The world’s shipping industry is experiencing strong growth, which is expected to continue. Ships are getting larger and faster, sea-lanes are becoming more crowded, and crews are increasingly relying on electronic navigation systems to operate in this environment . The newly proposed concept of e-Navigation will improve safety, security, and protection of the marine environment as well as potentially reducing costs. It will provide bridge officers with all the information they need on a single display. In order to make these critical e-navigation services available, the system will require a supply of position and timing data of exceptionally high accuracy and reliability.
Systems like GPS, Russia’s GLONASS, China’s BeiDou, and Europe’s Galileo systems are Global Satellite Navigation Systems (GNSS) that provides real-time positioning, navigation and timing (PNT) data. However, in many environments in which military operates (inside buildings, in urban canyons, under dense foliage, underwater, and underground) have limited or no GPS access. Similarly, GPS signals can be significantly degraded or unavailable during solar storms. GPS is also vulnerable to jamming attacks, GNSS jammers are now being used by criminals or vehicle hijackers, as reported by the FBI: “… GPS tracking devices have been jammed by criminals engaged in nefarious activity including cargo theft and illicit shipping of goods.Typical military jammers are able to affect GPS receiver for many tens of kilometers by line of sight. It’s a problem because best accuracy, availability and global coverage of PNT data is through GPS/GNSS.
In September 2001, almost simultaneously with the “9/11” act of terrorism, the US Government published its “Volpe Report” . This spelled out the degree to which the US, like other nations worldwide, was starting to base its critical infrastructures on GPS. The Report explained the vulnerability of GPS (and similar GNSS systems) to disruption by intentional or unintentional interference. It identified Loran as a potential solution to this important problem. This attracted interest worldwide, and provided an impetus to modernize the Loran system in the US.
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. Loran-C, delivered a positioning accuracy of 460 meters , principally to mariners sailing in coastal and oceanic waters. When the Global Positioning System (GPS) appeared in the1980s, with its positioning accuracy of tens of meters, many began to regard Loran-C as irrelevant.
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 is an independent, dissimilar, complement to Global Navigation Satellite Systems (GNSS). It allows GNSS users to retain the safety, security, and economic benefits of GNSS, even when their satellite services are disrupted.
The US Loran evaluation and modernization program resulted in this new version of Loran with significantly improved performance. It has much better accuracy, integrity, and continuity while continuing to meet Loran-C’s traditional availability requirements. These improvements are realized mainly through the addition of a data channel. The data channel conveys corrections, warnings, and signal integrity information to the user’s receiver via the Loran transmission. 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.
As eLoran uses high-powered transmitters and low-frequency signals (not microwatts and microwaves like GNSS), it is very unlikely to be interfered with or jammed by the same causes that would disrupt GNSS signals. This means that small, low-cost, eLoran receivers, even built into GNSS units, can mitigate the impact of disruptions to GNSS.
A further important benefit of eLoran’s low frequency signals is their ability to penetrate into places where GNSS signals either cannot be received at all, or where they are intermittent or inaccurate. These include the urban canyons in the centers of major cities. Loran signals have been shown to penetrate reliably into steel shipping containers, refrigerated vehicles and storage warehouses. This ability has led to the development of systems that track items either of highvalue or whose safe and timely delivery must be guaranteed. The tracking of hazardous cargoes also demands the consistent updates and high availability of eLoran-based systems.
eLoran supplies the precise timing needed to support not only e-Navigation, but also the Automatic Identification System (AIS) and synchronized lights in harbor areas. Moreover, eLoran can do things GNSS cannot, such as acting as a static compass. An important bonus of using eLoran – something GNSS cannot provide – is the eLoran compass. When the receiver is used with an H-field (Magnetic Loop) antenna it can be employed as an automatic direction-finder taking bearings on the transmitting stations. From these, the receiver calculates the ship’s heading, generally with an accuracy of better than 1°, and independent of the ship’s movement.
At sea, a new concept of navigation enhanced navigation (e-Navigation) – is being developed which requires an exceptionally reliable input of position, navigation, and time data. Uniquely, the combination of GNSS and eLoran has the potential to meet its needs.
UK’s eLoran (enhanced Long Range Navigation) for ships and aircrafts
The General Lighthouse Authorities (GLAs) of the UK and Ireland have employed eLoran (enhanced Long Range Navigation), that enables ships and aircraft to determine their position and speed by triangulating low-frequency radio beacon signals transmitted by presently seven differential reference stations on the shore. U.K. has become first country to provide alternative position, navigation, and timing (PNT) information to ships fitted with eLoran receivers that can ensure their safe navigation in the event of GPS failure.
Captain Ian McNaught, deputy master of Trinity House, commented, “eLoran provides a signal around 1 million times more powerful than those from satellite signals, providing resilience from interference and attack.”
eLoran can provide navigation information for vessels as well as the timing data necessary to maintain the power grid, cell phones, financial networks, and the Internet in the event of an outage. Unlike space-based navigation, eLoran signals can also reach inside buildings, underground, and underwater.
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