Technology: Using Mapping Technology to Improve Our Understanding of the Ocean Floor

By Tim Battista, Center for Coastal Monitoring and Assessment, National Centers for Coastal Ocean Science

“Once a new technology rolls over you, if you’re not part of the steamroller, you’re part of the road.” -Stewart Brand

Introduction to Seafloor Mapping
Mapping of the seascape has been in existence for as long as mariners have been exploring our oceans. The necessity of these observations, such as those taken by Captain James Cook in the 18th century, are just as relevant and important today as they were centuries ago. We use these observations to better understand the condition and extent of seafloor habitats, the associations of animals with those habitats, and the impact of humans on the habitat and animals. Through the evolution of technology, maps are now able to detect and observe at finer scales and at greater accuracies the undulations and composition of the seafloor. So, while it took Captain Cook years to collect thousands of observations of the seafloor using lead lines during the course of his career, we now have the ability to acquire thousands of observations in mere seconds.

Traditionally, maps of the seafloor have required a human interpreter to “connect the dots” of sparse data to create a cartographic map. Those ink and paper maps evolved into digital maps with the creation of Geographic Information Systems (GIS), but even still, the maps were made by humans drawing lines based on some semi-informed decision. But humans are only able to process a finite amount of information to make a decision when creating maps. The advent of today’s technology, which collects data at several orders of magnitude faster, requires advanced techniques to assimilate and distill that information into a usable product. We use computer assisted processing to evaluate spatial and textural properties of the data to produce more efficient, timely, accurate, and resolved mapping products. The result of all of this technology is a map capturing the very fine details of the seafloor and of what it is comprised.

The technology used for acoustic data collection and habitat mapping is evolving at a very rapid pace. We work closely with industry partners and academic institutions to ensure that we are implementing the most advanced capabilities and are aware of the next-generation of advancements being developed. Furthermore, NOAA is advancing and investing in our own research and development, and, through our partnership with industry, we can ensure that they are best addressing our requirements. Our program recently released a methodology that greatly advances the ability to generate habitat maps through software automation. We hope to share these capabilities with other habitat mapping researchers so that they can utilize and improve their own efforts.

Current Mapping Technology
There are a number of technologies we use for habitat mapping, whose utility largely depends on the depth we are mapping. I like to think of it as a Swiss Army knife: our knife has a number of tools available, but we select the best one for the job at hand. Most of these technologies were developed with military applications, but have had valuable utility to civilian applications. Generally, the technologies are split into acoustic and optical techniques. In acoustics, we use sonar systems to transmit sound from a source down to the seafloor. Acoustics can be used in virtually any depth, but they become more efficient the deeper the water. Typical acoustic systems are from ships, small boats, or even autonomous underwater vehicles (AUVs). Acoustics are also very effective for mapping in areas which are too cloudy with sediment for optical systems. Additionally, these systems are effective for mapping not only the seafloor, but also objects in the water column like fish, whales, or other features of interest.

The time it takes for sound to travel from the ship to the seafloor back to the ship provides us with very precise and accurate measurements of depth and undulations of the bottom (Figure 1); it is like an echo. If you yell loudly and the echo responds immediately you intuitively know the object is close because the sound bounced back quickly. But if the echo takes seconds to return to your ear, than the object which it bounced off of is further away. Acoustic systems operate the same way and, since we know how fast sound travels in water, we can calculate depth. The only difference is the system we use (multibeam acustics) broadcasts many layers of sound out simultaneously (Figure 2) several times a second to map a larger area on the seafloor. We can also analyze the multibeam sound to better understand the composition what is on the seafloor, called “backscatter” (Figure 3). We know sound reflects better off hard objects and is absorbed by softer objects. So a coral reef or rocks will reflect more sound and create a stronger backscatter then something soft like mud. Different habitats like seagrass or algae will also look different. We use this piece of information to map what the habitat types are on the seafloor. The multibeam also helps us find interesting objects on the seafloor like lost fishing gear and ship wrecks (Figure 4)!

Clockwise from top left: Figure 1) Bajo de Cico, Puerto Rico color shaded bathymetry. Figure 2) Multibeam acoustic data collection. Figure 3) Multibeam backscatter of coral batch reff surrounded by a sand halo, seagrass (lighter) and sand (darker). Figure 4) barge shipwreck found south of St. Thomas, USVI. Credit: NOAA/NCCOS/CCMA

Optical systems use light to provide a picture of the ocean floor. There are both passive and active optical systems. Digital cameras flown on satellites, airplanes, or unmanned aircraft are examples of passive optical systems. They operate by recording the ambient light reflected back from features or objects (Figure 5). Active systems produce their own light source and project towards the seafloor. One example of these systems is the Light Detection and Ranging (LiDAR) system which we use routinely to measure the depth and composition of the seascape. The advantage of optical systems is that they work well for shallow water environments where it is too costly or dangerous to operate ships. The disadvantage of LiDAR is that it is only able to collect as deep as light can penetrate the water, which is typically 30 meters (~90 feet) (Figure 6).

Top: Figure 5) Commercial satelite imagery of Palmyra Atoll. Bottom: Figure 6) Airborne LiDAR sensor collecting data. Credit: NOAA/NCCOS/CCMA

Mapping Marine Life
While measuring the seafloor is important for understanding habitats that marine animals use, we also have technologies to map the marine life. Divers are one way to count and identify fish and marine mammals, but divers can only go so deep (~100 feet), can’t cover a lot of ground, and can’t stay down very long. We are able to use scientific grade fish acoustics to help us detect and identify fish. Fish acoustics broadcast sound which is reflected off the fish swim bladder to measure the exact location of each fish and how big it is (Figure 7a, 7b).

Left: Figure 7a) Fish school detected over the seafloor (seafloor represented by red band on bottom). Right: Figure 7b) Acoustically detected fish over the seafloor. Credit: NOAA/NCCOS/CCMA

While mapping the seafloor with remote sensing tools such as acoustics and LiDAR is useful, sometimes humans have difficulty telling what the data mean. Therefore, it is important to take pictures of these habitats so that we can train the users and the software used to generate maps we understand. We often use remotely operated vehicles (ROVs), which are tethered robots that we can drive to locations we are interested in exploring further (Figure 8). They have lights and cameras which send a signal up to the scientist on the ship real-time. And, unlike SCUBA divers, they can stay underwater indefinitely.  The pictures the ROVs take provide important information to confirm what type of habitat we are seeing in the acoustic data, how the animals use the habitat (Figures 8 and 9), and also the condition of the habitat (Figure 10). We can also use ROVs to explore the nooks and crannies of shipwrecks when it is too dangerous for divers to explore (Figure 11).

Clockwise from top left: Figure 8) Lionfish in a derelict lobster trap. Figure 9) Spiny lobster in a barrel sponge. Figure 10) Diseased coral head. Figure 11) 19th century shipwreck found off St. Thomas, USVI. Credit: NOAA/NCCOS/CCMA

Future Mapping Technologies
Producing products that scientists and managers can use to inform their research or decision can be costly and time intensive. In order for the products to be more useful and applicable, we need to provide timely and accurate information. The technologies described provide the means meeting that objective. We can now collect more and better data at a much faster rate than ever before. However, unless you can process and implement methods to use all that data, you have created an impediment rather than a solution. Therefore, the automated mapping techniques we have developed allow us to create products while taking advantage of the reams of data now at our disposal (Figure 12). However, ships and aircraft are still expensive to operate, so we are continuing to explore ways to drive those costs down even further. Many scientists believe that the unmanned military systems now being used can be adapted to provide the cost-effective platforms of the future. These unmanned underwater, surface, and airborne vehicles could conceivably multiply our abilities to collect data at much lower costs than traditional systems. But until then, we will continue to use our current technology to create the most detailed maps of the ocean floor as possible.

Figure 12) Habitat map produced from acoustic and optical data for Buck Island, St. Croix, USVI. Credit: NOAA/NCCOS/CCMA

This blog is one in a variety of technology posts designed to provide readers with insight into the  technologies that are being developed and used for research by NCCOS scientist and their partners.  

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