Experiences with Hydrographic Data Budgets Using a Low-logistics AUV Platform

Thomas Hiller Teledyne Marine Systems

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Teledyne Marine Systems Strategic Business Units

What is the Gavia? The Gavia is a low-logistics, fully modular AUV. It has field-changeable modules that can be replaced in minutes, allowing rapid sensor reconfiguration and battery replacement. Capable of operations in depths up to 1000m.

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20cm hull diameter & neutral buoyancy ballasting → roughly π kilos per 10cm length. Typical module lengths are between 20cm and 60cm.

Gavia AUV Base System

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• The Gavia is made up of several individual cylindrical modules forming a single hull

• All Gavia vehicles start with the 4 basic modules (Nose, Battery, Control, and Propulsion Modules)

• From this base configuration additional sensor modules can be added

• All modules are field swappable • Ethernet comms and 1PPS line for timing

Modularity

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Gavia AUV: Modular, Adaptable, Configurable

Survey

Hydrographic

Geophysical

Base AUV

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The Gavia Offshore Surveyor:

Typical Offshore Surveyor configuration • High-precision DVL aided Inertial Navigation

System • Swath Bathymetry Module • Sub Bottom Profiler Module • Side Scan Sonar, • Camera • Sound Velocity Meter , Obstacle Avoidance

Sonar, • USBL (Teledyne Benthos DAT) • DGPS • Single, dual or triple swappable batteries

The Gavia Offshore Surveyor: • Low Logistics : typically around

75 Kg and 3m in length (depending on configuration)

• 1000m depth rating • Integrated high accuracy

INS/DVL • Optional LBL / USBL aiding • Obstacle avoidance sonar • Fully Modular • Array of sensors

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• Side scan: – Marine Sonic dual frequency 900 / 1800 kHz – Edgetech 2205: 600 / 1600 kHz – Klein 3500: 450 / 900 kHz

• Swath Bathymetry: – 500kHz GeoSwath Plus interferometric sonar – Other options coming soon

• Sub-bottom profiler: – Teledyne Benthos CHIRP-III Technology

• Camera: – High-performance low-light variable frame rate digital

camera: various resolutions. Color or monochrome.

Payloads Typically Required by Commercial Operations: • Sidescan • Bathymetric mapping • Sub-bottom profiling • Camera

Gavia Survey Suite

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GeoSwath Module • GeoAcoustics GeoSwath Plus AUV • 500kHz cw interferometric sonar • Port and starboard transducers ping alternately • Sidescan-like pulse, multiple receive staves • Max range ~50m to 80m • Typical swath width 70m • Collects sidescan and bathymetry

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Cleared for Public Release (FAL-1404) 10

Low Logistics AUV Benefits • Vessels of opportunity • Easily transported • NO specialized LARS • Does not require surface vessel

contact during operations • Operate close to seafloor, pipeline. • Lower operational cost Considerations • Strategic Power Management • Power draw and size of sensors

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Ready for Operations Minutes After Arrival On-site

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Fully Co-registered & Geo-referenced Data

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Fully Co-registered & Geo-referenced Data

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Side Scan Mosiac and Bathymetry Image from GeoSwath

Boat-mount MBES image

Data processed and displayed in OIC CleanSweep

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Alexander Hamilton GeoSwath Mosaic Data processed in OIC CleanSweep

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Harbor Survey 3D Overview Showing Run Lines

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Harbor Survey Bathymetry Grid and Side Scan Mosaic

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Gavia AUV gathered 500kHz GeoSwath data around an oil rig in the Adriatic showing ocean floor features from previous jack up rig placement and legs of current rig extending from the ocean floor. Data courtesy of GAS Srl.

Survey of jack-up footprints

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Pier Launched Survey

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Position Checks: the FAT Survey Pattern

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500 kHz GeoSwath mounted on Gavia AUV

GeoSwath Side Scan and Bathymetry

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1800 kHz Marine Sonics at 10m range

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Northrop N3PB Captured with Edgetech 2205 600/1600 kHz – High Frequency

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Northrop N3PB Captured with Klein 3500 445/900 kHz – High Frequency

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Northrop N3PB Captured with Edgetech 2205 600/1600 kHz – Low Frequency

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Position Checks: the Reference Rock

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Position Checks: Multiple Vehicles, Multiple Runs

RMS: 2.4m 95%: 4m

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Speed of sound corrections

Manual entry Live SOS measurement

Sound velocity meter

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Positioning the AUV: Navigation GPS: • WAAS / EGNOS GPS as standard

-- 5 meter accuracy

• DGPS optional using WiFi transmitted correction factors

-- 1 – 2 meter accuracy -- Veripos ready GPS receiver already in Antenna Tower

INS:

• Kearfott T-24/ TeledyneRDI DVL-aided Inertial Navigation (SEANAV / SEADeViL)

• Error of ~0.01% distance travelled when in bottom lock, lawnmower pattern survey

Improving the Subsea Navigation Solution: • Surfacing for GPS fixes

• USBL Aiding using Directional Acoustic Transponder

• LBL

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• Kearfott T-24 aided by 1200KHz Teledyne RDI WHN DVL or • IxBlue ROVINS154 aided by 1200KHz Teledyne RDI WHN DVL

INS/DVL Module Options

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T-24 (KI-4092S High Performance IMU): • Accelerometer Bias Stability ~50µg • Position Accuracy 0.1% Distance Travelled , CEP50, DVL-aided • Heading Accuracy 1.0 mils, rms = 0.06° • Roll/Pitch Accuracy 0.5 mils, rms = 0.03°

ROVINS154: • Accelerometer Bias Stability ~80µg (est.) • Position Accuracy 0.2% Distance Travelled , CEP50, DVL-aided • Heading x secant latitude: 0.05° RMS • Roll/Pitch/Yaw accuracy: 0.01° RMS

INS/DVL Module Specifications

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Positioning the AUV: Depth. Vehicle depth relative to water surface is found by pressure aiding the INS

navigation solution using a high accuracy depth sensor

Keller-Druck 33XE sensor: specification 0.01% FS.

Errors: pressure-to-depth conversion, density profile, swell effects

Relates to water surface: vessel-local tide required

With care can achieve uncertainty of 10cm - 20cm in Absolute Pressure

Pressure relative to Tare (zero at water surface) is approx. the instrument resolution, equivalent to ~1-2cm

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Position Aiding: Low Logistics Navigation Solutions

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• All in one transponder and release with burn-wire

• Can be deployed with no surface expression

• Positively buoyant, no float needed • Unique coded reply to a broadcast

ping from Gavia • 6000 meter depth rating • 18 kg (40 lbs)

LBL Navigation using SM-976 Transponders

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LBL Field Tests:

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Conclusions:

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• Hydrographic surveys are being carried out using low-logistics AUVs • The survey results are being used for engineering, dredge and navigation

purposes • The accuracy of the survey results compare well with boat-mount, ROV

and towed platforms, within certain constraints: Navigation aiding is required for longer and deeper work

• Empirical studies using multiple configurations and multiple vehicles over several months show that the theoretical performance is achieved

Questions?

Dr Thomas Hiller Senior Geophysical Sales and Applications Engineer

Teledyne Gavia

thiller@teledyne.com

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