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Ocean Imaging Expedition – Log 4

This area in the image from the lidar data corresponds to the area covered by the mosaic image above. Click on image for larger version.

Ocean Imaging Expedition – Log 4

Seeing fine details in the deep sea

Nancy Barr

Images created from two days of surveying an extensive clam field in Monterey Canyon are impressive for their level of detail—especially when you remember that these pictures are coming from more than 2,800 meters deep (about 1.7 miles) in the ocean.

The surveys answered some science questions about this site. First, they showed that the turbidity current that moved a large amount of sediment down the canyon early last year did not make it this far. Second, it showed the boundaries of this particular clam field and documented the density of clams here. These images will also be compared with six earlier surveys in the same location to determine how the clam field may have changed over time.

The raw data from the lidar surveys come in as points from each location where the laser beam hit the bottom, as seen in the images posted earlier in these logs. Postdoctoral Fellow Monica Schwehr then processes these data to create images such as the one above, revealing details as small as one centimeter in size. The green objects here are clams. Notice that the tracks made by the clams’ movement across the seafloor are evident in this image. The range of colors depict slight variation in, and simulated illumination was added to make it easier to see the objects. The width of this image represents a swath of the seafloor 1.6 meters wide. Click on image for larger version.
Photos taken with the stereo cameras can be meshed into one large image. David Caress created this mosaic with software that matches up the overlapping parts of the images, and projects the images onto a seafloor map created with the multibeam sonar data. This image covers an area measuring 4 by 6.5 meters. Click on image for larger version.
This area in the image from the lidar data corresponds to the area covered by the mosaic image above. Click on image for larger version.
The vertical lines in this multibeam map are 100 meters long; the small yellow box indicates the area shown in the mosaic image above. Post-cruise processing will produce a mosaic image of the entire survey area. Click on image for larger version.

About Ocean Imaging Expedition

In early March, MBARI's Ocean Imaging Group conducted low-altitude seafloor surveys aboard the R/V Western Flyer as part of the Coordinated Canyon Experiment.