Application: Passive Acoustic Monitoring
Customer: Gulf of Mexico Research Initiative
Payload: Towed Hydrophone Arrays
Summary: The C-Enduro and C-Worker 6 carried out Passive Acoustic Monitoring (PAM) in the Gulf of Mexico following the Deepwater Horizon oil spill.
Benefit: Novel approach / Quiet platforms / Improved accuracy
Five years on from the Deepwater Horizon oil spill, work is still ongoing to assess and repair the damage caused by the sunken rig. Millions of gallons of crude oil were pumped into the sea over an 87 day period after the rig exploded and began to leak.
The Gulf of Mexico Research Initiative (GoMRI) awarded funding to The Littoral Acoustic Demonstration Center – Gulf Ecological Monitoring and Modelling (LADC-GEMM) consortium to study the long-term impact of the oil spill on deep diving marine mammals. In June 2015 as part of this project, ASV provided two vehicles (C-Enduro and C-Worker) to carry out Passive Acoustic Monitoring (PAM) in the Gulf of Mexico.
Commencing 23 June 2015, operations were carried out from the R/V Pelican, a LUMCON oceanographic research vessel which acted as the support vessel. C-Worker and C-Enduro were towed out to sea behind the R/V Pelican before being deployed. The vehicles were monitored from the support vessel and operated using the ASView control system over radio links. Both ASVs ran set lines autonomously whilst the Seiche team monitored sounds from the towed arrays in real time to detect, classify, and localize marine mammals. Both vehicles ran at an average speed of 3 knots.
C-Worker and C-Enduro travelled at varying distances from the R/V Pelican ranging from 500m – 1000m this was partly to minimize the noise affects from the support boat but was also a result of the varying operating patterns used to optimize the data collection. From these distances, the ASV operators were able to maintain a visual over the vehicles and maintain uninterrupted communication links.
ASV worked closely with Seiche Limited to integrate towed hydrophone arrays onto the C-Enduro and C-Worker ASVs to carry out the PAM. C-Worker deployed the array on a cable 220m in length and C-Enduro towed a smaller cable 55m in length.
The autonomous PAM system was configured to detect species from their acoustic phonations over a range of 20 Hz to 160 kHz. These would include the low frequency calls of Brydes whales, the broadband regular click patterns of sperm whales, higher frequency clicks and whistles of several different dolphin species, and the high frequency echolocation pulse trains of beaked whales and Kogia.
The use of ASVs provide a novel approach and quiet platform to improve signal response and expand the range of frequencies and distances that can be effectively monitored from a towed survey. In many cases it has been found that tasks are performed more accurately when using an ASV as opposed to conventional methods. Large survey vessels produce a significant noise signature that can mask weak/distant marine mammal sounds.
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