Celebrating World Hydrography Day 2020

June 21, 2020

In 2005, the United Nations adopted a resolution to recognize June 21 as World Hydrography Day , calling attention to the vital information that hydrography provides. But what is hydrography?

OER’s newest hydrographer, physical scientist and mapping lead Sam Candio, likes to think about it as if you drained the ocean and made a map of what lies below—“just because it’s easier if you picture it as if you’re on land.” Contrary to what many of us might imagine, the seafloor is much more than just a sandy bottom. It holds steep cliffs and canyons, underwater volcanoes and mountains, evidence of past tsunami damage, shipwrecks, and more. In turn, these features host a wide variety of animal communities, from veritable forests of deep-sea sponges and millenia old coral mounds, to chemosynthetic communities clustered around hydrothermal vents and seeps. The maps that modern day hydrographers create are part of a long tradition of use in navigating the ocean for fishing and commerce, transportation, and exploration. Today, hydrographic maps are also important in informing ocean resource management policies, predicting geohazards, and characterizing habitats. Aboard NOAA Ship Okeanos Explorer, deep-sea mapping work is also essential to selecting remotely operated vehicle (ROV) dive sites, and lays the groundwork for future scientific research and inquiry.

Hydrographic maps, like this one from the 2017 Laulima O Ka Moana expedition, help scientists decide which areas are good candidates for ROV dives.

Hydrographic maps, like this one from the 2017 Laulima O Ka Moana expedition, help scientists decide which areas are good candidates for ROV dives. Image courtesy of the NOAA Office of Ocean Exploration and Research, 2017 Laulima O Ka Moana. Download larger version (90 KB).

Over time, the tools and techniques used in hydrography have become more sophisticated. “Basically, all we’re trying to do with hydrography is to figure out where the bottom is—to get a measurement from the sea surface to the seafloor,” says Sam. “Initially, that was done with lead lines—a piece of lead on a line—that was dropped in the water, and then you’d measure the length of the line.” While this technique is sometimes still used today and works well in shallow areas where more technologically advanced methods are not feasible, it's not very efficient. To map the deep ocean, OER’s hydrographers use sonar, which uses sound in place of line. The multibeam sonar used on Okeanos Explorer allows for broad swaths of seafloor to be mapped at once. A fan of sound pulses is sent down from a transducer on the ship. When those signals hit the seafloor below, they are reflected back up to the ship. Because the speed that sound travels through water is known (after properties of the water that can affect this speed are taken into account), we can infer the depth of the ocean at the points where the sound pulses hit from how long it takes for them to travel back.

Okeanos Explorer, "America's Ship for Ocean Exploration", is equipped with the latest in technology systems, including multibeam sonar. This technology involves sending beams of sonar to the ocean floor and measuring the amount of time it takes for those beams to bounce back to the ship. In doing so, the sonar creates a 3-D "sound picture", or map, of the seafloor. Video courtesy of the NOAA Office of Ocean Exploration and Research. Download (mp4, 9.7 MB).

The theme of this year’s World Hydrography Day is autonomous technology, and inspires ideas and discussion about what the future of hydrographic field operations might look like. Recent high profile initiatives have called for increased seafloor mapping, from the international Seabed 2030  effort to map the entire seafloor in the next decade to national strategies for mapping, exploring, and characterizing the United States Exclusive Economic Zone and mapping the coast of Alaska. To meet the ambitious timelines of these initiatives, “it’s absolutely critical that we do things differently than we have done in the past,” says Sam. Autonomous technology will likely be part of the solution.

Though experienced, Sam is a relative newcomer to the field, but has nevertheless seen swift advancements—particularly around the automation of data processing: “things aren’t moving incrementally, it’s like a rocket forward—I don't even recognize hydrographic processes from when I started five years ago.” By automating file transfers and using machine learning to clean incoming data of noise, scientists can eliminate sources of error—as well as frustration. “The thing to keep in mind about autonomous technology,” remarks Sam, “is that it’s not about people not being needed, but rather about automating tasks to free up people’s time and brainspace to go on to bigger and better things.”

Automated technology can also act as a “force multiplier,” amplifying efforts already underway. One of the current hot topics in the world of hydrography is optimizing the use of autonomous underwater vehicles (AUVs) for mapping. One vision for this would be several AUVs equipped with multibeam sonar, which could be deployed from a larger vessel and used to map in tandem, collecting many times more data than a ship alone could. Senior mapping lead Meme Lobecker, who joined the office back in 2009, sees the potential that AUVs could lend to deep-sea mapping, as well as the challenges. One of the primary challenges is positioning. Once an AUV goes underwater, it loses its GPS signal completely. It can extrapolate its position with internal systems based on speed and direction, but will still need to surface periodically to take a GPS point and recalibrate its location. This task is simple and quick enough in shallow waters, but in the deep sea, traveling all the way up to the surface and back down again takes too much time. To get around this, ships today maintain station over an AUV to provide it with navigation information through an acoustic communication link. But the ultimate goal is to have them decoupled, says Meme, “part of the movement of the technology is for big ships to carry little independent launches, or autonomous surface vehicles (ASVs), that can do the tending over the AUVs. There are also ASVs in development that are large enough to carry deep-water sonars themselves, and can map from the sea surface. Imagine data hubs on shore receiving new data from autonomous platforms from all over the world.” Swarms of these AUVs and ASVs would then be able to carry out mapping independent of larger host vessels—a true force multiplier.

With less than twenty percent of the ocean mapped to modern standards, there’s still a long way to go to before anyone can truly fully visualize the seafloor. But the next time you step foot on the coast, or even the shore of a lake, imagine how the surface of the Earth continues beneath the water before you—and you’ll be one step closer to seeing the world through the eyes of a hydrographer.