Application: Hydrographic Survey
Vehicle: C-Worker 5
Payload: Reson 7101 multibeam / Edgetech 4200 side-scan / Applanix POSMVs
Summary: TerraSond used a C-Worker 5 in conjunction with a 105’ (32m) research vessel on a major hydrographic survey in the Bering Sea region of Alaska.
Benefit: On-site time saving of 25 days / Superior line handling ability / Operational window maximization
TerraSond chartered the C-Worker 5 from ASV Global’s facility in Broussard, LA USA. They wanted to use an ASV to reduce their time on site. The C-Worker 5 served as a force-multiplier, collecting multibeam and towed side-scan data alongside the Q105 research vessel, which surveyed adjacent lines simultaneously. The 18’ (5.5m) ASV collected 2,275 nautical line miles (4,213km) – 44% of the project total — and achieved an industry-first in terms of data production rates utilizing ASV technology in the Arctic.
TerraSond’s survey equipment was integrated into the C-Worker 5 and tested at ASV Global’s facility in Broussard. Project requirements called for simultaneous multibeam and side-scan data collection. C-Worker 5 carried a multibeam-hull mount as well as a side-scan winch with a custom track/trolley system capable of deploying the side-scan tow fish and pulling it from the water again to be cradled and stowed on the C-Worker 5 deck when not in use.
C-Worker 5 was transported to Alaska where it was craned aboard the Q105, along with its supporting infrastructure and spares. The LARS system was welded to the Q105 deck and load-tested while the Q105 was mobilized simultaneously with survey and IT systems.
ASV Global designed a custom Launch and Recovery System (LARS) for the C-Worker 5. The LARS was a dual-lift point davit system which allowed C-Worker 5 to be deployed and recovered safely in conditions beyond that possible with a single-point lift, such as by vessel crane. C-Worker 5 recovered and deployed safely in marginal sea conditions, with some recoveries taking place in seas of 6’ (1.8 m).
The area of operation was the Etolin Strait located east of Nunivak Island in Alaska’s Bering Sea. Both C-Worker 5 and Q105 were configured with identical survey systems. Major components consisted of Reson 7101 multibeam, Edgetech 4200 side-scans, and Applanix POSMVs. C-Worker 5 ran continuously at survey speeds of 6 to 7 knots whilst handling marginal weather conditions.
C-Worker 5 was operated in an ‘unmanned but monitored’ mode. In this mode the vessel was kept within visual range at all times while running a survey line adjacent to the line being surveyed by the Q105. Line tracking was automated, with the vessel able to maintain a distance off-track of 1 metre or better, even in poor sea states.
ASV’s proprietary ‘ASView’ software served as the command and control interface with the C-Worker 5 which maintained a telemetry link to the vessel at all times via IP radio with antennas mounted on the Q105 mast. ASView was used to send commands to the vessel, including what line to track, and monitor and control on-board systems. A streaming camera view was also monitored for obstacle avoidance and docking with the larger vessel.
Survey systems were monitored by remote desktop methods over an independent IP radio system.
Radio bandwidth was adequate for real-time monitoring and tuning of the acquisition systems but insufficient to transfer raw data, which could be as great as 50 –100GB/day. Therefore, data was downloaded whenever the ASV was recovered aboard the Q105, which on one occasion was 3½ days after deployment.
Though the C-Worker 5 was primarily used to increase production, it was also used as the sole survey platform in particularly shallow (4-5m depth) portions of the area where it was deemed unsafe or impractical to survey with the larger vessel, which had a draft of 2m. In these cases the Q105 would follow the unmanned vessel to monitor it and keep it within radio range.
This production rate of the C-Worker 5 resulted in an on-site time savings of almost 25 days, allowing the project to be completed well ahead of schedule and during the optimal part of the Arctic summer.
Data quality compared well between the two vessels, with slightly more motion artifact apparent in the C-Worker 5 data due to the increased motion from its relatively small size. Line handling abilities were actually superior to the larger vessel even in marginal sea states.
Images credit: TerraSond
With thanks to TerraSond.
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