Project Cornerstone Using AUVs for Bathymetry Measurements in the - - PowerPoint PPT Presentation

Project Cornerstone – Using AUVs for Bathymetry Measurements in the Arctic

SNAME Lecture Series December 21, 2011 David Hopkin Head, Maritime Asset Protection Section

Presentation Overview

• Cornerstone Background
• Technical Challenges and Solutions
• Arctic Field Operation 2010 and 2011
• Few results and Summary

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UNCLOS

• The United Nations Convention on the Law Of the Sea provides

a framework for a maritime state to define the outer limits of its continental shelf

• Canada has until 2013 to make its submission to UNCLOS to

substantiate the outer limit of the continental shelf where it extends beyond 200 nautical miles

• Represents a huge

area with many potential resources

• scientific data is key
• NRCan, DFO, CHS

collecting data

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UNCLOS Limits

Formula Line Constraining Line

Article 76 of UNCLOS requires the analysis and interpretation of the shape of the seabed, depth of seafloor and thickness of the underlying sedimentary layer.

These measurements result in two limits:

• 1. the formula line, obtained by the

application of distance formulas, and

• 2. the constraining line, defining the

maximum extend of the outer limit.

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Project Cornerstone Overview

Objective: To use Autonomous underwater vehicles (AUVs) to collect high quality bathymetric data , in particular between the 2500 m contour line and the “foot of the slope”, in ice covered waters in the Arctic Benefits: – Provide risk mitigation against poor weather and poor ice conditions – Provide an improved UNCLOS submission Project Execution: Interdepartment MOU between DRDC, NRCan, and DFO

AUV Overview

• Unmanned vehicle that autonomously executes

preprogrammed missions

• Sophisticated fault management to increase mission

success

• Length 7m, Weight 1800kg
• Max Speed 5knots (2.5m/s), Survey Speed 3knots (1.5m/s)
• Propulsion: single thruster, 2 bladed propeller
• Endurance of >400km, 3 days
• Deep diving to 5000m
• Modular design
• Bathymetric data collection:

– single beam echo sounder (Knudsen) – multibeam echo sounder (EM2000)

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AUV Schematic

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Technical Challenges and Solutions

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AUV Concept for Collecting Bathymetry

2010 mission Remote camp Shore camp

Concept mitigates risk of reduced data collection due to poor weather

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Variable Ballast System

• The Concept of Operation required the AUV must be able to

park under the ice at the end of each mission

• Fault management also required ability to park on the sea

bottom

• Developed a variable ballast

system – Rating of 5000 m – Titanium sphere – Double pumps

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In water Charging

• CONOPS required continuous operations from

a remote camp with no facilities to recover the AUV

• Necessitated in-water recharging after each

mission

• Developed a novel pole assembly to capture

the vehicle and facilitate attaching the charging cable

• Also allows for rotating the vehicle to align

the INU if necessary

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Navigation

• Other than standard navigational issues and high latitude

problems with an Inertial Navigation System (INS) there are two additional difficulties:

• 1. On launch in deep water there is INS drift when the AUV is

working its way down to where a bottom-lock is possible. – Utmost accuracy requires the INS to be reset on the bottom

• 2. On recovery the ice camp has drifted erratically for 3 days and

may be as much as 50-60 km from the location where the vehicle was launched! – The vehicle has to find the ice camp by itself. We are not in control or communication with the vehicle

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Short range positioning system

• Uses 6 acoustic modems to track the AUV as it descends to the

sea bottom – Also provides a communication link to the AUV

• Modems are deployed through the ice, roughly 1 km from the

main ice hole

• Freewave radios are used to transmit information back to the

main camp

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Homing

• AUV must return to a drifting ice camp that is moving at up to 10

km/day! – For a 3 day mission, this is a total drift of up to 30 km!

• Developed a custom 7 element hydrophone array that is mounted

in the nose of the AUV

• Deploy a custom built 1300 hz,

>190 db sound source at the ice hole

• Using specialized software on

the AUV, the bearing angle from the AUV to the ice camp is calculated

• Homing at ranges greater than

50 km

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Resolute Bay Borden Ice Camp Cornerstone Ice Camp

Arctic Operation 2010

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Why the need for a small remote camp?

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Floe Drift - Problem

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And then we waited. And waited. And waited. For 3 days!!!!

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At the end of each mission the AUV parked up under the ice. The ROV was used to put a line on the AUV and the AUV was pulled over to the charging mechanism

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Putting the lines on the AUV

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AUV Survey Mission

• Distance of ~310km
• AUV depths down to

3300m

• Crossed 2500m contour

and two sea mounts

• 124
• 123
• 122
• 121
• 120
• 119

79.8 80 80.2 80.4 80.6 80.8

10 20 30 40 50 60 70

• 3500
• 3000
• 2500
• 2000
• 1500
• 1000
• 500

Vehicle Depth (m) time (hr)

• 119.9
• 119.8
• 119.7
• 119.6
• 119.5
• 119.4
• 119.3

79.8 79.85 79.9 79.95

Path of drifting ice camp Start of Homing

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How did it all end?

• Completed about 450 km of critical bathymetric measurements.
• In total, the AUV traveled over 1000 km during a continuous
• perating period of 10 days, at water depths of over 3300 m

under the ice. It also successfully homed to a moving ice camp from a distance of 50 km – Note, each of these achievements is remarkable. – Collectively they represent a world record for under-ice

• perations in the arctic, and have provided critical data for

Canada’s UNCLOS submission.

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2011 Arctic Expedition - Overview

• Combination of Seismic and Bathymetric data collection.
• Joint Canada/US activity (USCGC Healy & CCGS LSSL):
• Healy acquire multibeam bathymetric & CHIRP sub-bottom sonar data.
• LSSL used seismic streamer and air guns to collect data on thickness of

sedimentary layers.

• AUV collects both multibeam and single beam.

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2011 Arctic Expedition – Survey Area

The 2011 Arctic Expedition boundaries include:

• Southern Canada Basin (along

the Canadian-Alaskan margin).

• As far north as the Lomonosov

Ridge (~100 nm from the North Pole).

• To the seaward end of the

Canadian Archipelago.

AUV Ops were ship-based due to:

• Ice conditions too poor for ice camp.
• Out of aircraft range.
• Two data types needed, seismic &

sonar.

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Arctic AUV Operations – Important Factors

• Accurate Localization/tracking
• AUV Homing capability
• AUV Variable ballasting capability
• AUV High Quality Accurate Navigation
• Underwater Communications
• AUV Mission Planning
• OPS Planning and preps

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AUV Tracking

Acoustic Tracking System (ATS):

• Provide AUV tracking

at ranges up to 40 km.

• System estimates

range, bearing and elevation to AUV.

• AUV status indicated

by 1 of 4 chirps output (AUV Heartbeat).

• RX is a small

hydrophone array.

• Uses a high power

hyperbolic frequency modulated (HFM) chirp.

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• Used one side of the Hanger for

maintenance activities.

• Used additional space forward and

aft for ROV and tracking equipment.

LSSL Infrastructure for AUV Ops

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Challenges:

• Difficult to deploy large, heavy or delicate equipment in these ice conditions.
• Ice can close in within seconds and crush equipment and cables.

LSSL Infrastructure for AUV Ops

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• Used NRCan’s spare seismic tow-sled.
• Large weight lowered below the ice surface.
• Includes protective sleeve for cabling.

– GAPS and ATS (tracking) – Modem (Communications)

LSSL Infrastructure for AUV Ops

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Environmental Conditions

Sever Spur Area:

• Heavy ridging in the Sever Spur area.
• > 9/10ths covered.
• Large, thick ice flows.
• Ships entered this area for the first time.
• Requires two ice breakers to assist each other.
• Cold temps even in summer -22C Wind chill.

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AUV Mission Planning

• Mission Criteria: range, sensors, height, depth, energy reserve etc.
• Determine AUV fault responses.
• Default fault responses vastly different for Arctic operations:

– i.e. Cannot simply surface due to fault occurring. – Turn around , where will ship be? – Park on bottom or park up under ice? – Ignore fault and continue mission? – Decision depends on severity of fault and potential impact. – total loss of vehicle is possible.

• Multiple checks and validation, multiple reviewers, 13 page

mission plan.

• Final approval and sign off required.

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AUV Handling

• Ships crane and flight deck launch pad worked very well.
• Crew gained experience during work ups in April.
• Procedures developed during work ups.

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AUV Release

• Minimal in water checks, Quick release required.
• Ballasted heavy to sink and clear hull and tow-sled.
• Circle at 50m depth until satisfied – good to go.

Launch Site:

• Ice rapidly moving in/around the ships, with small open

water clearings.

• An artificial created opening would close in too fast.
• Had to find natural Ice Pond.

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Survey Objectives:

• Map the foot of the slope.
• Transit the gap to confirm existence.
• Chart data based on gravity readings.
• Depth of 3500 m.

Mission

Survey Route - 110 km survey of Sever Spur – Southern Portion.

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AUV Recovery

• The ROV proved ineffective in recovering AUVs in heavy ice
• Only option was to take the ship to the AUV and use the

LSSL to open up the ice sufficiently

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AUV Recovery (cont)

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Recovery using man-basket

Recovery Challenges and solutions:

• Unsafe to work on the ice and no

small boats.

• Requires ship based method to hook
• n lift lines.

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Recovery using man-basket

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2011 AUV Arctic Expedition Conclusions

Successes:

• Collected valuable Foot of the Slope data.
• Launched/recovered AUV in heavy ice 3 times.
• Completed :

– 6 hour test mission – 21 hour survey mission

• AUV dove to 3600m (1st mission) & 3500 m (2nd mission) depths.
• AUV INS operational up to 88.30N.
• AUV vessel based Arctic ops are possible.
• Homing & long-range tracking from a vessel is viable. >20km
• Deep water/long range modem communications is possible. >10km
• AUV can provide off-board real time environmental information.

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Questions?

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North Ridge

• Notice slight elevation change.
• Not as flat as chart gravity readings suggested.

AUV Mission – Data Results