Loran is the transmission of precisely spaced pulses from which users can derive information of position, velocity, time, and/or data. The low frequency system operates at 100 kHz in a band reserved for marine radionavigation. The most widely recognized format is Loran-C. A minimal Loran-C system includes three stations, typically located hundreds of miles apart, that transmit pulses at precisely timed intervals. The excellent stability of the system yields repeatable accuracies of 20-50 meters and Stratum 1 timing.
Historically, one station is designated the Master and the others as Secondaries. Using a Loran-C receiver, a user gets location information by measuring the very small difference in arrival times of the pulses for each Master-Secondary pair. Each Master-Secondary pair measurement is a time difference, mathematically, a hyperbola. Position is the intersection of two hyperbolas.
Affordable microprocessor technology led to significant adoption of the system by marine users and general aviation. The introduction of satellite technology and electronic charting increased the value of converting position from Loran coordinates to latitude and longitude and relating time to UTC. With Loran the absolute accuracy of the lat/lon position is a function of effects (Additional Secondary Factor or ASF) to the signal passing over irregular terrain. As a result, Loran is often thought of as a “quarter nautical mile system.”
Today, a new Loran concept is taking shape. Technology enablers include novel antenna designs, all-in-view digital receivers, system wide UTC synchronization, terrain effect modeling, and Loran data channel. Benefits from these improvements accrue to both provider and user. In the aviation world, certified receivers capable of meeting Non Precision Approach will support the concept of Area Navigation (RNAV) potentially increasing airspace capacity both en-route and in the terminal area. In marine transport, Loran will serve as an alternate source of position for Automatic Identification Systems (AIS) furthering safety in restricted waterways. Critical timing users such as telecommunication providers, power grids, governments, and financial institutions will be made more robust.
The future will also bring integration of systems. Loran not only complements satellite systems, it is a fully independent source of position, velocity, and time. Via the data channel, Loran can work as an augmentation similar to existing differential systems such as marine radiobeacons. With a common time scale, pseudoranges can be combined from two systems improving either one individually, especially in line-of-sight restricted urban areas. Satellite systems’ excellent accuracy can be used to calibrate Loran to compensate for ASF’s. Accuracy, availability, integrity, continuity and coverage are all greatly improved from Loran’s origins.