The White House is finalizing a plan drafted by the main federal-agency stakeholders in the GPS satellite navigation system to identify and mitigate sources of GPS signal interference, according to a U.S. Coast Guard officer.

Development of the GPS Interference Identification and Mitigation Plan was ordered by the White House as part of a 2004 National Security Policy Directive (NSPD), said Capt. Curtis L. Dubay, chief of the Coast Guard Office of Systems and Architecture, Maritime Domain Awareness.

Among other things, NSPD 39, also known as the U.S. Space Based Position, Navigation and Timing Policy, created a new GPS oversight structure to promote better interagency transparency and coordination in managing what has become a critical national resource for a variety of military and civilian applications.

Speaking at the Geoint 2007 Symposium, Dubay said the interference mitigation plan was drafted by the departments of Defense, Transportation and Homeland Security. In a brief interview following his presentation, he said the plan would be finalized soon but could not provide an exact date.

Meanwhile, the Transportation and Homeland Security departments are set to release before the end of this year an upgrade plan for a terrestrially based GPS backup system in North America. The plan would enhance the Loran system, which was widely used for maritime navigation before GPS receivers became ubiquitous.

The plan for the Enhanced Loran system would formalize a program that

already is under way, Dubay said. Upgrade work on Loran has been going on with funds provided through congressional earmarks, he said.

GPS is one of the primary means by which the Coast Guard, part of the Department of Homeland Security, tracks ships bound for U.S. territorial waters. But the signals are weak and highly susceptible to interference, Dubay said.

For example, in January, GPS service was knocked out in a

260 square kilometer area

around San Diego by a local emitter with only half a watt of power, Dubay said. The outage lasted four hours and ended only when the operators of the transmitter realized their mistake and shut it off.

declined to identify the operator of the transmitter, saying only that it was a government entity. However, Coast Guard documents said the Jan. 22 outage was caused by testing of a Defense Department transmitter operating in the L1 GPS frequency that had not been

coordinated properly.

The affected area ranged from San Diego harbor down to the Mexican border and 16 kilometers

inland the document, said. The incident disrupted pagers and cell towers in the affected area and caused Coast Guard vessels to operate on restricted status for two hours, the document said.