INS for DP – Methods – Full VersionIMCA Annual Seminar Singapore, November 2013, Jim Titcomb, Yann Casamajou

INS Introduction

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)

DP-PHINS : Bringing INS benefits to DP

12

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

13DP-PHINS What is it?

Time Signals

Time and Position For Initialisation Only

Time stamped beacon positions and heading

Processed Positions

Enhanced Position

Acoustic Positions

14DP- 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 Taught Wire Fan Beam Radascan Etc. Etc.

15Why this approach?

Augmented GNSS is an accurate and generally reliable positioning solution.

For DP in deep water, the primary issue would seem to be lack of other available 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

What does INS give you when you are relying on GNSS?

Data Example – Single PME

17Station keeping on GPS

181 minute outage

192 minute outage

203 minute outage

214 minute outage

225 minute outage

236 minute outage

247 minute outage

258 minute outage

269 minute outage

2710 minute outage

11m in 10 minutes

2820 minute outage

38m in 20 minutes

29Whats the alternative?

INS will drift quickly if the aiding sensor fails. 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.

DP-PHINS : Multiple aiding sensors

31DP-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.

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

32DP- 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

33DP- 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

34Acoustic Aiding Examples - Recap

ROV on Seabed. 850m water depth Well calibrated USBL About as good as it gets

with USBL

Standard Deviation

X Y Position

USBL 1.03

0.86

1.34

35INS Aided with USBL - Recap

Spikes in USBL rejected Automatically.

Much higher update rate. Smoother positioning. Reduced spread of

positions.

5 X improvement with INS

Standard Deviation

X Y

USBL 1.03

0.86

1.34

INS 0.16

0.2 0.26

36INS Aided with USBL & DVL

DVL update only every 3 seconds

Positioning now better than high accuracy GPS even in 850m

17 x Better than raw acoustics.

Standard Deviation

X Y

USBL 1.03

0.86

1.34

INS 0.16

0.2 0.26

With DVL 0.05

0.06

0.07

37What if we lose acoustics?

DVL update only every 3 seconds

Positioning now better than high accuracy GPS even in 850m

Standard Deviation

X Y

USBL 1.03

0.86

1.34

INS 0.16

0.2 0.26

With DVL 0.05

0.06

0.07

INS DVL 0.04

0.02

0.05

DP-PHINS : Future Developments

39DP-PHINS, LUSBL performances

Using range measurements on suitable beacons leads to better positioning accuracy than USBL

At Least three ranges are required for LBL positioning

Station keeping with only two ranges is possible with INS and LBL combined (with INS initialization)

With multiple beacons and appropriate field geometry, DP-PHINS brings LUSBL feature to INS, taking full benefits of

Outliers rejection using PHINS high grade INSPrecision on ranges measurement (even with CW beacons)Error bounding by computed USBL positions

System accuracy is then directly related to the range measurement precision

40DP-PHINS, LUSBL Accuracy and Geometry

Accuracy of results is dependant on a combination of geometry and range measurement accuracy

If the beacons are “in line” with the vessel, LUSBL improvement will be

Optimum on beacon axisPoor orthogonally to beacon axis……. But still bounded by USBL precision

Accuracy will be optimum on both axis if there is a high “Angle of cut”

DP-PHINS naturally takes the best of USBL angles

and distances information

41DP-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

Simply add a beacon... And take the full benefit of DP-PHINS !

DP-PHINS operating in 1364m (4475ft)

42DP-PHINS, LUSBL performances

The range measurements are far more precise than the angle measurements.

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

43

DP-PHINS, LUSBL performances

Performance improvement on latitude:

1DRMS Standard deviation on latitude

1DRMS precision (m) % slant range

USBL 5.09m 0.365%

DP-PHINS, USBL 1.65m 0.118%

DP-PHINS, LUSBL 0.32m 0.023%

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

Conclusions

45Conclusion: 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.

46Conclusion: Why moving to DP-PHINS ?

Intrinsic performance improvement 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…)

47

Thanks for your attention

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