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Glengarry Forest ELF

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Glengarry Forest was the site of proposed trial involving Extremely Low Frequency (ELF) transmissions, planned to commence in the period 1991 to 1992.

The project never materialised, and was confirmed to have been cancelled in reply to a question raised in the House of Commons on February 14, 1991.

Hansard reported a number of questions raised on March 17, 1989, querying the safety implications of the trial, and specific technical details of the project. The reply noted that "The fields that would be produced by the proposed system are several orders of magnitude less than the National Radiological Protection Board's reference level figures for the protection of persons."; with regard to the technical questions, the reply was "It is not our policy to give out details of expenditure on specific research projects."

On February 14, 1991, Hansard reported:

Sir Hector Monro : To ask the Secretary of State for Defence if he will make a statement on the plans for an experimental extremely low frequency transmitter in Scotland.

Mr. Kenneth Carlisle : We have reassessed this project in the light of current defence requirements and have decided not to proceed with the programme to construct an experimental transmitter in Glengarry forest. Accordingly, we shall not be proceeding with the notice of proposed development. We are notifying local authorities to this effect.

ELF

What is it, and why?

Nuclear submarines replaced bombers during the Cold War, and offered the advantage of continuous deployment, without the upkeep associated with keeping aircraft aloft for 24 hours a day. Carrying ballistic missiles rather than bombs, and with no need to surface during their patrols, they were effectively invisible once they left port and submerged.

There was however, one operational disadvantage. Submarine communica­tions presented a persistent command and control problem because conventional electromagnetic RF signals degrade rapidly while penetrating sea water. For this reason, submarines must leave the relative safety of the deep at scheduled times to deploy receiving antennas at or near the surface. Detection is much more likely when operating near the surface, and while submarines are hiding at depth between communication intervals they are unable to receive vital communica­tions.

ELF transmitters courtesy of http://www.vlf.it/
ELF transmitters

By using ELF techniques, operating at 76 Hz, equipment testing conducted in 1983/84, the shore station in Clam Lake, Wisconsin, was able to communicate reliably with a submarine cruising at depths down to 400 feet, travelling at 16 knots. The result being that ELF equipped submarines need not approach the surface to receive command communications. Note that ELF communications are one way links. Submarines can only receive signals, not transmit, as the transmission equipment, power supply and transmission antenna are huge, and must be land based.

ELF communications offer further advantages: low signal attenuation means only one transmitter is needed to achieve world-wide coverage; immunity to unreliability arising from propagation effects; immunity to the effect of an electromagnetic pulse; immunity to jamming, the jammer would require a transmitter of many times more power than the original, and a larger antenna.

This last point also introduces disadvantages of ELF communications: the transmitting antenna need to be similar in length to the transmission wavelength for maximum efficiency, in this case the length would be about 2,500 miles (4,000 km), an easy target for hostile action. The antenna is also inefficient, resulting in the need to input several megawatts in order to transmit only several watts, which must provide the required coverage, and overcome any local electromagnetic interference. Those familiar with communication theory will also realise that such a low frequency carrier signal can only transmit very simple messages within a reasonable time. A three letter message requiring some four minutes to complete its transmission.

Transmission/reception courtesy of http://www.vlf.it/
Transmission/reception

Tests showed that the best approach to overcoming the antenna problems was to use a long, horizontal aerial cable laid above and parallel to the earth's surface, installed over ground with a high electrical resistance, typically ancient granite rock, with the cable grounded at each end. The rock strata form a ground loop, which extends the antenna's effective length, and allows a higher power output. Techniques were also developed to allow the signal capacity to be improved, but these still required message repetition in order to ensure they were reliably detected over interference events such as magnetic storms.

Development actually began in 1958, with the first successful tests taking place in 1962. By 1969, a second facility had been added. Two further development programmes were proposed to increase the capacity of the system, however projects Sanguine and Seafarer were both cancelled. Sanguine was rendered obsolete by Soviet advances, and was redefined to become Seafarer, however, local objections at the site where the massive antenna the new project would have required led to its cancellation. The new antenna would have been 2,400 miles long, as opposed to ELF's 148 miles. By comparisons, Sanguine would have required a grid of cables over 22,500 square miles of northern Wisconsin and the Upper Peninsula of Michigan, an area larger than Belgium and Holland combined, and would have required 240 transmitters and 800 megawatts of power to operate, with a cost in the billions. In 1981, under President Reagan, ELF system development was restarted, with the emphasis on peacetime submarine communications, rather than emergency action message transmission. Development continued, with the concentration being on improved transmission techniques, and improvements to the transmit antenna. The system officially entered service in 1989, using two transmitters in Wisconsin and Michigan, connected by a 165 mile underground cable. The annual operating costs for both ELF transmitters is $13 million.

Submarine communications courtesy of http://www.vlf.it/
Submarine communications

In 1995, funding for the project ended, on the basis of the reduced Soviet threat, and potential cost saving. This was not the end of the project, and development work continued on the receiving antenna installed on the submarines. Initially developed as a long, trailing wire, development work progressed, and the antenna was first adapted such that it could be hull mounted, and later work and test were carried out to move the ELF antenna within the Submarine Integrated Antenna System (SIAS).

After 1995, research and development funding was provided from related programmes, however the system was finally closed down, and the ELF transmitters were closed down in 2004.

The arrival of more advanced and exotic communications technology, using satellites and high speed random data transmission methods means that submarines can approach the surface and carry out communications operations within very small time windows, meaning they are exposed to detection for relatively short periods of time, during with the probability of detection, before they return to deep water, is very low.

Deep Siren Tactical Paging system

Although it does not utilise the ELF concept as part of its system, information was released around 2007, describing a system for linking craft under the sea to surface, land, air and space borne communications sources.

The submarine’s underwater environment, platform stealth and historic mission requirements have characteristically limited it to independent operations. Contemporary national security interests and the recognized force multiplier enabled by network-centric operations have required the submarine to be fully interoperable with joint and coalition forces.

The US Navy submarine force has set a course to meet these requirements by fielding a Communications at Speed and Depth (CSD) capability. In response, Raytheon developed the Deep Siren Tactical Paging (DSTP) system. DSTP addresses the most significant capability shortfall in communicating to submarines today by providing the ability for an operational commander to contact a submarine in real time, regardless of the submarine’s speed or depth.

The Deep Siren system employs acoustic, expendable buoys that can be contacted through the Global Information Grid to enable long-range communications from a buoy to a submarine throughout its area of operations, depending upon environmental conditions. Buoys can be launched from multiple platforms, providing increased flexibility.[1]

References

1 Raytheon Deep Siren product data sheet

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