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The New BOBSled Underwater Camera System Records High-Definition Video of the Seafloor
A new underwater high-definition (HD) video camera system produced by the U.S. Geological Survey (USGS) made its debut this year, collecting more than 6 hours of HD video footage during field activities in February and March 2013. The Benthic OBservation Sled, or BOBSled, was developed at the Marine Facility of the USGS Pacific Coastal and Marine Science Center in Santa Cruz, California, by ocean engineer Gerald Hatcher.
"Benthic" refers to the seafloor, the object of the new system's imaging capabilities. The BOBSled's broadcast-quality HD video of the seafloor allows scientists to observe and identify organisms living there and to ground-truth maps of seafloor materials—such as mud, sand, and boulders.
Seafloor maps are made remotely by interpreting sonar (sound) signals that are bounced off the bottom and—in shallow areas where the water is clear—by incorporating data from aerial and satellite imagery and using lidar (light detection and ranging) to survey the bottom with pulses of laser light. The value of such maps is greatly enhanced by the close-up visual data in seafloor video footage. (Read about other USGS seafloor-imaging activities in "State and Federal Agencies Partner for a Second Year of Seafloor Sampling off Massachusetts" and "Sea Turtles Benefiting from Protected Areas," both in this issue.)
BOBSled has a single camera module housed in a titanium case with a wide-angle acrylic viewport, two 150-watt LED (light-emitting diode) lights, and a pair of lasers aligned to create two red dots 10 centimeters apart in the video image to provide scale. All camera functions, including zoom, white balance, aperture, and video resolution, are adjustable from the surface and in real time during video collection. The towed assembly, or "fish," is connected to the vessel by a 100-meter waterproof cable containing standard conductors for data and power transmission and a single fiber-optic line for the HD video signal. The cable is reinforced with a Kevlar layer for strength and a urethane jacket for water tightness and abrasion resistance. After transmission to the surface, the video is recorded to compact flash-memory cards that are "hot swappable" (they can be replaced without shutting down the computer system), thus creating a robust, solid-state, tapeless workflow. Its moderate size and weight allow the BOBSled to be deployed by hand from a small boat. Its cable length constrains its operation to water depths of 100 meters or less.
By April 2013, scientists from the USGS Pacific Coastal and Marine Science Center had used the new camera system to collect approximately 6 hours (nearly 400 gigabytes) of HD video footage during two field activities. In February 2013, they deployed the system in Hawai‘i from a 31-foot sport-fishing boat, the Alyce C., owned and operated by Joe Reich out of Moloka‘i. Video footage was collected to ground-truth maps of benthic (seafloor) habitat and to evaluate the condition, species diversity, and percentage of coral coverage on reefs near the islands of Lana‘i, Kaho‘olawe, and Maui. In March 2013, the BOBSled was deployed from the 34-foot USGS research vessel Parke Snavely in the Strait of Juan de Fuca to image the seafloor around the mouth of the Elwah River, Washington. This imaging was part of a multiyear research project to monitor the release of material into the Strait of Juan de Fuca by the removal of two sediment-choked dams upstream (http://www.usgs.gov/elwha).
Both field activities demonstrated the high quality of BOBSled's video output. See sample video clips below. The new system can record video footage at up to 1080i/59.94 full raster (1920x1080 pixels), 4:2:2 color, and a bit rate of 280 megabits per second—parameters that produce broadcast quality (or better) output. Each video frame is stamped with a time code synchronized with Global Positioning System (GPS) time, allowing other time-stamped data, such as navigational data, to be associated with the video on a frame-by-frame basis.
BOBSled's ability to record at a high bit rate enables relatively low compression (the selective removal of data to reduce file size) to be applied to the individual video frames, thus greatly improving the quality of still images captured from the video. For comparison, a contemporary Blue-Ray DVD's HD video stream is transmitted with a bit rate of approximately 30 megabits per second, considerably less than the 280 megabits per second that the BOBSled can record, or even the 100 megabits per second typically employed by BOBSled's users to keep datasets at a manageable size. Because of the human eye's ability to integrate images as they flash by at high speed, the Blue-Ray motion video can appear beautifully sharp, but compression artifacts (distortions of the image caused by compression) become obvious when such video is viewed frame by frame. This is especially true if the video contains a complicated scene with moving objects. The new BOBSled system can record video at a high bit rate if users want to extract high-resolution still images, but it can also record at a much lower bit rate if storage space is of greater concern.
BOBSled is a spin-off from the development, currently underway, of a system for recording HD video of seafloor as deep as 1,000 meters. The deepwater "Big BOBSled" will use two HD camera assemblies identical to the one mounted on BOBSled, and it will have the additional capacity to support a suite of oceanographic sensors and instruments that can be chosen to address specific experimental goals. Big BOBSled is scheduled for its first deployment in fiscal year 2014 (which begins October 1, 2013). Stay tuned!
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