This document discusses PHINS for DP applications. It begins with an introduction to inertial navigation systems (INS) and their components like gyroscopes and accelerometers. It then discusses how integrating a PHINS with dynamic positioning (DP) systems, called a DP-PHINS, can improve underwater acoustic positioning performances for DP. Specifically, a DP-PHINS can enhance raw USBL positioning through data fusion algorithms and provide continuous high-quality positioning even during GPS outages. Field tests showed a DP-PHINS improved USBL accuracy by 2-3 times and LUSBL accuracy up to 16 times. The DP-PHINS also allows vessels to maintain station keeping for over 10 minutes during a complete GPS failure through inertial navigation

1. PHINS for DP Applications
Yann CASAMAJOU
Europort 2013

2. Agenda

Introduction to INS

DP-PHINS : bringing INS benefits to DP

Augmented USBL Performances

LUSBL Performances

Robustness to Outages

Conclusion
2

3. 3
What'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

4. 4
What's in an INS?
3 “FOG” gyrometers
monitor rotation and speed in X, Y & Z axis
 3 accelerometers
measure acceleration (>> speed >> motion) in 3 axis
 Powerful electronic / firmware package
PHINS “knows” in real time its motion in space .
Firmware (Kalman filter) calculates its position in real
time + heading, pitch, roll, heave, etc…

All integrated
small, lean, powerful!
(PHINS 6000 example)

5. INS Introduction

What makes an INS good.. or not?



Gross figures:



Internal sensors (gyroscopes & accelerometers) are never perfect, bias and
scale factors accumulate over time
Navigation is mostly about Gyroscopes
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
5

6. INS 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



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
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.
6

7. Benefits of data fusion: Robustness to signal losses
GPS positioning
with masking
7

8. Benefits of data fusion: outages
GPS + INS
positioning with
masking
8

9. 9
Benefits 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)
3
position accuracy (m)

2,5
PHINS pure inertial drift (0.0002 x t^2
m)
2
Averaging of DGPS data (3 / sqrt(t)
m)
1,5
PHINS+DGPS
1
0,5
0
0
20
40
60
time t (s)
80
100

10. Benefits 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)
10

11. Agenda

Introduction to INS

DP-PHINS : bringing INS benefits to DP

Augmented USBL Performances

LUSBL Performances

Robustness to Outages

Conclusion
11

12. DP-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
12

13. 13
DP-PHINS What is it?
Missing link between PHINS and USBL PME
Goals of the system :
Improve USBL performances to make it usable for DP during
GPS scintillation
Use PHINS fusion algorithms to enhance raw USBL positioning
DP-PHINS cabinet extends PHINS capabilities to :
use raw acoustic detections from any USBL for positioning
provide positioning telegram to DP Desk
Context:
Offshore works and installation jobs
Deep sea (>1000m)
Necessity to pursue operations without any reliable GPS
Severe daily scintillation phenomena (Africa, Brazil...)

14. 14
DP-PHINS What is it?
DP-PHINS
USBL
system
Time stamped beacon
positions (in vessel
reference frame)
Enhanced Position
...
Time Signals
DP desk
DGPS
GNSS
Acoustic
Positions
Time and Position
For Initialisation Only
Processed
Positions

15. DP- PHINS, Features

PHINS Natural Features:




DP-PHINS cabinet additional improvements:






Native fusion of a wide range of sensors (GPS, DVL...)
Strong noise rejection
Sparse-array capability
Relative to Global co-ordinate transforms
Unlimited number of beacon
Sparse array LBL
Flexible
Expandable
Future Sensors




Taut Wire
Fan Beam
Radascan
Etc. Etc.
15

16. Agenda

Introduction to INS

DP-PHINS : bringing INS benefits to DP

Augmented USBL Performances

LUSBL Performances

Robustness to Outages

Conclusion
16

17. 17
DP- PHINS Performances:
Augmented USBL, case 1
Nov2012: 1300m depth operations
Single vessel, 2 cases:
DP with manoeuvring operations
1x standard omnidirectional transducer, tonal codes
DP with static vessel position
1x directional transducer  improved USBL accuracy
Test CASE
USBL SD
DP-PHINS SD
Accuracy
Accuracy Gain
(1DRMS,DGPS ref) (1DRMS,DGPS ref)
(%slant range)
Dynamic, omni
2.34m
0.71m
x3.3
0.055%
Static, directional
1.22m
0.46m
x2.65
0.035%
DP-PHINS raises USBL PME
to submetric performances on
performing vessels
USBL raw data
PHINS + USBL, SD live
PHINS + DGPS

18. 18
DP- PHINS Performances:
Augmented USBL, case 2
Less performing USBL
Kongsberg CAT, 1360m depth
Standard tonal transponders
DP performances in dynamic test
USBL vs GPS
accuracy
PHINS vs GPS
accuracy
Accuracy GAIN
(GPS ref)
% Slant range
max
86,79m
7,94m
x10,93
0.57%
1DRMS
6,21m
2,64m
x2,35
0.19%
Error Type
DP-PHINS raises poor DP-USBL
to acceptable levels of
performances in most fields

19. Agenda

Introduction to INS

DP-PHINS : bringing INS benefits to DP

Augmented USBL Performances

LUSBL Performances

Robustness to Outages

Conclusion
19

20. 20
DP-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)

21. DP-PHINS, LUSBL performances
Measured ranges extracted computed
from HiPAP USBL Data
 Slant range standard deviation on CW
signals: <30cm 1DRMS

B14
2 beacons used during this test
B14, 312m north
B15, 285m south
Vessel
B15
 LUSBL achievements in such a situation:
Optimum precision on latitude
No improvement on longitude
21

22. 22
DP-PHINS, LUSBL performances
Performance improvement on latitude:
1DRMS Standard deviation on latitude
At 1360m depth, LUSBL is
15.9x better than basic USBL
5.1x better than augmented-USBL
... With same beacons, same vessel, pole and USBL transceiver !

23. Agenda

Introduction to INS

DP-PHINS : bringing INS benefits to DP

Augmented USBL Performances

LUSBL Performances

Robustness to Outages

Conclusion
23

24. DP-PHINS: what if the positioning source fails ?

INS Station keeping on GPS
24

25. DP-PHINS: what if the positioning source fails ?

1mn outage
25

26. DP-PHINS: what if the positioning source fails ?

2mn outage
26

27. DP-PHINS: what if the positioning source fails ?

3mn outage
27

28. DP-PHINS: what if the positioning source fails ?

4mn outage
28

29. DP-PHINS: what if the positioning source fails ?

5mn outage
29

30. DP-PHINS: what if the positioning source fails ?

6mn outage
30

31. DP-PHINS: what if the positioning source fails ?

7mn outage
31

32. DP-PHINS: what if the positioning source fails ?

8mn outage
32

33. DP-PHINS: what if the positioning source fails ?

9mn outage
33

34. 34
DP-PHINS: what if the positioning source fails ?

10mn outage

11m in 10 minutes

35. 35
DP-PHINS: what if the positioning source fails ?

20mn outage

38m in 20 minutes

36. DP-PHINS: what if the positioning source fails ?

36
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

37. 37
DP-PHINS: what if the positioning source fails ?
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.

Error, %
DVL Update
travelled
Drift speed
Rate
distance
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
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


38. Agenda

Introduction to INS

DP-PHINS : bringing INS benefits to DP

Augmented USBL Performances

LUSBL Performances

Robustness to Outages

Conclusion
38

39. Conclusion: 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.

39

40. 40
Conclusion: 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. 41
Thanks for your attention
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