Global Flood Monitoring Product Launch
The Copernicus Emergency Management Service (CEMS) launched a new operational product: the Global Flood Monitoring (GFM). This is yet again a ground-breaking and unique CEMS tool: as part of flood early warning and monitoring component of CEMS, it consists in a fully automated tool that processes the entire influx (and past archive) of Copernicus Sentinel-1 radar imagery to extract ongoing (and past for the archive re-processing) flooding episodes on a global scale.
GFM represents a significant progress in the EU’s disaster awareness and prevention endeavours, complementing the current forecasting capabilities developed for the European Flood Awareness System (EFAS) and the Global Flood Awareness System (GloFAS). It combines Europe’s best technological advancements to enable continuous, systematic, and automatic monitoring of floods worldwide.
GFM in a nutshell: product workflow and benefits
CEMS’ latest tool, GFM, is designed to fully exploit the unique capabilities of the Copernicus Sentinel-1 (S-1) satellite mission, which is capable of all-weather and day/night imagery acquisition with a radar whose characteristics are ideally suited to discriminate water form bare soil, thus providing a monitoring of all land surface areas to detect flood events.
The GFM product is specifically designed to address three additional critical user requirements, namely:
- Significantly enhancing the timeliness of flood maps for emergency response,
- Enabling a global, large-scale monitoring of floods
- Improving the effectiveness of activation requests of the CEMS Rapid Mapping component, through a better identification of the areas of interest.
As a consequence of its timeliness, GFM is a truly operational service for decision makers. Key users include national and regional water authorities, civil protection and first line responders, insurance companies, international humanitarian aid organisations and the EU’s Emergency Response Coordination Centre (ERCC).
The methodology underpinning GFM is highly scalable and enables a fast and seamless access to, and dissemination of the products.
Figure 1. CEMS Global Flood Monitoring product workflow.
As shown in figure 1, the output layers of GFM can be grouped into 4 categories:
- water bodies (Observed Flood Extent, Observed Water Extent, Reference Water Mask): GFM builds upon the three best European flood detection algorithms which enable, through a majority weighing to lower the probability of “false positives”
- quality-related (Exclusion mask, Uncertainty values, Advisory flags): GFM includes built-in rules to exclude sources of error such as recently ploughed agricultural fields, permanent water bodies, elevated areas etc.
- S-1 data specifics (footprint of the S-1 image used for the analysis and the related metadata, schedule of the next acquisition in the area of interest) and
- impacts estimate (Affected population, Affected land cover).
Figure 2. CEMS Global Flood Monitoring map viewer showing a flooded area identified in New South Wales (Australia) on 3 March 2022.
GFM technical aspects and limitations
The uniqueness of GFM lies in the speed of data availability as a result of the automation of the input data analysis process.
After a pre-processing step, the S-1 data are processed in parallel by three algorithms (developed by the Luxembourg Institute of Science and Technology - LIST, the German Aerospace Centre - DLR and the Technische Universität Wien - TUW), which provide an initial identification of any flooding in the area of interest in near real time. From these three individual computations, the ensemble flood mapping is computed. In this last step, the areas classified by the GFM final products as flooded are those identified as flooded by at least two of the algorithms used for the analysis.
Figure 3. The GFM ensemble algorithm and the majority voting process involved in the pixel classification.
The breakthrough nature of this approach with respect to on-demand mapping is that absolutely no time is lost due to human intervention in the imagery analysis chain. Secondly, the ensemble approach to flood detection improves the robustness and accuracy of the flood and water extent maps and builds a high degree of redundancy into the tool.
Despite the high accuracy of GFM products (demonstrated to be greater than 94%), due to the use of S-1 radar images and their intrinsic difficulty to distinguish certain features, the GFM product can produce false and missed alarms. In order to avoid incorrect interpretations of GFM data, the Exclusion Mask and the Advisory Flags have been developed. These two layers are dedicated to the exclusion of particular ground surface characteristics, radar shadowing, or areas strongly affected by atmospheric effects.
As a consequence, all the output of the GFM elaboration have descriptions designed to enable the user to interpret the results largely autonomously, taking into account possible incorrect classifications.
Figure 4. An example of over-detection cause by irrigated fields.
By bringing together the best of European flood forecasting technology, the GFM product aims to establish itself as a revolutionary new addition to the Copernicus Emergency Management Service (CEMS) product portfolio.
In order to introduce the functionality of GFM, its benefits, the data access procedures and the current limitations of the product, on 28 April 2022 an online workshop has been organised. The interest in this new and revolutionary CEMS product was demonstrated by the large number of registrations for the workshop, which exceeded 450.
A first GFM quality assessment report will be published in the coming weeks. It will examine all technical aspects of the product, and further possible product improvements will be defined. Furthermore, in the coming months, the full Copernicus Sentinel-1 past archive will be processed using the GFM algorithms to produce the most comprehensive flood archive ever developed.
As per the full, free and open availability of CEMS products (with the exception of “sensitive” activations), all available layers will be available for download and useable in any GIS interface. On the other hand, all the data can be visualised on two portals, the GloFAS website and GFM Portal, after registration.
No less important, a comprehensive and accurate Product User Manual has been developed to let users gain a deeper understanding of how the tool works, of the specifications of each layer and to improve understanding of what is displayed. Likewise, it is possible to view the recording of the Product Release Workshop on YouTube, during which a complete use case is presented and analysed with a step-by-step explanation of how to download GFM data.
A detailed selection of useful use cases for civil protection activities, operational hydrological forecasting, DRR-related planning, researchers, insurance companies, is available here.
By Antonio Casino Sept. 8, 2022, 8:26 a.m.