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Ocean Imaging Expedition – Log 2

Ocean Imaging Expedition – Log 2

Taking in the big picture

Nancy Barr

While it has long been possible to capture video and still images in the deep sea, most cameras used at depth have a very limited field of view and—unless the water is perfectly clear—must be very close to their subject matter. The stereo cameras used in this week’s low-altitude surveys offer a major advantage to scientists who want to assess wide areas of the seafloor. These cameras mounted under ROV Doc Ricketts take pictures every two seconds as the ROV is flown in a lawn-mower pattern at two-and-a-half-meters altitude over the area of interest. MBARI Mechanical Engineer Brett Hobson took special care when designing the housings for the cameras to assure that the images were free of distortion across their wide field of view. Each image overlaps a bit of the area of the previous image, which makes it possible to stitch them together as a mosaic of the entire survey area.

The day’s survey began at the benthic instrument node. The ROV then flew an automated course to cover much of a 100-square-meter area surrounding the node, which is the area that experienced a large deposit of sediment in January of 2015. The day ended with a detour to a known rock northeast of the node, where it was learned that the large event of last year did not reach this spot; the terrain had not changed much since it was last surveyed.

The following preliminary images show the results of the different imaging systems. When all the data are processed, they can be meshed together to show large areas and can be used to compare with images and maps from previous surveys.

Four features seen on the seafloor at a depth of 1,850 meters in Monterey Canyon—from the top, the benthic instrument node, a rattail fish, a piece of wood, and a scour in the seafloor. On the left are photos taken with the stereo camera system (each shows an area 4.2 meters wide). In the center are bathymetry maps created from the lidar data with areas of interest highlighted by yellow boxes. At right are 3D “point clouds”, without vertical exaggeration, of the raw lidar soundings used to make the maps.”
Software Engineer David Caress, who leads the Ocean Imaging Project, reviews the day’s multi-beam seafloor mapping data with Postdoctoral Fellow Monica Schwehr. Photo by Nancy Ba