The earliest phase of a research cruise is supposed to be its easiest, with time to sun on an upper deck in front of the ship's command center - the "bridge." Scientists and crew can also read a book in Atlantis' quiet library, or watch a video in the ship's lounge. Both rooms are conveniently near the "mess deck," where Atlantis's steward, Carl Wood, and cook, Torii Corbett, serve up amazing menus that might include roasted cod with vegetables, parmesan-crusted chicken breast with tarragon and mustard cream, stir fried brussel sprouts with bacon and chestnuts, toasted orzo pasta and fennel, roasted red bliss potatoes, and spaghetti squash, all available at a single meal.
Fig. 1. Deployment of the DSL-120.
Side-scan sonar deployment
While most took at least some advantage of these amenities, the scientists were also busy connecting to the shipboard computer system and planning future strategy in the main laboratory, situated a short walk from where Alvin waits in its hanger and the DSL-120 side-scan sonar was finally lifted from the main deck on Thursday, Nov. 16th after a 6 ½-hour delay.
The original launch time had been set for about 8 a.m. on a bright warm morning with cloud-dappled skies and seas calm enough to look like wind-rippled rolling glass.
It was held up by an overheated motor that controls the movements of the "bow thruster," a special propulsive unit that allows Atlantis to turn its front, or bow, as well as its rear, or stern. The ship's engineering department sprang into action, replacing the defective parts and testing the repairs after allowing the system to cool down.
This sonar deployment, which finally occurred about 2:30 p.m., was more complicated than usual. That's because Jeffrey Gee, another Scripps geophysicist, had attached a trailing "magnetometer," to be towed behind it on a 75 foot long cable. A collection of gyrocompasses, electromagnets and sensors packaged inside a grey cylindrical pressure case, the magnetometer is designed to detect tiny magnetic field shifts in any direction. Such changes, called "anomalies," can reveal information about the geology the magnetometer is passing over. It provides clues that are combined with the sonar's reflected sound wave images.
In a coordinated effort designed to forestall collisions and cable entanglements, Gee, Sasagawa, Alvin expedition leader Patrick Hickey and Alvin pilot trainee Anthony Tarantino lowered the magnetometer over the port edge of the ship's rear "fantail."
Fig. 2. Deployment of the magnetometer. The people wrestling the magnetometer are from left to right, research participant from SIO - Jeff Gee, Alvin pilot in training - Anthony Tarantino, and Alvin expedition leader - Pat Hickey. Photo by Monte Basgall.
Yards in front, a separate team of engineers and technicians from the Woods Hole Deep Submergence Laboratory, supervised by burley Atlantis boatswain (pronounced "bosun") Wayne Bailey, steadied the DSL-120 as a crane lifted it up and over the ship's side. That happened after an attached "clump weight" was also lowered to pull the neutrally buoyant sonar towards the bottom, even as it's umbilical cable - playing out and in from a projecting reel - kept the whole ensemble linked to the ship.
After earlier postponements, the first watch, shift of scientists finally reported to the towed vehicle's control van, located above and forward from the submarine's shipboard home. But the launch wasn't over yet. Twice that afternoon, the sonar was returned to the deck to readjust its weight distribution so it would stop listing to one side.
Fig. 3. Donna Blackman's graduate student at SIO - Suzanne Lyons and Duke University graduate student - Niklas Bacher, getting an early start at photocopying dive logs for upcoming Alvin deployments.
"It hasn't gotten more than 150 meters out," said Blackman with remarkable forbearance and patience as a beautiful sunset transformed the horizon off Atlantis' starboard side. "It's lost a day." Back in Atlantis' main lab, Suzanne Lyons, a graduate student of Blackman's, and Niklas Bacher, a Duke graduate student in geology, were already photocopying divers' packets for upcoming Alvin excursions, like pitchers warming up for a future game.
Despite the unpromising start, action picked up in the control room after the "fish" reached its cruising altitude - about 100 meters above the massif's surface - about 8:30 p.m. Working on a map based on her 1996 bathymetric data, Blackman had earlier used colored grease pencils to lay out a set of tracklines that would make the sonar straddle the ridge's contours for a total distance of about 124 miles at a speed of about 1 knot over 4 ½ days round-the-clock towing. To maintain that precise course, Atlantis's rehabilitated bow thruster would work overtime.
Fig. 4. Proposed path of the DSL-120 with side-scan sonars.
She has since revised those track lines in response to feedback from the three watch leaders - Cann, Karson and Kelley - as well as some prioritizing in case the current run of good weather ends. "This kind of stuff is continually modified," she said before an upbeat Saturday evening science staff meeting. One week after the cruise's beginning, the researchers were reporting good sonar and magnetometer returns, with a number of promising spots to send Alvin.
Revisiting the Atlantis Massif | Technical Difficulties | Side-scan Sonar Deployment