drones

Review
A Comprehensive Review of Applications of Drone
Technology in the Mining Industry
Javad Shahmoradi 1 , Elaheh Talebi 2 , Pedram Roghanchi 1 and Mostafa Hassanalian 3, *
1 Department of Mineral Engineering, New Mexico Tech, Socorro, NM 87801, USA;
javad.shahmoradi@student.nmt.edu (J.S.); pedram.roghanchi@nmt.edu (P.R.)
2 Department of Mining Engineering, University of Utah, Salt Lake City, UT 84112, USA;
elaheh.talebi@utah.edu
3 Department of Mechanical Engineering, New Mexico Tech, Socorro, NM 87801, USA
* Correspondence: mostafa.hassanalian@nmt.edu




Received: 4 June 2020; Accepted: 13 July 2020; Published: 15 July 2020


Abstract: This paper aims to provide a comprehensive review of the current state of drone technology
and its applications in the mining industry. The mining industry has shown increased interest
in the use of drones for routine operations. These applications include 3D mapping of the mine
environment, ore control, rock discontinuities mapping, postblast rock fragmentation measurements,
and tailing stability monitoring, to name a few. The article offers a review of drone types, specifications,
and applications of commercially available drones for mining applications. Finally, the research needs
for the design and implementation of drones for underground mining applications are discussed.

Keywords: drones; remote sensing; surface mining; underground mining; abandoned mining

1. Introduction
Drones, including unmanned air vehicles (UAVs) and micro air vehicles (MAVs), have been used
for a variety of civilian and military applications and missions. These unmanned flying systems are
able to carry different sensors based on the type of their missions, such as acoustic, visual, chemical,
and biological sensors. To enhance the performance and efficiency of drones, researchers have focused
on the design optimization of drones that has resulted in the development and fabrication of various
types of aerial vehicles with diverse capabilities.
The use of aerial vehicles for industrial applications goes back to the 19th century. In 1860, balloons
were used to take pictures for remote sensing purposes [1]. In 1903, pigeons carrying a breast-mounted
aerial camera were used for photography [2]. Around the beginnings of World War I, aerial torpedoes,
which are known as the origin of drones, were developed [3,4]. In recent years, attention to research and
development of unmanned aerial vehicles has been growing by academic and industry communities
worldwide [5,6].
Depending on the defined mission, drones are generally classified widely based upon their
configurations [6]. Drones can be grouped into nine categories, such as fixed-wing, flapping wing,
rotary-wing, tilt-rotor, ducted fan, helicopter, ornithopter, and unconventional types [6].
Drones have a variety of capabilities for both military and civilian utilization [6–10].
These capabilities, along with the demand for unmanned technologies, has resulted in the integration
of drones into civil practices [11]. Toward this end, new unmanned aerial vehicles are being developed
that can perform various missions in a variety of environments [11,12]. For example, drones are
utilized in a vast range of civilian applications such as search and rescue, surveillance, firefighting,
weather monitoring, surveying [13], power infrastructure monitoring [14], and urban planning
and management [15]. Drones have also been used for building environment monitoring [13] and

Drones 2020, 4, 34; doi:10.3390/drones4030034 www.mdpi.com/journal/drones

Drones 2020, 4, 34 2 of 25

urban traffic monitoring [16,17], ecological and environmental monitoring [18], species distribution
modeling [19], population ecology [19], and ecological monitoring and conservation [20]. Archeology
and cultural heritage [21], human and social understanding [22,23], personal and business drones
for photography and videography, and even delivery services [13] are other applications of drones.
In addition, the unmanned aerial systems have been successfully used in different industries, such as
agriculture [24], oil, and gas [25], construction [26], environmental protection [27], mining [18], etc.
Recently the mining industry has shown increased interest in the use of drones for routine
operations in surface and underground mines [28–33]. This study aims to conduct a review of the
application of drone technology in the mining industry. For this purpose, previous studies and
information from the companies that provided drones for mining industries are explored. In this paper,
the applications of drones in surface and underground mines are reviewed. Applications of drones in
surface and underground abandoned mines are also highlighted. Furthermore, the commonly used
sensors on mining drones are presented. The challenges in using drone technology in underground
mines and potential solutions to those barriers are discussed.

2. Drone Technology Applications in the Mining Industry

There are two main advantages of using drones in mining operations [28]. First, drones equipped
with different types of sensors can conduct a quick inspection of an area, either in an emergency
situation or hazard identification. Second, inspection and unblocking of blocked box-holes and
ore-passes can be done using drones. Drones can also be used for blockage inspection, explosive,
and package delivery. Lee and Choi categorized the applications of drones in the mining industry,
including surface, underground, and abandoned mines, as demonstrated in Table 1 [18].

Table 1. The applications in mining [18].

Surface Mine Underground Mines Abandoned Mines

• Mine operation
• Subsidence monitoring
• 3D mapping • Geotechnical characterization
• Recultivation
• Slope stability • Rock size distribution
• Landscape mapping
• Mine safety • Gas detection
• Gas storage detection
• Construction monitoring • Mine rescue mission
• Acid drainage monitoring
• Facility management

3. Applications of Drones in Surface Mining

Generally, mines are located in vast and remote mountainous areas. This makes the monitoring of
mines and associated infrastructures a challenging task requiring extensive manpower [23]. Therefore,
monitoring mines by traditional methods are time and cost consuming [34]. Appropriately, drones
can be beneficial in monitoring, surveying, and mapping of mines’ environment [23]. Drones can be
applied to monitor activities in the mines and topography changes of the mining area, which can lead
to a guideline for mine planning and safety [23].
For example, in [23], a drone equipped with a hyperspectral frame camera was used to monitor
the safety of the production pit [23,35]. In open-pit mines, optimization of slope angle has an important
role in production cost reduction, mine efficiency, and recycling resources [36,37]. Tong et al. used
integration of terrestrial laser scanning and drone photogrammetry to investigate slope zones by
monitoring point displacement and 3D mapping of open-pit slope zones. They also did monitoring for
mine inventory and changes in mine area [23,37].
One of the main challenges in the mining industry is collecting geotechnical data from difficult
or impossible to access regions [38]. In addition, mapping discontinuity for slope stability could
be done by terrestrial LiDAR methodology. However, “shadow zones” or gap in data is repeatedly
produced, due to the small scan angle of LiDAR technology [38,39]. However, drones can be utilized
Drones 2020, 4, 34 3 of 25

to take photos and make measurements by using the analysis of overlapping photographs [39,40].
McLeod et al., in 2013, did an investigation in an open-pit mine to find the direction of discontinuity
on the surface of rock slope by using drones topographical survey [29].
Another challenge in the mining industry is mapping engineering geology of the site. Engineering
geology covers mapping outcrops, strikes, dips, features notation, and names that bring about the
characterization of the site [41]. Drones are able to take detailed images from outcrops [41–43]. Nevertheless,
most of the time, the results need to be checked by a human survey [41,44]. New algorithms in image
processing allow one to identify the type of rocks, strike, faults, and dips which decrease the manual
workload significantly [41,45–48].
One of the activities that is normally repeated in the mining industry is blasting. Blasting is always
involved with safety risks, which could be inspected by drones [33]. Important parameters in blasting
design are rock type, geology, topography, geometry, borehole location, etc. which can be controlled
by drones [49]. In addition, new low-cost data is available by using drones in blasting operations.
Medinac et al. used drones to analyze the rock block size before and after blasting [50]. In another case,
drones were put to work for monitoring dust particles after blasting operation in an open-pit mine [51].
Additionally, dust particle of mining activity and tailings has a significant environmental issue
on the neighboring environment of mine areas, which can be reduced by monitoring and controlling
the moisture of the mine and mine tailings [23]. In [52], thermal sensors are installed on drones to
capture changes in the spatial and temporal surface moisture content in iron mine tailings. However,
analyzing the relationship of moisture content and mine tailings managing could be helpful in mine
tailings management [23].
Adopting drones to the mining industry can ease automation by providing visual and various
types of sensing data. Considering excellent maneuverability and low-cost and maintenance [30],
drones can make a huge benefit to the mine by surveying large areas in a short period of time compared
to traditional methods that used the human workforce [53]. They can provide required data where
there are health and safety hazards like in slopes [51] or unstable cavities. Therefore, it makes mines a
safer workplace compare to the past.
In 2018, Rupprecht and Pieters proposed a drone to fly over the area for reopening of an old
abandoned mine in South Africa. The drone was financially evaluated, and its sensitivity and risk were
assessed. The used drone was able to take pictures of the whole targeted mine, which also included
images of damages and infrastructure [31].
In the University of Queensland, drone technology was used to investigate the characterization
of blasting plumes. Drones could measure blasting plumes with a concentration of 1 mg/m3
accuracy. The air quality sensor and autopilot data were integrated to produce an airborne particulates
characterization in time and space, which had not been accessed without using a drone. The challenging
part of this research was selecting a sensor for dust monitoring using drones [54].
In [29], a drone was used to measure fracture orientation in an open-pit mine. This research was
done in three main steps. First, the drone took pictures of the fractures. Second, three dimensional
(3D) point cloud (a set of the data point in the space is called point cloud) were produced by using
structure from motion (SFM) software. Third, an image processing algorithm was generated to estimate
fracture orientation in an open-pit mine. They used a multirotor drone, called Aeryon Scout, to carry a
100-gram camera for taking videos and images.
In 2013 the Aeryon Scout drone was used to obtain a three-dimensional point cloud of the surface
mine. In this research, the battery was installed on the top of the drone, and the payload was at
the bottom. For navigation system, the drone was equipped with GPS, sonar system for altitudes
higher than 2 to 4 meter, pressure altimeter for range altitude that sonar could not support accurately,
temperature sensor, a three-axial magnetometer, and a three-axis gyroscope. Collected data were
stored in internal storage to be downloaded after the ending the mission. The log file produced by this
drone includes the recorded altitude, speed, position (latitude and longitude), and camera orientation
Drones 2020, 4, 34 4 of 25

(pitch and yaw) [29]. The Aeryon Scout drone was connected to the base station by using a radio
modem with a range of 3 km.
In [30], a multihop emergency communication system was proposed to assist the miners and
rescue team in emergency situations and improve mining productivity. The idea was to use a drone as
a wireless communication framework, which was named SkyHelp, to monitor mining activity and
support search and rescue operations in deep open-pit mines. A simulation was carried out by using
MATLAB to assess the idea. Table 2 and Figure 1 summarize the characteristics of various types of
drones used in surface mines. Table 3 also shows the applications of drones in surface mining.

CommerCialized Drones for Surface Mining Applications

Besides the studies and tests carried out by researchers in the application of drones in mining
industries, there are some commercialized drones that have been applied by companies for surface
mining applications.
SenseFly (Switzerland, 2009): SneseFly is a commercial drone subsidiary of Parrot Group.
This company produces both the drone’s hardware and software for aerial data collection and analysis.
The general specification of Snesefly products is shown in Table 4. Applications of SenseFly drone are
inventory tracking (calculating stockpiles volumes, site surveying), traffic management (haul roads, loading
floors and stockpile location optimization, blast planning), water management (accurate management of
tailing dams, watersheds, drainage basins assessment and mapping the potential flow of water base on-site
current topography), collaboration (improving operational planning, depletion accounting, monitoring
environmental factors and making the decision on required maintenance work) [37,38].
Drone Deploy (USA, 2011): The company is a cloud software platform for commercial drones,
which is especially compatible with DJI drones. This company provides software for aerial data
analysis by drones for a variety of industries, including mining. The software is able to make 3D
modeling of the area, contour line map, offline mine inspection, and stockpiles volume calculation.
It has been claimed that Drone Deploy customers have mapped and analyzed more than 30 million
acres in over 160 countries [39,40].

Table 2. Characterization of the used drone in surface mining [28–31,35].

Type Wingspan Length Endurance Payload

Model Goal Weight (g)
of Drone (mm) (mm) (min) (g)
Characterization
Fixed-wing Teklite of blasting 900 575 900–950 45 200
plumes
Characterization
Fixed-wing GoSurv of blasting 850 350 900–1200 50 >300
plumes
Characterization
Swamp
Fixed-wing of blasting 1800 1000 4500 40 1000
Fox
plumes
Characterization
Multirotor Quadcopter of blasting - - 2500 20 150
plumes
Phantom 2 Topographic
Multirotor 35 cm - 1240 25 -
Vision+ Survey
Measuring
Aeryon
Multirotor fracture 80×80×20 - 1300 25 400
Scout
orientations
 Multiroto Aeryon Measuring 80×80×2 - 1300 25 400
r Scout fracture 0
orientations
Drones 2020, 4, 34 5 of 25

Figure 1. Views
Views of
of the
the some
some utilized
utilized drones
drones in
in surface
surface mining
mining (a)
(a) Teklite
Teklite [35], (b) GoSurv
GoSurv [35],
[35], (c)
Swamp Fox [35], (d) Quadcopter [35], (e) Phantom 2 Vision+ [36], (f) Aeryon Scout [29].

Table 3. Applications of drones in surface mining [18].

Applications Objectives

 Slump prediction, stability monitoring

 Erosion detection
 Asset location
Safety and risk management  Damage assessment
 Incident monitoring
 Livestock location

 Regular safety site survey

Daily routines and control  Management planning
 Security and asset protection

 Regular safety site survey

Daily routines and control  Management planning
 Security and asset protection

 Mapping inaccessible areas

Monthly routines  Boundary management

 Pit and leach pad design

 Road design
Strategic planning  Slope assessment
 Mineral exploration

 Stockpile volumetric calculation

Financial  Mobile and static resources calculation

 Boundary dispute data

Legal  Incident data capture

 Water leakage detection

Environmental  Vegetation encroachment
 Tailings management and assessment

 Track and access condition

 Watershed, drainage, hydrology
Infrastructure  Pipeline inspection
 Leach pad construction, change, and erosion
Drones 2020, 4, 34 6 of 25

Kespry (USA, 2013): Kespry Company produces both drone’s hardware and software for
application in the mining industry. The drone properties of the Kespry Company are shown in Table 4.
The services for the mining industry by Kespry Company include managing waste-rock and ore
stockpile inventories, generating cut-and-fill reports for dragline operations, evaluating slope stability
on active high-walls, reclamation planning, and verification of blasting pattern locations. The Kespry 2s
drone delivers images with the 0.5 cm per pixel resolution. Because of the low flight time of multirotor,
Kespry added the ability of field swappable battery on the drone. The obstacle avoidance of this drone
is about (50 m) forward-facing by LiDAR sensor [41,42].
Propeller Aero (Australia, 2014): Propeller Aero produces software for aerial data analysis and
uses customized DJI’s Phantom 4 Pro (P4P) drone for aerial data collection. The properties of the DJI
drones used by Propeller Aero are shown in Table 4. The Propeller Aero package provides a variety
of services for the mining industry including: track the status of the mine, volume measurement
tools for stockpile and pit volumes, plan blasting and extraction, monitor protected areas and avoid
environmental fines, track progress against design, safety inspection, and keeping the haul road grades
consistent. The Phantom 4 RTK is able to capture high-quality images with (2.1 cm) total vector
distortion. The propeller drone shows the accuracy at or below (3 cm) by using multiple independent
checkpoints over the site [43,44].
QuestUAV (United Kingdom, 2012): QuestUAV produces software for aerial data analysis and
uses fixed-wing drones for aerial data collection. QuestUAV drone properties are shown in Table 4.
These drones assist in a mining operation in a verity of disciplines (see Table 3). The drone has an
accuracy of 3.2 cm over areas. Because of difficulty landing fixed-wing drones, a parachute is deployed
by QuestUAV for a safe landing. In addition, launching is available by hand, designed air dock, or zip
line. In addition, QuestUAV drones allow a series of payloads to be attached to the drone [45].
Skycatch (USA, 2013): Skycatch uses a multirotor drone for aerial data collection, a site base station
which uses GPS and GNSS for accuracy in coordinates collection, and software for data management.
Explore-1 drone is designed by Skycatch base on DJI Matrice M100 drone and manufactured by DJI
Company. The general properties of Explore-1 drone are shown in Table 4. Komatsu Company tried to
make the earthwork machine autonomous with Skycatch drone data. They used machine learning and
deep learning to find patterns and improve data outputs [46,47].
Prioria (USA, 2003): Prioria was one of the first companies that has provided aerial data for the
mining industry. This company produces both drone hardware for aerial data collection and software
for data analysis. The general properties of Prioria products are shown in Table 4. These products
perform aerial imagery, mapping, stockpile volume calculation, and inspections like pipeline and
utility. The fixed-wing drones of this company are hand-launched and tube-launched. The precision of
vertical volume calculation is 4 cm and for ground sampling distance it is 1.4 cm [48,49].
3D Robotics (USA, 2009): 3D Robotics produces software for aerial data analysis, which is
compatible with Yuneec and DJI drones. The general specification of 3D Robotics drones is shown in
Table 4. The available services by 3D Robotics aerial scan are geo-referenced maps and point clouds
for mineral exploration, calculating the volumes of individual stockpiles, tracking inventory over
time by calculating the volumes of individual stockpiles in every flight, improving site planning
and coordination by pre- and postblast surveys, mitigating project risk and remote access to mine
information by having near real-time drone and maps and data [50,51].
Trimble (USA, 1978): Trimble Company provides positioning technologies for a variety of
industries, such as land survey, construction, agriculture, transportation, telecommunications, asset
tracking, mapping, utilities, mobile resource management, and government. However, recently,
this company applied drone technology for aerial data collection and analysis. The specifications
of the multirotor drones of this company are shown in Table 4. The Trimble drones can provide
boundary and topographic surveys, survey-grade mapping, power line modeling, field leveling,
site, and route planning, progress monitoring, as-built surveys, resource mapping, disaster analyses,
Drones 2020, 4, 34 7 of 25

volume determinations, topographic contours, 3D surface models, and orthophotographs for mining
industry [52,53].
Precision-hawk (USA, 2011): Precision-hawk offers software for aerial data analysis and uses other
company’s drones for aerial data collection. The specifics of DJI multirotor drones and birds-eye-view
fixed-wing drone, which is used by Precision-hawk Company, are shown in Table 4. The software of
this company provides the volume measurement tools for the pit, stockpile, and similar structure for
the mining industry. In addition, outputs of the software could be useful in monitoring, planning,
reports, safety and compliance, oversight, and reclamation. This company uses various kinds of
sensors on the drones for aerial data collection. Sensors, such as thermal for tracking the relative
temperature of the land and objects, multispectral for capturing near-infrared radiation and ultraviolet
light which is invisible to human eyes, hyperspectral for identifying minerals, vegetation and other
materials, LiDAR for collecting high-quality evaluation of natural and human-made objects, visual for
capturing high-resolution aerial images, and video for live streaming and capturing video to on the
ground devices can be integrated into the drones [54,55].
Pix4d (Switzerland, 2011): Pix4d uses images taken by drones, hand, or plane for data analysis
by using the photogrammetry method. The software of this company is compatible with a variety
of drone company products including DJI, Parrot, and 3DR. The services for the mining industry by
Pix4d Software Company are as follows: (1) supporting blasting operations by locating boreholes,
(2) monitoring blast sites without putting people in danger, (3) measuring stockpile volumes and
excavated materials, (4) Pit mapping, and (5) toxic tailing dam mapping. It has been claimed that drone
mapping could be performed in 20% of the traditional mapping method time, without disrupting
traffic [56,57].
Microdrones (Germany, 2011): Microdrones produces both drones hardware and software for
aerial data collection and analysis. The specification of the microdrone is shown in Table 4. The package
of drones and software is able to map the deposit site, survey mine, explore minerals, monitor
stockpile volume, track equipment, and make time-lapse photography. In addition, sensors like
multispectral, thermal, LiDAR, and methane gas detection could be added to the drone for inspection.
The drone positioning is carried out by GPS, and the postprocessing of the data method is aerial
triangulation [56,57].
Delair (France, 2011): This company creates both software and drone hardware for aerial data
analysis and collection. The package of software and drone of this company can provide stockpile
volume, contour maps of the pit, finding potential hazards, detecting anomalies and doing the
topography survey in the field without interrupting operation. Freeport-McMoRan, one of the largest
American copper and gold mining company, used the DT18 Mapper drone package of Delair Company
to do weekly topographical surveys for calculating the production capacity and creating digital surface
models of the copper mine at Tenke Fungurume (TFM) in the Katanga Province of the Democratic
Republic of Congo [58,59].
Table 4 and Figure 2 show the general specifications of commercial drones, including drone
type, size, weight, endurance, payload, speed, wind speed resistance, and model name for use in the
mining industry.
 Fixed-wing UX11 Delair 1100 1400 59 - 15
Fixed-wing DT18 HD Delair 1800 2000 120 - 17
DT26X
Fixed-wing Delair 3300 17000 110 - 17
LiDAR
Quadcopter
Drones 2020, 4, 34 ELIOS Flyability 400 700 10 - 6.5 8 of 25
Quadcopter ELIOS2 Flyability 400 550 10 - 4.68

2. Views
FigureFigure 2. Viewsof of
thethecommercialized
commercialized drones dronesfor forsurface
surface mining
mining applications;
applications; (a) eBee-X
(a) eBee-X [38], (b) [38],
(b) eBeeSQ [38], (c)
eBeeSQ[38], (c)eBee-Classic
eBee-Classic [38], (d)Kespry
[38], (d) Kespry2s2s[42],
[42],(e)(e) DJI
DJI Mavic
Mavic 2 [36],
2 [36], (f) DJI
(f) DJI Phantom
Phantom 4 Pro4 [36],
Pro [36],
(g) DATAhawk
(g) DATAhawk [60],[60],
(h) Q-200
(h) Q-200Surveyor [60], (i)
Surveyor[60], Explore-1[47],
(i) Explore-1 [47],
(j) (j) Leviathan
Leviathan [49],[49], (k) Maveric
(k) Maveric[49], (l) [49],
(l) HexHex
[49], (m)(m)
[49], Yuneec
Yuneec3DR3DRH520-G
H520-G [51],
[51], (n) DJI
DJI Inspire
Inspire22[36],
[36],(o)(o)
DJIDJI Matrice
Matrice 200200 [36],[36], (p) UX5
(p) UX5 HP –HP –
TrimbleTrimble [53],
[53], (q) (q) UX5-Trimble
UX5-Trimble [53],[53], (r) ZX5-Trimble
(r) ZX5-Trimble [53],
[53], (s) (s) FIREFLY6
FIREFLY6 PROPRO [55],(t)(t)DJI
[55], DJIMATRICE
MATRICE210 210 [36],
[36], (u) MATRICE
(u) MATRICE 600 PRO 600 [36],PRO[36], (v) md4–200
(v) md4–200 [62],md4–1000
[62], (w) (w) md4–1000 [62],[62], (x) md4–3000
(x) md4–3000 [62],(y)
[62], (y)UX11
UX11 [59],
[59],HD
(z) DT18 (z) DT18 HD [59],
[59], (aa) DT26X (aa)LiDAR
DT26X LiDAR
[59]. [59].

4. Application of Arones in Underground Mines

Table 4. General specifications of commercial drones for use in the mining industry [38,40,42,44,47,49,51,
Despite advancements in drone technology, the use of drones in underground mines has been
53,55,57,59–61].
limited [63]. This is because the application of drones in underground mines is challenging. Harsh
underground Typeenvironments pose many obstacles Wingspanto flying drones. ConfinedPayload
Endurance space, reduced
Speed visibility,
Model Company Weight (g)
of Drone
air velocity, (mm)
dust concentration, and lack of wireless communication (min) system(g)make it (m/s)
a difficult task
Fixed-wing eBee X Sensefly 1160 1400 90 - 11–30
for an operator to
Fixed-wing
fly a drone
eBee SQ
in underground
Sensefly
working
960
areas.
1100
Furthermore,
55
access
-
to unreachable
11–30
and
dangerous locations in
Fixed-wing eBeeunderground
Classic mines is1100
Sensefly practically690impossible50 for a drone
- operator
11–25[63].
Quadcopter Kespry 2s Kespry - 2000 30 -
Drones in underground
DJI Mavic 2
mines have numerous
Kespry, 3D
potential applications in health and -safety. These
Quadcopter 350 907 30 - 20
applications include surface Pro roughness
Roboticsmapping, rock mass stability analysis, ventilation modeling,
Propeller
hazardous gas detection,
Quadcopter
and 4leakage
DJI Phantom monitoring
Aero, 3D 350
[32,63–68].
1388 30 - 20
Pro
Robotics
Q-200
4.1. Geotechnical
Fixed-wingCharacterization of Underground
QuestUAV 1950Mines 4600 60 590 -
Surveyor
Fixed-wing datahawk QuestUAV 1164 2150 45 - 19
Rock mass data collections
Quadcopter Explore-1 in underground
Skycatch 650 opening3600usually 17
require the- inspector(s)
17 to survey
the rock Fixed-wing
mass physically. The presence
Leviathan Prioriaof the personnel
2590 in unsupported
5897 90 areas907
such as open- stope and
Fixed-wing Maveric Prioria 749 1179 45–90 - 13.5
newly blasted working
Hexacopter faces
Hex endangers
Prioria the safety
800 of the
6350 personnel
15 [69]. Drones
- are tools
6.2 that are
more suitable to
Hexacopter be used in
Yuneec 3DR underground
3D mines- during the
1645 monitoring
28 of unreachable
- 13.5areas. Small
Robotics
size andQuadcopter
maneuverability of
DJI M200 drones allow them
Precision-hawk 643 to access hard-to-reach
6140 13–24 areas in
1610 underground
23 mines
3D
Quadcopter DJI Inspire 2 427 4250 32–27 - 26
Robotics
Hexacopter Trimble ZX5 Trimble 850 5000 20 2300 9
Fixed-wing Trimble UX5 Trimble 1000 2500 50 - 22
Trimble
Fixed-wing Trimble UX5 1000 2900 35 - 24
(HP)
FIREFLY6
Fixed-wing Precision-hawk 1524 4500 50–59 700 15–18
PRO
Quadcopter DJI M210 Precision-hawk 643 4570 13–24 1570 24
Hexacopter MATRICE 600 Precision-hawk 1133 10000 18 5500 18
Quadcopter md4-200 Microdrones 540 800 25 250 8
Quadcopter md4-1000 Microdrones 1030 2650 45 1200 12
Quadcopter md4-3000 Microdrones 2052 6000 45 5000 20
Fixed-wing UX11 Delair 1100 1400 59 - 15
Fixed-wing DT18 HD Delair 1800 2000 120 - 17
Fixed-wing DT26X LiDAR Delair 3300 17000 110 - 17
Quadcopter ELIOS Flyability 400 700 10 - 6.5
Quadcopter ELIOS2 Flyability 400 550 10 - 4.68
Drones 2020, 4, 34 9 of 25

4. Application of Arones in Underground Mines

Despite advancements in drone technology, the use of drones in underground mines has been
limited [63]. This is because the application of drones in underground mines is challenging. Harsh
underground environments pose many obstacles to flying drones. Confined space, reduced visibility,
air velocity, dust concentration, and lack of wireless communication system make it a difficult task for
an operator to fly a drone in underground working areas. Furthermore, access to unreachable and
dangerous locations in underground mines is practically impossible for a drone operator [63].
Drones in underground mines have numerous potential applications in health and safety. These
applications include surface roughness mapping, rock mass stability analysis, ventilation modeling,
hazardous gas detection, and leakage monitoring [32,63–68].

4.1. Geotechnical Characterization of Underground Mines

Rock mass data collections in underground opening usually require the inspector(s) to survey the
rock mass physically. The presence of the personnel in unsupported areas such as open stope and
newly blasted working faces endangers the safety of the personnel [69]. Drones are tools that are
more suitable to be used in underground mines during the monitoring of unreachable areas. Small
size and maneuverability of drones allow them to access hard-to-reach areas in underground mines
without endangering the life of the miners. Imagery techniques such as photogrammetry and FLIR
(forward-looking infrared) allow characterizing rock masses. Photogrammetry can provide data for
generating geological models and structural data for kinematic and numerical analyses. In addition,
FLIR imagery can be used to recognize areas of loose rock, which normally remain unnoticed until it
becomes a hazard [69].

4.2. Rock Size Distribution Analysis in Underground Mines

The majority of underground hard rock mines use drilling and blasting methods for rock extraction.
Assessment of rock size distribution after blasting is an important measurement for next production
phases (i.e., loading and hauling) [70,71]. There are some methods for rock size distribution analysis,
including visual observation by an expert, sieve analysis, and image processing. Image analysis
methods are fast and relatively accurate for rock fragmentation measurements [71,72].

4.3. Gas Detection in Underground Coal Mines

A set of sensors to continuously measure atmospheric parameters and gas concentration will
enable a drone to be used for hazardous gas detection in underground mines. Lucila and Masami
used an unmanned aerial vehicle for gas detection in underground coal mines [32]. In this research,
a gas sensor installed on a drone utilized as a safe and reliable surface measurement of coal fire gases
for assessing characteristics of underground coal fires. DJI S1000 Octocopter drone (specification in
Table 5) was used for carrying gas sensors. With the combination of this drone and sensor, they could
achieve 10 to 15 minutes flight time [32].

4.4. Mine Rescue Mission in Underground Mines

Hoffman and McAllister, in 2018, proposed using an Unmanned Ground Vehicle (UGV) combined
with a drone to find the location of trapped workers [73]. The UGV scans the tunnel map during
the drive to the destination and provides a variety of information about the conditions of the tunnel.
The scenario is that the UGV, which would carry a drone onboard, drives to the location. Then, the drone
would launch at the appropriate location to assess the collapsed area and to find any gap through
the pile of rock or soil. The role of UGV is to carry the drone, scan the tunnel with a LiDAR sensor,
and dock the drone when the mission is completed or drone battery needs recharging [73]. They used
a Flame Wheel D JI’s F450 drone as a joint with UGV to carry sensors to the corners of the space that
UGV does not access to them. Quadcopter F450 is a multirotor drone designed by the DJI Company.
 Drones 2020, 4, x FOR PEER REVIEW 11 of 28
Drones 2020, 4, 34 10 of 25
underground mines
[65]
Its takeoff weight is 1600 grams, which is mentioned as a low payload for this kind of mission [73].
Table 5 summarizes
Quadcopt MATRICEthe characteristics of various types of drones in underground mines. Figure 3
Geotechnical data
showser the drones 100
that havecollection
been used 650 2431 23 1169 5
[66]in underground mines.
Quadcopt Underground void
F450 5. Characterization of the used 450
D JI'sTable drone in underground
- mining.
- -
er mapping [67]
Wingspan Endurance Payload Speed
Type of Drone Model Goal Weight (g)
Quadcopt Underground mine (mm) 800– (min) (g) (m/s)
D JI's F450 Monitoring inaccessible
450 33 -
er
Helium gas
Zeppelin
rescue
areas in an underground 1200 -
1600 - - -
balloon
mine [64]
Supporting backfilling
Gas detection of
Octocopter DJI S1000 underground
operations bycoal 1045 4.2 15 1800~6800 -
fire [32]
monitoring shadow
Reduce personnel
exposure to unsafe
Quadcopter DJI M210 643 4570 13–24 1570 12
areas, identifying
conditions of
underground mines [65]
Quadcopt MATRICE ground conditions
Geotechnical data in
Quadcopter ELIOS 650400 2431700 23 10 1169 - 5 6.5
100 collection [66]
er open stopes, void
Underground and
Quadcopter D JI’s F450 450 - - -
mapping [67]
inspecting
Underground
conveyor
Quadcopter D JI’s F450 450 800–1600 33 -
mine rescue
belts without
Supporting backfilling
operations by monitoring
interrupting operation
shadow areas, identifying
Quadcopter ELIOS [68]
ground conditions in
400 700 10 - 6.5
open stopes,
Quadcopt and inspecting conveyor
ELIOS2 Same as ELIOS
belts without interrupting 400 550 10 - 4.68
er operation [68]
Quadcopter ELIOS2 Same as ELIOS 400 550 10 - 4.68

Figure Commonly used

Figure3.3. Commonly used drones
dronesininunderground
undergroundmines
mines(a)(a)Zeppelin
Zeppelin[64],
[64],(b)(b)
DJIDJI M210
M210 [65],
[65], (c)
(c) ELIOS
ELIOS 1 [68],
1 [68], (d)(d) ELIOS
ELIOS 2 [68].
2 [68].

4.5. Common Sensing Methods for Drones in Underground Mining

4.5. Common Sensing Methods for Drones in Underground Mining
Many sensing technologies are used for underground mining applications, including the stereo
Many sensing technologies are used for underground mining applications, including the stereo
camera, ultrasonic sensors, dual redundant IMUs, and infrared sensors used by DJI [36,74]. Ultrasonic
camera, ultrasonic sensors, dual redundant IMUs, and infrared sensors used by DJI [36,74]. Ultrasonic
sensors are low-cost sensors for obstacle detection that have been tested by several studies. Other
sensors are low-cost sensors for obstacle detection that have been tested by several studies. Other
kinds of obstacle detector sensors that are repeatedly used by researchers include infrared sensors,
kinds of obstacle detector sensors that are repeatedly used by researchers include infrared sensors,
stereo cameras, and laser range finders (LRFs) [75–80].
stereo cameras, and laser range finders (LRFs) [75–80].
4.6. Challenges in Using Drones in Underground Mines
4.6. Challenges in Using Drones in Underground Mines
The nature of underground mine environments and other obstacles (e.g., surrounding walls, loose
The nature
bolt, cables, of underground
and equipment) mine
require the environments and other
drone to be collision obstacles
tolerant. (e.g.,the
Ideally, surrounding
drone shouldwalls,
be
loose bolt, cables, and equipment) require the drone to be collision tolerant. Ideally, the drone
able to detect and avoid obstacles during its flight in the indoor environment. Since the underground should
be able
mine sitesto
aredetect and expanding,
constantly avoid obstacles during area
the coverage its flight in the indoorincreases
of communication environment. Since the
as the operation
underground mine sites are constantly expanding, the coverage area of communication increases
continues [81], which creates a challenge for a drone to cover the entire mine during regular working as
operation as well as in emergencies [82].
Drones 2020, 4, 34 11 of 25

Due to the existence of obstacles in underground mines, the main problem of using drones is
signal propagation. There is a need for a radio signal connection between the drone and the remote
controller in order to fly the drone. The environment continually absorbs the signal’s energy. Therefore,
if a drone flies far in the underground environment, it will lose its signal, and consequently, it is not
able to return to the deployment point [83]. To solve this challenge, a transmission system can be
integrated into the drone. This is efficient enough to allow the drone to fly far away into the down
curved, underground passages and tunnels without loss of signal coverage. It also sends a constant
video stream of what the drone camera is recording [83].
The battery life limits the flying time of drones. In many circumstances, battery replacement
is required to extend the flying time. The weather situation in underground mines also can affect
battery life and safety [84,85]. There are drones that employ hybrid power systems (i.e., batteries plus
combustion engine) to perform longer-duration missions [86,87].
Additionally, humidity or water leakage damage the electronic components of the drones and
interfere with the communication between the drone and its controller [86,88]. The visibility of people
and objects in real-time is important to avoid accidents. However, there are many circumstances in
which visibility is not sufficient to proceed with a mission using a drone [63,89].

5. Application of Drone Technology in Abandoned Mines

The website of the Bureau of Land Management reports as of 2016, in the United States, tens of
thousands of abandoned mines have been registered [90]. The website also estimates that approximately
500,000 abandoned mines exist in the nation [90]. Abandoned mine lands (AMLs) pose environmental,
health, and safety threats to humans [90]. An example is the miners of Somerset, Pennsylvania,
who accidentally died by breaching an abandoned flooded mine. The miners were not aware of
the existence of the nearby abandoned mine [91,92]. Another example is the existence of “bord and
pillar” underground mines in Newcastle (NSW) and Ipswich (QLD) in Australia. The mines are now
abandoned and located beneath residential areas, which elevates the risk of ground subsidence [93].
Similarly, subsidence is being monitored for the abandoned gold mines in Nova Scotia and Ontario,
Canada and coal mines in Illinois and Ohio, USA [94].
Moreover, when a coal mine is abandoned, the methane emission is reduced but does not
completely stop. Abandoned mines can liberate methane at a near-steady rate for an extended period
of time. Flooding of the mines can inhibit gas emissions and buildups in the empty spaces; this would
also help to mitigate the danger level of working in active mines nearby [95,96]. Therefore, monitoring
and mapping abandoned mines are important to decrease the risk of environmental hazards. However,
monitoring of such vast areas with the traditional, labor-intensive, expensive monitoring methods
is challenging. Drone technology, as a financially efficient approach, can be an alternative solution.
Tables 6 and 7 summarize the applied drone’s missions in abandoned mines.

Table 6. Applications of drone technology in abandoned mines missions.

Mine Type Application Description

- Creating a subsidence inventory map
Surveying photogrammetry and
demonstrating the locations and details of
hazardous subsidence mapping
past subsidence occurrence [18,97–99].
- Creating a high-quality 3D digital
Surface Mines

Photogrammetry and filling elevation model (DEM) to calculate the

material calculation amount of required soil for the recultivation
of a closed mine [100,101].
- Creating a map and determining accurate
Anthropogenic formations of dimensions and volumes of anthropogenic
invasive plants on Abandoned landscape forms, such as landfills [102].
Mine Lands - Mapping of places where some invasive
plants exist [102].
- Creating a 3D train model of mine lake in
Rehabilitation order to rehabilitate the abandoned
mine [103,104].
Drones 2020, 4, 34 12 of 25

Table 6. Cont.

Mine Type Application Description

- Collecting data, communicating,
and mapping pillars in abandoned
Pillar mapping
underground mines when there is a risk of
Underground Mines deploying a crew [105–107].
- Creating a 3D virtual mine map from 3D
point cloud information of optical sensors
Detection of gas storage
to calculate the volume capacity for gas
storage in abandoned mines [95,96].
- Investigation and monitoring of acid mine
Monitoring acid mine drainage drainage from abandoned mines and
tailings to the water stream [108].
- Combination of the GPS data with the
digital photographs taken by the drone to
Mine shaft investigation
create orthorectified photography
maps [18,109–111].

Table 7. Characterization of the drones used in abandoned mines.

Type Endurance
Model Goal Where Wingspan (mm) Weight (g)
of Drone. (min)
Open-pit
Surveying limestone
Multirotor Phantom 2 Vision+ 3500 1240 25
photogrammetry mine in
Korea
Open-pit
Fixed-wing - Photogrammetry 1000–3000 2000–5000 -
mine
AeroVironment
Fixed-wing Rehabilitation Coal mine 1372 1906 60–90
RQ-11 Raven
SenseFly Mine shaft Coal mine in
Fixed-wing 116 1100–1400 -
swingletCAM investigation UK
Honeywell RQ-16
Multirotor Rehabilitation Coal mine - 8390 40
T-Hawk

6. Application of Drones in Search and Rescue Operations

Most of the mines are in a remote area where common, reliable communication systems may
not be available. Drones provide rapid solutions in support of communications coverage of rescue
operations [112,113]. Drones can provide disaster warnings and assist with accelerating rescue and
recovery operations when the communications networks are not serving anymore. Drones also have
the capability to carry medical supplies to hard-to-reach areas. In certain circumstances (e.g., poisonous
gas infiltration and searching for missing persons), drones can support the role of accelerating these
operations [114]. Table 8 shows a few examples of the application of drones in mine rescue missions.

Table 8. Examples of mining industry safety and rescue drone applications.

Company Mine site Application

- The thermal image camera of the drone detects heat arising
from the facilities in the dressing plant, such as the conveyor
Hexagon Coal mine belt system, to prepare for the problems due to the overheating
of the facilities. It can also quickly detect the self-ignition point
of the coal in the coal mine to monitor accidents [115].
- The drone technology helps to prevent the environmental
Abandoned mineshaft in an
Tir3D disruption caused due to mining by effectively investigating
exhausted mine
the location of the mineshaft of an exhausted mine [116].

7. Commonly Used Sensors on Mining Drones

Fast technological advancements in both passive and active sensors have empowered the capability
of drones in various types of missions [117,118]. Sensors on drones facilitate image capturing at
centimeter and spatial resolution and time-dependent resolution at temporal [117,119–122]. The sensors
on a drone depend on drone size and the mission. However, depending on the goal of the aerial
investigation and the lighting condition, various kinds of sensors need to be attached to the drone.
Drones 2020, 4, x FOR PEER REVIEW 14 of 28

Table 8. Examples of mining industry safety and rescue drone applications.

Compan
Drones 2020, 4, 34 13 of 25
Mine site Application
y
- The thermal
These include the RGB sensors, ultrasonic sensors,image camera
Infrared of the
Sensors (IR),drone
stereodetects heat
camera, arising
laser range
finders (LRFs), Ultra-Wideband Radarfrom the and
(UWB), facilities in the dressing
hyperspectral plant,
sensors. such
Figure as theexamples
4 shows conveyorof
commonly
Hexagonused sensors in drones in belt
Coal mine the mining
system, industry.
to prepare for the problems due to the overheating
of the facilities. It can also quickly detect the self-ignition point
7.1. Infrared Sensors (IR)
of the coal in the coal mine to monitor accidents [115].
Infrared Sensors (IR) are a kind of low-cost obstacle detector sensor. Infrared radiation can be
Abandoned - The drone technology helps to prevent the environmental
either detected or emitted by IR. Generally, all materials above absolute zero emit waves in the infrared
Tir3D Infrared
spectrum. mineshaft
sensors,in considered
an disruption
as heatcaused
sensors, due
cantodetect
mining thebyenergy
effectively investigating
radiation of objects.
exhausted mine the location of the mineshaft of an exhausted mine
Despite the limited resolution, infrared sensors have the ability to detect human [75,80,132]. On the [116].
one hand, it has the advantage of sensing through fog, smoke, day, and night. However, on the other
7. Commonly
hand, it can be Used Sensors
distorted on Mining
by flame and anyDrones
other high-temperature sources. Moreover, it does not work
well through thick dust [75,132].
Fast technological advancements in both passive and active sensors have empowered the
capability
7.2. of drones
Ultrasonic in various types of missions [117,118]. Sensors on drones facilitate image
Sensors (US)
capturing at centimeter and spatial resolution and time-dependent resolution at temporal [117,119–
122].Being inexpensive
The sensors and uncomplicated
on a drone depend on drone make
size ultrasonic sensorsHowever,
and the mission. viable fordepending
various applications.
on the goal
These sensors detect the obstacles by radiating high-frequency sound waves and collecting
of the aerial investigation and the lighting condition, various kinds of sensors need to be attached reflected
to
waves. The distance to the obstacles can be determined by considering the time-of-flight
the drone. These include the RGB sensors, ultrasonic sensors, Infrared Sensors (IR), stereo camera, technique.
An
laserultrasonic sensor
range finders is the
(LRFs), only commonRadar
Ultra-Wideband sensor in theand
(UWB), drone technologysensors.
hyperspectral that isFigure
not based on
4 shows
electromagnetic
examples of commonlywaves (EM).
used The disadvantage
sensors of the
in drones in the mining
ultrasonic sensor is detecting sound-absorbing
industry.
materials, like cloth, for example. Besides, it has a shorter range than another type of sensors [75,76,80].

Examplesofofcommonly
Figure 4. Examples commonlyused usedsensors
sensorsonon thethe mining
mining drones:
drones: (a) (a) infrared
infrared sensor
sensor [123],
[123], (b)
(b) ultrasonic
ultrasonic sensor
sensor [124],
[124], (c) RGB
(c) RGB camera
camera [125],
[125], (d) (d) stereo
stereo cameras
cameras [126],
[126], (e) (e) laser
laser range
range finders
finders [126],
[126], (f)
(f) ultra-wideband
ultra-wideband radar
radar (UWB)
(UWB) [127],(g)
[127], (g)hyperspectral
hyperspectralsensors
sensors[128],
[128],(h)
(h)magnetic
magnetic sensors
sensors [129], (i) gas
detector [130], (j)
detector[130], (j) visible
visible and
and near-infrared
near-infrared spectral range (VNIR) [131].

7.3. Red-Green-Blue (RGB) Sensors

7.1. Infrared Sensors (IR)
RGB camera can be used in surveying and mapping, stockpile volume calculation, road traffic
Infrared Sensors (IR) are a kind of low-cost obstacle detector sensor. Infrared radiation can be
monitoring, security monitoring, inspection, etc. RGB camera is a sensing system that takes RGB
either detected or emitted by IR. Generally, all materials above absolute zero emit waves in the
(Red Green Blue) images, including a per-pixel depth report. RGB cameras work with one of two active
stereos [133,134] or time-of-flight sensing to create depth evaluation at a huge number of pixels [133].
Drones 2020, 4, 34 14 of 25

Camera selection needs to be done carefully, considering the drone’s fuel consumption. Generally,
a compact camera is preferred for fixed-wing drones because heavy devices cannot be carried [18].

7.4. Stereo Cameras

The stereo camera is a kind of camera that is equipped with two or more lenses to create 3D
images, similar to the human visual system. Stereo cameras are able to develop three-dimensional
images by their separate image sensors. High resolution and accuracy in a clean environment are the
advantages of stereo cameras. However, it has poor performance in smoke, fog, or dust, because the
light waves are distorted in such conditions [80].

7.5. Laser Range Finders (LRFs)

Laser range finders (LRFs) are expensive sensors commonly used for obstacle detection in drone
technology. In LRFs, a laser beam is radiated to an obstacle, and by receiving a reflected wave and
considering time-of-flight, the distance to an object can be measured. As LRFs use optical wavelengths
of light, it is not suitable for conditions like fog, smoke, dust, or similar adverse conditions [80].

7.6. Ultra-Wideband Radar (UWB)

Obstacles detection by Ultra-Wideband Radar (UWB) is carried out by emitting electromagnetic
waves in the radio spectrum. Similar to US and LRFs, the distance to the target can be measured by
taking into account the reflected wave and times-of-flight. However, radar’s radio waves have a longer
wavelength than visible light and infrared. Therefore, radio waves have better penetration than visible
light in the dust, fog, smoke, and other adverse conditions [80,135].
Ultra-Wideband Radar (UWB) has some features that make it suitable for mining drones. First,
it has a more precise and higher image resolution compared to the ultrasonic sensors in harsh
environmental conditions like fog, smoke, dust, rain, snow, gas, and aerosols [77,80,132]. Second, UWB
uses low energy that is generally less than 1 Watt. This means drone battery power can be saved for
other utilities [80,136]. Third, regarding low spectral density, UWB has minimum interference with
other wireless uses like flight controller and telemetry link [80,136]. Fourth, UWB can detect different
characteristics like walls, edges, and corners. Finally, it can identify the three-dimensional coordinates
of the nearest object [137].

7.7. Hyperspectral Sensors

Recently, lightweight hyperspectral imaging (HSI) sensors are being developed for use on
drones [138–140]. Most of the multispectral imagers (Landsat, SPOT, and AVHRR) detect reflectance of
Earth’s surface material at several wide wavelength bands which are separated by spectral segments.
In other words, hyperspectral sensors assess reflected radiation as a series of narrow and contiguous
wavelength bands. Typically, bands are measured at 10 to 20 nm intervals by hyperspectral sensors [141].
These sensors can provide information that is not accessible by traditional methods. In general, this
kind of sensor is widely used in geology, mineral mapping, and exploration [140,142–145].

7.8. Magnetic Sensors

The magnetic sensors produce an accurate measurement of the magnetic field. Moreover, magnetic
sensors assess disturbances and changes in the magnetic field include flux, strength, and direction [146].
The normal weight of a Cesium magnetometer, such as the Scintrex CS-3Sl, is about 0.82 kg. It should
be noted that for deriving three-dimensional magnetic field gradients, there is a need for four
magnetometers. This means 3.28 kg would be the total weight of the Magnetic sensors. This kind of
sensor could be useful in mineral exploration [147].
Drones 2020, 4, 34 15 of 25

7.9. Visible and Near-Infrared Spectral Range (VNIR

VNIR sensors of the electromagnetic spectrum are usually preferred to be installed on drones due
to their small size and low weight. The wavelength at intervals of about 400 and 1400 nanometers (nm)
is called the visible and near-infrared (VNIR) portion of the electromagnetic spectrum [148]. This range
consists of the complete visible spectrum with an adjacent part of the infrared spectrum up to the water
absorption band at intervals 1400 and 1500 nm [149]. In addition, there are some definitions that cover
the short-wavelength infrared band from 1400 nm up to the water absorption band at 2500 nm [149].
These sensors could be used for surface moisture of open pits [150], tailing dams, underground spaces
wall, and surfaces. In addition, each particulate mineral has a special signature in VNIR spectra [151],
which is an advantage in mineral exploration by drones equipped with VNIR sensor.

7.10. Air Quality Sensors

On top of the aforementioned sensors, specific sensors (e.g., air quality, gas sensing, dust
monitoring, etc.) can be installed on a drone for a particular mission. Table 9 shows examples of
sensors that are used for air quality testing and gas detection. Typically, the air quality sensors are based
on optical, ultrasound, and electrochemical sensing elements [35]. These sensors could be handheld
personally, installed on the vehicle, or from ground-based network systems. Many of these sensors can be
installed on a drone depending on the type of contamination, release time, and measurement requirements.
For example, rotary-wings drones have been used to sense water vapor and CO2 , CH4 [152], ethanol and
CH4 [96,153], NO2 and NH3 [154,155], CO2 [154,156], SO2 [157]. Lega et al. visualized air pollutants in
3D and real-time by using a multirotor drone [158]. Moreover, different types of this platform were used
to identify sewage discharges along with Italy coastline by sensing gases include CO, C6 H6 , NO2 , O3 ,
SO2 , NOX, and PM10, besides thermal IR images [154,158,159]. At present, fixed-wing drones can stream
real-time monitoring as well as supplying indexed-linked samples [154,158].

Table 9. Examples of sensors used in mining, oil, and gas industries for sensing gas and dust [35].
Instrument Description Gases/Particles Characteristics
Handheld
Close-packed instrument for the O2 , Cl2 , CO, CO2 , H2 , H2 S,
Dimensions:
measurement of up to 6 gases; follow HCN, NH3 , NO, NO2 , PH3 ,
Dräger X-am 5600 4.7 × 13.0 × 4.4 cm
standard IP67; IR sensor for CO2 and SO2 , O3 , Amine, Odorant,
Weight: 250 g
electrochemical for other gases. COCl2 and organic vapors.
Installed in ground vehicles
Cavity ring-down spectroscopy
Dimensions: Analyzer
(CRDS) technology, sensitivity down
43.2 × 17.8 × 44.6 cm;
to parts-per-billion (ppb); survey gas
CO2 , CO, CH4 , external pump
Picarro Surveyor at traffic speeds and map results in
and water vapor 19 × 10.2 × 28.0 cm
real-time; real-time analysis to
Weight: 24 kg + vehicle
distinguish natural gas and other
Power: 100–240 VAC
biogenic sources.
Continuous particle monitoring.
The tapered element consists of a
Dimensions:
Tapered Element filter cartridge installed on the tip of
Total suspended particles 43.2 × 48.3 × 127.0 cm)
Oscillating a hollow glass tube. Additional
(TSP), PM10, PM2.5 Weight: 34 kg
Microbalance (TEOM) weight from particles that collect on
Power: 100–240 VAC
the filter changes the frequency at
which the tube oscillates.
Networks
Wireless monitor; high sensitivity Dimensions:
(levels to ppb); designed to work NO, NO2 , O3 , CO, SO2 , humidity 17.0 × 18.0 × 14.0 cm
AQMesh
through a network of and atmospheric pressure. Weight: <2 kg
arrayed monitors. Power: LiPo batteries
Airborne
LIDAR technology with a total Dimensions:
weight of 2.2 kg; 17.2 × 20.6 × 4.7 cm
Yellow scan Dust and aerosols
80,000 shots/s; resolution of 4 cm; Weight: 2.2 kg
class 1 laser at 905 nm. Power: 20 W
Drones 2020, 4, 34 16 of 25

8. Discussion

8.1. Challenges in Using Drones in the Mining Industry

In surface mines, weather conditions present a challenge by inducing deviations in drone’s
predesignated paths compared to underground mines. In some cases, weather conditions can be
damaging to the drones, leading to failure in their missions [113,160]. In the mining industry, as well as
other industries, energy consumption during a mission can impose many challenges. Normally, drones
run on battery and consume the energy for hovering, wireless connection, data, and image processing.
Due to the power restrictions as such, a decision needs to be made on whether data and image analysis
should be performed onboard in real-time or offline to reduce energy consumption [113,161,162].
In underground mines, confined space, heat and humidity, dusty air and poor lighting conditions
are the main issues that mineworkers generally face. Some concepts have been proposed for using
drones in underground mines, but usually are applying manual techniques for control and navigation.
At a minimum, the designed drone should be capable of fully autonomous navigation in a completely
GPS-denied environment and fly in an environment with no lighting other than that provided by the
drone. Nature of underground mine environments and other constraints (e.g., surrounding walls,
loose bolt, cables, and equipment) require the drone to be collision tolerant. Ideally, the drone should
be able to detect and avoid obstacles during its flight in the indoor environment. The drone should also
tolerate harsh underground mine environments and fly in heavy dust and smoke. Therefore, the drone
should be waterproof, dustproof, shockproof, and should resist pressure, temperature, and humidity
changes throughout the mine site. For underground coal mine applications, due to the presence of
methane and potential explosion/fire hazards, the battery and the electronic sensors must be insulated.
Adding to the above-mentioned requirements, the drone should provide other features, including low
power consumption and human body detection.

8.2. Suitable Drone Configuration for Underground Mining Applications

As mentioned above, there are some challenges in using drones in underground environments.
To this end, there is a need to design an optimized microdrone that can address all of these challenges.
The first step in designing a drone is configuration development. Considering an underground mine
environment, a drone with hovering capability can be designed. One of the types of microdrones is
multirotors, which allow them to fly in confined spaces. These drones, which can hover and have
high maneuverability due to rotary blades or propeller-based systems, are called rotary-wing drones.
Unlike the fixed-wing models, these drones can fly in every direction, horizontally, vertically, and also
can hover in a fixed position. Rotary wing drones, similar to helicopters, generate lift from the constant
rotation of the rotor blades. In this type of drone, several blades may be used. Thus, nowadays,
researchers designed and fabricated different types of drones ranging from one to twelve motors.
These characteristics make them the perfect drones for surveying hard-to-reach areas, such as pipelines,
bridges, mines, etc.
Having drones that are confined in boxes is necessary for situations in which the surrounding
environments are unknown. To this end, there is a need to design structures to keep the drones safe.
Different structural configurations have been proposed in order to be able to use these drones in
underground mines, in the wake of natural disasters, and in the presence of people (Figures 5 and 6).
The structure around the drones allows safety for the drone, along with allowing the drone to have a
rolling feature. The drones, with their encasing optimized structure, have the ability to fly through
confined spaces like mines and have the capability to roll on the ground and walls of the mines if
needed. Considering the environment, a drone with a flexible spherical structure can be designed,
which will be able to fly in high temperatures and dusty air in the mines. In the following, different
types of the encased drones are discussed. Table 10 shows examples of encased drones for industrial
and research applications.
Drones 2020, 4, 34 17 of 25
Drones 2020, 4, x FOR PEER REVIEW 19 of 28

Figure5.5.View
Figure Viewofofencased
encaseddrones,
drones,(a)
(a)Fleye
FleyeRacer
Racer[163],
[163],(b)Fleye
(b)FleyeHelmet
Helmet[163],
[163],(c)
(c)Fleye
FleyeDucted
Ducted [163],
[163],
(d)
(d)Flybotix
Flybotixdrone
drone[164],
[164],and
and(e)
(e)Elios
Elios22[68].
[68].

Table10.
Table 10.The
Thecharacteristics
characteristicsof
ofindustrial
industrialencased
encaseddrones
drones[68,164,165].
[68,164,165].

Type Model Goal Company

Diamet
Diameter Weig
Weight (g)
Spee
Speed (m/s)
(mm)
Type
Single rotor Model
Fleye Racer Goal
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In
In this
thispaper,
paper,recent studies
recent andand
studies developed commercial
developed dronesdrones
commercial and services in the mining
and services in theindustry
mining
were discussed. In addition, the drone applications in the mining industry for
industry were discussed. In addition, the drone applications in the mining industry for search search and rescue
and
missions were discussed.
rescue missions Besides,Besides,
were discussed. common remote remote
common sensingsensing
tools that have
tools been
that have mounted on drones
been mounted on
in the mining industry were reviewed. Drone technology is a common tool in surface
drones in the mining industry were reviewed. Drone technology is a common tool in surface mining. mining. It is
efficient and low cost compared to the traditional monitoring methods. Drones in surface
It is efficient and low cost compared to the traditional monitoring methods. Drones in surface mining mining have
ahave
variety of applications,
a variety such as
of applications, oreas
such control, rock discontinuities
ore control, mapping,
rock discontinuities 3D mapping
mapping, of theof
3D mapping mine
the
environment, blasting management, postblast rock fragmentation measurements,
mine environment, blasting management, postblast rock fragmentation measurements, and tailing and tailing stability
monitoring, to name atofew.
stability monitoring, nameFixed-wing and rotary-wings
a few. Fixed-wing drones are the
and rotary-wings mostare
drones commonly
the mostused drones
commonly
in
usedthedrones
mininginindustry, including
the mining both
industry, researchboth
including and commercial
research andapplications.
commercial applications.
Despite significant advancement in drone technology, the applications of drones in
underground mines are still limited. This is due to challenges like GPS-denied environments, lack of
wireless signal, confined spaces, the concentration of dust and gases, and generally harsh
environments. The possible solution for the use of drones in underground mining was suggested.
Encased drones can be a solution to the environmental obstacles in underground mine environments.
Drones 2020, 4, 34 18 of 25

Despite significant advancement in drone technology, the applications of drones in underground

mines are still limited. This is due to challenges like GPS-denied environments, lack of wireless signal,
confined spaces, the concentration of dust and gases, and generally harsh environments. The possible
solution for the use of drones in underground mining was suggested. Encased drones can be a solution
to the environmental obstacles in underground mine environments.

Author Contributions: Writing—original draft, J.S. and E.T.; Writing—review & editing P.R., and M.H. All authors
have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Conflicts of Interest: On behalf of all authors, the corresponding author states that there is no conflict of interest.

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