Laser Scanning: There’s More Than One Option
Recent applications of laser scanning technology within the mining community have achieved improvements in operational efficiency, reduced costs and minimized risk to personnel and equipment.
By Graham Hunter
The use of lasers to capture highly accurate measurements is not a new concept for those charged with managing and monitoring mining operations across the world. For example:
Fixed / Static
The laser scanning system used by Gold Fields to help improve safety and increase production at the Damang gold mine in Ghana, West Africa, includes a Riegl LMS-Z420i long-range laser scanner, which can capture up to 11,000 point measurements per second, to an accuracy of 10 mm and at a range of up to 1,000 m. A rugged and fully portable sensor, the system also includes a calibrated and accurately orientated high-resolution digital camera. The data captured is analyzed using 3D Laser Mapping’s SiteMonitor analysis software, which tracks and compares displacement measurements over time, providing early warning of abnormal movement and therefore potential failures in the active mining area that may impact on production, cause damage to equipment or even injury to personnel.
“During the trial phase the SiteMonitor system was used to scan several unstable areas across an entire pitwall,” commented Gordon Sweby, principal geotechnical engineer. “Operating in continuous monitoring mode, data was streamed to the geotechnical office via a wireless LAN. The next phase of the project will be to integrate the system within mine operations, realizing the potential already identified and turning the system into an effective tool to aid safe mining.”
Meanwhile, gold producer AngloGold Ashanti has selected a Riegl LPM-2K long-range laser scanner, which can capture up to four point measurements per second, to an accuracy of 50 mm and at a range of up to 2,500 m, plus an integrated high-resolution digital camera. Used to improve safety at the Geita gold mine in Tanzania, the system, which also includes SiteMonitor software, is being used to continuously monitor an area of the mine that has been prone to failure, giving early warning of movements in the mine wall allowing managers to take preventative action.
“Before using this system we relied on conventional prism monitoring and Slope Stability Radar,” commented Sean Jefferys, chief mine surveyor. “Operating from a permanent, secure location and at a safe distance the laser scanning system gives us comprehensive, continuous monitoring of the active mining area for the duration of mining. The solution is reliable, economical and effective - improving the safety of personnel and equipment and minimizing the impact of failures on our operations.”
Sometimes the area of interest is inaccessible or unsuitable for a manually operated laser scanning system due to size restrictions, or where there is an element of risk from rock falls or ceiling collapse. To address these conditions the 3D-R1 remote operated survey vehicle was developed by 3D Laser Mapping in partnership with Jobling Purser RSV LLP from a prototype vehicle first designed by James Jobling-Purser as part of an undergraduate project at the Camborne School of Mines part of the University of Exeter.
3D-R1 is designed to be compatible with both the LMS-Z series of laser scanners and the new V-Line 3D scanners from Riegl; combining a high performance long-range 3D laser scanner, software and an integrated high-resolution digital camera with the latest in advanced robotic technology, the 3D-RI can be deployed in any environment where a risk to personnel may be present. 3D-RI has successfully completed a project to create a highly detailed and accurate 3D map of the San Jose silver mine in Mexico. The project to survey the mine was commissioned by Arian Silver Corp., who added the brownfield project to their portfolio.
“3D-R1 is extremely efficient, the speed of data capture is astonishing and the end results far exceed anything that can be produced by conventional surveying techniques,” commented Owain Morton, Arian’s mining engineer. “I estimate that you could employ a mine surveyor for a complete year and not get the same amount of data and accuracy of plans as delivered by the robot. The added advantage we experienced was the transference of existing GPS point data at surface to underground. The GPS points could be accurately represented in the underground workings and used to update the ‘antique’ surveying network that partially exists on site presently.”
Airborne laser technology is, however, suitable for other applications within the sector. For example, a Riegl LMS-Q240i unit is being used by ARKeX to improve the accuracy of their airborne geological mapping. ARKeX specializes in airborne gravity gradiometry, which measures very small variations in the earth’s gravitational field caused by density contrasts, as a result of sub-surface geology.
The major density contrast—between the surface of the earth and air above it—known as terrain correction needs to be removed if the sub-surface geology is to be accurately observed. By using airborne LiDAR (Light Detection and Ranging), ARKeX is able to accurately map the terrain that they fly over and use this highly detailed data to remove terrain correction. LiDAR data is therefore an essential component in processing airborne gravity gradiometer data and due to demand and the successful application of a Riegl Q240 two years ago, this is the second unit to be purchased from 3D Laser Mapping.
LiDAR can also be used for large area mapping projects. Although relatively costly to deploy and dependent on suitable weather conditions, an airborne LiDAR survey is advantageous when ground conditions are unsuitable for a static/fixed or mobile survey perhaps due to safety considerations or if the area is simply too large to complete within the project timescales.
Laser scanners will continue to be developed with longer range, faster data capture rates and improved accuracies, so their use within the mining industry is probably here to stay. What the industry needs to perhaps think about is how the data is used: Who looks at the laser scanner measurements or resulting models, how often and for what purpose? With the advent of “cloud computing” perhaps one way forward is remote monitoring. A Global Operations center has recently been launched in the UK, using the latest Web and laser mapping technology to remotely monitor mining operations as far afield as Africa, Australia and North America. With millions of measurements every minute from gold, platinum and diamond mines in South Africa, for example, 3D Laser Mapping’s technicians continuously monitor system performance and check the data for consistency. This proven technology could be also be applied at the client end; reducing the need for specialist staff onsite and delivering real savings in costs and resources.
Dr. Graham Hunter is managing director of 3D Laser Mapping Ltd., Nottingham, U.K., a developer of laser scanning solutions for mining, mapping, and other industrial applications.