NOAA 2004-021
Contact: Glenda Powell

NOAA News Releases 2004
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“Air Gap” Sensor Provides Bridge Clearance Data to Help Avoid Dangerous Collisions

The National Oceanic And Atmospheric Administration (NOAA) announces the addition of a new capability to its suite of observations available through the Physical Oceanographic Real-Time System (PORTS®) program. PORTS® supports safe, cost-efficient navigation by providing accurate real-time oceanographic and meteorological data. Air Gap, a bridge clearance sensor will assist mariners in avoiding collisions with bridges by providing real time data on the distance between bridges and the waters surface. NOAA is an agency of the U.S. Department of Commerce.

Mariners need to know under keel clearance, the distance from the bottom of the vessel to the bottom of the waterway, in order to avoid groundings. But as ships become larger and taller there is a vital need to know clearance in terms of height — to accurately assess the height of bridges which span waterways of maritime commercial significance.

Administered by NOAA National Ocean Service’s Center for Operational Oceanographic Products and Services (CO-OPS), the air gap sensor has been extensively tested, evaluated and adapted by CO-OPS for use as a bridge clearance device. A major advantage is that it is a non-contact device that does not need to be physically in the water, eliminating many of the problems associated with reliably operating a sensor in the challenging marine environment. A CO-OPS technical report documenting the testing and integration of the air gap sensors into the CO-OPS product suite will be available soon.

On March 1st, two air gaps sensors deployed on the center spans of the Reedy Point, Del., and Chesapeake City, Md. bridges on the Chesapeake-Delaware Canal went operational. Their observations, which measure the distance between low steel of the bridges and the waters surface, are being publicly disseminated along with the rest of the Chesapeake Bay PORTS® information. PORTS® will disseminate air gap readings every six minutes because changes in tidal water level, bridge loading (traffic patterns), and air temperature all cause fluctuations in bridge clearance. The Chesapeake Bay PORTS® also provides observations of water level, currents and winds to mariners navigating the Bay and Canal.

The Chesapeake PORTS® air gap system is the first of its kind in the nation, but other PORTS® such as the New York/New Jersey PORTS® are anticipated to add this capability. There are nine other PORTS® distributed across the United States.

Funding for the air gap systems and other enhancements to Chesapeake Bay PORTS® is provided by the Maryland Port Administration. “Quality controlled, real time bridge clearance information was the number one request from our customers and NOAA is excited about being able to deliver this important new product” said Mike Szabados, director of CO-OPS. “Partnering with our users to help make our vital marine transportation system as safe as possible is critical to our nation’s economy.”

NOAA's National Ocean Service, which includes CO-OPS, is dedicated to exploring, understanding, conserving and restoring the nation’s coasts and oceans. It balances environmental protection with economic prosperity in fulfilling its mission of promoting safe navigation, supporting coastal communities, sustaining coastal habitats and mitigating coastal hazards.

NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of our nation’s coastal and marine resources.

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