Through-the-Earth (TTE) signalling is a type of radio signalling used in mines and caves that uses low-frequency waves to penetrate dirt and rock, which are opaque to higher-frequency conventional radio signals. In mining, these lower-frequency signals can be relayed underground through various antennas, repeater or mesh configurations, but communication is restricted to line of sight to these antenna and repeaters systems.

Overview

Radio communication within caves is problematic because rock is a

conductor Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble, such as an orchestra. * ''Conductor'' (album), an album by indie rock band The Comas * Conduction, a type of structured free improvisation ...

and therefore absorbs

radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (short ...

s. Ordinary radios typically have a very short range within caves.

Low frequency Low frequency (LF) is the ITU designation for radio frequencies (RF) in the range of 30–300 kHz. Since its wavelengths range from 10–1 km, respectively, it is also known as the kilometre band or kilometre wave. LF radio waves exh ...

(LF) or very low frequency (VLF) radio with

single-sideband modulation In radio communications, single-sideband modulation (SSB) or single-sideband suppressed-carrier modulation (SSB-SC) is a type of modulation used to transmit information, such as an audio signal, by radio waves. A refinement of amplitude modul ...

is more commonly used today. Through-the-Earth transmission can overcome these restrictions by using

ultra-low frequency Ultra low frequency (ULF) is the ITU designation for the frequency range of electromagnetic waves between 300 hertz and 3 kilohertz, corresponding to wavelengths between 1,000 to 100 km. In magnetosphere science and seismology, alternative defini ...

(300–3000 Hz) signals, which can travel through several hundred feet of rock strata. The antenna cable can be located on the surface only at a mine site, and provide signal coverage to the mine. The antenna may be placed in a "loop" formation around the perimeter of the mine site (or wherever coverage is needed) for systems using magnetic fields to carry signals. Systems that use electric fields as the signal carrier are not subject to this limitation. Transmissions propagate through rock strata which is used as the medium to carry the ultra-low-frequency signals. This is important in mining applications, particularly after any significant incident, such as fire or explosion, which would destroy much of the fixed communication infrastructure underground. If the terrain makes a loop surface antenna impractical to install, then the antenna can be installed underground or a non-magnetic field type carrier may be used. But because the signal travels through rock, the antenna does not need to run into all parts of the mine to achieve mine wide signal coverage, thus minimizing the risk of damage during an incident.

Cave radios

Portable magnetic-loop cave radios have been used by

cavers Caving – also known as spelunking in the United States and Canada and potholing in the United Kingdom and Ireland – is the recreational pastime of exploring wild cave systems (as distinguished from show caves). In contrast, speleology is ...

for two-way communication and cave surveying since the 1960s. In
typical setup
the transmitting loop, consisting of many turns of copper wire, is oriented horizontally within the cave using a spirit level, and driven at a few kHz. Though such a small antenna is a very poor radiator of propagating radio waves at this low frequency, its local AC magnetic field is strong enough to be detected by a similar receiving antenna up to a few hundred meters (yards) away. The received signal's strength and its dependence on orientation of the receiving coil yields approximate distance and directional information. Early models were called "

speleophone Through-the-Earth (TTE) signalling is a type of radio signalling used in mines and caves that uses low-frequency waves to penetrate dirt and rock, which are opaque to higher-frequency conventional radio signals. In mining, these lower-frequency ...

s"—examples include Bob Mackin's "Molefone". The Molefone is called "one of the first practical cave radios," though it is no longer manufactured. Other popular LF/VLF radios include the HeyPhone and the Nicola System. All three operate single (upper) sideband on 87 kHz in the LF band. Systems like ''Molefone'' and ''HeyPhone'' operate as single-sideband (USB) 87 kHz radio with earthed electrodes of 25–100 metres (80' to 330') length. Design for ''HeyPhone'' system is openly available.

Personal emergency device

There are several systems that have been recently developed. One system is known as the PED System, where PED is an acronym for personal emergency device. Initially developed after a mining disaster in

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

at Moura No. 4 Coal Mine in 1986, and further developed after the Moura No. 2 Coal Mine explosion in 1994 where the need for a communication system to survive major incidents underground was identified in the inquiries into the disasters. PED is a one-way text paging device, with wide use in

, as well as installations in the United States,

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

, Canada, Mongolia, Chile, Tanzania, and

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

. Australian compan
MST Global (formerly Mine Site Technologies)
began the development of PED in 1987, and it became commercially available and

Mine Safety & Health Administration The Mine Safety and Health Administration (MSHA) () is a large agency of the United States Department of Labor which administers the provisions of the Federal Mine Safety and Health Act of 1977 (Mine Act) to enforce compliance with mandatory safet ...

(MSHA) approved in 1991. The best documented use of PED during a mine emergency is from the Willow Creek Mine Fire in 1998 in Utah, where it was able to quickly alert miners underground of the need to evacuate before toxic fumes from the fire filled the mine. Reports of this use can be seen on the MSHA website.

Development

Emerging technologies have recently been developed such as th
Rescue Dog Emergency Through the Earth Communication System
developed by E-Spectrum Technologies. The Rescue Dog is a two-way extended-range portable through-the-Earth solution that was developed in the US in cooperation with The National Institute for Occupational Safety and Health (or NIOSH) which does not rely on large loop surface antennas for signal transmission. New non-portable systems have also been developed by companies such a
Lockheed Martin
for use in emergency chambers to provide post-accident, two-way, emergency voice and text communications independent of surface or in-mine infrastructure.

New technologies

A new wireless "Miner Lifeline" telecommunication technology is being tested in 2012 at the West Virginia Robinson Run mine (recent production per year of coal using 600

miner A miner is a person who extracts ore, coal, chalk, clay, or other minerals from the earth through mining. There are two senses in which the term is used. In its narrowest sense, a miner is someone who works at the rock face; cutting, blasting, ...

s). The system supports voice, text, or

SOS is a Morse code distress signal (), used internationally, that was originally established for maritime use. In formal notation is written with an overscore line, to indicate that the Morse code equivalents for the individual letters of "SOS" ...

sent on a "bubble" of magnetic waves, and "can move more than up or down and laterally, arriving in less than a minute." The Israeli company Maxtech has developed a software system that automates the optimal organization of a set of limited-range communications devices, using any mixture of types of communication (through-the-earth radio, line-of-sight radio or optical, etc.). This system was used in the Tham Luang cave rescue.

References

External links

Rescue Dog Emergency Communication System

Nicola System
A two-way communication system developed for speleologists.
CREG
Journal of the Cave Radio and Electronics Group of the

British Cave Research Association The British Cave Research Association (BCRA) is a speleological organisation in the United Kingdom. Its object is to promote the study of caves and associated phenomena, and it attains this by supporting cave and karst research, encouraging orig ...

MST Global (formerly Mine Site Technologies)
for more information on the PED through-the-earth communications system.
Radius 2
Russian wireless TTE underground system of alarm reporting, personal calling, observation and people search in case of mine accidents
Cave-Link
Data communication and measurement system for cave research and mining. {{DEFAULTSORT:Through The Earth Mine Communications Radio communications Telecommunications techniques Underground mining