A Review of Underwater Robotics, Navigation, Sensing Techniques and Applications

Abstract

The focus of this paper is to review the history of underwater robotics, advances in underwater robot navigation and sensing techniques, and an emphasis towards its applications. Following an introduction, the paper reviews development of the underwater robots since the mid 19th century to recent times. Advancements in navigation and sensing techniques for underwater robotics, and their applications in seafloor mapping and seismic monitoring of underwater oil fields were reviewed. Recent navigation and sensing techniques in underwater robotics has enabled their applications in visual imaging of sea beds, detection of geological samples, seismic monitoring of underwater oil fields and the like. This paper provides a recent review of underwater robotics in terms of history, navigation and sensing techniques, and their applications in seafloor mapping and seismic monitoring of underwater oil fields.

Full text

A Review of Underwater Robotics, Navigation, Sensing
Techniques and Applications
Swagat Chutia1, 2, Nayan M. Kakoty1 and Dhanapati Deka2
1Embedded Systems and Robotics Lab
2Biomass Conversion Lab
Tezpur University, Assam, INDIA
swagat.energy@gmail.com
ABSTRACT
The focus of this paper is to review the history of underwater
robotics, advances in underwater robot navigation and sensing
techniques, and an emphasis towards its applications. Following
an introduction, the paper reviews development of the underwater
robots since the mid 19th century to recent times. Advancements
in navigation and sensing techniques for underwater robotics, and
their applications in seafloor mapping and seismic monitoring of
underwater oil fields were reviewed. Recent navigation and
sensing techniques in underwater robotics has enabled their
applications in visual imaging of sea beds, detection of geological
samples, seismic monitoring of underwater oil fields and the like.
This paper provides a recent review of underwater robotics in
terms of history, navigation and sensing techniques, and their
applications in seafloor mapping and seismic monitoring of
underwater oil fields.
Keywords
Underwater robotics; navigation; sensing techniques
______________________
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AIR '17, June 28-July 2, 2017, New Delhi, India
© 2017 Association for Computing Machinery. ACM ISBN 978-
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https://doi.org/10.1145/3132446.3134872
1. Introduction
The ocean covers about two-thirds of the earth and has a great
effect on the future existence of all human beings. About 37% of
the world’s population lives within 100 km of the ocean [1]. The
ocean is generally given less importance or overlooked as our
prime focus lies on land and atmospheric issues. Mankind has not
been able to explore the full depths of the ocean and its abundant
living and non-living resources. Underwater robotics is by far the
best option to explore and harness the vast energy which lies
amidst the water bodies. The recent advances in underwater
robotics are opening a myriad opportunity for the researchers and
industries. Situations which earlier seemed to be impossible to
solve due to technical limitations, are now solvable because of the
advancement in the navigation and sensing technology of
underwater robotics in the recent decade [2]. Extensive use of
manned submersibles and remotely operated vehicles are
currently limited to a few applications because of very high
operational costs, operator fatigue, and safety issues [3].
The demand for advances in underwater robot technologies is
growing and will eventually lead to fully autonomous, specialized,
reliable underwater robotic vehicles. In recent years, various
research efforts have increased autonomy of the vehicle and
minimized the need for the presence of human operators [4].
Unmanned underwater vehicles are either tethered which are
called remotely operated vehicles (ROVs) or untethered which are
known as autonomous underwater vehicles (AUVs). ROVs are
further classified as observation-class, working-class and special
use vehicles [5]. ROVs can also be classified depending upon
their size, weight, operating depth and operating power.
The motivation for reviewing the advancements in navigation and
sensing techniques for underwater robotics is that underwater
robots used are highly dependent on their ability to sense and
respond to their environment for their exploration activities. They
can operate in a previously unmapped environment with
unpredictable disturbances and threats [6]. Moreover underwater
robots can handle harsh underwater environment and are capable
of overcoming static as well as dynamic obstacles. In view of the
future scope of underwater robotics, use of the advances in
navigation and sensing techniques is of utmost importance. This
leads to the needs of reviewing the recent advances in the area and
an approach for less explored applications. Following a brief
history of underwater robotics, this paper reviews the recent
advancement in navigation and sensing techniques and application
in seafloor mapping and seismic monitoring of underwater oil
fields.
2. History of Underwater Robotics
The use of underwater robotic vehicles was dated back to 1950’s.
The Royal Navy of Great Britain employed an underwater vehicle
for recovering of torpedoes and removal of underwater sea mines.
In 1960’s, a Cable-Controlled Underwater Recovery Vehicle
(CURV) intended for rescue and recovery operations in a deep-
sea was realized by US Navy that were succeeded by CURV II
and CURV III recovery vehicles in early 1970’s. With the
development and growth of offshore industry in 1980’s and 90’s,
the trend of military Remotely Operated Vehicles (ROVs) shifted
towards the underwater oil and gas exploration, education and
ocean science research [7]. Underwater robotic vehicles have been
in service to the human beings for exploring oceanic world and
dealing with underwater deployments since the mid 19th century.
Although scientific literature does not pin point the first
underwater robotic vehicle developed historically, the CUTLET
ROV (shown in Fig. 1) has been categorically highlighted as a
pioneer remotely operated underwater vehicle which was
developed and introduced by the Royal Navy in 1950’s to recover
practice torpedoes [7].

Fig 1: CUTLET ROV (Adopted from [7])
CUTLET’s main frame was made of aluminum and it was
equipped with lights and camera. An electric motor was used for
its manipulation. To grip the target objects, a metal claw was
mounted on the arms attached to the main frame as end effectors.
This vehicle remained operational till 1980’s. XN-3 underwater
vehicle of US Navy is also considered amongst the early
developments, which were further modified in 1960s as CURV
and shown in Fig 2.
Fig 2: CURV (Adopted from [8])
It was the first time that ROVs gained significant recognition [8]
because CURV was used in human life recovery operations in
Mediterranean Sea. The vehicle was facilitated with onboard
hydraulic power system, operations and maintenance van, and
acoustic tracking system for navigation. Electrical power for the
system was provided through a diesel generator. The vehicle
offered remote maneuvering with six degrees of freedom (DoF)
for depth, altitude and heading using altimeter and depth-meter
sensors. Later, the CURV was tailored to develop CURV II (as in
Fig. 3) and a series of advanced ROVs including CURV II-B,
CURV II-C, and CURV III (Fig. 4).
Fig 3: CURV II (Adopted from [8])
Fig 4: CURV III (Adopted from [8])
Among all the CURV vehicles, CURV III was the most
sophisticated CURV series operating at 6000 feet under water
with a weight of 5.85 tons using fiber-optic support. To interact
with the targets, it was equipped with continuous transmission
frequency modulated (CTFM) sonar sensors, TV cameras, digital
cameras and two manipulators. The recent advances in navigation
and sensing techniques for underwater robots have motivated
designers and engineers to build far superior underwater robotic
vehicles such as VICTOR 6000 and PEMEX’s ROV. VICTOR
6000 (shown in Fig. 5) project started in 1992 by a French
research organization and was completed in 1997. It was a 6000m
underwater vehicle with 0.77m/s speed. It was a 4 ton vehicle
with six thrusters and 8000m tether with 6 optical fiber cables.
Real time system was employed for the vehicle control with 2
VEM computers, one each in the vehicle and another on the
surface unit. Vehicle was equipped with 2 pilot cameras, 3CCD
camera, sonar, altitude and pressure depth sensors, a 7- function
arm for manipulation with a 5-function arm for grasping
applications [8].
Fig 5: VICTOR 6000 (Adopted from [9])
Fig 6: PEMEX’s ROV (Adopted from [9])

PEMEX’s ROV (as shown in Fig.6) is consisted of surface unit,
launching unit, tether management unit and the vehicle. The
vehicle was designed to operate at the depth of 2000 m with six
thrusters, 5-function hydraulic manipulator and a 3-phase power
supply of 440VAC. The manipulator was operated from the
surface unit using a joystick. It was equipped with depth sensor,
compass, altimeter, rate gyros, sonar, 3 cameras and 4 lights. The
velocity of the vehicle was 0.55 m/s vertically, 1.25m/s in forward
and 1m/s in reverse direction. It was mainly designed to monitor
underwater oil field [9].
3. Sensing Technology
Navigation and sensing are the key features of an underwater
robot. Some of the widely used sensors in underwater robotics are
depth sensor, proximity sensor, two-axis and three-axis magnetic
sensors, roll and pitch sensor, angular rate sensors, three-axis
gyrocompasses, etc. The motivation for improving underwater
vehicle navigation arises from the need to expand the capabilities
of these underwater robotic vehicles and further increase their
value to oceanography [10]. This part of the paper reviews the
existing navigation and sensing techniques used in underwater
robotic vehicles. Some of the navigation sensors that are used in
underwater robotics are tabulated in table 1.
Table 1: Sensors for underwater Vehicle navigation [11]
Sensors
Sensing Principle
Acoustic Altimeter
Echo Sounding
Pressure Sensor
Piezoresistive, Piezoelectric
12 KHz LBL
Transponder
Inclinometer
Tilt sensor technology
Magnetic Compass
Earth's magnetic field
Gyro Compass
Torque induced gyroscopic precession
Acoustic Altimeter: An acoustic altimeter is also known as an
underwater or subsea altimeter. It is primarily used to measure the
altitude (height) of an object above the seafloor. They are also
suited to various other applications including positioning, berthing
and below surface monitoring. The underwater vehicle industry
(remotely operated vehicles and autonomous underwater vehicles)
is the primary user of altimeters [12].
Pressure Sensors: A pressure sensor is used to sense the pressure
of gases and liquids. Some of the applications of pressure sensor
are altitude sensing, flow sensing, level/ depth sensing, leak
testing and ratio metric correction of transducer output [13]. The
two basic sensing principles of pressure sensors are [9]:
1) Force collector types: These sensors are electronics in nature
and use a force collector such as diaphragm, piston, bourdon
tube, or bellows to measure strain or deflection due to applied
force over an area i.e. pressure.
2) Other types: These types of electronic pressure sensors use
other properties (such as density) to infer pressure of a gas, or
liquid.
Long baseline (LBL) acoustic positioning sensor: LBL sensors
are generally deployed around the perimeter of a work site. The
LBL technique results in very high positioning accuracy and
position stability that is independent of water depth [14]. They are
generally employed for precision underwater survey work where
the accuracy or position stability of ship-based positioning
systems does not suffice [15].
Inclinometer: It is used for measuring angles of slope or tilt,
elevation or depression of an object with respect to gravity. It is
also used as a tilt meter, tilt indicator, slope alert, slope gauge,
gradient meter, gradiometer, level gauge, level meter,
declinometer, and pitch and roll indicator [16]. Inclinometers
generate an artificial horizon and measure angular tilt with respect
to this horizon. The tilt angle range and number of axes are the
vital parameters to be considered for inclinometer sensing
applications [16].
Magnetic compass: It is used for navigation and orientation that
shows direction relative to the geographic cardinal directions [17].
Earth’s magnetic field is utilized by the magnetic compass to
show the direction.
True North-Seeking Three-Axis Gyrocompasses: A gyroscope
is a device used primarily for navigation and measurement of
angular velocity. Gyroscopes are available that can measure
rotational velocity in 1, 2 or 3 directions. 3- axis gyroscopes are
often implemented with a 3- axis accelerometer to provide a full 6
DoF motion tracking system. A gyrocompass consists of a rotor
that is made to spin about an axis. Often the spinning rotor is
gimbaled and allowed to move freely [18]. The earth’s rotation
and earth’s gravitational field are employed by North-seeking
gyrocompasses to determine the direction of local vertical and
true North. True North-Seeking Three-Axis Gyrocompasses are
however not used on non-military underwater vehicles due to their
bulky size and high power consumption [18].
Two-axis and three-axis magnetic sensors: Most modern
navigation magnetometer units incorporate an on-board
microprocessor to provide a serial digital data output. These units
are economic and can be relied upon. The two-axis and three-axis
magnetic sensors are widely available in varieties in the market
and when properly calibrated can provide heading accuracies
accurately. They consume very less amount of power.
Roll and pitch sensors: Roll axis is often termed as the
longitudinal axis. It is an axis drawn through the body of the
vehicle from tail to nose in the normal direction of movement.
Pitch axis is also known as lateral axis or transverse axis. This
axis runs from left to right of the vehicle. Roll and pitch sensors
are used extensively in underwater robotic vehicle [19]. Low cost
roll and pitch sensors are most commonly based upon measuring
the direction of the acceleration due to gravity with pendulum
sensors, fluid-level sensors, or accelerometers [20].
Angular rate sensors: Rate sensors measure angular rate directly,
without integration in conditioning electronics. Some of the
technologies related with angular rate sensors are
electromechanical, vibrating structure gyroscopes including
micro-electro-mechanical systems (MEMS) gyroscopes, ring laser
gyroscopes, fiber optic gyroscopes, MHD sensors based on the
magneto hydrodynamic effect, electrochemical sensors [21].
Optical gyroscopes remain the most accurate available angular
rate sensors [19], yet their comparatively high cost and power

consumption has limited their use. Fiber optic gyroscopes (FOG)
and ring-laser gyroscopes (RLG) can provide angular drift rates
typically on the order of 0.1–10 per hour. Low-end FOG motion
units employ FOGs, accelerometers, and flux-gate compasses to
estimate angular position, angular velocity, and translational
acceleration.
Multiple sensor data fusion
Multi sensor fusion system refers to the phase in integration
process where there is a combination (or fusion) of different
sources of sensory information into one representational format
[29]. Multiple sensor data fusion (MSDF) systems can fuse
information from complementary sensors, redundant sensors or
even from a single sensor over a period of time. The advantages
of fusion of sensor data are: reduction of uncertainty, rejection of
noise, toleration of sensor failure, increase in resolution and the
extension of sensor coverage. The MSDF techniques have been
summarized into four main categories on the basis of the
applications of the sensor fusion techniques: filtering and
estimation, mapping-oriented, behavior oriented and machine
learning [30].
4. Navigation Technology
The techniques that are currently used for the autonomous
underwater vehicle navigation can be classified into three
categories.
Inertial navigation: Gyroscopic sensors are used to detect the
acceleration of the underwater robot in inertial navigation. This
technique is successor of the dead reckoning technique and is
often combined with a Doppler velocity log (DVL) that can
measure the vehicle’s relative velocity [10, 22].
Acoustic navigation: Acoustic navigation uses acoustic
transponder beacons to allow the autonomous underwater vehicle
to determine its position. The most common methods for
autonomous underwater vehicle navigation are LBL that uses at
least two, widely separated transponders and ultra short baseline
(USBL) that generally uses GPS-calibrated transponders on a
single surface vessel [10, 22].
Geophysical navigation: Geophysical navigation uses physical
features of the underwater robot’s environment to produce an
estimate of the location of the robot. Magnetic compass and Gyro
compass are generally used in geophysical navigation [10, 22].
Table 2 describes the principles of various methods applied for
underwater robot navigation.
Table 2: Methods applied for underwater robot navigation
Methods
Principles
Terrain-aided navigation
for underwater robotics
[23].
Scanning sonar is used to
generate navigation estimate
based on a simultaneous
localization and mapping
algorithm.
Doppler based navigation
[11].
Bouncing a microwave signal off
a desired target and analyzing
how the object's motion has
altered the frequency of the
returned signal.
Combined Doppler/ LBL
based navigation [11].
Complementary linear filters are
utilized to combine low passed
LBL position fixes with high-
passed Doppler position fixes.
Dead Reckoning and
inertial navigation [25].
The accelerations of the vehicle
are integrated twice in time to
derive the updated position.
Terrain-aided navigation for underwater robotics
While many land-based robots use GPS or maps of the
environment to provide accurate position updates for navigation, a
robot operating underwater does not typically have access to this
type of information. This is where terrain aided navigation comes
in. It uses SONAR based on a simultaneous localization and
mapping algorithm to navigate. Sonar targets are currently
introduced into the environment in which the vehicle will operate
in order to obtain identifiable and stable features. The OBERON
vehicle designed and built at the Australian Centre for Field
Robotics is an example of terrain aided navigation. The vehicle is
equipped with two scanning low-frequency terrain-aiding sonar’s
and a color CCD camera, together with bathymetric depth sensors,
a fiber optic gyroscope and a magneto-inductive compass with
integrated two-axis tilt sensor [8, 23].
Doppler based navigation
The Doppler transducer unit has four downward looking beam
transducers oriented at about 30 degree from the instrument
vertical axis. A minimum of three beams are required. First the
Doppler sensor measures the apparent bottom velocity along each
of the beams. The velocity measurement in broadband dopplers is
performed with an ensemble of one or more discrete pings
employing the entire set of four beams [11]. The Doppler unit
digitally processes the four ping responses to compute a 4x1
vector of velocities. Single ping velocity error standard deviation
varies with beam frequency. Typical velocity error standard
deviation is under 1% [11].
Combined Doppler/ LBL based navigation
This method is used to take advantage of the incremental
precision of the Doppler with the absolute precision of LBL. It
uses complementary linear filters to combine low-passed LBL
position fixes with high-passed Doppler position fixes. This
system introduces a conventional magnetic heading compass and
conventional gravitational roll/pitch sensors. In normal operation
this system requires only standard LBL sea-floor transponders
unlike the simple Doppler based navigation which requires
additional fixed seafloor mounted continuous tone beacons [11].
The combined Doppler system provides significant improvement
in vehicle navigation precision and update rate of over 12 kHz. It
is particularly useful for real world ROV operations.
Dead Reckoning and inertial navigation
The longest established navigation technique is to integrate the
vehicle velocity in time to obtain new position estimates [24].
Compass and water speed sensor are the key devices to measure
the velocity components of a vehicle. The principal constrain is
that the presence of an ocean tide will add a velocity component
to the vehicle which is not detected by the speed sensor. In the
vicinity of the shore, ocean currents can exceed 3.7 kilometer per
hour. Consequently, dead reckoning for AUVs, operating at small
speeds (5.5 km to 11 km per hour), involving water-relative speed
measurements can generate extremely poor position results. It has
been found that in inertial navigation systems, the accelerations of
the vehicle are integrated twice in time to derive the updated
position. Position drift rates for high quality commercial grade
INS units are on the order of several kilometers per hour.
Moreover, dead Reckoning and inertial navigation systems are
costly and highly power consuming. The problem with exclusive
reliance on dead reckoning or inertial navigation is that position

error increases without bound as the distance travelled by the
vehicle increases. The rate of increase is a function of ocean
currents, the vehicle speed, and the quality of dead reckoning
sensors [10].
5. Application of underwater robots
In this section, application of underwater robotics for seafloor
mapping and seismic monitoring of oil fields are reviewed.
Seafloor mapping
Developing visual image of the seafloor has always been a
particular challenge to mankind. The first modern breakthrough in
seafloor mapping came with the innovation of underwater sound
projectors called “sonar,” which was used in World War I to
detect enemy submarines and torpedoes. By the 1920s, the Coast
and Geodetic Survey (the predecessor agency to NOAA’s
National Ocean Service) was using sonar to map virtual image in
deep water. During World War II, technological advancement in
sonar and electronics led to much more improved systems that
was able to capture precisely timed measurements of the seafloor
in depths. These systems provided the primordial databases used
to construct the first real maps of important features, such as the
deep-sea trenches and mid-ocean ridges [24]. Autonomous
underwater robot is used to gather a high resolution near-bottom
dataset of bathymetry, magnetic, temperature and optical
backscatter across the active tectonic and neo volcanic zone of the
Southern East Pacific rise [25]. High resolution mapping of
individual fault scarps, fissures, lava tubes, open-lava channels
and lava pillars were obtained by the underwater robot. The
underwater robot used was the Autonomous Benthic Explorer
(ABE) of the Woods Hole Oceanographic Institute. ABE uses
acoustic travel time from a 4 transponder network moored to the
seafloor to determine its position during surveying. Imagenix 855
mechanically scanned pencil-beam sonar was used for data
collection. Fig 7 and Fig 8 shows an underwater robot collecting
sonar data and the surface model from the sonar data.
Fig 7: Underwater robot collecting sonar data [26].
Fig 8: Surface model from the sonar data [26]
Seismic monitoring of oil fields underwater
A promising application for underwater robots or sensor networks
is seismic monitoring for oil extraction from underwater fields
[27]. Frequent seismic monitoring is of importance in oil
extraction. Studies of variation in the reservoir over time are
called “4-D seismic” and are useful for judging field performance
and motivating intervention. Monitoring of underwater oil fields
is a challenging task than monitoring terrestrial oil fields. This
constraint is mainly because seismic sensors are not currently
deployed in underwater fields. Instead, seismic monitoring of
underwater fields typically involves an underwater robotic ship
with a towed array of hydrophones as sensors and air cannon as
the actuator. Underwater robot could overcome this challenge and
help in seismic monitoring of the oil fields. Federal Mexican Oil
Company developed an underwater robot to inspect pipelines, oil
production units and other structures in deep waters [9]. It was
mainly used for visual analysis of underwater structure and was
named as PEMEX’s ROV (as shown in Fig 9).
Fig 9: PEMEX’s ROV for underwater oil field monitoring
(Adopted from [9])
Conclusion: This paper reported a review on the underwater
robotic vehicles and recent advancement in the field of navigation
and sensing techniques. Underwater robotic vehicles were in use
since the World War II. The pioneers of the underwater robots
which are CUTLEY and CURV series were reviewed in technical
terms. The navigation sensors such as acoustic sensors,
inclinometer, magnetic compass, gyro compass are discussed. All
the three basic navigation systems for underwater robot navigation
which are inertial navigation, acoustic navigation and geophysical
navigation were reviewed. The applications of underwater
robotics in seafloor mapping and seismic monitoring of
underwater oil fields are reviewed. The reported work shall be
helpful to the mankind to understand the history of underwater
robotics and their navigation and sensing techniques.
Acknowledgement
This research is financially assisted under the Department of
Biotechnology, Govt of India funded Indo-Brazil project entitled
“Integrated Biorefinery Approach towards production of
sustainable fuel and chemicals from Algal biobased systems”
approval no. DBT/IC-2/Indo-Brazil/2016-19/04.
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