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Earth observation satellites starting to bring benefits to mining sector

2nd June 2017

By: Keith Campbell

Creamer Media Senior Deputy Editor

     

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JOHANNESBURG (miningweekly.com) – At last month’s International Symposium on Remote Sensing of the Environment, held at the Council for Scientific and Industrial Research (CSIR), in Pretoria, one of the very many topics addressed was the use of remote sensing, particularly from earth observation (EO) satellites, to support the mining sector. This is an emerging endeavour but it is already showing much promise.

GLOBAL PROMISE
“Oil, gas and mineral deposits are the raw materials that drive the global economy,” points out the European Space Agency on its website. “As existing reserves dwindle, ensuring an adequate supply for the future requires the exploration of frontier regions for new supplies. Hospitable and inaccessible environments such as desert and Arctic regions are increasingly the focus of survey activities, but exploration managers find it demanding to operate in such uncharted territory, often lacking detailed maps and basic geological information about the areas they are interested in.

EO makes possible the large-scale surveying of unexplored regions in a cost-effective manner, providing an additional layer of information to managers before they make the expensive decision to commit to on-site exploration. Satellite data can map and identify large-scale geological structures related to hydrocarbon and mineral deposits that ground-based surveys may find more difficult to see: satellite radar interferometry can precisely identify surface faults or slight ground motion connected with hydrocarbon reservoirs. Multi-spectral optical sensors can directly identify different minerals, either valuable in their own right or chemi- cally altered by contacts with oil and gas deposits . . . As well as assisting with direct search efforts, satellite images can also provide indirect logistics support, for instance planning the most effective placing of sound sources and geophones in order to carry out a seismic survey, or selecting the most suitable sites for extraction facilities.”

Satellite imagery can also be used to identify, monitor and help address the various impacts of mining and hydrocarbons extraction, such as various forms of pollution (including acid mine drainage), subsidence and the impact on the environment. “Until recently, satellite imagery has lacked the spatial, temporal and radiometric resolution to compete especially at small scale and quantification of target materials,” notes the EO Miners website. (EO Miners is a project of the European Commission.) But, with the most recent EO satellites and sensors, this has changed. And not only are the sensors on the satellites getting better, but they are also getting cheaper.

For example, University of Alabama Birmingham (UAB) researcher Reda El-Arafy has been developing techniques to use satellite EO data to locate uranium and other metals ores. Ground-penetrating radar on satellites can penetrate no more than a couple of centimetres – if that – below the ground surface, while the ores he is seeking lie scores, if not hundreds, of metres underground. According to the university’s online publication, UAB: The Mix, he has identified certain electromagnetic spectra that serve as signatures, suggesting the presence of uranium and gold at some depth. So far, he has achieved an accuracy of about 90%. Related techniques could be used to locate other economically valuable metals, including copper, iron-ore and manganese, among potentially many others.

Meanwhile, India is using satellite data for a very different end: fighting illegal mining in the country. The Indian Bureau of Mines (an agency of the Ministry of Mines) has, in collaboration with the Ministry of Electronics and the Bhaskaracharya Institute of Space Applications and Geo-Informatics, developed a mining surveillance system. This covers the whole country and was launched late last year.

SOUTH AFRICAN INITIATIVES
It should be no surprise that South African institutions and researchers are heavily involved in applying satellite EO data to mining, mining-related events and the consequences of mining. The country has a long tradition and great experience in receiving and analysing EO data from satellites. In this regard, the core entity today is the Earth Observation Directorate of the South African National Space Agency (Sansa), but such analytical expertise is also found in other institutions, agencies, universities and companies.

For example, the CSIR has developed what it describes as a “robust system” which can quickly detect the deformation of land surfaces. This capability is of special relevance in areas which have been mined, where detection, in good time, of such deformations is very important. Across the country, there are large areas affected by surface deformation – which includes sinkhole formation – associated with mining or natural processes. These events can be most hazardous for people and damaging to infrastructure.

The system developed by the CSIR is called Azimuth, which uses data from satellite- borne synthetic aperture radar (SAR) sensors. These measure the time delay and amplitude of the microwave signals returned from the earth’s surface. Azimuth is a large-area system, covering up to 150 km by 150 km. The deformation measurements are available on an Internet-accessible platform. The system, for example, allowed the detection of the formation of a sinkhole in an uninhabited part of Centurion (south of Pretoria, in the Tshwane Metropolitan area) between June and August 2015. Azimuth detected a subsidence of 6.6 cm with a diameter of some 100 m. When visited by scientists on the ground, a sinkhole was indeed discovered to have been formed.

In a further development, CSIR researchers have been using differential interferometry SAR (dinSAR), which can provide centimetre- and even millimetre-scale deformation measurements to detect surface deformation over operational and abandoned underground coal mines. These employed and still employ room-and-pillar mining to extract as much coal as possible while ensuring support of the overburden. But, over time, the pillars will collapse and create subsidence at the surface. This programme uses data from the two Sentinel-1 radar satellites, launched in 2014 and 2016 and funded by the European Union, the data from which is freely available. The combination of the satellite sensors and the open data policy allows for the routine monitoring of large areas. The CSIR has been using this data to monitor mine-induced surface deformation for some two years to identify areas associated with underground pillar collapse and monitor the consequent surface subsidence. The results indicate that surface subsidence associated with the collapse of pillars can be detected and measured to a high degree of confidence. This, in turn, suggests that early warning of such dangerous developments, using long-term monitoring, could be possible.

Sansa has been using satellite imagery in a case study of land use and land cover changes associated with coal mining in the Emalahleni municipality (which is centred on Witbank), in Mpumalanga province. High-resolution satellite imagery has been used to monitor the development of mines, the consequent dynamics in the near-by populated areas, and the impact of both on agricultural land and natural ecosystems. The preliminary results of this case study have established that the growth in mining activities has led to urban development – thereby indicating the economic benefits of mining – but that another consequence has been an encroachment on agricultural land, thus presenting a threat to food security.

Land cover is the focus for another research project, at the University of Johannesburg. This is concerned with changes in land cover within granite quarries (each with an area greater than one hectare) in the Brits region of the North West province. The intent is to develop knowledge, and provide continuous satellite monitoring, to mitigate the environmental impact of quarrying. Images from the American Landsat EO satellite family were obtained free from the US Geological Service; the images covered the period 1998 to 2015. The analysis showed that, during this period, the area of the granite quarries had increased by some 1 175 ha and the number of bodies of water needed for quarry- ing had also risen, while 1 308 ha of vegetation had been lost and 18 ha of bare land had been created around the quarry areas. Thus, the environmental impact of the quarrying was established and the practicality and the value of satellite (in particular, Landsat) monitoring proven.

Another area in which South African researchers are working is using satellite data to monitor postmining rehabilitation. Thus, a team from the CSIR and Stellenbosch University have been using dinSAR techniques to monitor surface deformation in backfilled openpit mines. Backfilling is a common way to carry out the rehabilitation of decommissioned openpit mines, but, over time, this backfilled material settles and the settling rate can vary across the backfilled area. These differing settlement rates can be a hazard to adjacent buildings and people and harm the environment. They have to be monitored and mining companies in South Africa have developed surface deformation monitoring systems. But these surface-based systems are inefficient over wide areas – hence, the team’s use of dinSAR techniques to detect and monitor the settling of ground in backfilled areas of rehabilitated openpit mines. The outcomes of this study could be applied to guiding the design of long-term operational monitoring of rehabilitated postmining areas.

A team from the University of the Witwatersrand and the mineral and metal processing and beneficiation science council Mintek are looking at using satellite data to support the rehabilitation of asbestos mines, in particular. The Department of Mineral Resources, with Mintek, is busy rehabilitating derelict and abandoned asbestos mines. This is being done using localised management plans, the success of which needs to be monitored. Currently, this is often done using labour-intensive and tedious fieldwork. The team has been using data from the Landsat and high-resolution Worldview-2 and RapidEye satellites to map vegetation species and their density around the mine sites as an indicator of the success of the rehabilitation. Normalised difference vegetation indices were developed from Landsat data to quantify the recovery and density of the vegetation following rehabilitation.

AFRICAN ACTION
Worldwide, there is also, of course, a strong and growing private sector in all aspects of EO, from owning and operating satellites to producing products and services based on imagery and other data provided by satellites. And, important for the continent’s mining sector, Africa is no exception.

A report into the private-sector African EO services industry last year (‘A Survey into the African Private Sector in Earth Observation and Geospatial Fields’) by the African Association of Remote Sensing of the Environment and the European Association of Remote Sensing Companies received useful responses from 78 companies employing 1 417 people in 21 of Africa’s 54 countries. These countries were Botswana, Burkina Faso, Egypt, Eritrea, Ethiopia, Gabon, Ghana, Kenya, Madagascar, Mali, Morocco, Nigeria, Rwanda, Senegal, South Africa, Sudan, Tanzania, Tunisia, Uganda, Zambia and Zimbabwe. The region with the most EO services companies was West Africa, followed by East Africa, then Southern Africa, North Africa and, lastly, Central Africa. About half of the companies are concentrated in just four countries – South Africa, Kenya, Nigeria, and Ethiopia.

Currently, the business of these companies is dominated by local and regional planning (66% of the companies surveyed); the environment, pollution and climate (59%); and agriculture (51.43%). But mining is already an important segment for 21%. “The results show an industry in development,” notes the report. “There has been growth in revenues in the past few years, accompanied by a good growth of employment in the sector. We find an optimistic outlook, albeit cautious, on the near future.”

Edited by Creamer Media Reporter

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