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
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 2
UNCLOS Limits 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. Formula Line Constraining Line 3
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 4
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)
AUV Schematic 6
Technical Challenges and Solutions 7
AUV Concept for Collecting Bathymetry 2010 mission Remote camp Shore camp Concept mitigates risk of reduced data collection due to poor weather 8
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 9
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 10
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 11
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 12
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 13
Cornerstone Ice Camp Borden Ice Camp Resolute Bay Arctic Operation 2010 14
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Why the need for a small remote camp? 25
Floe Drift - Problem 26
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And then we waited. And waited. And waited. For 3 days!!!! 29
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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 31
Putting the lines on the AUV 32
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AUV Survey Mission 79.95 • Distance of ~310km 79.9 • AUV depths down to 3300m 80.8 79.85 • Crossed 2500m contour and two sea mounts 80.6 79.8 -119.9 -119.8 -119.7 -119.6 -119.5 -119.4 -119.3 0 80.4 -500 80.2 Start of -1000 Homing Vehicle Depth (m) -1500 80 -2000 79.8 -2500 -3000 -124 -123 -122 -121 -120 -119 Path of drifting -3500 0 10 20 30 40 50 60 70 ice camp time (hr) 34
How did it all end? • Completed about 450 km of critical bathymetric measurements. • In total, the AUV traveled over 1000 km during a continuous operating 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 operations in the arctic, and have provided critical data for Canada’s UNCLOS submission. 35
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. 36
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. 37
Arctic AUV Operations – Important Factors • Underwater Communications • Accurate Localization/tracking AUV Mission Planning • • AUV Homing capability OPS Planning and preps • • AUV Variable ballasting capability • AUV High Quality Accurate Navigation 38
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. 39
LSSL Infrastructure for AUV Ops • Used one side of the Hanger for maintenance activities. • Used additional space forward and aft for ROV and tracking equipment. 40
LSSL Infrastructure for AUV Ops Challenges: • Difficult to deploy large, heavy or delicate equipment in these ice conditions. • Ice can close in within seconds and crush equipment and cables. 41
LSSL Infrastructure for AUV Ops • 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) 42
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. 43
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. 44
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. 45
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