inertial fog and acoustic aiding references for dynamic positioning applications

PHINS for DP Applications

Yann CASAMAJOUEuroport 2013

2Agenda

Introduction to INS

DP-PHINS : bringing INS benefits to DP

Augmented USBL Performances

LUSBL Performances

Robustness to Outages

Conclusion

3What's in an INS?

What is an Inertial Navigation System (INS)?An instrument (electronic + sensors) which is using its initial state (position) and internal motion sensors (gyroscopes + accelerometers) to measure and calculate its subsequent positions in space with high accuracy, stability and update rate

PHINS PHINS 6000 ROVINS

4What's in an INS?

3 “FOG” gyrometersmonitor rotation and speed in X, Y & Z axis

3 accelerometersmeasure acceleration (>> speed >> motion) in 3 axis

Powerful electronic / firmware packagePHINS “knows” in real time its motion in space . Firmware (Kalman filter) calculates its position in real time + heading, pitch, roll, heave, etc…

All integratedsmall, lean, powerful!(PHINS 6000 example)

5INS Introduction

What makes an INS good.. or not? Internal sensors (gyroscopes & accelerometers) are never perfect,

bias and scale factors accumulate over time Navigation is mostly about Gyroscopes

Gross figures: Accelerometers errors are not heavily involved in the position drift –

4m – Schuller period Gyroscope are heavily involved in the drift – 400 m

Conclusions A good INS requires good gyro’s IXBLUE manufactures FOG (Fiber Optic Gyroscope) and controls the

whole process A range of FOG’s (FOG90, FOG120, FOG180…) for a range of INS

6INS Introduction

The best sensors are still not perfect, accumulating small errors vs. time makes the system drift on the long term

External sensors (aiding) are required to bound drift within acceptable limits.PHINS & ROVINS includes interfaces for most common external sensors

GPS DVL (Doppler Velocity Log) Pressure sensor Acoustic positioning references (USBL, LBL) …and all IXBLUE products!

IXBLUE INS are fully integrated Inertial Positioning solutions designed for ease of installation & operation, flexible enough to fit most requirements, with no specialist engineer to install / operate.

7Benefits of data fusion: Robustness to signal losses

GPS positioning with masking

8Benefits of data fusion: outages

GPS + INS positioning with masking

9Benefits of data fusion: accuracy

Data Fusion Use various and different technologies to measure the same parameter Blend (fuse all this data (Kalman filter) in order to correlate it and obtain a

better result A simple example GPS + INS (PHINS or GAPS typical use case)

0

0,5

1

1,5

2

2,5

3

0 20 40 60 80 100

time t (s)

po

sit

ion

ac

cu

rac

y (

m)

PHINS pure inertial drif t (0.0002 x t^2m)

Averaging of DGPS data (3 / sqrt(t)m)

PHINS+DGPS

10Benefits of data fusion: accuracy (USBL case)

Acoustic positioning can be poor, low update rate, or out of range. INS + USBL combination / data fusion provides continuous high quality positioning:

Survey @2500m depth: INS accuracy is much better than USBL’s one (noise rejection)

11Agenda

Introduction to INS



LUSBL Performances


Conclusion

12DP-PHINS, Why raising expectations?

Augmented GNSS is an accurate and generally reliable positioning solution.

For DP in deep water, the main issue is the lack of other performing positioning systems.

What to do in water that is too deep for useful acoustics? After a certain depth acoustics become too noisy, too deep for taut

wire, no other structures for relative based systems.

Too many vessels relying on single PME – GNSS

DP PHINS is the simplest way to raise positioning performances on a vessel

13

DP-PHINS What is it?

Missing link between PHINS and USBL PME

Goals of the system :

DP-PHINS cabinet extends PHINS capabilities to :

Context: Offshore works and installation jobsDeep sea (>1000m)Necessity to pursue operations without any reliable GPSSevere daily scintillation phenomena (Africa, Brazil...)

Use PHINS fusion algorithms to enhance raw USBL positioning

Improve USBL performances to make it usable for DP during GPS scintillation

use raw acoustic detections from any USBL for positioningprovide positioning telegram to DP Desk

14DP-PHINS What is it?

Time Signals

Time and Position For Initialisation Only

Time stamped beacon positions (in vessel reference frame)

Processed Positions

Enhanced Position

Acoustic Positions

USBL system

...

DGPSGNSS

DP desk

DP-PHINS

15DP- PHINS, Features

PHINS Natural Features: Native fusion of a wide range of sensors (GPS, DVL...) Strong noise rejection Sparse-array capability

DP-PHINS cabinet additional improvements: Relative to Global co-ordinate transforms Unlimited number of beacon Sparse array LBL Flexible Expandable

Future Sensors Taut Wire Fan Beam Radascan Etc. Etc.

16Agenda

Introduction to INS



LUSBL Performances


Conclusion

17DP- PHINS Performances: Augmented USBL, case 1

USBL raw dataPHINS + USBL, SD livePHINS + DGPS

Nov2012: 1300m depth operations

Single vessel, 2 cases:

DP with manoeuvring operations1x standard omnidirectional transducer, tonal codesDP with static vessel position1x directional transducer improved USBL accuracy

Accuracy Gain

x3.3

x2.65

Accuracy (%slant range)

0.055%

0.035%

Test CASE USBL SD (1DRMS,DGPS ref)

DP-PHINS SD (1DRMS,DGPS ref)

Dynamic, omni 2.34m 0.71m

Static, directional 1.22m 0.46m

DP-PHINS raises USBL PME to submetric performances on

performing vessels

18DP- PHINS Performances: Augmented USBL, case 2

Less performing USBL

Kongsberg CAT, 1360m depthStandard tonal transpondersDP performances in dynamic test

Error Type USBL vs GPS accuracy

PHINS vs GPS accuracy

max 86,79m 7,94m

1DRMS 6,21m 2,64m

Accuracy GAIN (GPS ref)

x10,93

x2,35

% Slant range

0.57%

0.19%

DP-PHINS raises poor DP-USBL to acceptable levels of performances in most fields

19Agenda

Introduction to INS



LUSBL Performances


Conclusion

20DP-PHINS, LUSBL performances

In May this year iXBlue commissioned DP-PHINS onboard Subsea7 vessel Simar Esperanca.

Augmented-USBL brings x2 to x3 improvement over raw USBL, operating in over 1,350m on acoustics

LUSBL makes it even better Most of the USBL error is on the angle

measurements Range measurements are always consistent Extract ranges out of USBL data string and

generate Pseudo LBL data Simply add a beacon... And take the full benefit

of DP-PHINS ! DP-PHINS operating in 1364m (4475ft)

21DP-PHINS, LUSBL performances

Measured ranges extracted computed from HiPAP USBL Data

Slant range standard deviation on CW signals: <30cm 1DRMS

B14

B15

Vessel

2 beacons used during this testB14, 312m northB15, 285m south

LUSBL achievements in such a situation: Optimum precision on latitude No improvement on longitude

22

DP-PHINS, LUSBL performances

Performance improvement on latitude:

1DRMS Standard deviation on latitude

At 1360m depth, LUSBL is 15.9x better than basic USBL5.1x better than augmented-USBL

... With same beacons, same vessel, pole and USBL transceiver !

23Agenda

Introduction to INS



LUSBL Performances


Conclusion

24DP-PHINS: what if the positioning source fails ?

INS Station keeping on GPS


1mn outage


2mn outage


3mn outage


4mn outage


5mn outage


6mn outage


7mn outage


8mn outage


9mn outage

34

11m in 10 minutes

DP-PHINS: what if the positioning source fails ?

10mn outage

35

38m in 20 minutes

DP-PHINS: what if the positioning source fails ?

20mn outage


INS will drift quickly if the acoustics fail. 3m in 2 min, 20m in 5 min. 0.6Nmi in an hour

When using INS with a single aiding sensor, a single failure will take out your INS also.

INS is most effective with multiple aiding sensors.

INS SHOULD be used with multiple aiding sensors


INS free inertial specification is based on time. The more time, the greater the drift. Adding a DVL to DP-PHINS is an option to contain this drift DVL aided INS specification is based on distance travelled. If you don’t move the error

can’t grow as much.

PHINS-DVL performance is still good at low update rate compatible with deep water Problem: DVL is only available in water depths up to around 1,000m

DVL Update

Rate

Error, %

travelled

distance

Drift speed

m/h

1S 0.03% 0.18

2S 0.13% 0.82

3S 0.26% 1.67

4S 0.27% 1.77

6S 0.32% 2.08

8s 0.30% 1.98

38Agenda

Introduction to INS



LUSBL Performances


Conclusion

39Conclusion: DP-PHINS as a PME

INS is a proven technology on Land, Under water, in Space, why not in DP?

INS has a long track record, Modern FOG based systems bring extreme robustness and reliability.

INS can produce heading and attitude data as well as positioning. INS Should not be aided just by GPS for DP applications.

DP-PHINS can make your acoustics as good as high accuracy GPS. The biggest benefits can be obtained by combining aiding sensors. With the addition of DVL, PHINS can even be considered a stand

alone PME for a significant period of time.

40Conclusion: Why moving to DP-PHINS ?

Intrinsic improvement of USBL due to PHINS IMU performances Augmented-USBL: x2 to x3 better than USBL with single USBL beacon Augmented-LUSBL: up to 16x times better with additional beacons

Sequential use of beacons for LUSBL ➯ battery savings of field transponders

Extended acceptable water depth for DP ➯ extended DP class Continued operation in case GPS outage ➯ recurring financial gain Easy refit of vessels with existing USBL

➯ unchanged USBL, pole… DP-PHINS can be installed anywhere on board

Fuel saving thanks to DP-PHINS output position smoothness Positioning system open to any additional sensor (DVL, deep water CVL…)

41

Thanks for your attention

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