acoustic ins aiding nasnet® & fileinertial navigation systems ... similar to that in the dp...
TRANSCRIPT
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Acoustic INS aiding
NASNet® & PHINS
Aberdeen Houston Rio
NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Sam Hanton
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Positioning Options www.nautronix.com
Satellites
GPS, GLONASS, COMPASS
Acoustics
LBL, SBL, USBL
Relative sensors
Laser systems
Radio Systems
Inertial Navigation Systems
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• Inertial Navigation Overview
• General Integration Considerations
• Specific NASNet® INS Aiding Challenges
• Review of trials data
• Summing up
Overview www.nautronix.com
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Inertial Navigation Overview
NAUTRONIX www.nautronix.com
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Inertial Navigation Concept www.nautronix.com
• 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
INS “knows” in real time its motion in space .
Firmware (Kalman filter) calculates its position
in real time + heading, pitch, roll, heave, etc…
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Inertial Navigation History www.nautronix.com
Basic ‘INS’ developed in 1940’s for WWII rocket guidance
Military developments during 1950’s & 1960’s
First commercial use 1970’s
Extensive use in – Aircraft
– Guided missiles
– Submarines
– Spacecraft
Lots of talk (3rd INS presentation of the day!) – not so much action...
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Complementary Characteristics www.nautronix.com
Acoustics
• Real World Positioning
• Long term Accuracy
• Short term instability (deep
water particularly)
• Vulnerable to
environmental effects
(noise)
INS
• Relative Positioning
• Short term Stability
• Long term drift
• Independent of
environmental effects
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Inertial Navigation Benefits www.nautronix.com
Various generic benefits to vessel positioning:
• Improved position stability
• Faster position update
• Protection against drop-out of other position sensors
0
0,5
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1,5
2
2,5
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3,5
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General Integration
Considerations
NAUTRONIX www.nautronix.com
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Requirements
1. Inertial Navigation System
2. Aiding System (acoustic positioning)
3. Ability to provide data from ‘2’ to ‘1’
Optional
• Understanding of relative data qualities
The Basics www.nautronix.com
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Considerations www.nautronix.com
Physical Interface
Data Formats
Position vs. observation
Weighty Issues
Sound Velocity
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Where is the data generated, transferred and processed?
• Different applications – vessel DP or ROV
Physical Interface www.nautronix.com
IMU
topside
IMU
Acoustic
Topside
Acoustic
Transducer
IMU
topside
IMU
Acoustic
Topside
Acoustic
Transducer
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Generic String (GPS Position)
• Quick and Easy – Plug and Play
• Optimal solution?
$GPGGA,111828.00,0615.9594002,S,01043.3028162,E,2,09,1.0,53.75,M,0.00
,M,23.7,0069*61
Quality related data:
• GPS quality indicator (0=invalid; 1=GPS fix; 2=Diff. GPS fix)
• Number of satellites in use
• Horizontal dilution of precision
Data Formats www.nautronix.com
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INS Aiding using LBL acoustics can provide
• Calculated Acoustic Position
• Observed acoustic Time of Flight
• Distance (TOF x Speed of Sound)
Position vs. Observation Aiding Loosely Coupled vs. Tightly Coupled www.nautronix.com
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0
500
1000
1500
2000
2500
3000
1480 1490 1500 1510 1520 1530 1540 1550 1560
De
pth
(m)
Sound Velocity (m/s)
LBL Acoustic systems measure travel times
Distance = time x speed (velocity)
Sound Velocity www.nautronix.com
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Position and Range Aiding for LBL www.nautronix.com
• 3 Ranges necessary for
position to be generated
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Position and Range Aiding for LBL www.nautronix.com
• If less than 3 ranges
available no acoustic
position is available
??
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Position and Range Aiding for LBL www.nautronix.com
• If less than 3 ranges
available no acoustic
position is available
• But range aiding still
provides useful information
to INS
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Different data types combined within INS solution
• Gyro and accelerometer data – from IMU
• Position/time/distance – from acoustic aiding source
Optimal positioning requires appropriate weighting of observations –
similar to that in the DP system
Weighting is primarily affected by accuracy and latency (age) of data
Weighting www.nautronix.com
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Custom strings better suited to conveying quality information
GPGGA contains no quantative accuracy or age information
• INS may assume GPGGA data has same parameters as GPS
Position aiding relatively simple
• Calculated accuracy (residuals, error ellipse etc)
• Uses position solution range rejection and adjustment
Observation aiding more tricky
• How do you QC a single observation?
• Can you determine the accuracy of one measurement?
Weighting www.nautronix.com
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NASNet® - PHINS Integration
NAUTRONIX www.nautronix.com
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NASNet®
• Acoustic Long Baseline (LBL) subsea positioning system
• One-way broadcast transmissions
• High update, low latency positioning
PHINS
• PHotonic Inertial Navigation System
• FOG based strap-down INS
• Subsea and surface versions
The components www.nautronix.com
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• Moving range source
NASNet® Features www.nautronix.com
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• Low Latency
• Simpler to deal with!
NASNet® Features www.nautronix.com
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Interface Path www.nautronix.com
Acoustic
Data
Digital
data
Position/Range
Combined
Acoustic/INS
position
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$BFUSBLllmm.mm,a,LLLmm.mm,b,±dd.d,cc.c,cc.c,cc.c,cc.c,e.e*hh<CR><
LF>
• Vehicle Latitude, Longitude & Depth
• Latitude, longitude and depth Standard Deviations
• Age of Data
Specific String (Acoustic Position) www.nautronix.com
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$BFLBL,llmm.mmmm,a,LLLmm.mmmm,b, dddd.d,xx,rrrr.r,ccc.c,
e.e*hh<CR><LF>
String contains:
• Acoustic source Latitude, Longitude and Depth
• Measured Range
• Range SD (estimation of accuracy)
• Age of Data
Specific String (Acoustic Range) www.nautronix.com
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Trials Vessels www.nautronix.com
Loch Shiel
Talon
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Interface Arrangement www.nautronix.com
NASNet® Beamforming
Transducer (vessel)
NASNet® VTrx (ROV)
− Bottle
− Transducer
PHINS
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Interface Arrangement www.nautronix.com
NASNet® Beamforming
Transducer (vessel)
NASNet® VTrx (ROV)
− Bottle
− Transducer
PHINS
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Interface Arrangement www.nautronix.com
NASNet® Beamforming
Transducer (vessel)
NASNet® VTrx (ROV)
− Bottle
− Transducer
PHINS
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Interface Arrangement www.nautronix.com
NASNet® Beamforming
Transducer (vessel)
NASNet® VTrx (ROV)
− Bottle
− Transducer
PHINS
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NASNet® - PHINS
Initial Trials Data
NAUTRONIX www.nautronix.com
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www.nautronix.com 1m Range Weighting
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www.nautronix.com 0.1m Range Weighting
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www.nautronix.com 0.5m Range Weighting
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www.nautronix.com Acoustic drop out trial
0
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368800
368850
368900
368950
369000
369050
369100
369150
1900 2080 2260 2440 2620 2800 2980 3160
CNAV
PHINS
VTRx
# of Ranges
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Summing up
NAUTRONIX www.nautronix.com
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Acoustic aided INS can provide operational performance and
safety benefits
A basic interface is fairly straightforward and will provide some
benefits to positioning quality and reliability
To achieve the maximum performance a custom interface should
be created
Observation aiding (close coupled) is preferable to position aiding
(loosely coupled)
In conclusion www.nautronix.com