The U.S. Coast Guard’s aids to navigation (ATON) have become far more extensive – and digital – in recent years. The traditional buoys marking safe lanes in shallow waters have been joined by technologies like the Automatic Identification System (AIS), Maritime Differential GPS (DGPS), Long Range Identification and Tracking (LRIT), electronic navigation (e-Nav), and vessel traffic management (VTM).

Combined, the various Coast Guard systems provide private, commercial, and even military vessels with vital position, navigation, and safety information and coverage. With more than 40,000 commercial transport ships and thousands more naval, cruise, and private ships at sea every day – a large percentage moving in, out, and around U.S. coastal and inner waterways – these systems help keep them from grounding, prevent collisions, assist emergency response, and even track smugglers and hijackers.

Much of the responsibility for ATON falls to the service’s Navigation Center (NavCen), a designated Coast Guard Center of Excellence responsible for maintaining DGPS (which corrects some of the deliberate location error built into GPS by the U.S. military, which maintains and operates the Global Positioning System’s constellation of satellites). NavCen services include:

• providing nationwide GPS augmentation signals;
• tracking vessel movements for enhanced situational awareness;
• publishing maritime advisories and related navigation information;
• managing the Coast Guard’s electronic chart portfolio; and
• receiving and coordinating investigation of GPS outage reports.

“We provide the nation with corrections for whatever errors the GPS signals experience, as well as integrity monitoring to alarm if something happens to one of the signals that is outside the boundaries of a good fix,” Rick Hamilton, NavCen’s GPS Information Analysis Team lead, explained.

“GPS is all about timing of the signals between the satellites and the ground. If a clock on one satellite fails, that signal would have to be eliminated from our differential corrections. There is a 6-second time to alarm, so within that 6 seconds, our system can tell us if there is something wrong. It also would tell us if there was some interference with a satellite signal, and we could eliminate a specific satellite or stop broadcasting from that station.”

While the vast majority of interference events have been accidental or due to the failure of some system element, deliberate jamming or spoofing of GPS has long been a concern for the military, which uses it for navigation, position, and location of everything from combat aircraft and precision-guided weapons to supply convoys and individual warfighters.

Although no large-scale attacks on the civil side have been reported via open source, terrorists and smugglers could seek this avenue to disrupt maritime traffic, including the delivery of oil, liquefied natural gas, and consumer goods – or make it more difficult for the Coast Guard and others to intercept criminal vessels carrying illegal drugs, people, or other contraband.

And while the vast majority of buoys have no electronics themselves, the service relies on GPS to place them.