The first survey

Nancy Barr

The first low-altitude survey of this expedition centered on an area surrounding an instrument node located about 30 kilometers offshore at a depth of 1,850 meters in Monterey Canyon.

Here’s how it works: Four systems record data as the ROV runs a preprogrammed path across a 100-meter-square section of the seafloor. The multibeam sonar system sends sound waves toward the bottom; the time it takes for the sound to bounce back indicates the depth. The lidar system is similar in terms of sending a signal to the seafloor and recording the time it takes to bounce back, but it uses laser light beams instead of sound. Two strobe lights fire to provide light for a stereo-image camera system that takes photos as the ROV flies just two and a half meters above the bottom. Finally, an inertial navigation system records the speed, orientation, and velocity of the vehicle—important information for helping to tie all the data together.

On a full-day’s ROV dive, these systems would bring back more than a terabyte of data, which researchers then piece together to create detailed seafloor images. Processing that much data continues late into the night, so images are not immediately available.

—Nancy Barr