The process of providing accurate and timely geospatial data of disaster events stands to greatly improve through the practice of “pre-tasking” satellites. Pre-tasking triggers satellites to proactively capture readings of an event in order to provide response agencies with immediate data, cutting down on collection and response time. This approach utilizes existing Early Warning Systems (EWS) to initiate data collection before a hazardous event has occurred (pre-) rather than waiting for a tasking request from a national authority.

Why pre-tasking?

  • To reduce the time between a catastrophic event and satellite data acquisition
  • To increase the chance of acquiring images at a critical moment
  • To help delivering crisis information shortly after the event, and earlier than with the standard rapid mapping workflow

The most time consuming phase of rapid mapping of disasters takes place during the acquisition of satellite data. The resulting delay between a request and image acquisition often prevents geospatial data providers from capturing the initial phases of a hazardous event.

Time required in the Rapid Mapping Service, from product request to product delivery (average since 2012).
Fig 1. Time required in the Rapid Mapping Service, from product request to product delivery (average since 2012).

The forecasting capacity of the EWS helps strategic planning of the satellite image acquisition based on predicted timing and potential impact of the event (up to 48hours before the event starts). This has two positive consequences:

1. The likelihood of acquiring a useful image increases. Predicting an event, such as a flood, increases the chance of capturing the early phases of that flood and maximum flood extent. This provides additional relevant information for a service activation.

As satellites rotate around the earth on fixed rotational orbits, they can only view the earth at specific moments in time and many satellites need to be programmed to acquire an image. Proactive data acquisition increases the number of opportunities that a satellite has to capture an event passes over an event.

2. Precious time is saved. Instead of waiting for a formal request from an authorised user, the system proactively triggers the tasking of image acquisitions at the time predicted by the EWS. The earlier information availability can significantly improve the overall situational awareness and effective crisis response.

Timeline of Rapid Mapping activation, without EWS (A) and with EWS (B).
Fig 2. Timeline of Rapid Mapping activation, without EWS (A) and with EWS (B).

HOW DOES PRE-TASKING WORK?

For this system to be effective in potentially high impact events, an alert is sent simultaneously to national/local partners and authorities in the field, and to the satellite operators.

Figure 3 - workflow
Figure 3 - workflow

Satellite operators can begin tasking images immediately following an EWS prediction.

In the event of an alert, the national/local partners and authorities are informed about the high risk forecasted by the EWS. Partners can compare data provided against their own EWS and information sources. They can also take action if needed. This includes the decision to trigger the Copernicus EMS Rapid Mapping service. Typically the EWS partners and the RM authorised users in one country are not the same organisation. It is strongly recommended that both entities coordinate with each other.

Map producers can start analysing provided data as soon as the first image becomes available. The outcome of the analysis is delivered to local/national partners and authorities within hours.

CASE STUDY: Pre-Tasking with EFAS

The integration of Early Warning Systems and Rapid Mapping services is clearly feasible for hydro-meteorological events that can be forecasted up to a few days ahead.

The Pre-Tasking workflow was developed in 2016 to integrate EFAS (European Flood Awareness System) into the Copernicus Rapid Mapping workflow.

For this system to be effective, a command chain was set-up with a clear workflow to follow.

Figure 4 - Full workflow
Figure 4 - Full workflow

 

Frequently asked questions:

 

▶ Q: What events are covered by EFAS alerts?  
A: EFAS Alerts are issued for river floods. Pluvial floods, flash floods or coastal floods are not considered.
▶ Q: How does EFAS estimate the impact of an event?  
A: EFAS estimates the areas of the river network where the magnitude of the forecasted event (e.g. peak river flow) can exceed local flood protection levels. The resulting flood impacts are estimated by combining the exposure data (e.g. population density, roads, land cover) with the estimated flood extent. Total flood impact is aggregated over administrative units. For a detailed description, please refer to the EFAS website ( https://www.efas.eu/en/flood-impact-forecasts ).
▶ Q: What does “high impact” mean?  
A: EFAS employs the concept of a risk matrix where events are evaluated based on their potential impact and likelihood to occur. In general, an event is labelled as high impact when more than 10.000 people are potentially affected. Risk information is used as guiding criteria to trigger pre-tasking. Pre-tasking is generally done for the events with high likelihood of medium impact (> 1.000 people affected) and/or events with medium to high likelihood of high impact (>10.000 people affected), but can also be done for events with different probabilities of occurrence and potential impact.
▶ Q: Are reservoirs and dams taken into account when estimating possible floods along river basins?  
A: Some large reservoirs and dams are included in EFAS estimates. EFAS can reproduce a certain degree of natural behaviour from the reservoirs. Human control of reservoirs is not represented in EFAS predictions. Therefore, model estimates for cases where these infrastructures are considered might not be completely accurate due to the unpredictability of human control.
▶ Q: I am a user, how should I react if I receive an EFAS alert?  
A: Within two hours after receiving an EFAS alert from the ERCC, you will receive the schedule of the planned image acquisition(s). You can then decide whether or not to activate the Rapid Mapping service.
If you consider the risk to be high, you confirm with the ERCC that you would like to activate EMS pre-tasking. Discussions on the details will follow (about e.g. the location of the area(s) of interest, the type of product(s), etc.). If you consider the risk low, you can answer negatively to the ERCC. If you do not answer, the images acquired will not be analysed but instead directly archived.
▶ Q: Are there other sources I could consult before taking a decision?  
A: We strongly recommend that you connect as soon as possible with your local EFAS Partner, local Civil Protection and EWS authority to compare information and make a joint decision. The complete list of EFAS partners is available here: https://www.efas.eu/partners-list-0
▶ Q: What if, after consultations with local experts, we identify a different Area of Interest (AOI)?  
A: You can still activate the Rapid Mapping services, but, depending on the new AOI and the pre-tasked image acquired, it is not guaranteed that the pre-tasking procedure will be effective as expected.
▶ Q: I am an Authorised User (AU) and I noticed that the local EFAS Partner receives alerts earlier than me, how is it possible?  
A: EFAS Partners receive notification directly from the EFAS team, while the AUs are informed by the ERCC. The time difference is usually of 30 to 60 minutes. To become an EFAS partner, as EFAS third party partner, please follow the instructions on this link: https://www.efas.eu/become-efas-partner .
▶ Q: I am an EFAS partner, how should I react if I receive an EFAS alert?  
A: We strongly recommend that you connect as soon as possible with your Copernicus Authorised User and other AWS local authorities to compare information and make a joint decision about a possible Rapid Mapping activation.
▶ Q: Where do I find more information about EFAS Service?  
A: Some useful training materials, tutorials and webinars on how to use EFAS are available at: https://www.efas.eu/en/training
The basic description of EFAS products is available at: https://www.efas.eu/en/products
Scientific publications related to EFAS can be found here: https://www.efas.eu/scientific-papers-on-efas
▶ Q: What is the role of the ERCC during the pre-tasking?  
After receiving the EFAS alert, the ERCC forwards it directly to the authorised user of the country concerned. A couple of hours later the ERCC receives the schedule of the planned image acquisition(s) and forwards it also to the authorised user.
The ERCC keeps the rapid mapping service provider informed about the decision of the authorised user to activate or not the service.