Through-the-Earth (TTE) signalling is a type of

radio Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...

signalling used in

mines Mine, mines, miners or mining may refer to: Extraction or digging *Miner, a person engaged in mining or digging *Mining, extraction of mineral resources from the ground through a mine Grammar *Mine, a first-person English possessive pronoun Mi ...

and

cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...

s 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 In radio-frequency engineering, an antenna (American English) or aerial (British English) is an electronic device that converts an alternating electric current into radio waves (transmitting), or radio waves into an electric current (receivi ...

repeater In telecommunications, a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction. Some ...

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: Biology and medicine * Bone conduction, the conduction of sound to the inner ear * Conduction aphasia, a language disorder Mathematics * Conductor (ring theory) * Conductor of an abelian variety * Cond ...

and therefore absorbs

radio wave Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths g ...

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 waves. LF radio waves ...

(LF) or

very low frequency Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave ...

(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 signal modulation used to transmit information, such as an audio signal, by radio waves. A refinement of amplitu ...

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

ultra-low frequency Ultra low frequency (ULF) is the International Telecommunication Union, ITU designation for the frequency range of electromagnetic waves between 300 hertz and 3 kilohertz, corresponding to wavelengths between 1,000 and 100 km. In magnetosphe ...

(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 (United States and Canada) and potholing (United Kingdom and Ireland), is the recreational pastime of exploring wild cave systems (as distinguished from show caves). In contrast, speleology is the scientific st ...

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 Mining, 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-fre ...

s"—for instance 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, Nicola System and Cave-Link. HeyPhone and Nicola operate single (upper) sideband on 87 kHz in the LF band, while Cave-Link uses different frequencies between 20-140 kHz depending on the expected distance at 30 W power. Systems like ''Molefone'' and ''HeyPhone'' operate as single-sideband (USB) 87 kHz radio with earthed electrodes of 25–100 metres (80 to 330 feet) length. Design for ''HeyPhone'' system is openly available. European Cave Rescue Association (ECRA) maintains a list of systems scalable and reliable enough to be used for cave rescue operations. As of April 2023 the catalogue lists CaveLink (Germany), Nicola (Great Britain), μHeyPhone (Great Britain) and Pimprenelle (France) as operational wireless systems.

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 country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

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 The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

Tanzania Tanzania, officially the United Republic of Tanzania, is a country in East Africa within the African Great Lakes region. It is bordered by Uganda to the northwest; Kenya to the northeast; the Indian Ocean to the east; Mozambique and Malawi to t ...

, and

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

. 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 small 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 safe ...

(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 Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

, 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 West Virginia is a mountainous U.S. state, state in the Southern United States, Southern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States.The United States Census Bureau, Census Bureau and the Association of American ...

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 (mining), face; cutt ...

s). The system supports

voice The human voice consists of sound made by a human being using the vocal tract, including talking, singing, laughing, crying, screaming, shouting, humming or yelling. The human voice frequency is specifically a part of human sound produ ...

text Text may refer to: Written word * Text (literary theory) In literary theory, a text is any object that can be "read", whether this object is a work of literature, a street sign, an arrangement of buildings on a city block, or styles of clothi ...

, or

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

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 In June/July 2018, a junior association football team became trapped for fifteen days in Tham Luang Nang Non, a cave system in Chiang Rai province, northern Thailand, but were ultimately rescued. Twelve members of the team, aged 11 to 16, and ...

. Sybet developed an underground communication network system based on a large number of autonomous, portable transceiver nodes (BatNode) which operate in mesh architecture, forwarding voice calls over long distance with no radio connection between the end stations, as long as the BatNodes can see their neighbours.

References

External links

Rescue Dog Emergency Communication System

Pimprenelle (Nicola version 2 System)
A two-way communication system developed by the Spéléo Secours Français for

speleologists Speleology () is the scientific study of caves and other karst features, as well as their composition, structure, physical properties, history, ecology, and the processes by which they form (speleogenesis) and change over time (speleomorpholog ...

.
CREG
Journal of the Cave Radio and Electronics Group of the

British Cave Research Association The British Cave Research Association (BCRA) is a speleology, 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, encou ...

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