SURVEYING INNOVATIONS INQUARRYING

White Paper

CONTENTS

1. INTRODUCTION 4

2. SURVEYING TECHNOLOGIES 5

2.1 Aerial Photography and

Photogrammetry 7

2.2 Aerial LiDAR 8

2.3 Total Stations and GPS 10

2.4 Laser Scanning 11

2.5 Unmanned Aerial Systems 12

2.6 Echo Sounders 14

2.7 Smartphone Apps 15

3. APPLICATIONS 17

3.1 Volumes 18

3.2 Mapping 19

3.3 Planning 21

3.4 Setting Out 22

3.5 Cadastral Surveys 23

3.6 Blasting Surveys 25

3.7 Plant Surveys 26

3.8 Monitoring Surveys 27

4. STOCKPILE VOLUME CALCULATION

RESEARCH 29

4.1 Accuracy 30

4.2 Time Spent on Your Site 33

4.3 Number of Sites per Day 35

4.4 Cost Comparison 37

5. CONCLUSION 39

4

Surveying has always been an essential component of successful quarrying in areas such as planning and monitoring.

In the past two main surveying approaches for quarry applications were used: ground surveys or aerial surveys using fixed wing aircraft. Today, there are many more options available along with a broader range of applications.

This paper will discuss three different aspects of surveying technology, namely the types of surveying technologies available for use in a quarry environment, the types of applications the surveying technologies are used for and comparative performance of different surveying technologies in measuring stockpile volumes.

1. INTRODUCTION

5

Presently there are many different types of technology that can provide survey solutions for quarry requirements including:

1. Aerial Photography and Photogrammetry

2. Aerial LiDAR

3. Total Stations and GPS

4. Laser Scanning

5. Unmanned Aerial Systems (drones)

6. Echo Sounders

7. Smartphone Apps

2. SURVEYING TECHNOLOGIES

SURVEYING HAS ALWAYS BEEN AN ESSENTIAL

COMPONENT OF SUCCESSFUL QUARRYING

Aerial photos may be vertical (straight down) or oblique (at an angle to the ground) and are usually captured from a fixed wing aircraft; however

helicopters may also be used. Aerial images may also be obtained from satellites. The earliest aerial photos were taken in the 1850s from kites and balloons and the first photos from an aeroplane for mapping purposes were taken in 1913.

Photogrammetry refers to the process of recording, interpreting and measuring from photographic images. The most common applications are for preparing topographic maps and the production of digital orthophotos.

Topographic maps allow for the determination of volumes and the calculation of changes in quantities. Three dimensional mapping requires stereo aerial photographs: vertical photos that overlap (usually by 60%) enabling two different views of the same ground features.

All photographs are prone to some distortion due to differences in the depth of field, lens distortions, atmospheric distortions etc. Orthophotos are photographs with all distortions removed and allow distances, angles, areas and positions to be measured directly from the photos. For accurate photogrammetry and orthophotos ground control points are required.

2.1 Aerial Photography and Photogrammetry

7

8

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

times how long it takes for the beam to return to the sensor. The information collected is the distance of each point measured to the sensor together with the intensity of the return signal.

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. The varying intensities of the return signal may also be used to determine clearances of power lines above vegetation and canopy heights.

Some forms of LiDAR may also be used to measure the earth’s surface under shallow water.

2.2 Aerial LiDAR

LIDAR CAN MEASURE THE ELEVATION OF

THE EARTH’S SURFACE UNDER TREES

10

Traditionally, land surveyors use total stations and GPS to measure points on the land or to mark out designs onto 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 also use lasers to measure distances without the needing a reflector.

Using trigonometry the 3D coordinates of the point measured is determined. Each point on a feature may also be assigned a code that describes the feature. For example toe of bank, edge of concrete. The data measured is

usually downloaded onto a computer in the office for processing and preparing plans in CAD. The accuracy of coordinates can be down to the mm level.

Survey grade GPS technology is accurate to around ±10mm horizontally and ±20mm vertically. Surveyors require a base GPS receiver and a rover GPS receiver both communicating with each other to cancel out the errors from the satellites to get an accurate measurement. GPS rover receivers may use publicly available base station networks by connecting over the internet. Each point measured is also assigned a feature code.

2.3 Total Stations and GPS

11

There are many different types of laser scanners: terrestrial, airborne, mobile and handheld. For each point, the scanner measures one slope

distance and a horizontal and vertical angle. The collection of the points measured is called a point cloud.

There are two main types of scanners used in surveying:

1. Time of flight and

2. Phase shift.

Time of flights scanners are also known as laser pulse scanners and use our knowledge of the speed of light to determine a range. They are long range scanners (up to several km) but are slower than pulse scanners. Time of flight scanners measure in the order of 50-100 thousand points per second.

Phase shift scanners compare the phase of the laser transmitted and received. These scanners are more precise and have higher speeds (up to one million points per second) but have a shorter range (50-300 metres).

Terrestrial laser scanners may be mobile or static. Static laser scanners measure points with 3D coordinates and intensity. Some scanners can also colourise the points to give them true colours. The scanner is set up on a tripod and it systematically sweeps the area of interest until it has a complete picture of the visible space. These scanners are particularly useful in preparing accurate 3D models of existing plant and infrastructure.

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.

2.4 Laser Scanning

12

Unmanned Aerial Systems (UAS) are Unmanned Aerial Vehicles (UAV’s) with sensors (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 (CASA) to fly a drone for commercial purposes. Drone Operators need a UAV Operators Certificate, Operations Manual, Flight Manual and Maintenance Manual.

CASA must give a specific Area Approval for the following:

• to fly above 120 meters (400 feet)

• inside controlled airspace

• within 4.8 km (3 miles) of an aerodrome

• over populated areas.

An area is a populated area if in the event of a fault in the UAV there would be an unreasonable risk to the life, safety or property of somebody who is in the area but is not connected with the operation.

Common uses for drones include preparing orthophotos and calculating approximate volumes.

2.5 Unmanned Aerial Systems

THERE ARE A NUMBER OF REGULATORY

REQUIREMENTS TO FLY A DRONE

14

Echo sounders are a type of sonar device. They transmit sound pulses into the water and time the interval between transmission and receipt of the sound from which the distance is determined.

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

2.6 Echo Sounders

15

Smartphone apps may use overlapping imagery combined with known dimensions of objects to determine approximate volumes or approximate

dimensions of features.

2.7 Smartphone Apps

SMARTPHONE APPS DETERMINE

APPROXIMATE VOLUMES

17

Surveys are required for many applications on a quarry site. These applications include:

1. Volumes

2. Mapping

3. Planning

4. Setting Out

5. Cadastral Surveys

6. Blasting Surveys

7. Plant Surveys

8. Monitoring Surveys

3. APPLICATIONS

18

Perhaps the most common surveying application in a quarry environment is volume determination. Volumes may be measured for royalty payment

purposes, resource planning, stripping volume determination, checks on dredging, dam capacity and stockpile volumes.

Many quarries request surveys at six monthly intervals to determine the volume of stockpiles. They request this information for auditing, stockpile management or valuation purposes.

Auditors can use the surveyed volume of the stockpiles to compare the tonnage of material going over the weighbridge compared to the tonnage of material being output from the plant, which may be determined using a conveyor belt scale or a weight belt feeder.

The difference between the tonnages shown at the weighbridge and at the plant should be contained in the stockpiles. From the surveyed stockpile volumes, a tonnage may be calculated using the specific gravity of the material.

Stockpile volumes may be measured by aerial photogrammetry, ground survey, laser scanning, drones and smart phones.

3.1 Volumes

19

Mapping of a site refers to measuring features on the Earth’s surface in 3D such as tops and toes of batters, changes in ground profile, spot heights,

benches and drainage patterns. Once these ground features are measured then a 3D model of the Earth’s surface can be prepared allowing for volume determination, engineering design, pit design, haul road design, haul road grade checking and drainage design.

Other features typically measured in mapping a quarry include man made features such as buildings, fixed plant, fences, roads, tracks, overhead power lines and vegetation.

Mapping of whole quarry sites is usually performed by aerial surveying but smaller areas may be mapped using ground survey or drones.

3.2 Mapping

MAPPING OF WHOLE QUARRY SITES IS

USUALLY PERFORMED BY AERIAL SURVEYING

21

An orthophoto (aerial photo with all distortions removed) may be used as a basis for preparing Safety Management, Traffic Management and Underground

Services plans.

To prepare an Underground Services plan a surveyor using either GPS or total station will measure the locations of underground services determined by an underground services locator or ground penetrating radar. These locations are then plotted on an orthophoto.

3.3 Planning

22

Any design may be set out on the ground using GPS or total station. Some examples include new fixed plant, haul roads, benches, stripping limits,

extraction limits, underground services, dredge limits, work authority boundaries and bench marks.

3.4 Setting Out

23

Cadastral surveys are surveys that relate to land title boundaries. The title boundaries may need to be defined and marked on the ground for fencing,

royalty volume calculations or placing structures near the boundaries. Easements may also need to be marked on the ground to ensure quarrying does not encroach.

Subdivisions of land and the creation and removal of easements are also examples of cadastral surveys. These surveys are undertaken using GPS or total stations and must be performed by a registered or licensed surveyor. Sometimes Work Authority boundaries are related to the title boundaries.

3.5 Cadastral Surveys

CADASTRAL SURVEYS RELATE TO

LAND TITLE BOUNDARIES

25

Blasting survey are undertaken prior to blasting. The rock face is measured in detail to determine actual burdens in front of each planned borehole to avoid

excessive burden (vibration, oversize) and insufficient burden causing flyrock or airblast. A blast hole layout and blast design plan can then be designed based on the surveyed rock face.

Static or mobile laser scanners are usually used to measure the face profile. The drill hole pattern may then be set-out using GPS or total stations. After drilling, the accuracy of the drill holes may be checked using inclinometers and the blast design may be amended if necessary.

3.6 Blasting Surveys

26

To enable the design of new fixed plant where it interfaces with existing plant an accurate survey of the existing plant is required.

If an accurate 3D model of the existing plant is prepared, it enables plant designers to design with confidence, ensuring the new design fits, determining the best installation methodology and helping minimize plant shut-downs. Laser scanners are the best tools for plant surveys.

3.7 Plant Surveys

27

Monitoring surveys are undertaken to measure the movement of objects over time. Typical examples are dam walls and rock faces.

Targets are usually installed in locations where movement is expected. These targets are measured weekly, monthly or yearly depending on the risk. Total stations and GPS are usually the best tools for this.

3.8 Monitoring Surveys

TOTAL STATIONS AND GPS ARE USUALLY

THE BEST TOOLS FOR MONITORING SURVEYS

29

On 19 June 2014 we measured stockpile volumes at a site in Brooklyn in Melbourne’s western suburbs. The purpose of this research was to

compare different methods of determining the volume of stockpiles. We used:

• Aerial photogrammetry

• GPS land survey

• Laser scanning

• Drone with a camera

We compared:

1. Accuracy

2. Time spent on site

3. Number of possible different sites to survey per day

4. Cost

The site chosen for the research was a small quarry and materials recycling facility. The size of the site was 220 metres by 500 metres. Stockpile sizes ranged from 35m³ to 29,000m³.

4. STOCKPILE VOLUME CALCULATION RESEARCH

30

Conventionally it is assumed by industry that a GPS ground survey is the most accurate.

On this site difference in total volumes between GPS and both the UAV and photogrammetry was much less than 1%. For common stockpiles with a total volume of 17,000m³ the differences were less than 15m³.

For both photogrammetry and the drone, individual larger stockpiles averaged accuracies of 2%.

Laser scanning had poor accuracy for this site. Either a mobile or static scanner can only measure what is in the line of site so dips, holes or valleys are not measured. For the common stockpiles measured the scanner gave a 12% greater volume than the other three methods.

4.1 Accuracy

High

Average

Low

GPSLand

Survey

MobileLaser

Scanning

Photo-gram-metry

Drone

ACCURACY

Volume Difference to GPS

Stockpile ID

GPS Laser Scanning

Photogram- metry

Drone Laser Scanning

Photogram- metry

Drone

m3 m3 m3 m3 % % %

1 4,349 5,367 4,460 4,426 23.4 2.5 1.8

2 9,346 10,050 9,172 9,298 7.5 -1.9 -5.1

8 121 n/a 130 n/a n/a 7.4 n/a

9 192 n/a 215 n/a n/a 11.9 n/a

25 2,962 n/a 2,980 2,760 n/a 0.6 -6.8

Weighted Average Variance (%) 12.8 0.1 0.0

33

The time spent on site is important for safety reasons. Obviously the less time surveyors are on site the better from both a safety point of view and to minimise

interruptions to your normal operations. GPS, laser scanning and drone surveys require site inductions.

To survey the stockpiles on the Brooklyn site the GPS survey would require three teams working all day.

Mobile laser scanners drive all around site interacting with mobile plant and other vehicles.

Drone survey also requires a lot of time on site: the operator needs to see the drone at all times. At the Brooklyn site the drone survey took about two hours plus two hours of surveying a dense ground control points grid. Drones require more ground control points than photogrammetry.

For this survey, photogrammetry required zero time on this site. The photo control points were placed five years previously external to site.

4.2 Time Spent on Your Site

100%

30%

GPSLand

Survey

MobileLaser

Scanning

Photo-gram-metry

Drone

TIME SPENT ON YOUR SITE

35

GPS, laser scanning and drone surveys require site inductions and travel time between sites and time spent on site carrying out the survey. This limits the

amount of sites that can be surveyed in one day.

Photogrammetry allows for surveying up to 12 sites per day, drone and mobile laser scanning surveys could complete two sites per day, however GPS surveys require multiple teams just to complete one site in a day.

The amount of time spent measuring stockpiles is also important because on some sites stockpile volumes can change rapidly. Photogrammetric surveys allow a snapshot to be taken of stockpiles and all volumes calculated for the same instant in time.

4.3 Number of Sites per Day

10

5

1

DroneGPSLand

Survey

MobileLaser

Scanning

Photo-gram-metry

NUMBER OF SITES PER DAY

37

We estimated the cost for measuring all 26 stockpiles at the Brooklyn site and for calculating volumes.

The GPS land survey estimate was based on extrapolating the five stockpiles measured.

Mobile laser scanning cost were estimated based on the equipment hire rates.

Photogrammetry costs were based on our current rates.

Drone costs include actual costs of flying plus extrapolation of the three stockpile volumes calculated.

4.4 Cost Comparison

$6,000

$4,500

GPSLand

Survey

MobileLaser

Scanning

Photo-gram-metry

Drone

$3,000

COST COMPARISON

39

This paper has discussed some of the surveying technologies available on a quarry site and some of the different applications of surveying technologies for a quarry business.

The paper also examined research undertaken by Landair Surveys on different methods to determine stockpile volumes. The research proved that drone surveys and photogrammetric surveys are just as accurate as GPS surveys. The research further showed that photogrammetry was the safest and most cost effective way to determine the volumes of stockpiles.

Technology can be fast, accurate and bright and shiny, but it is important to know what to do with the data produced, the limitations of the data and the most efficient way of satisfying requirements.

5. CONCLUSION

1300 130 158

info@landair.com.au

www.landair.com.au