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Ocean Imaging Expedition – Log 3

Ocean Imaging Expedition – Log 3

Clams as far as they can see

Nancy Barr

When the ROV Doc Ricketts arrived at an extensive clam bed deep in Monterey Canyon this morning, it was soon evident that things had not changed drastically since the last time the site was mapped by David Caress and his team. That answered the first question of the day: Did the large turbidity current that moved a massive amount of sediment from high up Monterey Canyon in January 2016 travel this far? Obviously not. This is an important piece of information for Scientist Charlie Paull and his colleagues who are studying the movement of sediment in the deep sea.

But Paull is looking not only at major changes in the shape of the seafloor, but also for small changes in texture that can indicate the movement of sediment. Today’s low-altitude survey conducted with the lidar, multibeam sonar, and stereo camera will provide the close-up look to determine if there have been those fine-scale changes. About half of the 100-meter-square survey area was covered today before high winds required bringing the ROV back up to the ship a little early. Tomorrow the team will continue the survey of this clam bed at 2,850 meters depth. The results of these surveys will be compared with maps of this same site from six previous surveys conducted from 2012 to 2014 to learn more about where and how the seafloor is changing.

Above, a frame grab from the video of the clam field surveyed today. If we were doing just a video survey, we would fly the vehicle closer to the seafloor, and the video would be sharper, but at the cost of covering a narrower swath (one meter) of the seafloor with each pass. Below, an image from the stereo camera system in use on this survey provides greater detail over a 4.2-meter-wide swath of the seafloor.
The laser beam of the lidar imaging system sweeps back and forth over the clams; the length of time it takes for the laser light to bounce back indicates the terrain.
On many cruises, the science team spends hours in the lab processing biological and geological samples after a full day in the ROV control room. This cruise is different—the focus is on technology, not samples. Left, Software Engineer Mike Risi, who wrote the code for the ROV to run autonomously on a preprogrammed path over the survey area. Right, Operations Engineer Erik Trauschke, is our expert on the inertial navigation system running in the imaging system. Also aboard is Electrical Engineer Eric Martin, who manages the lidar imaging system.