Underwater Gliders

By Craig Collins

They headed out to sea in July 2020, in the early part of hurricane season, into the Gulf of Mexico and off the coasts of Puerto Rico and the eastern United States: 30 underwater gliders, equipped with sensors to measure temperature and salinity throughout the water column, from the surface to depths a half-mile undersea.

The 2020 hurricane season deployment was a collaboration between NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML), the U.S. Navy, and the U.S. Integrated Ocean Observing System (IOOS®), a national-regional partnership for observing and collecting data from the oceans and Great Lakes. Navy researchers were among the first to experiment with underwater gliders – unmanned torpedo-shaped robots that can operate for months, monitored and controlled from terminals on land – in tracking submarines.

In just a few years, uncrewed gliders have proved indispensable to NOAA’s mission of science, service and stewardship. Gliders have been deployed throughout the last several hurricane seasons, gathering data on warm water masses that can feed and intensify passing tropical storms, as well as cooler upwellings of saltier water than can draw energy from and weaken storms. AOML research has shown that data gathered from these gliders and other platforms are key to improving the accuracy of hurricane intensity forecasts.

The gliders offer clear advantages over other data-collection platforms in terms of flexibility, safety and cost. They can traverse the open ocean for months while consuming very little energy – they are called “gliders” because, like aerial gliders, they don’t have their own propulsion systems; they are outfitted with fins that act like wings, responding to slight changes in buoyancy to convert vertical motion into horizontal motion. The gliders navigate with the help of periodic fixes from the Global Positioning System, pressure and tilt sensors, and magnetic compasses. Their original navigation and mission parameters can be altered remotely, via satellite, and they can transmit data from their sensors – including measurements of temperature, salinity, dissolved oxygen, chlorophyll concentration, and dissolved organic matter – in real time, along with video and sound. And they’ve proven capable of withstanding serious beatings, from hurricane-force winds to attacks from sharks that mistake them for prey. The Navy estimates that the gliders gather data at about only 1% the cost of manned surface ships.

While they are still a relatively new technology, these capabilities have enabled gliders to support a range of operations in support of NOAA’s mission. Recent and near-future projects involving gliders include deployments to:

• the Northeast, where NOAA and the Woods Hole Oceanographic Institution have teamed up on a project to monitor shipping lanes using gliders equipped with acoustic sensors, which can detect endangered right whales, alert mariners and fishermen, and help mariners avoid ship strikes;

• the Great Lakes – western Lake Erie, specifically – where gliders have been deployed to monitor and measure the toxicity of harmful algal blooms, in order to help predict and protect the safety of drinking water supplies;

• the California coast, to monitor ocean conditions, including harmful algal blooms, that could endanger crab fisheries;

• Alaska waters, including the Cook Inlet and Chukchi and Bering Seas, to monitor the locations of marine mammals such as bowhead whales, belugas, walrus and ice seals, and help federal and state managers monitor ecosystem and habitat changes;

• the Gulf of Mexico, where data on currents can help to ensure safe offshore energy operations, and chemical data can detect and characterize oil in the water column;

• the Northwest, where data on currents, upwelling and water temperature can help ensure safe navigation, fishing and aquaculture; and

• the Hawaiian Islands, where glider data improves forecast models used by the U.S. Coast Guard for search and rescue operations, and supports public health advisories about toxic warm-water bacteria.

On their 2020 voyages, NOAA’s “hurricane gliders” set off to collect data in the upper ocean to sample from areas – such as the Gulf Stream of the Atlantic coast, and the Loop Current of the Gulf of Mexico, and areas where fresh water sits on top of the ocean – that are linked to strengthening or weakening hurricanes. The 2020 fleet was expected to collect up to 50% more observations than the previous year’s – moving NOAA and its partners closer than ever to improving our understanding and prediction of the ocean’s role in tropical storms.