Notes from the Belfast waterfront

NOAA brass visits Belfast during rare update of seafloor surveys

By Ethan Andrews | Sep 20, 2017
Photo by: Ethan Andrews Shepard Smith, rear admiral in the National Oceanic and Atmospheric Administration Corps, strolls through Belfast Sept. 15 with fellow NOAA officers. With them are contractors from Fugro Pelagos, the company that is helping NOAA update seafloor surveys in the Stonington area.

Belfast — With some exceptions, the sea floor doesn't change quickly. But technology has improved dramatically since 100 years ago, which is when some of Maine's coastal waters were last surveyed.

Since July, a team led by the National Oceanic and Atmospheric Administration has been roving a patch of water that includes Eggemoggin Reach, Stonington and the Deer Isle thoroughfare. Shepard Smith, a rear admiral in NOAA Corps, said the work has been surprisingly worthwhile.

"We've made very significant findings of some dangerous rocks and shoals that some locals learned about the hard way but haven't been fully mapped," he said during a stroll on the Belfast waterfront Sept. 15.

Smith was in Belfast to host a pair of stakeholder meetings about the project at the University of Maine Hutchinson Center. With him were two NOAA colleagues and representatives of Fugro Pelagos, the contractor doing the hydrographic mapping work.

NOAA surveys form the basis of those ubiquitous nautical charts used by boaters. Those in the current survey area were last done more than a century ago with lead lines and sextants. Smith said the charts used today typically aren't wrong — geologic time is slow, and NOAA issues weekly updates based on new findings — but they were never very detailed to begin with.

"They would do spacing every hundred yards," Smith said. "If they saw signs it was getting shallow, they would go back" and survey more in that area.

Even so, the pockmarked and glacier-mangled seafloor in Maine is so irregular that many hazards slipped between the lead lines.

In an area marked 29 feet deep, Fugro's survey boats recently logged a protuberance that came within seven feet of the surface. In the cluttered gap between Stonington and Isle au Haut — an area that already bears a foreboding resemblance to a meteor field — they found more than a half-dozen uncharted navigation hazards.

"This is a not-very-well-behaved seafloor," Smith said.

The 2017 hydrographic survey started with a flyover by an airplane equipped with light detection and ranging (Lidar) equipment. Lidar works by bouncing lasers off the seafloor, so the planes fly when the water is clearest. The lasers don't always reach the bottom, but as Smith and his companions explained, neither does the hull of a boat.

If the survey ended here, it would be a vast improvement. Today's navigational maps of the area are based on a total of 7,500 lead-line soundings. By contrast, a single "ping" from a Lidar-equipped plane grabs 1,024 soundings. A presentation by NOAA and Fugro at the University of Maine Hutchinson Center Sept. 14 included an image of an airplane flying over open water superimposed with an unremitting field of bell-buoy-sized green dots.

After the initial aerial survey, a pair of sonar-equipped boats sets to work ranging methodically over the survey area, filling in what will become a seamless three-dimensional painting of the seafloor. Project Manager Dean Moyes of Fugro Pelagos described it as "literally, like mowing the lawn or painting a wall."

For all the tedium of driving a boat back and forth, the process under the hood is highly sophisticated. In contrast to the narrow spotlight of single-beam echo soundings or the pinpricks of lead line drops, the multi-beam sonar used on the survey boats illuminates the seafloor like a floodlight. Additional equipment accounts for the tilt and speed of the boat, light refraction, the tides and other variables that could distort data from the soundings.

The data will eventually be used for marine nautical charts, environmental studies, shipwreck exploration and anything else anyone can think of. The administration has vast troves of data, all of which is available to the public for free.

NOAA revises its surveys based on need. The process is time-consuming and expensive, so areas with higher volumes of marine traffic typically are given priority. Alaska has been bumped up the list, Smith said, because of an increase in sea navigation there. The 49th state accounted for more than half of the NOAA Office of Coast Survey's list of 2017 projects.

Last year, NOAA mapped the areas around Rockland, Port Clyde, Vinalhaven and North Haven. The current survey, which places the next piece in a puzzle headed up the coast, is expected to be done in October.

Marine traffic drops off beyond Bar Harbor, so boaters Down East might have to continue finding hazards the hard way. Smith wagered that even some higher traffic areas could be put on hold in the immediate future on account of changes caused by hurricanes this summer.

"It's likely we won't survey anywhere but Florida and Texas next year," he said.

Comments (0)
If you wish to comment, please login.