Pieter Toor Veripos
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Transcript of 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
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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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
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
Positioning for Success
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)
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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
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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
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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
Positioning for SuccessPositioning for Success
Thank you for your attention
? QUESTIONS