Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Radar satellite service checks stability of Africa’s largest artificial hole

03.01.2006


Palabora open pit


International engineering firm AMEC is working with ESA to improve monitoring of ground subsidence linked to mining activity. Radar satellites in orbit 800 kilometres away can reveal millimetre-scale elevation shifts across wide areas of land.

The largest man-made hole in Africa is located 360 kilometres north-east of South African capital, Pretoria. The Palabora copper mine was excavated open-cast for 38 years: the end-result is easily visible from space: a yawning pit approaching 2000 metres in diameter and 762 metres deep (more than 230 metres beneath sea level).

In 2002 owner Rio Tinto declared the pit’s depth meant surface extraction was now uneconomic, instead developing an underground mine to work the copper ore beneath the pit bottom. The decision was good news for the regional economy, as it should extend the life of the mine and associated copper smelter and refinery by at least another 20 years.

Mining at Palabora uses a highly-efficient method called ’block caving’. It is based on extracting thin blocks of rock to induce large-scale cave-ins in overhanging ore. However, even though the excavations are being carried out more than a kilometre underground, last year they induced dramatic surface instabilities. More than 60 million tonnes of mass collapsed into the pit from its north wall, with movements of up to two metres in the vicinity and cracking as far as 300 metres away from the pit rim.



Rio Tinto was concerned that further subsidence might threaten mine infrastructure on the pit’s east rim. AMEC’s Earth & Environmental Division were called in to evaluate the threat posed - who then turned to an innovative deformation-measuring method based on imagery from radar satellites flown by ESA and the Canadian Space Agency (CSA).

AMEC is working within the ESA Earth Observation Market Development (EOMD) programme to evaluate the commercial possibilities of a technique known as Synthetic Aperture Radar Interferometry (InSAR). Through InSAR, multiple satellite radar images of the same site - acquired from as near as possible to the same point in space though at different times - can be combined together to highlight slight changes in surface elevation that occurred between the image acquisitions.

Think of it as a space-based version of ’spot-the-difference’, which sees down to a few millimetres. Even the tiniest vertical surface shift changes the distance it takes for the radar signal to travel down to the surface of the Earth and back to the satellite, and so alters the phase of the signal. Just like sets of ripples meeting in water, the combination of radar signals that have different phases sets up interference patterns – so these combined images are known as ’interferograms’.

Such interference ’fringes’ can be thought of as resembling contour lines, but on vastly reduced scales. Once topographic and atmospheric effects are accounted for, the fringes remaining on an interferogram can be used to precisely measure the extent of any ground shifting over the entire area covered – usually tens of kilometres across.

"While traditional survey techniques and geotechnical instrumentation can provide detailed information at specific points of interest, InSAR provides continuous data coverage over large areas to sub-centimetre accuracy within a particular timeframe of interest," said Stu Anderson, AMEC Project Manager. "These data are often available back to the early 1990s for many locations."

For this mining problem at Palabora, AMEC sat down with Rio Tinto and together they designed test cases to see what InSAR could deliver and how it could be used by Rio Tinto. Various SAR images were acquired for two consecutive 24-day periods in 2004. The news turned out to be good: the affected area was restricted to the northeast sector of the pit, away from the east-side infrastructure, and the size and magnitude of the deformations was reducing.

During the first period the maximum measurable subsidence was found to be five centimetres nearest the large north wall failure, tapering to zero in the east. During the second period the maximum value was two centimetres, and the affected area was reduced, with the east wall again proving unaffected.

Based on the products developed during this investigation, InSAR will also be performed over Palabora to serve as a means of early warning of future subsidence.

Regulators typically compel most mining companies to regularly check for deformation. In a bid to see if InSAR can bring benefit to other companies in the mining industry, AMEC has been consulting with more of its extensive list of clients. To this end, AMEC also completed satellite-based subsidence tests over Germany’s Bad Reichenhall salt mine on behalf of owners Südsalz, a slip-prone mine waste rock dump at the closed Hayden Hill gold and silver mine in northeast California in the US for the company Kinross Gold and the closed Hollinger gold mine near Timmins in Ontario, Canada, for Placer Dome.

In this case, an extension of the InSAR method, based on historical available satellite data such as the 14-year archive from ESA’s ERS archive, was utilised. Known as Coherent Target Monitoring (CTM), this method provides detailed quantification of land motion. Results were compared to in-house survey findings, with promising results.

For Hollinger Mine, AMEC employed satellite data between 1992 and 2003 to detect subsidence in the range of 25 to 55 millimetres within an area previously identified as stable using traditional geological instrumentation and survey techniques, showing that CTM provides additional insight into deformation occurring in the vicinity.

"Another advantage of using SAR interferometry is that it is not dependent on sending crews into the field," commented Timothy Conley, Vice President and Managing Director of AMEC’s Earth & Environmental operations in Europe. "It is therefore valuable for acquiring information at remote sites or areas considered unsafe for personnel to enter."

InSAR and CTM subsidence monitoring have many other commercial applications beyond the mining sector. Testing is also either already under way or being finalised by AMEC for railways in Germany for Die Bahn and in the UK for Network Rail, as well as for a mine access road in the Peruvian Andes for Teck Cominco.

Future tests are proposed for a pipeline corridor in British Columbia for Terasen Gas and tunnel construction in Germany for DYWIDIG Bau (formerly Walter Bau). AMEC is also using InSAR as part of a landslide warning system at Turtle Mountain in Alberta, Canada.

Project team

AMEC is an international project management and services company with office networks across Europe, Asia and the Americas. It employs 45 000 people across more than 40 countries. Its Earth & Environmental Division operates 100 offices and specialises in environmental, water resources, geotechnical and materials engineering projects.

AMEC is being assisted in the project by subcontractor and strategic partner Vexcel Canada (formerly Atlantis Scientific Inc), a world-class Earth Observation specialist supplying products and services related to satellite data acquisition, radar remote sensing, InSAR and image analysis. Also participating is UK-based Infoterra, supplying high-resolution optical imaging services in support of InSAR interpretation.

Additionally the Land Use Planning and Natural Risks Division of the French Geological Survey (Bureau de Recherches Géologiques et Minères, BRGM) is providing a scientific review of the project.

This activity has been carried out within ESA’s EOMD Programme, aimed at strengthening European and Canadian capacities for the provision of geo-information services based mainly on Earth Observation data. To find out more about using Earth Observation for hazard mapping or further opportunities with EOMD, please contact eomd@esa.int .

Pierre-Philippe Mathieu | alfa
Further information:
http://www.esa.int/esaEO/SEMX4QVLWFE_economy_0.html

More articles from Earth Sciences:

nachricht From volcano's slope, NASA instrument looks sky high and to the future
27.04.2017 | NASA/Goddard Space Flight Center

nachricht Penn researchers quantify the changes that lightning inspires in rock
27.04.2017 | University of Pennsylvania

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Bare bones: Making bones transparent

27.04.2017 | Life Sciences

Study offers new theoretical approach to describing non-equilibrium phase transitions

27.04.2017 | Physics and Astronomy

From volcano's slope, NASA instrument looks sky high and to the future

27.04.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>