Enhanced Long-Range Navigation (eLORAN)
LORAN, short for long-range navigation, was a hyperbolic radio navigation system developed in the United States during World War II. It was first used for ship convoys crossing the Atlantic Ocean, and then by long-range patrol aircraft. The US Navy began development of Loran-B, which offered accuracy on the order of a few tens of feet, but ran into significant technical problems. The US Air Force had worked on a different concept, which the Navy picked up as Loran-C. Loran-C offered longer range than LORAN and accuracy of hundreds of feet. The US Coast Guard took over operations of both systems in 1958.
With the perceived vulnerability of GNSS systems, and their own propagation and reception limitations, renewed interest in LORAN applications and development has appeared. Enhanced LORAN, also known as eLORAN or E-LORAN, comprises advancement in receiver design and transmission characteristics, which increase the accuracy and usefulness of traditional LORAN. With reported accuracy as good as ±8 meters, the system becomes competitive with unenhanced GPS. eLORAN also includes additional pulses, which can transmit auxiliary data such as DGPS corrections. These enhancements in LORAN make it a possible substitute for scenarios where GPS is unavailable or degraded.
View the Wikipedia article on eLORAN
View Presentation: Enhanced Loran by Sherman Lo and Benjamin Peterson, Stanford GPS Lab, with contributions from the FAA Loran Evaluation Team, June 2009