NOAA’s “air gap” technology received the ultimate test on the morning of June 27. The technology passed with flying colors as the new U.S. Navy LPD ship, the USS New York, sailed down the Mississippi River, clearing the underside of the Huey P. Long Bridge just north of downtown New Orleans by 64 centimeters (2.1 feet). The San Antonio-class $1 billion naval vessel, built in part from steel salvaged from the World Trade Center towers, sailed downriver, heading out for a month of sea trials.

The air gap sensor is part of the installation of NOAA’s Physical Oceanographic Real Time System (PORTS ™) for the port of New Orleans. NOAA, in the process of completing the installation of real-time air gap sensors on the Huey P. Long Bridge, has been conducting data-testing trials for the past several weeks and contacted Northrop Grumman to offer the technology to assist in the USS New York’s passage. The system, when complete, will also include current meters, a water-level gauge, and air gap sensors at the Crescent City Connection Bridge. The New Orleans PORTS™ is expected to be completed by the end of the summer and will be fully operational this fall.

Built in part from steel from the World Trade Center towers, the U.S. Navy LPD ship the USS New York travels down the Mississippi River, heading out for a month of sea trials.

The challenge facing the Northrop Grumman ship builders and the Navy was making sure that, despite high water levels in the Mississippi River due to spring runoff, the vessel could clear the bridge by at least 60.7 centimeters (2.0 feet). The NOAA air gap technology measures the distance between the bottom of the bridge and the surface of the water flowing underneath. Using both the National Ocean Service air gap measurements and river surge forecasts from the National Weather Service River Forecast Office, NOAA’s Center for Operational Oceanographic Products and Services (CO-OPS), the U.S. Coast Guard, Northrop Grumman, the Navy, and local port authorities determined that the morning of June 27 would be the best time to make the attempt.

The calculations forecast a possible clearance under the bridge of about 64 centimeters (2.1 feet). Given roughly 42.6 meters (140 feet) of clearance under the bridge, this would mean the ship would occupy about 98.5 percent of the available clearance as it passed under the bridge.

With a 3 a.m. Saturday final check from the bridge deck, NOAA signaled the ship would clear, and, at 6 a.m., the USS New York set sail under tug boat guidance for the middle of the channel. With the CO-OPS Director and PORTS Program Manager on the bridge of the ship, at 6:51 a.m., and just as predicted by NOAA experts, the ship’s two mast towers slipped under the bridge signaling by a margin of approximate 64 centimeters (2.1 feet)…a safe transit!