Optical sensor monitors fog for San Francisco Bay mariners

Jan 23, 2014 04:59 PM
Vaisala Inc.’s FS11 fog sensor, which is in use in San Francisco Bay and other harbors. The transmitter shoots an optical beam toward a receiver.

Photos courtesy Vaisala Inc.

Vaisala Inc.’s FS11 fog sensor, which is in use in San Francisco Bay and other harbors. The transmitter shoots an optical beam toward a receiver.

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A new fog sensor installed in San Francisco Bay and in other waterways nationwide is the latest tool to provide mariners with real-time information on whether it is safe to leave the dock and transit fog-bound waters.

That new sensor, called the FS11 Vaisala sensor, is seen as crucial to containership traffic in San Francisco Bay, where 3,500 ships travel yearly.

That is no small matter there given the collision potential in San Francisco Bay which was underscored in January 2013 when the oil tanker Overseas Reymar struck a tower of the San Francisco-Oakland Bay Bridge after unloading crude at a Royal Dutch Shell refinery.

“Since the Overseas Reymar we have put into practice a best practice within our region that if the fog density is less than a quarter mile, you do not leave the dock,” said Lynn Korwatch, chair of the Harbor Safety Committee in Oakland. “The sensor provides the information of when visibility is less than a quarter-mile so ships know not to leave the dock.”

Korwatch said the Reymar collision — and the 2007 collision when Cosco Busan hit the Bay bridge, spilling 53,000 gallons of crude oil — would have not been prevented by the sensor given the ships were underway. However, she said that the sensor readings may have kept them at the dock.

The sensors will likely be installed at other locations in San Francisco Bay, said Korwatch, including one at the upper reaches of the bay near the Benicia-Martinez Bridge at the Carquinez Strait.

The sensor was recently integrated into National Ocean Service’s Physical Oceanographic Real-Time System (PORTS) in San Francisco Bay. It is expected to give pilots and other mariners an indication of visibility conditions at the entrance to the inner and outer harbor areas in advance of arrival or departure from Oakland, said Chris Peterson, chief wharfinger at the Port of Oakland.

“This only measures visibility at that exact location,” said Peterson. “We hope that if this system shows value that the Coast Guard will look to install more sensors around the Bay Area.”

Indeed more sensors are planned, said Darren Wright, PORTS program manager with the National Oceanic and Atmospheric Administration (NOAA). Wright said NOAA has been working in tandem with the Harbor Safety Committee and the San Francisco Bar Pilots Association as well as the Coast Guard in identifying 10 to 12 additional sites that would be good candidates for sensors.

And their use will likely become widespread as part of the PORTS system nationwide. Two sensors are already in use in Alabama’s Mobile Bay, and sensors are destined for Jacksonville, Fla., Narragansett Bay and Chesapeake Bay, said Wright.

“The ability to make decisions prior to experiencing adverse or favorable conditions has increased safe and efficient navigation in areas that have a PORTS system,” said Wright.

“Economic benefit studies in four PORTS locations have shown a 50 percent reduction in groundings, and millions of dollars in annual benefit through more efficient navigation.”

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