hydrofest 2011 acoustic positioning systems · acoustic positioning hydrofest 2011 1.an...
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Acoustic (Subsea)
Positioning Systems
Hydrofest 2011
The Hydrographic Society in Scotland
13thApril 2011
Aberdeen
Edward Moller
Survey Support Manager
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Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
•Why, Where and How
•Simple Terminology
•Acoustic Signals
•Acoustic Positioning Methods
2.Long BaseLine (LBL)
•Hardware Setup
•Calibration
•Accuracy and Update rates
3.Ultra Short BaseLine (USBL)
•Hardware Setup
•Calibration
•Accuracy and Update rates
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
•Why, Where and How
•Simple Terminology
•Acoustic Signals
•Acoustic Positioning Methods
2.Long BaseLine (LBL)
3.Ultra Short BaseLine (USBL)
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
Acoustic Positioning
Spheres of Operation
The Offshore Industry utilise Acoustics
in a whole host of operations:
•Exploration
•Hydrographic Survey
•Drilling
•Construction Survey
•Dynamic Positioning
•Production
•Decommissioning
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Acoustic Positioning
Spheres of Operation
Non Oil and Gas operations
include;
•Civil Engineering
•Defence
•Communications
•Ocean Science
•Search and Recovery
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Acoustic Positioning
What is it used for?
Examples of Acoustic Positioning
•Towfish Tracking
•ROV, Plough and AUV Tracking
•Structure Installation and Monitoring
•Vessels and Drilling Platforms DP
•Civil Engineering
•Bundle Tows
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Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
•Why, Where and How
•Simple Terminology
•Acoustic Signals
•Acoustic Positioning Methods
2.Long BaseLine (LBL)
3.Ultra Short BaseLine (USBL)
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
Acoustic Positioning
Simple Terminology
Transponder
Depending on the type of transponder, they can often be used in two ways:
1.They can be positioned from an
Acoustic Positioning System to
determine their position. Rather
like your SatNavin your car.
2.They can be used to form an
Acoustic Positioning Network
(commonly referred to as an
‘array’) rather like the GPS
satellites
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Acoustic Positioning
Simple Terminology
Transponder Types
Transponder:
It can both receive and transmit signals. More advanced
transponders can operate autonomously enabling them to
measure to other sensors and also position themselves.
Responder:
This sensor transmits only. It is called a responder because
it transmits in ‘Response’to a GO command such as an
electrical trigger
Beacon:
A generic term for the most basic of transponders. It
transmits continuously and does not require any interrogation
or trigger. A good example of such a beacon is a GPS
satellite.
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Acoustic Positioning
Simple Terminology
Transceivers
Transceivers are typically wired sensors capable of
receiving information from, and transmitting information
to transponders.
1.Basic transceivers can be used much like the
antenna inside your SatNavto receive signals
from transponders
2.Advanced, multi-element transceivers can
determine range and bearing and hence calculate
the relative position of a transponder
3.Transceivers can also be used as modems
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Acoustic Positioning
Simple Terminology
•A baseline is the distance
between two transponders, or a
transponder and the receiving
elements in a transceiver.
•With three baselines from known
positions (transponders set out
like GPS satellites), trigonometry
can be used to determine the
position at which the baselines
converge.
Baseline
All acoustic positioning systems use baselines to determine a position
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Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
•Why, Where and How
•Simple Terminology
•Acoustic Signals
•Acoustic Positioning Methods
2.Long BaseLine (LBL)
3.Ultra Short BaseLine (USBL)
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
Acoustic Positioning
Baseline Measurement
Acoustic Positioning Systems Measure Time, Not Distance
1.A signal is sent from the transceiver or transponder and an internal clock is
started.
2.The reply signal is received from the target, the clock stops and the total time
for the signal cycle is logged.
3.Add the Speed of Sound along with the TurnAroundTime (TAT) and you
have distance
Interrogate
Reply
Note: Sound Speed constantly changes so has
to be measured on a regular basis
Turnaround
Time (TAT)
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Acoustic Positioning
Tone Signal –Correlation Processing
Tone Signal
good time of
arrival estimation
Analogue is traditional acoustic signal technology
•One transmission per carrier frequency, means limited
number of channels
•Processing affected by high noise
•Range determination can be better than 20cm
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Acoustic Positioning
Digital Signal –Correlation Processing
Digital Acoustic Signal Technology
•Unique codes rather like serial numbers, meaning hundreds of channels
•Digital signals are more robust than analogue in high noise
•Range determination can be better than 1cm
Wideband Signal
excellent time of
arrival estimation
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Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
•Why, Where and How
•Simple Terminology
•Acoustic Signals
•Acoustic Positioning Methods
2.Long BaseLine (LBL)
3.Ultra Short BaseLine (USBL)
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
Acoustic Positioning Techniques
Long BaseLine (LBL)
100s/1000s of Metres
•Seabed transponder array
at known co-ordinates
•Ranges are derived and
position calculated
•Up to Centrimetric
accuracy
•Accuracy independent of
water depth
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Acoustic Positioning Techniques
Long BaseLine (LBL)
Seabed transponder array
can also be used to position
subsea vehicles such as an
ROV
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Acoustic Positioning Techniques
Short BaseLine (SBL)
10s of Metres
•Single seabed transponder is
interrogated
•The reply is received at 3 or 4
transceivers on the vessel
•Range is derived from timing
and sound speed
•Direction is derived from
differences in the arrival time
at each of the vessel
transceivers
•SBL rarely used today due to
improvement of USBL
systems
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Acoustic Positioning Techniques
Ultra Short or Super Short BaseLine (USBL or SSBL)
Centimetres
•Single seabed transponder is
interrogated
•The reply is received at the
USBL/SSBL Transceiver array of 3 or
more transducers
•Range is derived from timing and
sound speed
•Direction is derived from differences
in phase of the signal at the array
transducers
•Accuracy dependent on water depth
and quality of vessel sensors
This transponder can be
mounted on an ROV
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Acoustic Positioning Techniques
Inverted USBL
iUSBL Transceiver
•Positioning for ROVs, AUVs and deep-tow vehicles
•Simpler mobilisationwhere through hull deployment is unavailable
•Increased range
•Increased accuracy
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Acoustic Positioning Techniques
Long & Ultra Short BaseLine (LUSBL)
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Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
2.Long BaseLine (LBL)
•Hardware Setup
•Calibration
•Accuracy and Update rates
3.Ultra Short BaseLine (USBL)
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
LBL Equipment
Topside ORSubsea
Transceiver
Used to communicate to LBL
transponders in an array.
Are deployed either over the side of
vessels (Dunkers) or on subsea
vehicles such as ROV’s
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LBL Equipment
Subsea
1.Collect data or configure operational settings
2.Measure acoustic travel time to a second transponder
3.Respond as an array transponder
4.Observe and report two-way travel times to an array of
Compatts
5.Respond to an interrogation from a USBL system
An Intelligent Transponder that can;
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Long BaseLine (LBL)
System Overview
Vessel Equipment
ROV Equipment Seabed
Equipment
+
+
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Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
2.Long BaseLine (LBL)
•Hardware Setup
•Calibration
•Accuracy and Update rates
3.Ultra Short BaseLine (USBL)
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
Acoustic Positioning
LBL Calibration
Observations
•Depth
•Baselines Distances
•Trial Positions
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Acoustic Positioning
LBL Calibration –Relative Array Positions
Least squares
adjustment to
derive best
estimate of
transponder
positions and
depths
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Acoustic Positioning
LBL Calibration –Absolute Global Positions
Angle of cut
Data collection procedures minimises the effect of observationalerror (fixed offset
from the transponder and constantly changing heading)
R
www.sonardyne.com
Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
2.Long BaseLine (LBL)
•Hardware Setup
•Calibration
•Accuracy and Update rates
3.Ultra Short BaseLine (USBL)
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
Acoustic Positioning
LBL Accuracy
LBL System Accuracy
Depending on the quality of the absolute calibration and sound speed
knowledge, LBL systems offer the most accurate positioning in any
water depth.
LBL arrays can offer 0.05m accuracy and precision
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Acoustic Positioning
Update Rate
Update Rates
Acoustic positioning systems vary in their update rate and tend to
provide slower update rates than surface based positioning sensors.
This is due to the fact that acoustic
signals travel at approximately
1,500m/sec through seawater. This
means that for a 1,500m baseline, the
acoustic signal would take 2 seconds
to travel to and from the transponder.
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Acoustic Positioning
LBL Update Rate
LBL Systems Update Rate
Using digital signals, the signals themselves can be interleavedallowing
simultaneous transmission of signals from all the array transponders.In the
past, tone signal based transponder replies had to be delayed toavoid any
signal overlap.
700
800
900
1000
1100
1200
1300
1400
1500
1600
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.91
Same code four orthogonal carriers
Beacon (pinger) type LBL systems can
transmit acoustic signals once a
second allowing an update rate of once
per second.
Modern LBL systems utilising
transponders can provide update rates
between 1 and 3 seconds depending
on the physical size of the array.
www.sonardyne.com
Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
2.Long BaseLine (LBL)
3.Ultra Short BaseLine (USBL)
•Hardware Setup
•Calibration
•Accuracy and Update rates
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
USBL Equipment
Topside
USBL Transceiver
A single unit which contains a minimum of three elements to form
the
Ultra Short Baseline
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USBL Equipment
Topside
Through Hull
Deployment Machine
Over the Side Deployment Machine
Deployment Machine (Pole)
Most USBL transceivers need to be mounted
securely to the vessel by the means of either a
pole that descends through the hull of the
vessel, or via a pole lowered over the side of
the vessel.
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Sensors required for a USBL system
Pitch and Roll
Tracking relative to the USBL transceiver requires
pitch and roll sensors
USBL tracking requires knowledge of the pitch and roll of
the transceiver to determine the transponder position in
relation to the transceivers orientation. This can be
achieved using the internal low grade sensors in the
transceiver or by using a high grade external sensor
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USBL Equipment
Subsea
Transponders
Omni, Directional or Super Directional transducers
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Ultra Short BaseLine (USBL)
System Overview
Vessel Equipment
Seabed Equipment
++
+
+or
or
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Sensors required for a USBL system
Heading
Tracking relative to the vessel also requires a
heading sensor
To determine the relative position of the transponder
in relation to the vessel, a heading instrument aligning
the transceiver to the ships forward axis is required.
This is achieved using an external gyrocompass or
equivalent
Zoom
ed In
NORTH
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Sensors required for a USBL system
GPS
Tracking with absolute co-ordinates or calibrating requires a position
sensor
To determine the absolute co-ordinates of the transponder, and to calibrate the
interfaced sensors, a position instrument is required. This is achieved by
interfacing a GPS instrument
NORTH
X
YLat 57.2897ºN
Long 2.3881ºW
GPS enables
absolute
positioning
NORTH
Lat 57.2903ºN
Long 2.3897ºW
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Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
2.Long BaseLine (LBL)
3.Ultra Short BaseLine (USBL)
•Hardware Setup
•Calibration
•Accuracy and Update rates
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
Acoustic Positioning
USBL Calibration
USBL Calibration
A USBL system for calibration consists of:
•USBL software
•USBL transceiver
•Vessel Attitude sensors (pitch, roll and heading)
•GPS
•Seabed transponder
A calibration routine is required to ensure
all these sensors are precisely aligned and
offset from each.
The better the calibration (system
alignment), then the more accurate the
system performance will be
High precision with no
systematic or gross errors
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Acoustic Positioning
CASIUS –Calibration of Attitude Sensors In USBL System
The process starts by
deploying a reference
acoustic transponder on to
the seabed
The vessel then sails in a pre-
determined calibration pattern
over and around the
transponder whilst
simultaneously collecting
DGPS, USBL, and attitude
data
During this process, the data
is logged by the USBL
system.
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Acoustic Positioning
CASIUS –Calibration of Attitude Sensors In the USBL System
CASIUS Calibration
Data Collection
N S
E
W
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Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
2.Long BaseLine (LBL)
3.Ultra Short BaseLine (USBL)
•Hardware Setup
•Calibration
•Accuracy and Update rates
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
Acoustic Positioning
USBL Accuracy
USBL System Accuracy
USBL transducers offer positioning precision that deteriorates the further the
transponder is from the array.
System accuracy is dependent on the quality and calibration of all the integrated
sensors.
USBL system accuracy is normally quoted in terms of a percentageof slant range.
Survey grade USBL systems can offer up to 0.1% of slant range (1m in 1,000m)
7.2m (0.12% of slant range)
1 DRMS (63.2%) of
observations
CASIUS Results
Statistic
A CASIUS in 4,870m Water Depth –Bay of Biscay+
++
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Acoustic Positioning
USBL Update Rate
USBL System Update Rate
USBL systems are also dependent on the speed of sound.
Responders do not require the interrogation signal so the updaterate will be half
that of a transponder.
Techniques such as ‘Ping Stacking’and the
use of digital signals, modern USBL systems
can achieve updates rates of 1 second in any
water depth and with any number of
simultaneous received transponders
www.sonardyne.com
Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
2.Long BaseLine (LBL)
3.Ultra Short BaseLine (USBL)
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
Inertial Navigation Systems
It’s Not New
•Commercial, Military, Space Aircraft
•Submarines, AUV, ROV
•Tanks –Payload Stabilisation
•Mobile Remote Sensing Survey
•Airborne Survey and Inspection
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Track Performance Improvement Through Aided INS
What it Does
•••••••Actual vehicle track
•••••••USBL generated track
•••••••INS dead reckoning track
•••••••AINS track
Simulated data
N
E
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USBL aided INS Positioning Example
Touch Down Monitoring (TDM)
INS
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ROV INS -SPRINT
Sparse LBL aided INS Example
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USBL aided INS Positioning Example
ROV Transiting Along Pipe to Touch Down Point
•USBL + DVL +
Depth
•INS filling in the
gaps
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USBL aided INS Positioning Example
ROV relocates to next Field Joint
•ROV static on a
field joint
•USBL (5s) +
DVL + Depth
aiding
•Range 400m
•Depth 100m
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Acoustic Positioning
Hydrofest 2011
1.An Introduction to Acoustic Positioning
2.Long BaseLine (LBL)
3.Ultra Short BaseLine (USBL)
4.Aided Inertial Navigation Systems
5.Choosing a System
www.sonardyne.com
www.sonardyne.com
Acoustic Positioning
Choosing a System
The accuracy requirements of the task to be carried out will determine
the Acoustic System that should be used.
For example;
Pipelay Operations
Often this would
require high update
rates over high
accuracy. Therefore a
USBL system would
be considered.
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Acoustic Positioning
Choosing a System
Often this would
require a high update
rate, high accuracy
system. Therefore, an
optimised USBL
system utilising survey
grade sensors and
transceivers would be
considered. USBL or
LBL aided INS could
also be utilised.
An ROV Pipeline Out Of Straightness Survey (OOS)
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Acoustic Positioning
Choosing a System
A Deepwater Structure Installation
This operation would require increased accuracy over update rate.
Therefore, LBL would be considered.
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Head Office
Sonardyne International Limited
T. +44 (0) 1252 872288
Blackbushe Business Park
F. +44 (0) 1252 876100
Yateley, Hampshire, GU46 6GD
United Kingdom
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