Skip to main content

Scanning the depths

NOAA is using the latest technology to find uncharted obstructions and accurately sound the bottom

NOAA is using the latest technology to find uncharted obstructions and accurately sound the bottom

Crammed into the 29-foot welded-aluminum cabin boat that Julie Oberg steers through the Atlantic chop a mile off Virginia Beach, Va., are some mighty sophisticated electronics.

A video screen mounted above the helm, unlike anything on your boat, shows if she is holding precisely to a computer-generated course through the 3-foot waves. A cable runs from her screen to the cabin, where, like some video pinball wizard, her crewman, Peter Lewit, stares intently at a bank of four more colorful screens.

Oberg, the navigator, and Lewit, a senior survey technician, are government employees who are remapping the shifting seabed here near the busy shipping channels that lead into the mouth of Chesapeake Bay. Compared with the technology in use only seven years ago, the machines Oberg and Lewit employ are up to 100 times more accurate, according to officials at the National Oceanographic and Atmospheric Administration. Other NOAA technology assures that the information the pair gather can be available to mariners within a few months.

Yet when you, the recreational boater, are gunkholing and in need of accurate charts to keep your keel off the rocks or out of the mud, there is a strong likelihood you are relying on information gathered before 1940, with the technology of the ancients. At best, NOAA says, your chart probably is based on surveys done before 1998, when the available electronic sounding machinery routinely missed much of what was on the bottom. And despite the tools on Oberg’s and Lewit’s boat, recreational boaters are not about to see change soon, NOAA officials say.

Headquartered in Silver Spring, Md., NOAA is responsible for charting 3.4 million square nautical miles of water, slightly less than the entire land mass of the United States and Mexico. Of this water, 500,000 square nautical miles — about twice the size of Texas — are “navigationally significant,” saysW. Michael Gibson, chief of NOAA’s Hydrographic Surveys Division. “We’re talking at least 70 years to complete [recharting] the navigationally significant area,” Gibson says. “For the whole [3.4 million square nautical miles], that’s certainly not within our lifetime.”

In 1994 there were 43,000 square nautical miles that NOAA deemed “critical” for new surveys. That work has been reduced significantly over the last 11 years, but it will be 2018 before the remaining 23,000 square nautical miles are recharted, Gibson says.

Hydrographic surveys — taking a physical look at the seabed to see what is there and how deep it is — are but one part of chart-making at NOAA’s Marine Chart Division. In addition to the vital survey information, the chart-makers also depend on the Army Corps of Engineers for dredging depths in shipping channels, the Coast Guard for the location of buoys and other aids to navigation, and other federal agencies for details on offshore oil rigs and pipelines, dump sites and the like.

“All kinds of organizations are building artificial reefs,” which need to be noted on charts, says Capt. James Gardner, chief of NOAA’s Marine Chart Division. And there are sunken ships, boats and barges, as well as shifting silt and drifting sand, that mariners report through NOAA channels. “There are massive amounts of data that have to be reviewed by our people,” says Gardner. In fact, about 20,000 details have to be changed on charts each year, he says.

Gardner’s office has a system for getting new information onto charts in as little as a month or two. But the reality for pleasure boaters concerned about the shallow, near-shore fringes of water is that few of those thousands of changes concern them.

“We don’t have enough resources,” Gibson says. “The hydrographic survey program is focusing on areas that are primarily important to commercial navigation. The reason is we want to prevent commercial ship groundings, oil spills, hazardous cargo spills, that sort of thing.”

(The most frequently cited incident is the November 2004 rupture of a 750-foot petroleum tanker by an uncharted 15-foot piece of curved metal on the bottom of the Delaware River near Philadelphia. That incident caused a 265,000-gallon oil spill. “The existence of the bottom debris was unknown to the maritime community and was not included on any navigational chart or in any notice to mariners,” concluded a report by a congressional hearing on the incident.)

The United States conducts a quarter of the world’s merchandise trade, according to NOAA’s 2004 Hydrographic Survey Priorities report, and “a vast majority of it is transported by sea. Approximately one half of marine cargo is petroleum or hazardous materials,” the report states. “Additionally, over 3,800 cruise ships, carrying 8 million passengers, departed U.S. ports in 2003.”

“So even though we have the responsibility for areas that are of interest to recreational boaters, that is not our first priority at this point,” Gibson says. “If you think about that, unless you’re in the approaches to most of the major ports and harbors, the area that, let’s say, is inside the 4-meter [depth] curve is not important to commercial navigation, so we’re not addressing those areas with the same aggressiveness.”

NOAA’s problems, according to Elaine Dickinson, a lobbyist for BoatU.S., are money and time. NOAA got $3.5 million less in the 2005 federal budget than it did the year before, says Dickinson, a member of a NOAA advisory committee comprising members of the maritime industry. “I think it’s a shame that it’s gotten to that point where they have a 10- or 15-year backlog.” But she says money alone won’t solve the problem of poor charts. “It takes something like three years to train a cartographer because everything has to be so exact,” she says.

Hydrography may be the weak link in the chart-making chain, but it is a very old one, as well. “Descriptions of coastlines, evidently for the seaman’s use, were published in the years before Christ and survive today,” reports Australia’s Institution of Surveyors. “Exploratory voyages of Cook, Vancouver and many others provided a wealth of hydrographic information and material on which the publication of more dependable charts was possible. Spurred on by the experiences gained in war and by the actions of other sea powers, the British Admiralty founded the Hydrographic Department in 1795.”

In those years, surveying was done by lead line — dropping a weight attached to a string overboard to measure depth. By following straight, parallel courses and dropping the lead periodically, early chart-makers were able to produce a rough map of the seabed. But, NOAA’s Gibson says, a lot of bottom features were missed. Much of that information remains on the charts aboard recreational boats.

“We used to use a number that over 50 percent of the soundings data on charts was acquired using old technology — that is, lead line,” says Gibson.

Lead lines were replaced by U.S. hydrographers in 1940, according to Gibson. At that point, a single-beam echo sounder was introduced. This was about the same as a recreational boater’s depth sounder. “You got a continuous measurement along a track, but you still had wide spacing between the tracks,” Gibson says. Think of a lined legal pad of paper, where the lines are the hydrographer’s track and the spaces between the lines are the places where no data is gathered.

In 1998 NOAA began using a new device called a multibeam, an echo sounder that can sweep the bottom like a broom. “With multibeam, we’re getting — and this is a dangerous thing to say — you’re scanning the entire bottom. [But] you don’t get a ping on every spot on the bottom.”

To compensate for that shortcoming, NOAA now also uses high-resolution side-scanning sonar that looks across the seabed. “We get grayscale imagery which makes it easy to pick up objects that could be sitting on the bottom or features that could be rising off the bottom,” Gibson says.

The improved technology, despite its weaknesses, is a vast improvement over lead line soundings. In the same area where a lead line survey would produce 1,000 to 2,000 soundings, a single-beam echo sounder would give 500,000 to 750,000 soundings, Gibson says, and a multibeam sounder will provide 4 million to 100 million soundings.

Even with these advanced electronics, hydrographers are left with much the same process that their grandparents might have used: steering boats in straight, parallel paths across the water, one sweep at a time. But there is promise in a new airborne light detection and ranging device that goes by the acronym LIDAR. A laser mounted in an aircraft fires its beam down through the water to scan the seabed, and records the beam’s return, calibrating the distance from the plane’s known altitude.

“Where you can use it, you can cover a lot more area potentially faster,” Gibson says. “[But] it’s absolutely not a magic bullet.” The problem with LIDAR is that it only works in depths of up to about 50 meters and in clear water. “Places like the Florida Keys, down in the Caribbean, out in the Pacific islands, remote areas of Alaska in the near shore,” he says. “We’ve had some tests done in New England, but it’s very seasonal. You have to plan it so you get up there when you’re not having a lot of river runoff or algae or plankton blooms.”

LIDAR wouldn’t work well on the Chesapeake, with its turgid water, he says. “The problem is there is so little area that you can effectively use it that we have to be careful about overpromoting that,” Gibson says. “The other problem is multibeam is high resolution. LIDAR is much lower resolution, so with LIDAR you may not find all the potential hazards to navigation. A submerged piling may not show up.”

The limitations of LIDAR aren’t the only constraint on producing up-to-date charts. There is the diminutive scale of NOAA’s fleet of vessels. For the entire U.S. coast, the agency has four hydrographic ships. The Rainer, a 231-foot vessel stationed in Alaska, carries six 29-foot launches like the one Oberg and Lewit were using off Virginia Beach. Another 231-footer, the Fairweather, also is assigned to work Alaskan waters with its four launches. (Alaska has 40 percent of the nation’s uncharted waters, plied by fleets of oil-laden tankers and crowded cruise ships.) On the East Coast, the Thomas Jefferson is a 208-foot ship that sails from Norfolk, Va., with two launches, including Oberg’s. And the Rude is a 90-foot Norfolk-based vessel with no launches. The Bay Hydrographer, a 56-foot research vessel, works primarily on Chesapeake Bay testing hydrographic equipment.

While all of the East Coast vessels have multibeam sonar and high resolution side-scanners, the West Coast ships rely primarily on multibeam alone, Gibson says. NOAA helps its fleet by spending more than half of its hydrographic survey funds on private contractors. All of the LIDAR work is contracted, Gibson says. Contracting allows NOAA to reduce the backlog of surveys, he says.

Typical of NOAA’s ships is the Thomas Jefferson, named for the president who in 1807 authorized NOAA’s predecessor, the Survey of the Coast. The ship’s authorized crew numbers 42, including 19 deckhands, four licensed engineers, up to 11 scientists, and eight officers, members of the NOAA Commissioned Corps. These uniformed officers are assigned rank precisely like their Navy counterparts, from ensign to admiral, and are paid the same wages.

The Thomas Jefferson is at sea for weeks at a time, and its crew lives aboard. The skipper is Cdr. Emily Christman, a 21-year veteran of the Commissioned Corps. Last summer the ship worked coastal Long Island Sound after spending the winter months closer to its Norfolk home port. Christman says that while her ship has “chewed away” at a backlog of survey needs in deep-draft areas, technological limitations have limited their work on shallow areas.

“Multibeam may be ineffective in the shallow water but good in 10 meters or more,” Christman says. She says that the boating public is “the biggest source” of point information. “The information they send us is … usually ‘chartable,’ ” she says, because of new depth-sounding technology available for private boats. She notes that the U.S. Power Squadrons has a program for gathering hydrographic information that it shares with NOAA. (For more information, visit and use the site’s search function with keyword “reporting.”)

And boaters with local knowledge that differs from published charts can pass that information along to NOAA’s Coast Surveys Navigation Managers, who are assigned to regional NOAA offices. These managers give the reports to the Marine Charts Division for inclusion in future charts, Christman says. (To report a discrepancy, log on to and complete the form.)

As for the work of the Thomas Jefferson, Christman says some surveys the ship conducted in 2004 will get onto charts this year. The information from other ’04 surveys “got off the ship in six weeks,” she says. While the average time from survey to chart is 18 months, the skipper says her goal is two to three months. Her timetable was delayed this year for three months while the Thomas Jefferson worked in the Gulf of Mexico charting changes along the coast from Mississippi to Texas after hurricanes Katrina and Rita.

Christman’s executive officer, Lt. Shep Smith, recalls three incidents where local knowledge revealed information that was inaccurate on NOAA charts. Two islands in the Florida Keys were shown on charts with a channel between them. But a hurricane had created a sandbar that actually joined the islands, says Smith. In another case, he says charts showed a wreck where a tugboat was believed to have sunk, but surveys of the area were unable to locate any wreckage. The third instance was in the harbor of Gloucester, Mass., where charts showed a rock at a depth of 6 feet when it was actually only a foot below the surface at mean low water. “I’m sure every 10-year-old on the coast knew he could swim out to that thing and stand on it,” Smith says.