Sentry's Dive a Success

Fri, 25 Jul 2008 11:49 PM PDT

The calm weather holds, significantly easing deployment and recovery of equipment over the side of the ship. We have yet to experience the heavy seas so common in this part of the North Pacific, even in the best part of the seasonal “weather window” of May to October. Early deployment and operation of each of our main research “platforms”-- the Sentry AUV and the TowCam--have gone smoothly.

First Real Science Dive for Sentry
A science meeting at the end of the day provided a chance for the scientific crew to be fully debriefed on the activities of the day, as everyone summarized their progress. The big success was the first real science dive for Sentry, Dive #010. Sentry is a free-swimming, untethered vehicle that looks like a well-used bar of soap with wings, and so far has a “clean” history. Dana Yoerger, one of Sentry’s “parents,” was glowing about how well the vehicle performed during its 12-hour deployment. “Flying” at 80 meters above the bottom, it successfully navigated the preprogrammed tracklines and test maneuvers that he had programmed into its “brain” prior to deployment. Sentry covered the area identified yesterday as the optimal site for Node 1. The mapping data collected by Sentry has been downloaded and is being processed as we began to prepare for the next survey of the Hydate Ridge experimental node sites that will be located in more interesting, but more hazardous areas. An early look at the data indicates that the only issues are readily dealt with and the small tweaks are in place for Sentry’s “run” tomorrow.

Sentry is powered by more than 1,000 lithium-ion batteries, the same type used in laptop computers. Although the batteries had been extensively tested before this cruise, there were unknowns related to how much energy would be expended during a 12-hour deployment. As Sentry spends the next half day on deck, recharging the batteries, analyses of energy usage will help us to carefully husband the battery resources that drive this remarkable new addition in the oceanographic “tool chest.”

Graceful Minuet
The Sentry/TowCam “minuet” described in yesterday’s Daily Log was both successful and seemingly graceful as TowCam passed briefly above Sentry as the AUV singlemindedly followed its path like a deep-sea bloodhound. While Sentry was still mapping, the TowCam was again lowered, retrieved, and deployed once more in a novel attempt to capture a gravity-driven core of seafloor sediments. The camera took pictures of the bottom, TowCam then rose to 10 meters, dropped a weighted tube into the sediments, and then  returned to photograph the results at seafloor level. Only a small sample of mud made it back to the surface. Further design work is required to refine this seemingly simple operation.

Mud for the Desert Oceanographers
The small amount of mud that did come back will be analyzed for DNA by the Arizone State University “Oceanographers From the Desert” when they return to their home laboratories. Joseph Chao and his ASU colleagues collected another set of deep-water samples from TowCam, which they will analyze for background microbial populations. Finally, TowCam conducted a routine survey for conductivity, temperature, and depth to constrain the sound velocity profile. Seafloor mapping photographs of the bottom held few surprises, showing a host of well-recognized denizens of abyssal plains everywhere such as rat fish, brittle stars, and sea cucumbers.

Measuring Light

An ongoing project operating today was the one Stephanie Harrington and student Erik Terpstra are conducting for UW Professor of Oceanography, Miles Logsdon. Using optical sensors to measure light during a sunny period while we were on station, they took measurements from the deck of the ship and then, holding the optical sensor out over the ocean on an extension pole, they measured the amount of light coming in and the amount of light being reflected off the ocean’s surface.

The Collaborative Ocean Visualization Tool

An evolving tool being actively developed onboard a research cruise for the first time is the Collaborative Ocean Visualization Tool (COVE), a software application developed by UW graduate student Keith Grochow.  COVE was intended as a design package to facilitate design of the regional observatory and was initiated using NSF funds from the “LOOKING” program, a cyberinfrastructure grant to the UW. COVE is now proving to be an essential part of this cruise for planning the next survey based on new data incorporated from the previous survey.

Next Up

EM300 surveys, a 17-hour Sentry run, and TowCam lowerings on Hydrate Ridge itself, which is on the continental shelf and is due east of the primary node site on the abyssal plain. In this more interesting, active, and hazardous seafloor area there will be one secondary node and one tertiary node for Ocean Observatories Initiative instruments. Both will be connected to the primary node and main cable by extension cables. Hydrate Ridge is the site of active venting of methane in places where gas hydrates are exposed on the surface. There are biological communities of microbes and larger fauna that feed off the venting gases.

Contributed by Chief Scientist John Delaney