Perspective From Above
Photographs from aircraft and satellites have long had application in the mining business, particularly exploration. However, recent developments in the field of remote sensing can help with all stages of a mine’s life–from evaluating the resource, to making extraction more cost-effective, through to monitoring, mine closure and remediation.
Becoming adept at using remote sensing can give mining companies an edge in reducing costs, shortening timelines and building better relations with external stakeholders. It is also important to understand the limitations of the technology and how to work within those limitations.
Mining company executives familiar with grainy black-and-white images from the early days of satellites may be surprised at some of the more recent developments in remote sensing imagery. Those familiar with Google satellite image maps will be pleased to know that better detail, precision and more variety of images are available. These include:
* images with a high degree of detail, so users can pick out objects as small as 30 cm across;
* technologies such as infra-red imagery that can help map geological faults, outcrops and vegetation cover giving clues to mineralization; radar imaging that can help evaluate structural geology by penetrating cloud cover, often looking at the Earth’s surface from an angle that best highlights terrain; and LiDAR imaging (using lasers rather than the radio waves of radar) to precisely develop bare earth topography by “seeing” through almost all types of forest cover;
* LiDAR terrain models combined with high-resolution satellite images, which can easily develop 3-D pictures of a site that can be moulded into physical 3-D models; and
* better technology for interpretation that can help indicate, for example, whether a particular type of vegetation is likely to be associated with environmentally sensitive areas or aggregate sources.
Life-cycle approach to satellite imagery
Mining companies are just starting to discover that remote sensing can add value and provide a competitive edge throughout the life of the mine, not just at one stage such as exploration. Planning for image requirements following exploration should include executive, engineering and environmental team input to select ideal data that may be more timely and less costly.
Widespread availability of archived satellite imagery allows companies to cost-effectively evaluate multiple potential properties for development, using false-colour imagery to assist in field mapping and to guide “boots-on-the-ground” evaluations. Imagery of the site before activity starts can help establish an environmental baseline, to guide mitigation measures and eventual remediation. The technology can also help inform the economics of extraction–finding potential access road routes including determining the amount of cut-and-fill needed for more accurate costing, estimating the amount of work needed to prepare the mine site, and guiding the siting of tailings deposits.
As work on the mine begins, remote imagery can demonstrate the company’s adherence to plan, to regulators, NGOs and leaders of communities close to the mine site. At closure, an organized series of images can guide the work plan for efficient and comprehensive closure to develop the best possible outcome. Monitoring reclamation, including the growth of planted vegetation, can be done cost-effectively through remote imagery of the mine site and surrounding area.
In some cases, mining companies tend to purchase remote sensing imagery and evaluation services partway through the mine planning process for a specific purpose, such as environmental baseline studies. However, it might have been better to obtain the imagery at an earlier stage, and with other potential uses in mind. For example, those planning the mine infrastructure may say, “We could have used this information a month ago for planning the access road and mine facility layout.”
Remote sensing imagery can also be particularly useful in cases where a mining company takes over site operations from a previous owner. Images taken at the time of transaction can determine liabilities and impact cost negotiations.
Working with remote sensing imagery
Companies have a choice of whether to work with archived images taken during the normally scheduled passes of a satellite (or in some cases, aircraft), or custom imagery in which the satellite or aircraft is specifically tasked with providing data for the area of interest.
Archived images have the advantages of being both more cost-effective than custom acquisitions and available sooner–within a few days, versus a couple of weeks (or more) for custom acquisitions. However, the right level of resolution may not be available for the area in question, and the images may not be current.
New acquisitions are specific to the area in question, and are right up to date. However, they generally cost more. Also, there may be delays in obtaining new acquisitions. This is because it may be necessary to wait some time until a satellite passes over the area of interest. Or, in the case of airborne imagery, some time will be required to mobilize the airplane. This delay can play havoc with mining schedules, particularly if it is necessary to get equipment onto a mine site over an ice road, for example. So, it is important to plan any delay in imagery availability into the schedule.
One advantage of custom imagery is competitive–it could be that nobody else has access to information on the area of interest. Another is that the company can likely get imagery that meets its needs more closely regarding resolution, time of year, and the part of the spectrum for the imagery.
With all these choices, it is common to enlist the services of a specialized consulting firm with remote sensing expertise. It can often process the images to maximize the benefit for internal engineering or CAD technicians.
Knowing the limitations
Like any analysis tool, remote sensing imagery has its limitations and it is important for mining companies to understand these.
Some areas of the Earth’s surface are particularly challenging because they may be cloud-covered much of the time. In a recent instance, while trying to get pictures of one site in southern Africa, a chartered aircraft sat on the tarmac for most of a month, rarely able to work because cloud cover obscured the site. The plan was eventually altered to acquire high-resolution satellite imagery with the benefits of a fixed cost and continuous colour imagery over the entire study area.
Airborne imagery has traditionally had the advantage of being higher-resolution because it is taken from much closer to the ground. However, the higher-resolution sensors on some recently launched satellites now provide imagery close to the quality from aircraft. Because of their height above the Earth, satellites are generally able to provide images that are less distorted towards the edges than can aircraft.
Satellites have the advantage of anonymity, important particularly at the exploration stage. Confidential work may more easily be noticed by competitors if aircraft are taking off from remote landing strips, pilots are discussing activities with their other clients and there are survey crews in the field.
Rush service and priority image acquisition can shorten the time needed to acquire imagery, but it comes at a price that can double or triple the basic data costs.
It is important to understand the licensing agreements that go along with each different image product. Specific restrictions can often limit the number of projects, number of companies or resale of image data.
Selecting the correct resolution is a big part of success. Generally, lower-resolution data will be less costly, available more quickly and will cover a wider area of the Earth’s surface. It is also gen
erally easier to work with because the data files are likely smaller. On the other hand, low-resolution data may not tell a company all it needs to know. For this reason the goal is to review all foreseeable project requirements for imagery and to select the appropriate dataset for the most demanding requirement.
Finally, it is important to “ground-truth” remote-sensing imagery with people on the ground.
In selecting a consulting company to provide remote-sensing imaging and interpretation services, it is important to select a supplier that understands the purposes to which the information will be put. This includes having familiarity with the mining process and with all stages of a mine’s life, so that the advice offered will have the greatest possible utility.
Justin McPherson is a geomatics specialist and project manager in the Calgary office of Golder Associates Ltd. He is responsible for project co-ordination for a complete range of geomatics solutions, providing support for remote sensing, global positioning (GPS), geographic information systems (GIS) and spatial database development. He can be reached at tel. 403.299.5600; [email protected].