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Detection and quantification of ground deformations in mining environnements using radar interferometry C.Carnec, C. King, S. Le Mouélic, D. Raucoules,

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Presentation on theme: "Detection and quantification of ground deformations in mining environnements using radar interferometry C.Carnec, C. King, S. Le Mouélic, D. Raucoules,"— Presentation transcript:

1 Detection and quantification of ground deformations in mining environnements using radar interferometry C.Carnec, C. King, S. Le Mouélic, D. Raucoules, BRGM, France

2 Plan Introduction Radar interferometry Examples Conclusion and perspectives

3 Ground deformations : A parameter to integrate into a global environnemental monitoring system Industrial exploitation of natural ressources : mining activity, gaz stocking (natural ou artificial), oil industry, geothermal field Underground urban works Underground water pumping… Natural processes - Potential damages to the existing overlying buildings - Instabilities to be considered for land use planning

4 Aménagement et Risques Naturels Where? When ? How do they evolve (space /time) ? Detection and quantification of ground deformations Problem... …and solutions Conventional - levelling - GPS,... Satellite observations

5 Radar interferometry - principles

6 Amplitude (backscattering coefficient) : roughness, dielectric properties Phase : distance Radar pulse Backscattered signal dist  intrinsic is random can be eliminated by difference Satellite Radar interferometry : principle

7  = BB DEM Surface deformations (accuracy ~cm)  topo +  mvt  orbit +  ellips Phase difference between two acquisitions : interferogram, or difference of distances (modulo 2  ) +  atmos + noise Differential interferometry : principle Orbital parameters

8 geophysical applications Landers - 1992 - Magnitude 7.5 (JPL) Piton de la Fournaise Volcano périod 1996-1998 (CNES) périod 1996-1998 (CNES) Earthquakes VolcanologyGlaciology Glacier evolution in Antarctique (JPL)

9 Applications in mining environnements - Framework : RESUM project - Examples of results

10 RESUM project : Urban and Mining subsidence network Partners Spatial Agency (*) CNES 4 public organizationsBRGM, IGN, LCPC-CETE 1 National SchoolECP Ecole Centrale de Paris 3 small businessKINOA (INSAR processing) companiesTRE Telerilevamento Europa (INSAR) Magnitude (microsismic surveys) Final end-users PMEMagnitude 2 IndustriesCdF Charbonnages de France GdF Gaz de France (*)support from ESA : provides ERS data (for research purpose)

11 0202 Example 1 : inflation caused by water recharge in an abandoned mine (Montceaux-les Mines, France) Period 12/1995 and 12/1998.

12 Inflating mean velocity between 1995 and 1998 estimated by radar interferometry Example 1 0 1.2 2.5 (cm/yr) The study has shown that the deformation (up to 7.5 cm) occurs beyond the limit of the exploited area

13 1992199219921992 1994199419941994 1995199519951995 h=1100 m Example 2 : subsidence caused by underground mining (Gardanne, France) The subsidence bowl migrates with the advance of the coal working face Carnec and Delacourt, 1999

14 Example 3 : subsidence over a salt exploitation 0 -1.5 -3 (cm) InSAR : better evaluation of the amplitude and 3D geometry of the deformation The position of the levelling network is not optimal The deformation is not exactly centered on top of the cavity Period 1993-1999 (Raucoules et al., in préparation)

15 Example 3 InSAR results compatible with ground truth (Raucoules et al., in préparation)

16 Exemple 4 : A ground uplift in Paris linked to underground works The observed uplift is correlated in time with the increase of the piezometric level after the end of an important underground construction work Le Mouélic et al, 2002 1 fringe = 3 mm of uplift


18 Example 5 : Sometimes, it does not work at all !!! (loss of coherence) Limiting factors : Vegetation (forest) Fast evolving phenomenons (collapses)

19 An alternative for the most difficult cases : the permanents scatterer approach (Ferretti, 2000) Retrieve the phase history of stable targets (constructions, bare soils) of a site Powerful, but also time consuming method based on statistical analysis (30 to 60 images required)

20 Test of this approach in Lorraine (France) (In collaboration with C. Colesanti from TRE)


22 19 november 1996 14 november 1996 Retrospective analysis of the deformation events Collapse event

23 (18 cm) Begining of the leveling survey Detection of precursor signs First structural disorders constated

24 Conclusion Radar interferometry : a powerful complementary tool to monitor ground deformations Best performances in urbanized (or desertic) areas Ongoing research effort in radar image processing  Overcome the actual limits (loss of coherence)  ERS 2 (no more gyroscope) and Radarsat  New generation of instruments : ASAR/ENVISAT (launched 2002), Radarsat 2, ALOS,... More information :

25 Performances, avantages and limitations Advantages : Synoptic view of the deformations (100 x 100 km) No ground instrumentation (confidentiality) Days and night observations indenpendently of the cloud cover Performances : Spatial resolution (pixel) 4 x 20 m Vertical accuracy : few mm Revisite cycle 35 j (ERS, ENVISAT), 24 j (Radarsat) Archive : 1991-2001 (ERS) + ENVISAT (2002 - …) Limitations : Surface variability: Stability of the targets (forest) Slow deformations only ( max 1/2 frange/pixel ) Atmospheric artifacts (classical interferometry) Poor performances in areas covered by vegetation

26 Origin Problems InSAR contribution Miningactivity inprogress  Monitoring ofthe impact of undergroundmining  Precise andregular mesurements ofthe displacementfield  Mapping surface deformationsfromfield leveling data  Confidential  Monitoringthe migration ofthe subsidence halo  Regular radar acquisitions  Discretion (noground instruments) abandoned  Rehabilitation ofthearea  Stability  recovering of pressures through water recharge  Dissociation ofminingeffect fromnaturalphenomenon (dryness, …)  Geodeticnetworkunavailable  Confidential  Drawingup aninventory of mining damages  Optimization of ground control networks design  Availability of archive ERS data Subsidence monitoring by InSAR

27 radar interferometry : principe Raw Interférogram Interférogram corrected from orbital fringes Butte Montmartre Interférogramme corrigé de la topographie 1 cycle of color (fringe) = 2,8 cm toward the satellite (3 cm in vertical). accuracy : few mm

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