GMES Terrafirma – A Pan-European Ground Motion Hazard Information Service

Country / Region: Europa

Begin of project: January 1, 2003

End of project: December 31, 2013

Status of project: December 31, 2013

Terrafirma is one of a number of GMES Service Element projects being run by the European Space Agency under the Global Monitoring for Environment and Security (GMES) initiative, which was renamed to Copernicus in December 2012. Terrafirma is a pan-European ground motion hazard information service aimed at providing civil protection agencies, disaster management organisms, and coastal, rail and motorway authorities with support in the process of risk assessment and mitigation. The basis of this service is ground motion data derived from the „Persistent Scatterer Interferometrie (PSI)“ technique, which is interpreted by geologists and geophysical experts.

The precondition for PSI is the existence of a large number (e.g. 20 – 100) of Synthetic Aperture Radar (SAR) scenes of the same region collected over a considerable time span (e.g. several years). The radar signal is most intensely reflected by objects on Earth’s surface, such as buildings, industrial installations, bridges and electricity pylons. For these fixed reflectors, providing a stable signal during the entire monitoring period, ground movements can be calculated with a precision in the millimetre range.
During the first two stages of Terrafirma (2003 – 2009), the BGR evaluated PSI ground motion data for Berlin, Hamburg and Staßfurt. The results of these cities as well as of several other European cities analysed during Terrafirma Stage 1 and Stage 2 are published in the Terrafirma Atlas.
In Terrafirma Stage 3 (2009 – 2013) the analysis of ground motion is separated in the following thematic services:

Tectonics
Coastal Lowland Subsidence & Flood Defense
Hydrogeology (including groundwater management, abandoned and inactive mines as well as landslides)

Figure 1: Location of the WAP-dataset in North Germany (dataset of ascending orbit (red frame) and descending orbit (blue frame)) Source: BGR

In addition, a new service called the “Wide Area Mapping service” was developed by the German Aerospace Center (DLR). This new “Wide Area Product (WAP)” offers an operational PSI processing for wide-area mapping with millimetre accuracy of ground deformation measurement on a country or continental level.
Within the theme service “Coastal Lowland Subsidence”, a WAP was processed for an approximately 21,000 km² wide area in the North German Plain, extending between Wilhelmshaven and Hamburg in the east-west direction and between Kiel and Bremen in the north-south-direction (figure 1).The North German Plain is characterised by a flat relief and low areas. Especially areas along the North Sea coast and the rivers Elbe and Weser are prone to potential flooding (figure 2).

Figure 2: Map of flood prone areas in Lower Saxony (NIBIS® Map server (2014): Flood prone areas 1:500,000 – State Authority for Mining, Energy and Geology of Lower Saxony (LBEG), Hanover) Source: BGR

The analysis of vertical ground motion in coastal lowland areas is therefore important in assessing flood risk.The new developed “Wide Area Product” is best suitable for this application as it gives an overview of vertical terrain motion over large areas and can be used to identify areas for further detailed investigation.The WAP is based on 191 Synthetic Aperture Radar (SAR) scenes of the ERS-1 and ERS-2 satellites, which were recorded between May 1992 and January 2001. About half a million Persistent Scatterers (PS) were identified, providing measurements of the average annual terrain velocity for each point across the study area.
The dataset was examined for plausibility and a geological interpretation of regions with high motion rates was carried out.

To identify potential causes of the observed ground motion, the PSI based ground motion data was analysed with geological, hydrogeological, geotechnical and topographical maps as well as geohazard information in a Geographic Information System (GIS). Additionally, fieldwork was carried out to investigate possible effects of the observed ground motion to the ground surface.
Several areas of subsidence were identified from the PSI result, located mainly in the marshland along the North Sea Coast and the rivers Elbe and Weser (figure 3). In general, the land subsidence in the marshland is characterised by motion rates of 1 to 7 mm/year and is likely to be due to compaction of the quaternary deposits consisting of a mixture of peat, clay, silt and fine sand.

Figure 3: This map shows the ground motion results in the North German Plain (background image: two Landsat 7 pan satellite images recorded in Mai 2000). Green points indicate stable areas, blue points show uplift and yellow to red points show subsidence. The marsh areas along the North Sea coast and the rivers Elbe and Weser are very well visible with the PSI data showing subsidence with values between 1 and 7 mm/year (blue line: boundary between marsh and Geest) Source: BGR

Areas of higher rates of subsidence were identified and further investigated on-site. For example, ground motion rates up to -2 cm/year occurring in the harbour and industrial areas of Bremerhaven are associated with anthropogenic activities and heavy load on a building ground with low bearing capacity. In a residential area in the north of the city, the effects from these movements are clearly visible on the basis of building damages (figure 4). Further subsidences could be identified in regions where natural gas is produced or underground storage facilities are in operation.

Figure 4: 1. PSI-WAP data of Bremerhaven (green: stable, yellow to red: subsidence), 2. Bearing capacity of the building ground (engineering-geological map), 3. Building damage in Bremerhaven Source: BGR

The utility of the final interpretation result was evaluated by the State Authority for Mining, Energy and Geology of Lower Saxony (LBEG). Joachim Fritz, former Head of the Section of Construction, Subsoil and Geohazards sees the utility of the data in the identification of ground motion regions, support for the design of monitoring systems and enhancement of terrestrial measurements.

Further information:

GMES-Terrafirma- stage 1 and 2: Preliminary Results

BGR Report of the Federal Institute for Geosciences and Natural Resources, Edition 2012 (page 20/21)

Terrafirma brochure

Project contributions: