May 10, 2010

Acoustic Glider

Listening to the Seafloor from Afar
Acoustic Glider Team

The glider in the water soon after deployment.

Scientists and engineers from NOAA/ Pacific Marine Environmental Laboratory’s Vents Program successfully flew an ocean glider for hunting underwater volcanic plumes and eruptions in the Northern Lau Basin in the South Pacific near Samoa and Fiji. The team of scientists and ship's complement on the R/V Kilo Moana deployed and recovered the glider while 5000 miles away a team of engineers on shore controlled the glider 24 hours a day during this two-day mission. The ocean glider “flys” by controlling its buoyancy with respect to surrounding seawater and repeating dives and ascents between the surface and 950 meter depths at 3-3.5 hour intervals. The ocean glider can go up and down in the water column by use of a pump pushing oil in and out of its internal oil reservoir to an external bladder in the nose cone and converting the resulting vertical motion to horizontal momentum through its wings. During each surfacing, the glider calls in via satellite to a shore side team and transmits data from its latest dive and ascent. The lack of a physical propulsion system allows for “quiet” operation of the glider, enabling high quality sound recordings of nearby erupting volcanic vents. In addition to the hydrophone used for recording volcano sounds, the glider is equipped with instruments able to detect temperature, conductivity and turbidity anomalies associated with hydrothermal and eruptive plumes.

The glider path from launch to recovery.
The yellow points are the positions when the glider surfaced.

The glider performed flawlessly during the mission. Ironically the only problems arose because of the delicate nature of the technology and communications issues. A two day window of calm seas was critical because the glider had to be recovered carefully by small boat and towed carefully over to the ship and hooked onto a lifting line. Choosing the launch time required constant coordination between the shore and ocean teams over a week period. Also, during the pre-dive diagnostics prior to deployment of the glider, satellite communication between the glider and the PMEL shore station was less than ideal and attributed to interference from the steel structure of the ship. However, once deployed in the water, we experienced very few satellite communication issues. The Kilo Moana’s e-mail service was excellent and helped tremendously in coordinating the operations between the ship and shore teams.

Recovering the glider using the ship's Zodiac.

During this mission, engineers at PMEL in Seattle and Newport worked together to monitor the progress of the glider and report its position and status to ship board personnel around the clock. Over the two-day mission, the glider travelled roughly 50km from the Northeast Lau Spreading Center (NELSC) to the volcanic cone at West Mata where it was met by the ship and recovered. Despite working upstream against a surface current of 30-40cm/sec, the glider made good forward progress averaging 30cm/sec headway toward its waypoints. The glider’s navigation was amazingly accurate during a nearly flawless flight. Currently, data from the mission are being analyzed and we expect that it will reveal new insight of the plumes near the West Mata area as well as the acoustic signature unique to active seafloor volcanism.