Measuring Air Gap Aids Navigation

A new navigation tool that measures clearance between the water surface and bridges, also known as air gap, is now available. The first sensors to measure air gap were placed recently on the center spans of two bridges over the Chesapeake and Delaware Canal. The sensors take readings every six minutes to account for changes in water level, volume of traffic crossing the bridges, and air temperature, all of which cause bridge clearance to fluctuate. As ships become taller, some are passing under bridges with just inches to spare. This new capability is available through NOAA's Physical Oceanographic Real-time System, which provides quality-controlled oceanographic and weather data at U.S. seaports to aid navigation.