Mapping Sur Ridge

The surface of the ocean can look flat and featureless, but the deep seafloor lying beneath has complex and variable terrain. Just like here on dry land, there are sharp peaks, rolling hills, rugged valleys, massive canyons, and towering cliffs—they’re just obscured by water. Leveraging the experience of MBARI’s science, engineering, and marine operations teams, we’re able to visualize the beautiful bathymetry of the deep seafloor in remarkable detail. Our mapping techniques have revealed the impressive and ever-changing landscape of the Monterey Canyon and are now shedding new light on Sur Ridge. Mapping the seafloor provides the critical baselines required for understanding our changing ocean. Repeated mapping efforts can help our scientists understand geologic processes, monitor ocean health, and detect the impacts of human activities.

For 20 years, MBARI engineers have worked to improve our ability to map the deep seafloor. We’ve developed revolutionary technology to map objects as small as one centimeter (less than half an inch) on the seafloor. At this resolution, we’re able to marry geology and biology—we’re mapping at the scale of individual animals. By developing new mapping and imaging tools, we’re enhancing research on geological processes and the health of deep-sea marine life.

To survey Sur Ridge, MBARI has employed a suite of technologies to build maps of increasing detail and resolution. Nested surveys provide a progressively richer picture of Sur Ridge. Ship-based multibeam sonar pings the seafloor with sound, providing a rough picture of the topography below. This tried and true technology reveals features on the seafloor to a resolution of 25 meters (82 feet). The maps are suitable for navigation and guiding dives with MBARI’s robotic submersibles, but leave out details important to our scientific understanding. Robotic technology has proven critical to taking a closer look at Sur Ridge.

Autonomous underwater vehicles (AUVs) use sound to map the seafloor. Image: Phil Sammet © 2010 MBARI

Autonomous underwater vehicles (AUVs) are self-guided robots that can be equipped for a variety of missions. Our engineers program the AUVs at the surface, but once these torpedo-shaped robots are launched into the ocean, they navigate through the water on their own, collecting data as they go. MBARI has deployed AUVs to profile oceanographic conditions below the surface, process environmental DNA (eDNA) to survey marine biodiversity, and conduct transects to take a census of marine life.

Since 2006, MBARI has also employed AUVs for mapping the seafloor. MBARI’s two mapping AUVs use four mapping sonars—a swath multibeam sonar, two sidescan sonars, and a sub-bottom profiler—and because they’re closer to the seafloor than the surface ships, they map the seafloor at finer resolution. These sonar systems collect topography, backscatter intensity (which can distinguish between hard rock or sediment cover), and subsurface profiles at a horizontal resolution of one meter (about three feet) when the mapping AUV flies at an altitude of 50 meters (164 feet) above the seafloor. Maps from these AUV surveys help researchers identify areas of interest for further study, examine lava flow morphology, find hydrothermal chimneys, identify faults, and monitor the seafloor for changes.

But MBARI’s Ocean Imaging Project is developing significantly higher resolution mapping capability that combines one-centimeter-scale topography with color photography to fly much closer to the seafloor while working in areas with complex, steep, or even vertical terrain.

MBARI’s ROV Ventana carries the Low-Altitude Survey System (LASS) for detailed mapping of the deep seafloor.

By mounting this Low-Altitude Survey System (LASS) to MBARI’s remotely operated vehicles (ROVs), we’ve taken our closest look yet at Sur Ridge. These robotic submersibles remain tethered to a research vessel at the surface. Pilots control the sub’s movements, allowing scientists to view life deep below. But cameras aren’t the only research equipment MBARI’s ROVs carry into the deep sea. Our engineers have adapted a number of tools like samplers to collect animals, push cores to sample deep-sea sediments, and lasers to run complex analyses of chemicals and organic structures. Interchangeable ROV toolsleds can be customized with tools required for specific missions.

Nested surveys from ship-based multibeam sonar, autonomous underwater vehicles (AUVs), and remotely operated vehicles (ROVs) allowed MBARI researchers to capture Sur Ridge in incredible detail. Figure A shows a map of Sur Ridge using AUV bathymetry at one-meter resolution on top of the ship-collected bathymetry gridded at 10-meter resolution. The small rectangle labeled “B” is the extent of one of the surveys by the Low-Altitude Survey System (LASS). Figure B shows the wide-swath lidar bathymetry from the LASS at two-centimeter resolution over AUV bathymetry at one-meter resolution of the northern end of Sur Ridge. Figure C shows a detailed look at the seafloor. The dark speckles are the corals, sponges, and fishes detected by the lidar. Image: Jenny Paduan © MBARI 2021

MBARI’s revolutionary mapping toolsled uses sound (sonar), light (wide-swath lidar lasers), and stereo photography (illuminated by strobe lights) to map the seafloor in incredible detail. When this mapping system is mounted, the ROV is flown in an automated mode (with our pilots standing by) just three meters (10 feet) above the seafloor. This allows the sonar to map at five-centimeter resolution and is close enough that light can penetrate for lidar mapping (at one-centimeter resolution) and photography (at millimeter-scale). The toolsled can articulate to map inclined surfaces, like the steep cliffs of Sur Ridge.

Thanks to this groundbreaking mapping system, we’re able to map Sur Ridge’s extreme topography and its delicate coral and sponge gardens. These low-altitude surveys enable pioneering studies of the geological, geochemical, and biological processes that modify the seafloor at fine scales; they also support ecological research through comprehensive mapping of seafloor habitats at the scales of the animals that live there. Eventually, MBARI engineers hope to migrate this technology to autonomous robots, which can run automated surveys and exponentially expand our mapping capacity.

Low-altitude surveys at Sur Ridge generated topographic maps by lidar (top, to one-centimeter resolution) and multibeam sonar (bottom, to five-centimeter resolution). The lidar reflects off the soft tissues of the animals, while the multibeam passes through them and shows only the seafloor. The difference reveals the distribution of animals like fish, deep-sea corals, and sponges. Photography shows the colors of the animals, which can aid with identification and health assessment. Image © 2019 MBARI

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