The Terrafirma program
In November 2001 the ESA (European Space Agency) Council approved a new 5-years ESA programme dedicated to GMES (Global Monitoring for Environment and Security), called GSE (GMES Service Element) for short.
GSE will deliver policy-relevant services to end-users, primarily (but not exclusively) from Earth Observation sources. GSE is a key element of GMES, because it will enable end-users to become key players in the move from present generation Earth Observation satellites to future European systems that will deliver vital information on global environment and security.
GMES is a system supporting decisions, public services, politicians and authorities. Its activities include acquisition, processing and delivery (realized by the national geological surveys) of information about environmental conditions and major natural or human-caused hazards. At a regional level of EU countries, GMES, through the offices of national geological surveys, is to make available information on the regional development, transport, agriculture, and natural resources and their rational use. GMES could also assist local authorities in solving geoenvironmental problems.
The Terrafirma program* led and coordinated by the Nigel Press Associates (NPA Group, UK), is one of the ten services being supported by the ESA-GMES Service Element Programme. It aims to provide a Pan-European ground motion hazard information service, to be distributed throughout Europe via the national geological surveys. Terrafirma phase 1 (2003-2005) will reinforce his activities, actions and developments during a second phase (2006-2008). (* This page will open in a new window)
On the 13th May 2004, the Geological Survey of Belgium signed a partnership agreement with Terrafirma. In 2004 (Terrafirma, phase I), the Geological Survey of Belgium has received the first area of radar interferometry investigations. The area included Brussels and its suburbs. The radar images (descending orbit) processing has been conducted by Tele-Rilevemento-Europa (TRE - a spin-off of the "Politecnico di Milano"). In 2006 (during the fist year of the Terrafirma phase II), the radar images (descending orbit) of the second area (the cities of Liège-Visé-Maastricht-Hasselt) have been processed by NPA.
Radar images from the european satellites (ERS1, ERS2 and ENVISAT), used in Terrafirma, come from thousands of images stored in the archives of the European Space Agency since 1992.
Acquisition of satellite data allows to identify ground movements at the scale of one millimetre of the earth surface. The radar interferometry (PSInSAR technique) is used by the GSB. This technique will enhance the monitoring of the ground motions in urban and mining areas in Belgium.
Studied areas in Belgium
During 15 years, the European satellites ERS-1, ERS-2 and ENVISAT provided data (radar images) of high quality. They are used for scientific and commercial purposes. The satellite images archives of the European Space Agency include more than one million satellite images. Each image corresponds to a surface of 10,000 km2. The PSInSAR technique allows the identification of thousands control points which indicate the ground deformations at the millimetre scale.
Currently, two zones are under study (green) and the third one (in red) is the subject of a forthcoming project within the framework of a new contract for which fundings are investigated.
Topographic background, 1:100,000 scale-map (© National Geographic Institute). Regional limits (Flanders, Wallonia and Brussels) are represented by black polylines.
Zone A: Brussels, Zone B: Liège-Campine, Zone C: Mons-Strépy.
The first area studied in Belgium covers a superficy of 900 km2. This area contains nearly all the territory of the Brussels Region and covers partly the communes of Vilvoorde-Zaventem (north) to Louvain-la-Neuve (south) and from Halle (west) to Wavre (east). These satellite data are under study using a GIS environment which contains the geological data of the BUG project which aims to model in three dimensions the underground sratas of the Brussels territory and to produce new digital 1:5,000 scale-maps.
Topographic background, 1:100,000 scale-map (© National Geographic Institute). Regional limits (Flanders, Wallonia) are represented by black polylines.
In the framework of the second phase of the Terrafirma programme, a new area centred on the Liège city and the Campine has been received. It covers 3000 km2 both in Flanders and Wallonia (Liège and Limbourg provinces). A small part of the Netherlands is also included.
Topographic background, 1:100,000 scale-map (© National Geographic Institute). Regional limits (Flanders, Wallonia) are represented by black polylines.
A third zone (in red) located in the Hainaut Province represents the western part of the old coal industrial basin from the French border towards the Strépy-Thieu village.
Topographic background, 1:100,000 scale-map (© National Geographic Institute). Regional limits (Flanders, Wallonia) are represented by black polylines.
Available satellites
The first European Remote Sensing Satellite (or ERS-1) was launched in July 1991 by the European Space Agency. It uses advanced microwave techniques to acquire measurements and images regardless of clouds and sunlight conditions.
In comparison to contemporary satellite systems, the ERS-1 (and now ERS-2 too) is unique in the simultaneous measurement of certain parameters, including those of sea state, sea surface winds, sea surface temperature, ocean circulation and sea and ice level, as well as all-weather imaging of ocean, ice and land. These satellites are both an experimental and pre-operational system: the nature of their orbits and their complement of sensors enable a global mission providing a worldwide geographical and repetitive coverage, primarily oriented towards ocean and ice monitoring, but with an all-weather high resolution microwave imaging capability over land and coastal zones.
ERS-1 satellite (European Remote Sensing Satellite 1) - { http://earth.esa.int/ers/ }* - was launched on 17th July 1991, into a solar-synchronous orbit at an altitude of 780 km.
The satellite has three modes of operation in a recurrent period of:
- 35 days as standard
- 3 days for a cycle more adapted to the study of ice during the arctic winter, and
- 168 days for geodesic studies.
The volume of data produced by ERS-1 is enormous: over one million bits per second just from the "low bit rate" sensors and 100 million bits per second from the Synthetic Aperture radar (SAR). The Low Bit Rate data is stored on board and then dumped as the satellite passes over three dedicated ground stations. The SAR data is transmitted in real time.
The objective of the first European Remote Sensing Satellite is to substantially increase the quantity and quality of scientific data about the Earth and its environment. Initially of scientific interest, the (applicative) projects developed using ERS data have demonstrated that practical and even commercially viable applications are possible today. From the monitoring of crops, tropical deforestation and flooding on land, to the tracking of oil spills, sea-ice and weather conditions on the oceans, ERS-1 has provided a wealth of information which is being used practically.
ERS-2 satellite - { http://www.esa.int/esaEO/SEMWYN2VQUD_index_0_m.html }* - launched on 21th April 1995, is circling the Earth every 100 minutes at an altitude of 780 km in an orbit passing over the North and South poles. As the orbit itself is fixed, the Earth in effect turns below the satellite around its own axis, which means that its instruments scan the Earth's surface and atmosphere in "swaths". In this way it takes ERS-2 three days and 43 orbits to observe the entire planet. The imaging radar does however require more time to do so, 35 days as standard, owing to its higher resolution and narrower swaths. ERS-2 has worked in a tandem mission with ERS-1 until the 10th march 2000.
Processing and distribution of ERS data takes place in two stages. Part of the data is further processed on location in the ground stations and then transmitted to users by satellite or data network. The result is that wind and wave data reach the world's weather offices within three hours of observation. SAR images can be delivered to users from some ground stations in less than an hour, though with some loss of resolution. High-resolution images are available in Europe within 24 hours.
ENVISAT satellite - { http://envisat.esa.int/ }* - has on board 10 optical instruments and sophisticated radars which make possible to provide continuous information and a monitoring of the ground on the lands, of the atmosphere, of the ocean and on the icecaps. The broadest instrument on board is the Advanced Synthetic Aperture Radar (ASAR) which operates in the C-band and ensures the continuity of the radar imagery of ERS-2. ENVISAT circle around the earth into a solar-synchronous orbit at an altitude of about 780 km. It's standard cycle corresponds to 35 days.
Other satellites used for radar interferometry are listed below:
New missions are planned for the next few years and concern the launch of the following satellites:
* This page will open in a new window
Goals of the GSB
The Geological Survey of Belgium started a programme of spatio-temporal identification of ground motions in relation to natural and geological risks in urban and rural areas. Some risks are known but their cartographic extension is rarely detailed. The identification of ground deformations observed by radar interferometry (PSInSAR technique) will make it possible to obtain useful and precise information on the stability of the ground in the studied communes.
In Belgium, radar interferometry data of the European satellites will be particularly useful to detect, map, quantify and monitor the evolution of the ground deformations:
- in the coal mining areas, ground motions (uplift) are related to rising mining groundwater after the end of groundwater pumpings and the caol mining activities. Localized collapse events related to the presence of mining infrastructures (shafts, mining galleries, etc.) at shallow depth,
- above old or unknown underground quarries (chalk, sandstones, slates, metallic ores, marbles, etc.),
- in areas of overexploited groundwater pumping activities,
- in urbanized areas located above karstic features,
- in urban environments,
- on historical or belgian heritage sites,
- on major works of structural engineering (bridges, motorways, tunnels, etc.),
- etc.
The PSInSAR data allows to obtain annual average velocity data (in mm/year) for thousands of points called Permanent Scatterers (PS) in large areas (hundreds of km2). A density of several hundreds of PS per km2 in urban areas cannot be achieved by other techniques such as levelling or GPS stations.
The GSB team
- Responsible of the project at the GSB and research partner in the european programme Terrafirma: Dr Xavier Devleeschouwer.
- Collaborator: Pierre-Yves Declercq (GIS-geologist, contractual)
- Collaborator: Franck Pouriel (Geologist - Geomatics, under contract in 2005 et 2006)
