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LBL Array Planning
Sam Hanton
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Overview
• Introduction to LBL and Array Planning
• Range Limitations for Positioning
• NASNet®
• Array Planning Tools – Past and Future
Introduction to LBL
and Array Planning
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Long Baseline in a nutshell
Trilateration – derivation of position from distance measurements
Distances (ranges) calculated from acoustic time of flight and
measured speed of sound in water
Minimum of 3 ranges from known
points required for a 2D position
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Basic requirements for Long Baseline Arrays
Accurate, reliable and cost effective positioning
• Ability to calibrate the array
• Minimum number of ranges available for positioning
• Good array geometry for positioning
Consequences of getting it wrong
• No positioning…
• Bad positioning – things in the wrong place
• Expensive positioning – install and calibrate extra units
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
What is ‘Good’ array Geometry?
For subsea construction tends to focus on the horizontal
• Positioning at a similar depth/elevation to the array provides poor
geometry for determining heights
• Heights derived from an external depth sensor
Good geometry has been defined by
a combination of
• Number of receivable ranges
• Angles of intersection (cut)
formed at receiver by ranges
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
What does it mean?
Example Criteria
• Minimum 4 ranges received
• Angles of cut between 30° and 150 °
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Mitigation of errors through geometry
Range errors with good array geometry
• Large range residuals
• Small error in derived position
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Mitigation of errors through geometry
Range errors with poor array geometry
• Smaller range residuals
• Larger error in derived position
Range Limitations
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Range limitation - Acoustic Ray-bending
0
500
1000
1500
2000
2500
3000
1470 1480 1490 1500 1510 1520 1530 1540 1550
WaterDepth(m)
SoundVelocity (m/s)
Typical deep water Sound Velocity Profile
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Range limitation – local topography
12
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Bathymetry (ft) Slope (°)
Example – undulating seabed
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Conventional Array Coverage
500m
radius
The Solution?
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
NASNet®
• Multi-user continuous
broadcast LBL system
• Extreme long range (4-5km at
seabed)
– Low frequency combined with
digital spread spectrum signalling
• Transmission from 100m above
seabed to mitigate against ray-
bending induced blind spots
• Buoy Tracking System used to
position buoys and maintain
high accuracy
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
NASNet Array Coverage
1500m
radius
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Long Range Challenges
0
20
40
60
80
100
120
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Heightaboveseabed(m)
Distance fromtransmitter (m)
Typical deep water acoustic ray path
100m elevated transmitter to seabed
Ray path
Straightpath
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Long Range Challenges
0
20
40
60
80
100
120
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Heightaboveseabed(m)
Distance fromtransmitter (m)
Typical deep water acoustic ray path
100m elevated transmitter to seabed
Ray path
Straightpath
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Shorter Range Challenges?
0
1
2
3
4
5
6
7
0 200 400 600 800 1000 1200 1400
Heightaboveseabed(m)
Distance fromtransmitter (m)
Typical deep water acoustic ray path
2m elevated transmitter
Ray path
Straightpath
Array Planning Tools
Past and Future
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Traditional Tools for Array Planning
Lots of methods used…but all ‘making do’ with what they could find
• Do it by eye – until it “looks about right”
– The traditional method, relying on experience and luck
• Do it by eye electronically, and then check it using straight line
assumptions
– CAD and experience to design the geometry
– Individual lines of position checked against DTM for straight line visibility
• Various software packages designed for land based line of sight
assessments
– From land survey planning…
– …to choosing sites for mobile phone masts
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Array planning for NASNet®
Requirements
• Array calibration visibility checks
• Basic range analysis
• Visibility ray-bending analysis
• Assessment of array geometry
• An intuitive method of presenting results
to customers
Solution
• Nautronix array planning specification
• Custom GeoLine3D array planning module
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Array Calibration Visibility Checks
Real-time visibility checks
• Green – ok
• Red – no visibility
• Blue – beyond max range
Straight line and ray bending
options
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Basic Analysis Options – max range no DTM
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Ray-bending Analysis
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Ray-bending Analysis
Straight line of sight Raybending Analysis
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
New measure of array geometry required
• Must be intuitive to expert and non-expert users alike
• To reflect current accepted ‘rules of thumb’
Defined as a percentage of ‘perfect geometry’…
- an infinite number of Stations evenly surrounding the point of
interest
62% 31%
Geometric Support - GSUP
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
GSUP
Example values
• Centre of equilateral triangle = 41%
• Centre of Square = 63%
• Outside of array extents = <50%
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Presentation of results
Images, DTMs or a 3D draped model for interactive viewing
Range reception = 4 GSUP = 62% 31%
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
What’s next
Nautronix and GeoLine development partnership formally extended
G3D User Forum introduced
Ongoing system development
• Automatic high point placement
– Completed
• Automatic array design
– User defined areas
– User selected base geometric shape (triangular, rectangular etc)
– User specified separation, high point selection etc
– User defined acceptance criteria (range visibility and geometry)
NAUTRONIX
MARINE TECHNOLOGY SOLUTIONS www.nautronix.com
Questions?

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LBL Array Planning

  • 2. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Overview • Introduction to LBL and Array Planning • Range Limitations for Positioning • NASNet® • Array Planning Tools – Past and Future
  • 3. Introduction to LBL and Array Planning
  • 4. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Long Baseline in a nutshell Trilateration – derivation of position from distance measurements Distances (ranges) calculated from acoustic time of flight and measured speed of sound in water Minimum of 3 ranges from known points required for a 2D position
  • 5. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Basic requirements for Long Baseline Arrays Accurate, reliable and cost effective positioning • Ability to calibrate the array • Minimum number of ranges available for positioning • Good array geometry for positioning Consequences of getting it wrong • No positioning… • Bad positioning – things in the wrong place • Expensive positioning – install and calibrate extra units
  • 6. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com What is ‘Good’ array Geometry? For subsea construction tends to focus on the horizontal • Positioning at a similar depth/elevation to the array provides poor geometry for determining heights • Heights derived from an external depth sensor Good geometry has been defined by a combination of • Number of receivable ranges • Angles of intersection (cut) formed at receiver by ranges
  • 7. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com What does it mean? Example Criteria • Minimum 4 ranges received • Angles of cut between 30° and 150 °
  • 8. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Mitigation of errors through geometry Range errors with good array geometry • Large range residuals • Small error in derived position
  • 9. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Mitigation of errors through geometry Range errors with poor array geometry • Smaller range residuals • Larger error in derived position
  • 11. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Range limitation - Acoustic Ray-bending 0 500 1000 1500 2000 2500 3000 1470 1480 1490 1500 1510 1520 1530 1540 1550 WaterDepth(m) SoundVelocity (m/s) Typical deep water Sound Velocity Profile
  • 12. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Range limitation – local topography 12
  • 13. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Bathymetry (ft) Slope (°) Example – undulating seabed
  • 14. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Conventional Array Coverage 500m radius
  • 16. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com NASNet® • Multi-user continuous broadcast LBL system • Extreme long range (4-5km at seabed) – Low frequency combined with digital spread spectrum signalling • Transmission from 100m above seabed to mitigate against ray- bending induced blind spots • Buoy Tracking System used to position buoys and maintain high accuracy
  • 17. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com NASNet Array Coverage 1500m radius
  • 18. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Long Range Challenges 0 20 40 60 80 100 120 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Heightaboveseabed(m) Distance fromtransmitter (m) Typical deep water acoustic ray path 100m elevated transmitter to seabed Ray path Straightpath
  • 19. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Long Range Challenges 0 20 40 60 80 100 120 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Heightaboveseabed(m) Distance fromtransmitter (m) Typical deep water acoustic ray path 100m elevated transmitter to seabed Ray path Straightpath
  • 20. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Shorter Range Challenges? 0 1 2 3 4 5 6 7 0 200 400 600 800 1000 1200 1400 Heightaboveseabed(m) Distance fromtransmitter (m) Typical deep water acoustic ray path 2m elevated transmitter Ray path Straightpath
  • 22. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Traditional Tools for Array Planning Lots of methods used…but all ‘making do’ with what they could find • Do it by eye – until it “looks about right” – The traditional method, relying on experience and luck • Do it by eye electronically, and then check it using straight line assumptions – CAD and experience to design the geometry – Individual lines of position checked against DTM for straight line visibility • Various software packages designed for land based line of sight assessments – From land survey planning… – …to choosing sites for mobile phone masts
  • 23. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Array planning for NASNet® Requirements • Array calibration visibility checks • Basic range analysis • Visibility ray-bending analysis • Assessment of array geometry • An intuitive method of presenting results to customers Solution • Nautronix array planning specification • Custom GeoLine3D array planning module
  • 24. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Array Calibration Visibility Checks Real-time visibility checks • Green – ok • Red – no visibility • Blue – beyond max range Straight line and ray bending options
  • 25. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Basic Analysis Options – max range no DTM
  • 26. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Ray-bending Analysis
  • 27. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Ray-bending Analysis Straight line of sight Raybending Analysis
  • 28. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com New measure of array geometry required • Must be intuitive to expert and non-expert users alike • To reflect current accepted ‘rules of thumb’ Defined as a percentage of ‘perfect geometry’… - an infinite number of Stations evenly surrounding the point of interest 62% 31% Geometric Support - GSUP
  • 29. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com GSUP Example values • Centre of equilateral triangle = 41% • Centre of Square = 63% • Outside of array extents = <50%
  • 30. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Presentation of results Images, DTMs or a 3D draped model for interactive viewing Range reception = 4 GSUP = 62% 31%
  • 31. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com What’s next Nautronix and GeoLine development partnership formally extended G3D User Forum introduced Ongoing system development • Automatic high point placement – Completed • Automatic array design – User defined areas – User selected base geometric shape (triangular, rectangular etc) – User specified separation, high point selection etc – User defined acceptance criteria (range visibility and geometry)
  • 32. NAUTRONIX MARINE TECHNOLOGY SOLUTIONS www.nautronix.com Questions?