acoustic positioning systems · – lbl – long baseline – sbl – short baseline – usbl –...

www.nautronix.com

NAUTRONIXMARINE TECHNOLOGY SOLUTIONS

Acoustic Positioning

Systemsa presentation by

Donald Thomson

International Product Manager - Acoustics

For The Hydrographic Society in ScotlandHydrofest 2005

NAUTRONIXMARINE TECHNOLOGY SOLUTIONS www.nautronix.com

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WHY ACOUSTICS?

Radio signals used by surface positioning systems are absorbed by water, as a result acoustic signals are the preferred technology

for in water signalling.


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WHAT IS ACOUSTICS USED FOR?

• Transfer of position from surface to seabed(most oil industry work relates to drilling and installations on the seabed)

• Positioning within the water column(tracking of ROVs, AUVs, and towfish (Survey Sensors)

• Relative positioning between locations(relative installations, metrology)

• Transmission of data(to support positioning and independent sensor data)


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EXAMPLE OF DEEPWATER FIELD DEVELOPMENT

Injection Flowline

FPSO Mooring Lines

Injection Wellhead

Flexible Riser Towers

Control Umbilical

2 Well Manifold

Loading Buoy

Production Wellhead

Production Bundle


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POSITIONING METHODOLOGIES

• There are 3 main methods of calculating a position using acoustics

• These are:-– LBL – Long Baseline– SBL – Short Baseline– USBL – Ultra Short Baseline (SSBL Super Short Baseline)


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ACOUSTIC POSITIONING METHODS

• UltraShort baseline (USBL)– Determines beacon position by measuring the relative phases of

the acoustic signal received by closely spaced elements in a single hydrophone

• Short baseline (SBL)– Determines beacon position by measuring the relative arrival times

at three or more vessel mounted hydrophones

• Long baseline (LBL)– Determines beacon position by measuring the slant ranges from

three or more widely spaced transponder


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ACOUSTIC INSTALLATIONS DRILLING


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ACOUSTIC INSTALLATIONS SURVEY


PLCUltra Short Base Line (USBL)


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ULTRA SHORT BASELINE THEORY OF OPERATION

Singlehydrophone

Single hydrophone phase comparison system

Free runningbeacon Individual

cycle of toneburst

Threeclosely

spaced sensorsToneburst

Phasemeasuring

receiver

Phase delay usedto compute position

Positioncomputer

Phasemeasuring

receiver

Phasemeasuring

receiver


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ERRORS IN USBL MODE

• Echo Range - timing errors

• Offset angles - phase detection errors

• Hydrophone Alignment - measurement errors

• Tilt Compensation - acceleration


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USBL ADVANTAGES AND DISADVANTAGES

• One time calibration - during installation

– Accuracy depends on good calibration and VRU accuracy

• Single transducer– Accuracy varies with range

• Works with Pingers or Transponders

– Needs depth data for Pinger “Z” data

• Works with a single subsea beacon


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SHORT BASELINE THEORY OF OPERATION

Ocean Floor

Hydrophones 1 & 22 1

Beacon

Note: the third hydrophonerequired for the minimumconfiguration is not shown onthis drawing

X =Z (c/d) tB B Δ

d

ZB

XB

Where:c - is the speed of sound in waterd - is the distance between the hydrophones

t - is the difference in time of arrival at the hydrophoneΔ


PLCLong Base Line (LBL)Long BaseLine (LBL)


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BEACON DEPLOYMENT


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ERRORS IN SBL MODE

• Range & Offset angles - Timing Errors

• Platform Alignment - Measurement Errors

– system accuracy directly related to accuracy of VRUs

– calibration methods mitigate errors


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SBL ADVANTAGES AND DISADVANTAGES

• One time calibration at installation– Accuracy depends on good

calibration and VRU accuracy

• Multiple solutions leads to improved accuracy over USBL

– Requires multiple hydrophones

• Works with Pingers or Transponders

• Works with a single subsea beacon


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LONG BASELINE THEORY OF OPERATION

Ship’s course

ShipfixHydrophone

Acoustic signaltransmission

from hydrophone

Transponded acoustic

signal frombeacon

Subeference reference

beacon no.1


beacon no.2


beacon no.3


PLCLBL Array Calibration


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ERRORS IN LBL MODE

• Range - Detection timing errors

• Field Calibration errors

• Ray Bending problems increase as slant range increases


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LBL ADVANTAGES AND DISADVANTAGES

• Independent of ship motion– Area of operation limited to location of subsea reference beacons

• Highest accuracy of three methods– Requires multiple reference beacons deployed

• Single Hydrophone on ship– System complexity decreased

• Requires calibration each time reference beacon(s) are redeployed


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CONSTRUCTION SURVEYING

• For high accuracy positioning on the seabed a different type of LBL is used. In this methodology more intelligent transponders are used which are individually addressable and commandable.

• A number (up to 100) are laid to cover the area of operation, boxed in and adjusted.

• Position is then carried out by range measurements to nearby transponders.

• This is the most common methodology for complex field developments.


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• There are issues with management of codes and frequency channels

• Different frequencies are used depending on the range and accuracies required.

LBL - Structure Positioning

• Accurate, repeatable and rigorous positioning solution independent of water depth

• Heading and attitude determination from acoustic observations


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ACOUSTIC ACCURACIES

• USBL– standard 0.5% slant range– best 0.2% slant range

• SBL– 0.5% water depth

• LBL– Vessel 0.1% water depth– Construction LF up to 2-3m

MF up to 1mEH5 up to 5 cm

-25

-20

-15

-10

-5

0

5

10

15

20

25

-40 -30 -20 -10 0 10 20 30 40

Easting Error (m)

Nor

thin

hg E

rror

(n)

3 SD 19.2m

1 SD 6.4m

Note 0.25% of slant range equals 6.3m

NOTES In Construction LBL accuracy is independent of water depth Accuracy also varies with array spacing


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TRADE OFFS USBL, SBL, LBL

OOppeerraattiinngg MMooddee AAddvvaannttaaggeess DDiissaaddvvaannttaaggeess LLoonngg BBaasseeLLiinnee •• HHiigghheesstt PPootteennttiiaall

AAccccuurraaccyy •• AAccccuurraaccyy pprreesseerrvveedd

oovveerr wwiiddeerr ooppeerraattiinngg aarreeaa

•• RReeqquuiirreess MMuullttiippllee SSuubbsseeaa TTrraannssppoonnddeerrss

•• MMuusstt hhaavvee ttwwoo--wwaayy rraannggiinngg •• UUppddaattee iinntteerrvvaallss lloonngg

ccoommppaarreedd ttoo ppiinnggeerr mmooddeess •• AAccoouussttiicc rraayy bbeennddiinngg

SShhoorrtt BBaasseeLLiinnee •• GGoooodd PPootteennttiiaall AAccccuurraaccyy

•• RReeqquuiirreess oonnllyy aa ssiinnggllee SSuubbsseeaa PPiinnggeerr//TTrraannssppoonnddeerr

•• AAccccuurraaccyy ddeeppeennddeenntt oonn sshhiippbbooaarrdd VVRRUU

UUllttrraaSShhoorrtt BBaasseeLLiinnee •• RReeqquuiirreess oonnllyy aa ssiinnggllee SSuubbsseeaa PPiinnggeerr//TTrraannssppoonnddeerr

•• HHiigghheesstt NNooiissee ssuusscceeppttiibbiilliittyy •• AAccccuurraaccyy ddeeppeennddeenntt oonn

sshhiippbbooaarrdd VVRRUU


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ACOUSTIC TRANSMISSION

FREQUENCY BAND BAND WIDTH TYPICAL POSITION ACCURACY

Low Frequency(LF)

7.5 – 15 kHz 0.5 – 2.5m

Medium Frequency (MF) 19-36 kHz 0.25 – 1m

Extra High Frequency(EHF)

50 – 110 kHz <0.05m


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THE BEST OF BOTH WORLDS

For critical operations systems combining two of the methodologies can provide a much more robust

position.


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NAUTRONIX NASDrill 925

Receiver HydrophonesInterrogateHydrophone

Signal ProcessingUnit

Display andControl Unit

InterrogateHydrophone

P.A. SignalJunction Box

Beacons

P.A.

Dual Redundant System

Maxi Beacon Mk 2

Interrogate/ReceiveHydrophone

Receive Hydrophones

Power Amplifier

Display and Control Unit

Signal Processing Unit


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POSITION MEASUREMENT

• In SBL mode– One Beacon has to reply to at least 3 Hydrophones.– Several Beacons to 6 Hydrophones gives multiple solutions.

• In LBL/SBL Mode– 4 Beacons are established in a grid– A Common Interrogation Signal (CIS) is transmitted , each beacon

replies to all the hydrophones.– All valid replies are used in the calculation of the vessel’s position.– System reverts to pinger SBL mode on loss of CIS.


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ADS2 RESULTS DEEPWATER EXPEDITION 580m


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NASDrill 925

• Acoustic Positioning – Robust – Accurate– Repeatable– Fast Update

• NASDrill 925 Positioning:– 2.5 metres RMS at 3500 metres– Update every two seconds– Acoustic path redundancy– Configurable as a Dual Redundant System

• Drilling Options– Riser Angle– Riser Profile– Riser Management


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CROWDED MF BAND

1 2 3 4 5 6 7 8 X 9 Y 6 7 8 9 1 2 3 X 4 5 Y

1 2 3 4 5 6 7 8 E6O6

E7O7

E8O8

E1O1

E2O2

E3O3

E4O4

E5O5TELEMETRY

SIMRAD418

LBL1 2 3 4 5 6 7 8 9 (CIF)

SIMRAD418 LBL

SIMRAD300

NAUTRONIXRS5D

NAUTRONIX910/925

SONARDYNE

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Frequency, kHz


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THE ACOUSTIC ENVIRONMENT

• Most manufacturers quote theoretical performance figures (Range and Accuracy).

• These are seldom achievable due to problems such as:

– Noise at the receiver (vessel, propulsion, ROV etc)

– Background noise (other vessels, operations, sea life)

– Reflections from solid objects and sea surface

– Interference from other acoustic systems

– Ray bending and refractions


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RAY BENDING EFFECTS


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EXTREME RAY TRACE EXAMPLE


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IMPROVING PERFORMANCE

• System performance can be improved by:

– Directional/Baffled hydrophones (reduce vessel noise)

– Directional Transponders

– Better signal processing

– Higher transponder power output


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DEEPWATER ISSUES

• More and more work is being carried out in deepwater (500 –2500msw).

• This creates additional problems:

– Slow update rates due to signal travel time (1500m/s)– Limited range due to signal fading– Reduced accuracy on USBL systems– Requirement for high accuracy sensors on USBL and SBL systems

(VRU, Gyro)– Ray bending can restrict operating areas.


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INDUSTRY DEVELOPMENTS

• Increased ID codes to allow better use of Spectrum(All manufactures, Sonardyne, 24 channels, 16 ID’s each)

• Integration of Doppler Velocity Logs(e.g. Sonardyne Fusion)

• Integration of Inertial Navigation Systems to seabed vehicles(e.g. Kongsberg HAINS and Ixsea GAPS)

• Development of new signalling technologies – (Nautronix ADS2, Sonardyne Wide Band)


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PULSE DETECTION


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SPREAD SPECTRUM v CONVENTIONAL SIGNALS

• Conventional acoustics use “narrowband” signals

• Spread Spectrum Signalling is being introduced by manufacturers such as Nautronix and Sonardyne

• Spread Spectrum employs Pulse (Time) Compression techniques. These provide a signal to noise benefit from the signal processing

• Nautronix Spread Spectrum Implementation is ADS2 (Acoustic Digital Spread Spectrum)


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CONVENTIONAL SIGNALS


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ADS2 SIGNALS


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MULTIPATH EXAMPLE


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MULTIPATH RESPONSE


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ADS2 MULTIPATH RESPONSE

Compatt 5 Baseline Measurements

778m

Tone Burst

WidebandSD 0.14m

SD 0.01m


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CONVENTIONAL CHANNEL SPACING


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ADS2 CHANNEL SPACING

More Efficient use of Bandwidth

COMPATT 4Tones

COMPATT 5Wideband

300 Series

400 Series

11

Wideband RepliesWideband Interrogations (C5+)

1 2 3 4 5 6 7 8 CIF CRF 0 9 10 11 12 13 14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 2 3 4 5 6 7 8 9 10 11 12 13 14C

MF Band

1 2 3 4 5 6 7 8 X 9 Y 6 7 8 9 1 2 3 4 5 YX

1 2 3 4 5 6 7 8

HPR Replies

Replies

E6 E7 E8 E1 E2 E3 E4 E5O6 O7 O8 O1 O2 O3 O4 O5

HPR Interrogations

Interrogations

COMPATT 5Wideband

SO

NA

RD

YN

ES

IMR

AD

300 Series

400 Series

COMPATT 4/5Tones

SO

NA

RD

YN

ES

IMR

AD

Robust

Command&

Reply

TELE

MET

R Y

CCF DCF

Wideband (Robust) Telemetry Robust

Tone (FSK) TelemetryCommand

&Reply

Code & Frequency Space

IRS 0310

IRS 0410

IRS 1511

IRS 0111

IRS 0211

IRS 0108

IRS 1309

IRS 1409

IRS 1509

IRS 0104IRS 0401

0007 0008 0009 00140010 0011 0012 00130003 0004 0005 00060001 0002

IRS 0607

IRS 0101

IRS 0201

IRS 0301

IRS 0601

IRS 0801

IRS 1001

IRS 1201

IRS 0803

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IRS 1401

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IRS 1002

IRS 1202

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IRS 1204

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IRS 1003IRS 1102

IRS 1302

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IRS 0103

IRS 0203

IRS 0303

IRS 1402

IRS 0501

IRS 0302

IRS 0102

IRS 0502

IRS 0901

IRS 0701

IRS 1301

IRS 0403

IRS 1304

IRS 1404

IRS 1504

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IRS 0704

IRS 0804

IRS 0904

IRS 0204

IRS 0304

IRS 0404

IRS 0504

IRS 0205

IRS 0305

IRS 0405

IRS 0604

IRS 1305

IRS 1405

IRS 1505

IRS 0105

IRS 0505

IRS 0605

IRS 0705

IRS 0805

IRS 1106

IRS 1206

IRS 1306

IRS 1406

IRS 1506

IRS 0106

IRS 0206

IRS 0306

IRS 0406

IRS 0506

IRS 0606

IRS 0706

IRS 0806

IRS 0906

IRS 1006

IRS 0908

IRS 1008

IRS 1108

IRS 1208

IRS 1308

IRS 1408

IRS 1508

IRS 0808

IRS 0710

IRS 0810

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IRS 1010

IRS 1110

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IRS 1310

IRS 0208

IRS 0308 IRS 0110

IRS 0210

IRS 0608

IRS 0708

IRS 0408

IRS 0508

IRS 1311

IRS 1411

IRS 1410

IRS 1510

IRS 0411

IRS 0511

IRS 0510

IRS 0610

IRS 0612

IRS 0712

IRS 0812

IRS 0311

IRS 0711

IRS 0811

IRS 0911

IRS 1011

IRS 1111

IRS 1211

IRS 0912

IRS 1012

IRS 1112

IRS 1212

IRS 1312

IRS 1412

IRS 1512

IRS 0112

IRS 0212

IRS 0312

IRS 0412

IRS 0513

IRS 0613

IRS 0713

IRS 0813

IRS 0913

IRS 1013

IRS 1113

IRS 0113

IRS 0213

IRS 0313

IRS 1213

IRS 1313

IRS 1413

IRS 1513

IRS 0314

IRS 0414

IRS 0514

IRS 0614

IRS 0714

IRS 0814

IRS 0914

IRS 1014

IRS 1114

IRS 1214

IRS 1314

IRS 1414

IRS 1514

IRS 0114

IRS 0214

IRS 1103

IRS 13030016

IRS 0503

IRS 0703

IRS 0903

IRS 1502

IRS 1501

IRS 1101

IRS 0905

IRS 1005

IRS 1105

0009

0010

0011

0012

0013

0014

0015

IRS 0707

IRS 0807

IRS 0907

0002

0003

0004

0005

0006

0007

0008

IRS 0909

IRS 1009

IRS 1109

IRS 1209

IRS 0509

IRS 0609

IRS 0709

IRS 0109

IRS 0209

IRS 0309

IRS 0409

IRS 0507

IRS 1107

IRS 1207

IRS 1307

IRS 1407

IRS 1507

IRS 0107

IRS 1403 IRS 12050001

Nav

igat

ion

Cod

es

Carrier Frequency

IRS 0207

IRS 0307

IRS 0407

IRS 1007 IRS 0809 IRS 0611 IRS 0413IRS 0512

COMPATT 5Wideband

Wideband RepliesWideband Interrogations (C5+)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 2 3 4 5 6 7 8 9 10 11 12 13 14CCOMPATT 5Wideband

SONA

RDY

NE

TRA

CK

ING

MF BAND

224 TRUE

simultaneous receive

channels


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BENEFITS TO CUSTOMER

• Increased battery life (up to 15 times)

• Increased accuracy

• Increased range (around 2 times)

• More noise tolerance (up to 12 dB)

• Increased reliability in shallow water


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NEW POSITION CONCEPT

ADS2 signalling capability has allowed Nautronix to develop a new concept in

positioning.


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THE PROBLEM


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Numerous independent systems

Duplicated effort and expenditure

Difficult integration of operations

Acoustic pollution

Short range

Limited operational life

EXPENSIVE

THE PROBLEM


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Surface positioning has been revolutionised by the Global Positioning System -GPS

GLOBAL POSITIONING SYSTEM


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• Unlimited user capability

• High accuracy

• A universal reference

• Improved efficiency

• Cost savings

GPS Provides

Imagine this underwater…

GLOBAL POSITIONING SYSTEM


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Nautronix Acoustic Subsea Network


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PROJECTOR ELEVATED BY 100 METRES


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THE MULTI-USER FIELD POSITIONING SYSTEM

NASNetTM


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"A step change in acoustic technology"

• An unlimited multi user field positioning system

• A global solution

• Integrated subsea positioning

Providing:

A MAJOR COST SAVING OPPORTUNITY


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IN-BUILT TRACKING


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Very long range

High accuracyUnlimited simultaneous users

Surface & underwater positioningMulti-function and tasking

High immunity to acoustic pollution & ray bendingData transmission capability

Environmentally friendly

KEY FEATURES


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“A GLOBAL SOLUTION TO INTEGRATED SUBSEA POSITIONING WITH SAVINGS OF OVER 68% ON TODAY’S METHODS WITH EVEN GREATER

POTENTIAL AS THE INDUSTRY MOVES TOWARDS DEEPER WATER”

CONCLUSION


‘Global Leaders in Through Water Communication and Positioning

Technology’



There are issues with management of codes and frequency channels

Different frequencies are used depending on the range and accuracies required.

acoustic positioning systems · – lbl – long baseline – sbl – short baseline – usbl –...

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