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Georeferenced and interpolated average annual displacement map over London. © NPA/TRE, 1992. ERS Data © ESA, 1995-2000. Distributed by Sarcom
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Service Examples [2/3]
Monitoring of ground subsidence associated with coal mining and oil extraction
Routine ground based monitoring of ground deformations through a GPS network maintained by the German coal company DSK has been integrated with a space borne SAR monitoring service to study subsidence associated to coal mining in Ruhrgebiet (Germany). Time series of deformations were elaborated by GAMMA, a Swiss based value-adding company providing consulting services and software, and supplied to the user as geocoded layers. The interferometry based deformation information is integrated into the users geo-database together with standard measurements, enabling the analysis of the correlation between subsidence and the coal-production panels. Radar interferometry, with its very high sensitivity to height changes appears to be extremely well suited to identify subsiding areas and especially to quantify and map residual deformations after the end of the excavation process.
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| Monitoring of underground coal mining induced surface deformation with differential SAR interferometry. ERS data © ESA, 1998-2001. Distributed by Eurimage. SAR and interferometric processing by GAMMA Remote Sensing, mining panel information DSK. |
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In the Belridge Oil Field (U.S.A.), the removal of fluids from the 3rd largest oil field in the U.S. has led to substantial reservoir compaction, causing surface subsidence and well failures costing millions of dollars per year and having a major impact on the economic viability of oil production.
Since the late 1980s a network of level survey measurements has been used by SHELL to monitor subsidence in the attempt to find a model for it. Radar data were acquired over the area by the ERS-1 and ERS-2 satellites of the European Space Agency in such a way that a quasi-continuous subsidence monitoring service could be guaranteed on a monthly basis for a period of 1 year. Additionally, ESA provided baseline values (a parameter characterising the “stereo” effect of a pair of interferometric images) within 3 days after the acquisitions in order to allow the most suitable data to be identified and the resulting service to be rapidly provided. The time required for the provision of the end- to- end service was systematically shorter than 2 weeks (1-2 weeks in average). In this example the products provided by Atlantis Scientific Inc., a Canadian company specialised in providing products and services based on radar satellite imagery, contributed to a better understanding of the relationship between injection, extraction, subsidence and oil-well failures, which coincide with high subsidence gradients: this forms critical input for assessing the impact of the density of oil wells in the planning of oil production. Moreover, the frequent and rapidly supplied subsidence maps by Atlantis are now an effective management tool for monitoring production and injection operations. They are also used in the form of well failure risk maps by engineers in the field during oil well maintenance activities. As a consequence of this activity, the customer has discontinued their conventional in-situ measurements, and placed a further follow-on contract for continued provision of this EO-based service. Deformation maps are delivered routinely within 2-3 days after SAR data acquisition.
Monitoring of subsidence for pipelines
In Southern California C-CORE a global research and development company based in Canada providing engineering solutions to clients in the natural resource sectors, used SAR data in a blind test to monitor ground motion of an oil field traversed by a series of gas pipelines. The results compared favorably with the concurrent in situ surveys. In related work C-CORE used archive data to identify possible subsidence features and generate a ground movement risk map for an area where very little ground motion information previously existed.
A series of passive corner reflectors are installed on slopes supporting buried gas pipelines maintained by TransCanada Pipelines Ltd in order to monitor, by means of D-InSAR, incremental small movements whose cumulative effects may affect pipeline integrity. In these regions of Canada pipeline corridors are cleared of trees for a width of 10 to 20m hence the study by C-CORE uses Radarsat fine mode data, providing higher horizontal geometric resolution. Monitoring is conducted from spring until fall and detected motion (ranging from 1 mm to 35 mm) are in accordance with field data. Information gained through SAR processing, coupled with geotechnical analysis, enabled understanding of mechanical behavior of the slope, the impact of rainfall events, and resulting pipeline stress.
Monitoring of Urban subsidence
Tunnelling activity for the Jubilee Subway Line extension in London triggered ground displacement phenomena, affecting also Thames Water’s infrastructures. Detection and monitoring of deformation has been performed by NPA -a company providing expertise in remote sensing and digital cartographic information- together with their Italian based partner TRE on archived SAR scenes by means of the Permanent Scatterers technique. From the analysis of the georeferenced and interpolated PS velocity field combined with Thames Water’s Ordnance Survey land-line vector data it was shown that the subsidence started occurring at the beginning of 1996; the spatial distribution of subsidence correlates well with the tunneling works.
Monitoring of Reservoirs
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| Radarsat imagery of a London reservoir shows an array of radar reflectors around the perimeter allowing millimetric measurements of stability. Processed by NPA. Radarsat data © CSA distributed by RSI |
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Thames Water needed to monitor in an effective way the integrity of a water reservoir, west of London. Traditional measurements carried out by means of GPS to measure the stability of reservoirs retaining walls have been coupled to InSAR processing performed by NPA. Corner reflectors have been installed on the retaining walls and any millimetric movement of the structure between two consecutive passes of the SAR sensor are routinely detected and monitored. The excellent results provided by this technique resulted in the extension of the monitoring service to another reservoir located in Turkey.
Analysis of landslides with InSAR
BC rail and highway 99 in Canada are endangered by the deep-seated Fountain slide. In the past 10 years, engineering works on the slopes and remedial works on the highway have been performed without the expected results. In order to analyse ongoing deformations and to plan mitigation interventions, BC Ministry of Transportation has asked Atlantis Scientific Inc. to analyse with InSAR extension, magnitude and direction of the landslide movements.
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| GIS used by the BC Ministry of Transportation showing Fountain slide data. Processed by Atlantis Scientific Inc. Radarsat data © Radarsat International (RSI), 2002. Distributed by RSI |
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The produced information was ingested in a GIS and successfully compared with geotechnical information. From the exploitation of the ERS archives it has been possible to delimitate, follow in time and understand the evolution of the landslide since 1995.
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