3 hpr jan 2010

DP Operator Course HPR

Training Manual

Jan. 2010 © Kongsberg Maritime AS Page 6.3.1

Rev. 07 Training

HPR

HPR - Hydroacoustic Position Reference System

HPR consists of transducer(s) onboard a vessel communicating with transponder(s)

placed on the seabed. The transducers are lowered beneath the hull, and when a

transponder is deployed on the seabed, the transducers can start interrogating. The

transponder is listening for the interrogation and it answers with its own frequency. The

transducer receives the answer and is able to determine range and direction to the

transponder. This defines the vessel position with reference to the seabed transponder

and this information is fed to the dynamic positioning system.

HPR DP Operator Course

Training Manual

Page 6.3.2 Kongsberg Maritime AS Jan. 2010

Training Rev. 07

Sound in Water

Various physical laws influence the signals travelling through water. The strength of the

signal, the direction from where it comes, and noise conditions are examples.

The speed of sound in sea water is approximately 1500 m/s. The sound waves will decrease in

power when they travel through water and the path from the surface to the seabed will depend

on salinity and temperature layers.


Training Manual


Rev. 07 Training

Ray bending

When the velocity increases from the surface to the bottom (higher salinity and/or

temperature), the signal path will be bent up. When the velocity decreases from the surface to

the bottom (lower salinity and/or temperature), the signal path will be bent down.

Without information about sound velocity in the HPR system, the transponder position will be

calculated along the dotted lines.

Sound profile

Below is an example of a profile. On the picture to the left you can see the profile. The

velocity increases quickly from the surface down to 20-30 m. This sudden change is also

found on the ray trace picture to the right.

The ray trace tells us it is impossible to have any direct contact with a transponder at, for

example, 700 m range and 40 m depth, since all the rays are bent up to the surface or down to

the seabed. If you received a reply from a transponder using the above example, it would be a

signal bounce, where the pulse would be going between the seabed and surface one or more

times.

The mean sound velocity is used to calculate the range, while the transducer sound velocity is

used to calculate the angles to the transponder.

VALUE POS IT ION

SYSTEM

SOUND VELOCITY

SOUND DATA :D ISPLAY DATA

DRAW INGTRANSD. DEPTH :SOUND V. LOW :SOUND V. H IGH :UPPER DEPTH :LOW ER DEPTH :RANGE RAY DIAG:RAY START :RAY STOP :RAY STEP :

ENTER

SIM RAD HPR 418941028 11 :02:14

PR OFILE

PR OFILE5.0m

147 0m /s150 5m /s

0m200m800m

3°89°

3°

Off line Nc Nc Nc

0

100

200

CALC, Os lo fjorden 26 okt M EAN : 1482.191470 SOUND P ROFILE 1505

VALUE POSIT ION

SYSTEM

SOUND VELO CITY

SOUND DATA :D ISPLAY DATA

DRAW INGTRANSD. DEP TH :SOUND V. LO W :SOUND V. H IG H :UPPER DEPTH :LOW ER DEPTH :RANGE RAY D IAG:RAY START :RAY STOP :RAY STEP :

ENTER

SIM RAD HP R 418941028 11 :03:54

COM 2 RX ERROR 32

PROFILE

PROFILE5.0m

1470m /s1500m /s

0m100m700m

60°89°

1°

O ff line Nc Nc Nc

0

50

100

CALC, Oslofjorden 26 okt 0 RAY DIAGRAM 700

(CD3175)

Higher velocity

Lower velocity

Higher velocity

Higher velocity

Lower velocity


Training Manual


Training Rev. 07

Signal Loss

The signal strength is reduced as a function of distance and frequency.

Transmission loss in dB

Alpha 1.5 db/km - 13kHz, 5dB - 25kHz, 8dB/km - 32kHz

404550556065707580859095

100105110115120

100

400

700

1000

1300

1600

1900

2200

2500

2800

3100

3400

3700

4000

4300

4600

4900

Range

dB

Tra

nsm

issio

n lo

ss

TL 13 kHz

TL 25 kHz

TL 32 kHz

From the table can be seen that low frequencies have less loss than higher, and should work at

longer range. The size of the transducer is determined by the frequency. To have low

frequency transducers with the same requirements as medium frequency transducers regarding

opening angles, requires bigger physical size.

Noise

The factor that causes most problems is noise. Noise can be generated from the vessel itself

(motors, thrusters etc.), from neighbouring installations or vessels, ROVs or from the waves.

ENVIRONMENTAL ACOUSTIC NOISE LEVEL

SPECTRUMLEVEL(DB RE 1UPA)

140

120

100

80

60

40

20

1 10 100 1000 10.000 100.000 FREQUENCY HZ

WIND FORCEBEAUFORTSHIP NOISE

THRUSTERNOISE

7

4

2

0

DRILLINGNOISE

(CD3942)

The diagram shows different types of noise with frequency and noise level.


Training Manual


Rev. 07 Training

The curves indicate clearly that thruster noise is far the strongest. Thrusters generate noise, but

they can also make air bubbles in the water, and if these come between the transducer and the

transponder, the signal can be blocked.

Going astern with the vessel using the main propellers normally pulls a lot of air under the

hull, this might cause signal blockage similar to that caused by the thrusters.

Operational Principles - LBL / SBL / SSBL


Training Manual

.3.6 Kongsberg Maritime AS Jan. 2010

Training Rev. 07

SSBL Principle (Super Short Base Line)

When using the SSBL principle, the distances between the elements inside the transducer

(base lines) are used to calculate the transponder position.

The position calculation is based on distance and direction measurements to one transponder.

An interrogation pulse is transmitted from the onboard transducer, which will interrogate the

subsea transponder, which again will answer with a reply pulse. If the transponder on the

seabed is slightly out of vertical line, there will be a small time difference from one element to

the other when the pulse hits the surface of the transducer. This time difference is extremely

small and hard to measure by a clock. Instead the system measures the phase difference when

the signal hits for instance the Ref. and Y element in the drawing below. When we know the

wavelength, and the phase difference, the time difference can be easily calculated. With this

information we can calculate the angle of the reply pulse and determine from which direction

the pulse is coming. When we know the speed of sound in water we can find the distance.

Angle measurement

Computation of position Computation of position

in the forward/aft direction in two planes


Training Manual


Rev. 07 Training

LBL Principle (Long Base Line)

The LBL system consists of one transducer and an array of transponders, where the exact

distance between each transponder is known. The base lines are no longer the elements inside

the transducer, but the distance between the transponders. For SSBL the base lines are less

than 10 cm, while for LBL the base lines can be more than 1000 m.

The distances between the transponders are calibrated, and LBL is therefore more time-

consuming to set up than SSBL. The calibration is done using a built-in mode in the

transponders. All the transponders will be interrogated simultaneously, and they will respond

with their individual replies. The LBL system will calculate the ranges from the individual

transponders, and by using the base lengths of the calibrated transponder array together with

these ranges in software algorithms, the vessel can be positioned.

The advantage of LBL systems over SSBL systems is that accuracy is maintained down to

decimetre level, even if the ranges are several hundred meters.

The transducer might be an SSBL type, or it can be a special one with only one element, since

angular measurements are not used. LBL requires intelligent transponders that can be

commanded to execute different operations using telemetry.


Training Manual


Training Rev. 07

Transducers and transducer elements

A transducer is an acoustic transmitter/receiver normally placed onboard the vessel,

approximately 3 m below the keel. Mounted on a pole which is remotely operated from the

bridge, it can be lowered or recovered whenever necessary. A transducer consists of several

transducer elements.

The elements will start vibrating when voltage is applied, transmitting sound waves with

correct frequency. When the pulses from the transponder are received, the elements start

generating voltage. The internal distances between these elements are known.

Steel block

Electric connection

2 blocks of ceramic

crystals

Transducer face

Electric connection

Magnesium block

Rubber cover


Training Manual


Rev. 07 Training

Typical System Overview - HiPAP transducer

There are different HPR systems and transducers on the market. Kongsberg Maritime is well

known for the efficient HiPAP transducer, (High Precision Acoustic Positioning).

The HiPAP hull unit uses the same relay

unit to lower and hoist as the two other

hull units.

The transceiver is installed close to the

hull unit, since the cable from the hull

unit to the transceiver is only 5 m.

Position data is sent from the operator

unit to other equipment. The digital

interface can be RS232, RS422, current

All interfaces to the transceiver (gyro and

VRU) are in serial format (RS422) loop

or ethernet.


Training Manual


Training Rev. 07

Transponders

A transponder is an acoustic receiver/transmitter placed on the seabed or onboard an ROV or

any other structure to be positioned. It is triggered from the vessel using acoustic signals, and

will in normal operation only answer if it is interrogated from the vessel.

The power source is normally a battery, the lifetime of which depends on how often the

transponder is interrogated and what kind of battery type is used.

The size and weight of the transponders are determined by the depth specification and battery

lifetime.


Training Manual


Rev. 07 Training

RPT type

For 1000 m depth rated

transponders an aluminium

housing is chosen.

The RPT type is a combined

transponder/responder, which

can use an external DC power

source in addition to internal

battery.

For 3000 m depth rated

transponders a stainless steel

housing is chosen

Transponder Deployment When deploying the transponder it is important to prevent the air produced by main

propellers, thrusters, diving bell, etc. from obstructing the path of communication between the

transponder and the transducer. When the HPR system is part of a dynamic positioning system

the current and wind direction must be considered before deploying the transponder. The

transponder must be deployed in a position where the current carries the air from a diving bell

or other air producing equipment away from the operating area.


Training Manual


Training Rev. 07

The transponders might be deployed with a rope or a wire going to a buoy or the vessel on the

surface, or they might be "thrown" over the side of the vessel if they have an acoustic release

mechanism.

The length of the rope between the transponder base and the weight can be 2-5 m.

The recommended weight of the sinker is different for 1000 m and 3000 m transponders.

• For 1000m transponders we recommend a weight of approx. 60 kg.

• For 3000m transponders we recommend 100 kg.

Keep in mind the current when transponders are deployed. The weight might be increased if

the current is strong, it is most important to get the transponder in the exact predetermined

position.

REMEMBER:

Make sure the weight of the transponder and the sinker is brought up in the sinker and

NOT in the protective cage on the transponder whenever the transponder is handled.

The cage is for protection of the transducer, and is certified for lifting the transponder with

flotation collar only.


Training Manual


Rev. 07 Training

Transponder models

We have three main groups of transponders:

- MPT Multifunction Positioning Transponder

- SPT SSBL Positioning Transponder

- RPT ROV Positioning Transponder

MPT transponders are used in: LBL positioning

Array calibration

SSBL positioning

General telemetry commands *)

SPT transponders are used in: SSBL positioning

General telemetry commands *)

RPT transponders are used in: ROV positioning

Tow-fish positioning

(The RPT does not have the telemetry option)

The transponder model name gives the user information about operating frequency, depth

rating, transducer beam width and any option. The transponder name is put together like this:

Transponder name = model name + model number + options

Model name:

- MPT = Multifunction Positioning Transponder

- SPT = SSBL Positioning Transponder

- RPT = ROV Positioning Transponder

Model number:

1. digit 2. digit 3. digit

1=15 kHz (low frequency) 1=1000 metre depth 1= ±15° beam width

3=30 kHz (medium frequency) 2=2000 metre depth 3= ±30° beam width

3=3000 metre depth 4= ±45° beam width

6= ±60° beam width

9= ±90° beam width

Some of the options available:

- D = Depth sensor

- H = Heading magnetic compass

- E = External power

- I = Inclinometer

- II = Internal and external inclinometers, (diff.inclo. TP)

- N = Rechargeable NiCAD or seal lead battery pack

- R = Release mechanism

- S = Split, separate transducer and housing

- T = Temperature sensor

- Rsp = Responder

- DuB = Dual Beam


Training Manual


Training Rev. 07

HPR 400 Mode

HPR 400 transponders are used by the Kongsberg HPR 400 series, as well as the HiPAP

sytem.

TP

Channel

1st Interro-

gation

frequency

2nd

Interro-

gation

frequency

Reply

frequency

B12 21000 21500 29250

B13 21000 22000 29750

B14 21000 22500 30250

B15 21000 23000 30750

B16 21000 23500 27250

B17 21000 24000 27750

B18 21000 24500 28250

B19

B21 21500 21000 28500

B22

B23 21500 22000 29500

B24 21500 22500 30000

B25 21500 23000 30500

B26 21500 23500 27000

B27 21500 24000 27500

B28 21500 24500 28000

B29

B31 22000 21000 28750

B32 22000 21500 29250

B33

B34 22000 22500 30250

B35 22000 23000 30750

B36 22000 23500 27250

B37 22000 24000 27750

B38 22000 24500 28250

B39

B41 22500 21000 28500

B42 22500 21500 29000

B43 22500 22000 29500

B44

B45 22500 23000 30500

B46 22500 23500 27000

B47 22500 24000 27500

B48 22500 24500 28000

B49

TP

Channel

1st

Interro-

gation

frequency

2nd

Interro-

gation

frequency

Reply

frequency

B51 23000 21000 28750

B52 23000 21500 29250

B53 23000 22000 29750

B54 23000 22500 30250

B55

B56 23000 23500 27250

B57 23000 24000 27750

B58 23000 24500 28250

B59

B61 23500 21000 28500

B62 23500 21500 29000

B63 23500 22000 29500

B64 23500 22500 30000

B65 23500 23000 30500

B66

B67 23500 24000 27500

B68 23500 24500 28000

B69

B71 24000 21000 28750

B72 24000 21500 29250

B73 24000 22000 29750

B74 24000 22500 30250

B75 24000 23000 30750

B76 24000 23500 27250

B77

B78 24000 24500 28250

B79

B81 24500 21000 28500

B82 24500 21500 29000

B83 24500 22000 29500

B84 24500 22500 30000

B85 24500 23000 30500

B86 24500 23500 27000

B87 24500 24000 27500

3 hpr jan 2010

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