The Transportation and Homeland Security departments want to hear from the public by Feb. 7 about whether to shut down a ground-based long-range radio navigation (Loran) system operated by the Coast Guard or develop an enhanced Loran (eLoran) system to back up the Global Positioning System. Here are facts about how those backup systems work.
Loran stations house two transmitters that operate in a low-frequency, 90 to 100 KHz band, with a range of about 1,200 miles.
Loran receivers determine their location based on the time difference between the signals they receive from the two transmitters. The U.S. Loran system covers much of the continental 48 states and parts of Alaska.
ELoran stations have an additional data channel for broadcasting as many as 16 messages, including station identification, absolute time and differential correction messages.
ELoran is as accurate as GPS, according to the General Lighthouse Authorities of the United Kingdom and Ireland, which operates Loran stations. It reported results from eLoran tests that demonstrated horizontal position accuracy of better than 30 feet.
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