Pieter Toor Veripos

26
Positioning for Success Real-time Tidal Observation using High-Accuracy GPS Positioning Pieter Toor Research & Development Manager VERIPOS Hydrographic Society Benelux, Dordrecht 7 th May 2008
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Presentation Pieter Toor gave during the Hydrographic Society Benelux workshop about the z-axis positioning with Veripos.

Transcript of Pieter Toor Veripos

Page 1: Pieter Toor Veripos

Positioning for Success

Real-time Tidal Observation using

High-Accuracy GPS Positioning

Pieter Toor

Research & Development Manager

VERIPOS

Hydrographic Society Benelux, Dordrecht

7th May 2008

Page 2: Pieter Toor Veripos

Positioning for Success

Company Information

- VERIPOS

- A product line within Subsea 7

- Established in 1989

- Providing precise navigation &

positioning services

- Global business

- Specialising in marine operations

in offshore oil & gas sector

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Positioning for Success

Corporate Structure

Subsea 7 Inc.

Construction / IRM

VERIPOSi-Tech

Drill Rig Support

Oslo S.E.

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VERIPOS Background

FORMED 1989 – JV BROWN & ROOT AND ORMTEC

1992 – BRS SOLD TO SUBSEA OFFSHORE

1994 – OSIRIS ENTERED VERIPOS ALLIANCE

1995 – CGG (TOPNAV) ACQUIRES OSIRIS

1989 2006

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

1990Association formed

with Boskalis division,Osiristo share H.F.

coverage in N.Sea

2001Fugro acquires

TopNav – VERIPOS now 100% Halliburton

Subsea

1999Coverage

Extended to Brazil

2003Fugro

Acquires Thales

2004VERIPOS 6 people

January 1989VERIPOS UK formed as JV

between Brown & Root

Survey & Ormtecto Operate HF DGPS

in North Sea

1995CGG acquires

OsirisVERIPOS 50/50

CGG & Subsea Offshore

1994VERIPOS-I Alliance

formed between Subsea Offshore,

CGG Topnav & Osiris to

establish Inmarsatsatellite DGPS

Service

2002Subsea 7

formedVERIPOS Expansion

plan formulated

1998CoverageExtended to GoM

2002VERIPOS-I CoverageExtended to Caspian

2001CoverageExtended to Africa

June 2005Coverage Global

extensive new product

range Launched

2006VERIPOS 50 people

February 2005Investment

for Expansion Approved

2006VERIPOS-UK Alliance with

Ormtec dissolved

2002 – FUGRO ACQUIRES TOPNAV – VERIPOS 100% SUBSEA

7

2003 – FUGRO ACQUIRES THALES GEOSOLUTIONS

2005 – EXPANSION PLAN FORMULATED

2008 – VERIPOS +/- 75 people

Page 5: Pieter Toor Veripos

Positioning for Success

Overview

- Advances in Positioning Technologies

- Overview of Tides

- Using High-Accuracy GPS to

Determine Tide

- Veripos Implementation

- Benefits and Applications

- Future

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Advances in Positioning Technologies

- Positioning is essential technology for offshore operations

- Satellite Navigation technology can now be considered a

mature and accepted technology

- Augmentation data from service providers allows a higher

level of accuracy & precision over standalone GPS

- Services offered range in accuracy from the metre level to the

decimetre level

- Satellite navigation will remain a key technology for offshore

operations

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Advances in Positioning Technologies

- Positioning techniques can now deliver position solutions at the

decimetre level

- Future enhancements will see new satellite constellations and

modernisation of the current systems

- Will see developments with new position solutions

- Different levels of accuracy

- Different combinations of satellite signals

- High-Accuracy positioning systems allow use in new applications

- One area is the determination of Tidal information

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What is Tide?

- Tide is the periodic rise and fall of the sea level under the gravitational pull of the moon and

sun

- Tides cause periodical variations in the ‘equilibrium’ sea level called Mean Sea Surface

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Tidal Trend in High-accuracy Positions

- Veripos Ultra DGPS (PPP) system offers 10-20cm vertical accuracy

High correlation between tides and DGPS heights after removing antenna motion relative to

waterline

Ultra PPP Height and Predicted Tide

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GPS to Vertical Reference - Offsets

Reduce GPS antenna height via a few basic steps:

1. reduce WGS84 height of antenna reference point to vessel’s CRP

- inputs: antenna offsets, pitch & roll and heading, heave

2. reduce vessel CRP to waterline

- inputs: draft, squat

3. correct for additional local effects to finally derive the waterline in WGS84 (optional)

- e.g. currents, atmospheric pressure

Geoid: T1 = h – H + D – NChart datum: T2 = h – H + D – LEllipsoid: T3 = h – H + D

waterline

MSS / Geoid

Chart datum

Elliposoid

Draft, squat

Vessel motion: dx,dy,dz, Rx, Rx, Rz, Δh

Antenna Ref Point

Hh

D

N

T1 T2 T3

L

C

CRP

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Veripos Tides Implementation

- Reduce the effect of heave, pitch and roll by averaging the Ultra high-accuracy heights

- ensure that the position used is an accurate Ultra position (not Standard DGPS or converging) using

QC tag to Error Ellipse/SD threshold of less than 0.1m

- After 39hrs de-tide the heights by using the Doodson filter

- Leave actual tidal reduction to client, i.e. antenna offsets, draft & squat

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Doodson Filter

- The Doodson X0 filter is a simple filter designed to damp out

the main tidal frequencies

- It takes hourly values, 19 values either side of the central one

- A weighted average is taken with the following weights

(1010010110201102112 0 2112011020110100101)/30

- ‘Ultra Tide’ estimate only available after initial 39hrs of

observation

- Secondary instantaneous tide value, ‘Geoid Tide’, is based

on the deviation from the EGM96 geoid model

JOB No: CLIENT: PROJECT:

Diagram: The surveyor shall provide a diagram showingthe points of reference and measurements.

Hour # Date TimeObserved Height (H)

Doodson Multiplier (M)

H x M

0 1 01 0 02 1 03 0 04 0 05 1 06 0 07 1 08 1 09 0 010 2 011 0 012 1 013 1 014 0 015 2 016 1 017 1 018 2 019 0 020 2 021 1 022 1 023 2 024 0 025 1 026 1 027 0 028 2 029 0 030 1 031 1 032 0 033 1 034 0 035 0 036 1 037 0 038 1 0

Sum = 30 0MSL = S (HM) / 30 = 0

(By 39 Hourly Observations / Doodson Filter)MSL TIDAL OBSERVATIONS

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Ultra Tide vs. Geoid Tide

39 hrs0 hrs

Doodson X0

Ultra Tide

- Ultra Tide can only be calculated after 39 hours

- Unbiased but long initialisation

- Geoid Tide can be calculated instantaneously by using

EGM96 Geoid Model as an approximate of mean sea level

- Instantaneous but biased

EGM96

Geoid Tide

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Ultra Tide vs. Geoid Tide

39 HOURS

1010010110201102112 0 2112011020110100101/30

Geoid Tide

Ultra Tide = Avg. Ultra Height – Doodson X0 output

Geoid Tide = Avg. Ultra Height – EGM96 (Earth Gravitational Model 1996)

Tide Value Availability

Ultra Tide

Start of Ultra

positioning

39 hours

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Application Level

- Tidal estimation is available in the Verify-QC positioning & QC software application

$UltraTide,20070827,12:20:00,989,600,600,5708.8614,N,00057.7000,E,20.76,0.06,1.17,18.98,22.45,20.62,0.14,-0.36,21.13,46.43,EGM96*08$UltraTide,20070827,12:30:00,990,600,600,5708.9052,N,00057.7425,E,20.80,0.06,0.97,19.28,22.21,20.62,0.18,-0.33,21.13,46.43,EGM96*06$UltraTide,20070827,12:40:00,991,600,600,5708.9503,N,00057.7887,E,20.83,0.06,1.02,19.47,22.18,20.62,0.22,-0.29,21.13,46.43,EGM96*0A$UltraTide,20070827,12:50:00,992,600,600,5708.9828,N,00057.8221,E,20.83,0.07,1.06,19.26,22.27,20.62,0.21,-0.29,21.13,46.43,EGM96*08

- Output average height and associated quality information to ASCII file

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Validation Against Predicted Tides

- Comparison of Veripos Tides against predicted tide (SHM159a v2.00) in Singapore

- C-O showed Standard Deviation of 11cm and a Mean of 1cm

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Validation Against Tide Gauge

- Comparison of Veripos Tide observation against tide

gauge close to work site

- Conducted over a three day period in United Kingdom

- Comparison of both the Geoid Tide and Ultra Tide at

10 minute intervals

- C-O for the Ultra Tide showed a Standard Deviation of

10 cm and a Mean of 5 cm

- C-O for the Geoid Tide (EGM96) showed a Standard

Deviation of 8 cm and a Mean of 12 cm

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Comparison Against Tide Gauge

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Comparison Against Tide Gauge

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Comparison Against Tide Gauge

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Validation on Subsea Vessel

- Comparison of Veripos Tide observation against tide

gauge close to work site

- Subsea 7 ‘Kommandor Subsea’, in Aberdeen

- Comparison of both the Geoid Tide and Ultra Tide at

10 minute intervals

- C-O for the Ultra Tide showed a Standard Deviation of

13 cm and a Mean of 2 cm

- C-O for the Geoid Tide (EGM96) showed a Standard

Deviation of 12 cm and a Mean of 50 cm

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Validation on Subsea Vessel

Veripos Tide and Tide Gauge Observations- Subsea 7 Komander Subsea, Aberdeen, 22-25 August 2007 -

-2.00

-1.60

-1.20

-0.80

-0.40

0.00

0.40

0.80

1.20

1.60

2.00

300 350 400 450 500 550 600 650 700 750 800

Observation Sample Number (10-minute interval)

Tid

e (m

)

Geoid TideTide Gauge - ObservedUltra Tide

Results highlight biases in EGM96 Geoid Model (accurate to +/- 1m)

Page 23: Pieter Toor Veripos

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Performance & Verification

- Veripos tide solution has ability to observe tide at different locations with different sea

state conditions

- Figure below is tide observations recorded during transit from Scotland to Cyprus

NORTH SEA

ENGLISH CHANNEL

ATLANTIC OCEAN

MEDITERANEAN SEA

Tide still useable

despite 6-7m swell

Page 24: Pieter Toor Veripos

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Applications & Benefits

- Real-time observation of tidal variations using high-accuracy GPS offers many advantages over

conventional methods

- Cost and time savings if deployment of tide gauges not required

- Correct bathymetric data in real-time removing need for post-processing

- Better representation of tides compared to model based predictions since it includes tidal variations

at a much higher frequency

- Used for tidal current prediction especially if tidal range is very high

- Current at minimum during peak or trough of tide and strongest current during the tide rise or

fall

- Useful when conducting critical operations

Page 25: Pieter Toor Veripos

Positioning for Success

Future Activities

- Further improvement with the inclusion of pitch and roll data

- During vessel operations (loading, unloading, crane movement, etc.) will affect the vessel

draft which can impact tidal observations

- Investigate how these values can be incorporated

- Any improvement in positioning accuracy will immediately benefit the tide observation

process

- Future enhancements to Satellite Navigation

- Improved MSS / Geoid models will aid in linking GPS height (ellipsoidal) to MSS

- New MSS anticipated with greater resolution than EGM96 but more importantly higher accuracy

Page 26: Pieter Toor Veripos

Positioning for SuccessPositioning for Success

Thank you for your attention

? QUESTIONS