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www.sonardyne.com
Applications of iUSBLTechnology overview
Tom BennettsProject Manager
www.sonardyne.com
Summary
1. What is iUSBL and its target applications
2. Advantages of iUSBL and sample data
3. Technical hurdles and Calibration methods
4. Improvements using Lodestar with iUSBL and an Inertial Navigation Solution
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www.sonardyne.com
What is the “i” in iUSBL
• Inverted USBL for operating at depth• Traditional vessel mounted USBL but with a
pressure balanced array for deep water use Rated to 7000m
• Utilises Sonardyne Wideband signals for optimal accuracy
• Can be used in any orientation giving rise to many applications
• Standard USBL systems usually hull mounted on the ship• Ultra short baseline to calculate azimuth and elevation the
acoustic signal arrives from.• Combine with GPS, Heading, Pitch & Roll at time of acoustic
receipt to give a transponder position
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Which way is it facing?
• The iUSBL already has a basic internal sensor but typically we want better than 0.5% SR• This involves mechanically mounting a Lodestar AHRS to the iUSBL• Installed in a multitude of survey scenarios on any vehicle
• Customers have approached Sonardyne with particular operational circumstances well suited to iUSBL
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Who uses iUSBLExample applications
• Deep water Oceanographic research• AUV docking and position re-initialisation or beneath extensive ice sheets• ROV positioning single reference ROV tracking instead of a full LBL array• Accurate streamer tracking for hydrocarbon mapping such as seismic & EM
• Review each application where the system is being used in a alternative way from standard vessel mounted USBL.
• Highlight the technical advantage
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NOC – Ultra deep water tow-fish tracking (6,000m range)Bay of Biscay 2007 - present
•Ultra long range requirement•Potential to deploy without surface USBL•iUSBL rated to 7000m
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Deep Tow Fish Tracking
Towed Ocean Bottom Instrument (TOBI 2)
• Used for very long ranges as the local SNR is very good
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AUV Guidance & Docking2007 – Present
•AUV nose cone with iUSBL transceiver•Also includes many military applications
Avtrack Navigator
iUSBL with & high speed acoustic modem link
Sends data back to the surface
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AUV Docking>1500m @ 15m shallow!
1,800 mBearing error
Cross track error
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ROV Based USBLSingle reference tracking
ROV can be tracked from the vessel If vessel based USBL is available
The ROV could track a mobile transponder outside the vessels USBL operating field or in/under a structure
Vessel of opportunity
ROV tracking relative to a fixed reference transponder
iUSBL mounted on ROV
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Streamer tracking, Singapore, Norway, Shetland, Atlantic and India2007 - present
• Mounted on a subsea vehicle• Facing rearward to track a Streamer
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iUSBL & Lodestar – An application used by Fugro
• GPS positions Vessel USBL• AHRS stabilises the USBL to
position Tpdr A• iUSBL and Lodestar position Tpdr B
AB
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Streamer trackingDetecting ballast bias along the streamer
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Streamer trackingMapping separation - seismic or electromagnetic Tx & Rx
dxB
eaco
n se
para
tion
Knowing the exact separation helps Geophysical interpretation of data. The exact position of the Tx and Rx are known better than if the locations been derived from a surface USBL.
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Technical advantages of iUSBL
• Operates beyond the range of a standard vessel based USBL system• Usually situated in low noise & low reverberation• Dynamically stable environment• Increased range capability due to better SNR• Positioning is locally accurate irrespective of depth• Shallow tracking where thruster wash would have been an issue• No re-calibration required• Rapid deployment – vessels of opportunity• Installed on most subsea bodies• Compatible with 3rd party survey systems
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www.sonardyne.com
Removing the transceiver from the vessel away from vessel noiseExample from a particularly noisy vessel
Observed noise drops from109dB @ 26kHz to 78dB = 31dB reduction
7,864m
2,398m
Theoretical max range
32.94dBiUSBL
6.94dBUSBL
SNR
Example: Ambient noise observed away from the vesselObserved noise @ 26kHz = 78dB
Noise plot taken from vessel’s USBLObserved noise @ 26kHz = 109dB
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NOC ~ 6000m RangeiUSBL origin
Transponder deployed from vessel
potentially no surface USBL
iUSBL Dynamically stable low noise environment Good SNR
Transponder in Responder mode
Ping stacking to give 2Hz update irrespective of range
6000m
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Achieving up to 10km Trenching work
Conventional vessel based USBL
Tracking to head towfish with USBLTotal distance between vessel and tail towfish could be over 10km
iUSBL mounted on head towfish or cage facing aft
iUSBL tracking Trencher
10,000m
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Rapid deployment
A combined Subsea Lodestar AHRS and MF iUSBL tracking trial before being mounted on an ROV or AUV.
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Vessel Based Remote USBL – The ApplicationiUSBL Positioned Towfish B
Tail towfish being positioned via the iUSBL
Multiple Transceivers require Fusion USBL
GPSpositioning vessel USBL to transponder to iUSBL totarget
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Mixing survey system tracking a mobile Compatt from the iUSBLCustomer demos Plymouth 2008
Sonardyne or Alternative
vessel based USBL
positions the iUSBL vehicle
Sonardyne iUSBL
positions the mobile
target
The output from the vessel USBL system
and Sonardyne iUSBL can be combined in a navigation package to
provide overall positioning
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Operation problems to overcome
• Sound velocity compensation• Depth aiding iUSBL position• Calibration• Stable vessel USBL position of towed body where iUSBL is mounted
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www.sonardyne.com
Sound VelocityHorizontal application
• Importance of Mini SV sensor• SV varies with depth therefore fast update required
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Depth aiding
• Compensate with onboard pressure sensor
• Pulse position depth on WSM beacons
Example of poor depth input degrading all data of the relative system
Improved by adding pressure sensor data to the USBL position for the towed iUSBL
At depth any errors in USBL derived depth are directly transferred to the iUSBL positions
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CalibrationOrientating the AHRS to the iUSBL
• We can further improve this…….
Co-ordinate Measuring Machine at Sonardyne head office
Accurate enough to highlighted a 0.1 deg roll error in 3rd party vessel USBL system in 1500m
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Improving iUSBL positioning
• Tightly coupled USBL• INS aided subsea positioning
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www.sonardyne.com
Lodestar on vessels of opportunityOver-the-side can provide excellent results if care is taken
• Understand twisting, flexing and motion of the pole relative to the vessel and compensate (Lodestar AHRS) appropriately.
Lodestar mounting plate
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USBL System PerformanceAn Average Fix in Deep Water for such operations
Easting vs Northing
-15
-10
-5
0
5
10
15
-15 -10 -5 0 5 10 15
2,070m
0.17m1.18m1.16m
SD DepthSD NorthingsSD EastingsAn Average Fix in 2,070m Water Depth
• Data is merged at source
• One time platform•Access to all high speed Data
Not limited to bandwidth of 232
•Immune to pole movement
•No induced errors from ship distortion where AHRS is on bridge
Wideband vs Tone
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INS on the towfishIt’s was there all along!
• Lodestar was designed as an inertial system from the start• Firmware upgrade to enable inertial output• Combined with surface positioning gives the ultimate iUSBL positioning
• Lodestar at surface to stabilise the vessel motion
• Tightly coupled USBL
• Aid positioning in deep water of towed body
• Lodestar subsea to stabilise the surface USBL position for the towed body
• Tightly coupled iUSBL
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INS proven track record demonstrated at OB09Real time DVL, USBL and LBL aided INS
Integrated DVL, SV, Pressure and USBL into one solution
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Sonardyne family of TransceiversTo meet your survey requirements
We have the solutions iUSBL is coreto our next generation of products
HP USBL
•High Precision USBL•Coupled AHRS•Combined Inertial system
Avtrack Navigator
•Subsea iUSBL•Acoustic modem
Do you have a new application?
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Head Office
Sonardyne International Limited T. +44 (0) 1252 872288Blackbushe Business Park F. +44 (0) 1252 876100Yateley, Hampshire, GU46 6GD E. [email protected] Kingdom www.sonardyne.com
Tom BennettsProject Manager
www.sonardyne.com/Products/PositioningNavigation/8091_8094.html