SENTRY’s Third Dive
The morning of the 28th dawned with a stunningly beautiful sunrise just as the Woods Hole and Thompson deck crews were launching SENTRY on its third and final survey in the Hydrate Ridge Area. I remember joking with Dana Yoerger, one of the major architects of the new AUV, about the parallel ‘dawning’ of a new era of sea floor mapping with the advent of such powerful autonomous platforms as SENTRY. He chuckled and took another picture of the launch and sunrise….
The third SENTRY ‘run’ lasted all day. The vehicle was brought back on board slightly early after completing the longest run to date for this “flying bar of soap”. In 19 hours of survey time in the water, the AUV had covered a distance of 64.6 km. That distance was broken up into a series of short closely spaced (250 meters) parallel lines that are covered as a linked set. In the aggregate these mini-lines cover crest of Southern Hydrate Ridge with a precision and resolution that has never before been possible with the tools available before this new class of mapping AUV’s. The early return was partly the result of over protective parents, and partly because all the crucial goals of the dive had been met.
Strong Batteries and Confused Directions
The engineering report from James Kinsey and Daniel Gomez-Ibanez indicated that even after nearly 20 hours, the batteries still had 20% power left before they would have be completely discharged. Of course this was very good news for the scientists, as it indicates there is potential for longer endurance surveys later in the cruise. James and Dana had diagnosed the earlier interruption of sentry’s previous dive as an ‘unscheduled holiday’ taken by the sophisticated Inertial Guidance System (INS) which SENTRY utilizes as part of its ‘brain’ to execute the many mini-lines programmed into the system by Dana before each dive.
A Clever Work-around
At Dana’s request, James designed a clever work-around in case this temporary memory lapse happened again – his solution was to route temporary control to the built-in compass that is also part of the sensing-logic circuits the AUV uses to find its way when it is alone on the seafloor. The next step is to ‘cycle’ the power to the INS system – just as you might restart your computer when it behaves in a slightly flaky manner. Once the INS is reinitialized, with all its memories intact, James programmed the ‘brain’ to pass control back to INS from the compass. Upon recovery of SENTRY after the third dive, it became clear that the built-in safety factor had actually saved the dive when the INS lost focus midway through the 19-hour survey. James and Dana make an awesome team.
Taste for ‘Bathymetric Meals’ to Come.
The processing to generate final mapping results from a SENTRY dive take significant time complete and are not yet complete and are not yet routine. The amount of raw data generated on a single dive can be more than 2 GB, and the ‘Pipeline’ for processing is being constructed on this cruise by the SENTRY Team. Both scientists and engineers agree that once we are confident that we have collected excellent data, our first responsibility is to keep the vehicle operating smoothly. That said, Master Chef Yoerger served up a few hors d’doeuvres from the overall data set by working late, late at night, and the first few tastes of this new autonomous mapping system are enough to seriously whet the appetites of all the geologists on board – we look forward to the banquet!
TowCam and Team Soldiers On
While the untethered Sentry was quietly laboring the fields of Neptune (Roman Lord of the Sea), the sturdy, tethered TowCam was producing dazzling photographs of the carbonate ‘roofs’ associated with venting on the crest of Southern Hydrate Ridge. This time the Sentry – TowCam dance had evolved from a stately minuet to Argentine tango. One could almost hear the rhythms of the deep playing in the background as the two vehicles worked around the same carbonate deposit. Dan Fornari, a seasoned veteran of operations in the deep submergence world, was guiding his TowCam team to get the best pictures and the optimal chemical measurements by guiding it along the search/survey path that Deb Kelly had laid out to ensure that the first Experimental Node Site is carefully within the vent field to be close enough to conduct the best science, but far enough away from the venting to survive for the lifetime of the Cabled Observatory (nominally 25 years). Almost as proof of the effectiveness of this teamwork, the unique vent detectors brought on board for both SENTRY and TowCam, by Koichi Nakamura, our honored Japanese geochemist, recorded a record low value on this morning’s TowCam dive.
Change is Coming
There was special intensity in Dan Fornari’s usually sharp focus on the performance of the TowCam team this morning. Dan departs our cruise tomorrow (29 July) in Newport, OR, during our three-hour port call. His colleague, Erich Horgan, takes over full control of the operations for the remainder of the cruise when we leave Newport and head directly west to Axial Volcano, about 250 nautical miles away on the other side of the Juan de Fuca Plate. Erich and Dan have been training students and cruise participants to navigate, “fly”, and generally service and launch, TowCam during the first half of the cruise. The volunteers have welded themselves into a smoothly functioning group made of Dax Soule, new UW graduate student, Jennie Mowatt, UW oceanography undergrad, Janet Beckmann, an former Dean of Nursing, who often comes to sea with us, and Cody Young, an exuberant, recent-PhD physicist from UW, now a research associate at Arizona State.
Tribulations
TowCam was brought on deck about 1300 hours, and quickly serviced for a second redeployment of the day. At about the same time, we now know, SENTRY was struggling silently with an INS dropout, by implementing James’ work-around then going on to set its own “personal record” of 19 hours. But the small gremlins that create mischief in sea-going equipment chose this moment to strike TowCam as it was being lowered into its second ‘Dive’ of the day. The system simply did not turn on properly as the camera sled was placed below the waterline. This initiated a complex and challenging search for the problem, which after many hours of multiple test-dunking and series of diagnostic “experiments”, turned out to be a faulty salinity cell which was used to ascertain that the vehicle was actually in salt water before allowing the key systems to be inialized. The faulty cell replaced, the period required to solve this problem did not leave enough time for a subsequent dive before the sentry signaled that it was ready to come back to the surface.
Assessment and Prospects for Continued Work in the Ocean
As the day ended, a time-distance record had been set by SENTRY collecting amazing high resolution bathymetric data, and a phenomenal suite of digital images of the Carbonate “Pinnacle” on Southern Hydrate Ridge by TowCam, had been delivered as key elements in our pursuit of critical environmental information to facilitate early and successful implementation of the Regional Cabled Observatory. The fact that SENTRY had ‘phoned home’ toward the end of the dive, and the faulty conductivity cell in TowCam at the end of the day, made it clear that operating on the edge of technology in a hostile ocean is not simple. We chose to view these complexities as roughly akin to what the airlines routinely call “technical difficulties”.
This pattern of success and failure is familiar to all who try to operate complex systems in a real ocean. The challenges are very serious, the successes very sweet, and the failures and delays are an integral part of the process of learning how the ocean works and how humans can interact with it in more and more sophisticated and insightful ways.
CONTRIBUTED BY CHIEF SCIENTIST JOHN DELANEY