The Global Flood Monitoring (GFM) product of the Copernicus Emergency Management Service (CEMS) provides a continuous monitoring of flood events worldwide, by processing and analysing in near real-time all incoming Sentinel-1 Synthetic Aperture Radar (SAR) satellite imagery. The GFM product utilizes a “data cube” (or time-series) approach, enabling high product timeliness. Central to the GFM product is an ensemble flood mapping approach that integrates three independent, state-of-the-art SAR-based flood mapping algorithms, in order to optimize the robustness and accuracy of the flood and water extent maps, and to build a high degree of redundancy into the service (Matgen et al., 2020; Wagner et al., 2020; Salamon et al., 2021).
The ten output layers of flood-related information that are generated by the GFM product are described in the following table.
|
Output layers |
Description |
Data formats |
|
1. Observed Flood Extent |
Flooded areas mapped by applying the GFM ensemble flood mapping algorithm to the latest Sentinel-1 images of SAR backscatter intensity. |
OCG/geojson |
|
2. Observed Water Extent |
Open and calm water mapped as the union of the Observed Flood Extent and the Reference Water Mask. |
OCG |
|
3. Reference Water Mask |
Normal (i.e. permanent and seasonal) water mapped by applying the GFM ensemble water mapping algorithm to the most recent historical, five-year time-series (“data cube”) of Sentinel-1 images of SAR backscatter intensity. |
OCG |
|
4. Exclusion Mask |
Areas where SAR-based water mapping is not technically feasible, due to no sensitivity (e.g. urban areas, dense vegetation), low backscatter (e.g. flat impervious areas, sandy surfaces), topographic distortions, radar shadows, or low coverage of Sentinel-1. |
OCG |
|
5. Likelihood Values |
Likelihood (0-100%) of correct flood classification for all pixels outside Exclusion Mask. |
OCG |
|
6. Advisory Flags |
Flags indicating potential reduced quality of flood mapping, due to prevailing environmental conditions (e.g. wind, ice, snow, dry soil), or degraded input data quality due to signal interference from other SAR missions; |
OCG |
|
7. S-1 Metadata&Footprint |
Image boundaries of the Sentinel-1 data used, and in addition information on the “metadata”, i.e. the acquisition parameters of the Sentinel-1 data used. |
json/geojson |
|
8. S-1 Schedule |
Next scheduled Sentinel-1 data acquisition. |
geojson |
|
9. Affected Population |
Number of people in flooded areas, mapped by a spatial overlay of Observed Flood Extent and gridded population, from the Copernicus GHSL project. |
OCG |
|
10. Affected Land Cover |
Land cover / use (e.g. artificial surfaces, agricultural areas) in flooded areas, mapped by a spatial overlay of Observed Flood Extent and the Copernicus GLS land cover. |
OCG |
Table 1. GFM output layers of global flood-related information, generated in near real-time based on Sentinel-1 SAR satellite imagery.
The GFM product and output layers of flood information are freely available through various dissemination channels, listed in Table 2, that are designed for flexible and easy access. All of the dissemination channels are routed to a central storage via a central access layer. The storage-access layer serves products in a desired format, by drilling down into the GFM Sentinel-1 SAR “data cubes” (time series), querying databases for meta-data or user-management, and receiving data for the WMS-T service. Further details on accessing the GFM product are available via the GFM wiki pages.
| GFM DISSEMINATION CHANNEL | URL |
| Global Flood Awareness Sytem (GloFAS) Map Viewer | https://global-flood.emergency.copernicus.eu |
| European Flood Awareness Sytem (EFAS) Map Viewer | https://european-flood.emergency.copernicus.eu |
| Full set of GFM-related Representational State Transfer (REST) APIs | https://api.gfm.eodc.eu/v2/ |
| GFM Web Map Service supporting temporal requests (WMS-T) | https://geoserver.gfm.eodc.eu/geoserver/gfm/wms |
| GFM dedicated web portal | https://portal.gfm.eodc.eu/ |
| GFM SpatioTemporal Asset Catalogue (STAC) | https://services.eodc.eu/browser/#/v1/collections/GFM |
Table 2: Dissemination channels for accessing the CEMS Global Flood Monitoring (GFM) product.
This Product Definition Document (PDD) provides the main reference information required to understand all elements of the various data processing chains that are implemented in the GFM product, and explains the contents of the GFM output layers, the main assumptions underlying their generation, and the limitations of the data. Specifically, the PDD describes in detail the following main methods and input and output datasets that form the core of the GFM product: