Environmental News

Surveying innovations in quarrying

This article discusses the different types of surveying technologies available for use in a quarry environment, and will then highlight the types of applications the surveying technologies are used for.

There are many different types of technology that can provide surveying solutions for quarry requirements:

  • Aerial photography and photogrammetry.
  • Aerial LiDAR.
  • Land surveying using total stations and GPS.
  • Laser scanning – mobile and static.
  • Unmanned aerial systems (drones).
  • Echo sounders.
  • Smart phone apps.

Aerial photos may be vertical (straight down) or oblique (at an angle to the ground) and are usually captured from a fixed wing aircraft, but helicopters or even satellites may also be used to obtain images.

Photogrammetry refers to the process of recording, interpreting and measuring from photographic images. The most common applications of photogrammetry are preparation of three-dimensional (3D) topographic maps and production of digital orthophotos.

Stereo aerial photos are produced by overlapping vertical photos (usually by 60 per cent), which enables two different views of the same ground features and the 3D mapping.

All photographs are prone to some distortion due to differences in the depth of field, lens and atmospheric distortions, etc. Orthophotos are photographs with all distortions removed; distances, angles, areas and positions can be measured directly from the photos.

For accurate photogrammetry and orthophotos, ground control points are required.

Photogrammetry is used for stockpile volume calculations, royalty volume calculations, quarry planning, resource volume calculations, stripping volumes, 3D modelling and quarry mapping. Orthophotos are used for traffic management plans, safety plans and quarry planning.

AERIAL LiDAR {{image2-A:R-w:220}}LiDAR stands for light detection and ranging. Essentially the LiDAR scanner is mounted on an aircraft and it shoots out laser beams towards the earth and measures how long it takes for the beam to return to the sensor. By combining this information with the position and orientation of the scanner, an accurate and detailed model of the earth’s surface may be obtained.

LiDAR can penetrate vegetation and so can measure the elevation of the earth’s surface under trees.

Some forms of LiDAR may also be used to measure the earth’s surface under shallow water. LiDAR is mainly used for 3D modelling.

Land surveyors use total stations and GPS to measure points on the land or to mark out designs on the earth.

Total stations measure horizontal and vertical angles and distances, and store this information electronically. Distances are measured by shooting infrared waves from the total station to a prism or reflector. Modern instruments use lasers to measure distances without the need for a reflector and can also operate in robotic mode, where the total station automatically “follows” the surveyor.

Using trigonometry the 3D co-ordinates of the point measured is determined. The accuracy of co-ordinates can be down to the millimetre level.

Survey grade GPS technology is accurate to about 10mm horizontally and 20mm vertically. To achieve this level of accuracy, surveyors use GPS base stations and GPS rovers.

A base station receives GPS signals from satellites and sends the information wirelessly to a GPS rover that compares the data received directly from the satellite and the base station, to cancel out the errors from the satellite. GPS rovers may also connect to the internet to use data from publically available networks of base stations.

Typical quarry applications are for stockpile volumes, stripping volumes, marking boundaries for extraction limits, leases, titles and works, setting out new plant and haul roads, measuring boreholes and detail surveys for design purposes.

Laser scanners collect points on objects by measuring one slope distance and a horizontal and vertical angle to each point. The collection of the points measured is called a point cloud.

Some scanners are long range (up to several kilometres) but are slower, measuring between 50,000 and 100,000 points per second. Other scanners are more precise and have higher speeds (up to one million points per second) but have a shorter range (50m to 300m).

Static laser scanners are particularly useful in preparing accurate 3D models of existing plant, infrastructure and quarry faces.
Mobile laser scanners are usually mounted on a vehicle and use GPS and inertial measurement units to control the location of the scanner. These scanners are commonly used for earthworks volumes and for mapping.

Unmanned aerial systems (UAS) are unmanned aerial vehicles (UAVs) with sensors. These vehicles are commonly called drones.

The sensors the drones carry may include cameras, GPS, LiDAR and others. There are a number of regulatory requirements from the Civil Aviation Safety Authority to fly a drone for commercial purposes. Drone operators need a UAV operator’s certificate, operations manual, flight manual and maintenance manual.

Common uses for drones include preparing orthophotos and calculating volumes.

Echo sounders transmit sound pulses into water. By measuring the interval between transmission and receipt of the sound they determine the distance.

Bathymetric surveys determine the depth of dam, lake, river and ocean floors. Dual frequency echo sounders may also be used to determine the thickness of sediment on dam or lake floors.

In a quarry environment bathymetric surveys are used for calculation of royalty volumes and determining dam capacity.

Smart phone apps may use overlapping imagery combined with known dimensions of objects to determine approximate volumes or dimensions of features.

There are many different surveying technologies available for applications in the quarry industry but technology alone is not the only factor to consider when looking for the right surveying solution.

Other factors to consider include experience of the provider, turnaround time, quality of data, accuracy and cost. 

Erik Birzulis is managing director of land, engineering and aerial surveying services firm Landair Surveys. He is presenting a paper on surveying technology at CMIC14, Brisbane, on 4 September, 2014.

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