areas. Global constellations of C- and L-band satellites now support near-real-time products, aiding disaster response, water resource management and flood risk modelling with unprecedented spatial and temporal coverage.

Research from Nature Portfolio

Recent studies have demonstrated that merging C-band SAR data from Sentinel-1 with optical observations from Landsat and Sentinel-2 markedly increases the frequency of usable flood images, raising the proportion of detected events with cloud-free coverage from under 10 per cent to over 60 per cent. This multi-sensor fusion has elevated the share of displaced populations observed by high-resolution imagery from one-fifth to three-quarters, and enables the near-complete monitoring of floods driven by tropical cyclones, tidal surges and complex hydrological drivers. Such integrated datasets underpin more effective humanitarian relief and water management strategies by offering consistent, high-frequency flood detection at regional to global scales.

Flood Mapping and Monitoring Using Synthetic Aperture Radar publication trend

The graph below shows the total number of articles in flood mapping and monitoring using synthetic aperture radar across all publications each year (not limited to Nature Index journals).

Technical terms

Synthetic Aperture Radar (SAR): A form of radar that synthesises a large antenna aperture by platform movement, producing high-resolution images independent of illumination or weather.

Backscatter: The portion of the radar signal reflected back to the sensor, with low values over smooth water and higher values over rough land surfaces.

Change Detection: Analytical process comparing images from different times to identify alterations in surface conditions, such as new inundation.

Polarisation: The orientation of the radar wave’s electric field; common modes include VV (vertical transmit, vertical receive) and VH (vertical transmit, horizontal receive).

Thresholding: A segmentation technique that classifies pixels as water or non-water by applying a defined backscatter intensity limit.

Inundation Mapping: The delineation of flooded areas by interpreting remotely sensed data to inform risk assessment and disaster management.

References

1. A multi-sensor approach for increased measurements of floods and their societal impacts from space. Communications Earth & Environment (2023).
2. Multi‐temporal synthetic aperture radar flood mapping using change detection. Journal of Flood Risk Management (2017).
3. Progress in integration of remote sensing–derived flood extent and stage data and hydraulic models. Reviews of Geophysics (2009).
4. Automated global water mapping based on wide-swath orbital synthetic-aperture radar. Hydrology and Earth System Sciences (2013).
5. Inundation Extent Mapping by Synthetic Aperture Radar: A Review. Remote Sensing (2019).