'Mapping the sea' appeared in the February 1985 issue of Popular Science. Popular Science

World - The centuries-long quest to map the seafloor’s hidden secrets

Ocean explorers have long tried to survey the contours of the seafloor, but today's charts still pale in comparison to those of distant planets.

From cities in the sky to robot butlers, futuristic visions fill the history of PopSci. In the Are we there yet? column we check in on progress towards our most ambitious promises. Read the series and explore all our 150th anniversary coverage here.

In 1984, marine geologists finally got a long-anticipated glimpse of our planet unseen. After crunching satellite data for 18 months, a geophysicist at Columbia University’s Lamont-Doherty Geological Observatory, William Haxby, revealed a stunning new panorama of the seafloor. It was the first time anyone spied a worldwide picture of what lay beneath the ocean in such detail—volcanoes, underwater mountains, fracture zones, and trenches. “Haxby’s maps of the world’s seafloors reveal a terrain as diverse as any found on the seven continents,” journalist and science writer Marcia Bartusiak reported for that year’s February issue of Popular Science, capturing the scientific community’s palpable excitement. At the time, the Martian landscape was more familiar.

Nearly four decades later, the surfaces of distant planets are still better imaged than Earth’s ocean floor. While exponential advances in computer processing power, considerably expanded satellite imaging capabilities, and the development of autonomous (robotic) underwater vehicles capable of reaching even the deepest ocean trenches have advanced deep sea exploration, a high resolution map of the vast expanse of our own planet’s crust that lies hidden beneath a watery cloak remains incomplete. That may be changing, and none too soon with climate change bearing down. With ocean waters covering more than 70 percent of Earth’s surface, having a clearer idea of the shape and composition of the sea floor will improve our ability to predict storm surge in hurricanes, forecast the path of tsunamis, calculate glacial melt, and monitor struggling marine habitats subject to commercial practices like fishery management and deep-sea drilling and mining.

“Seafloor mapping is critical to pretty much everything,” says Caitlin Adams, Operations Coordinator at the National Oceanic and Atmospheric Administration (NOAA) Office of Ocean Exploration and Research (OER), “from national security to blue economy [sustainable ocean] initiatives.”

Ever since Russia’s Sputnik took to the sky in 1957, artificial satellite networks have employed electromagnetic waves like radar and Lidar to map terrestrial—and extraterrestrial—surfaces. But traditional radar works best on arid topography (like Mars, the Moon, and landmasses on Earth) because it can only penetrate a few meters into water, limiting the reach of eyes in the sky for waterlogged planets like our own. Since water mutes electromagnetic waves, there are only two ways to truly see beneath the sea without journeying down to the seafloor: sonar, or echo-sounding, and gravimetry, which detects gravitational anomalies caused by large objects. In both cases, direct measurement is required—the devices must be underwater (sonar) or at least close to the surface (gravity meter) to work, which means they can only be operated from the hull of a ship. Therein lies the rub. Mapping Earth’s 139 million square miles of seafloor could take as long as 1,000 years (estimates vary widely) for one ship continuously crisscrossing the ocean.  

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