No. 551 December 2012

Through-the-Earth, Post-Accident Communications—an Emerging Technology 

Objective 

The objective is to provide a two-way communications 

system that can improve miners’ ability to communicate with 

personnel on the surface after an underground mine accident or 

emergency. This type of system could allow miners to directly 

communicate with others outside the mine without the need for 

any underground infrastructure other than a transceiver and an 

antenna. 

Background on Through-the-Earth 

In June 2006, Congress passed the Mine Improvement and 

New Emergency Response Act (MINER Act), requiring that 

underground coal mines develop emergency response plans that 

specify two-way wireless communications and electronic 

tracking systems. In the years following the MINER Act, the 

National Institute for Occupational Safety and Health (NIOSH) 

supported the development of a variety of communications and 

tracking technologies. Most communications systems use handheld, high frequency (HF) radios similar to systems used in 

other industries. These HF systems require the installation of 

extended underground infrastructure that may be susceptible to 

damage from fires or explosions. In contrast, through-the-earth 

(TTE) systems typically feature only a conductor encircling a 

coal pillar for the transmit antenna. Also, TTE systems can 

communicate directly through obstacles in the mine. They are 

considered highly survivable because the underground TTE 

components reside in a single location making them less 

susceptible to wide-scale damage. 

TTE systems generally operate in radio frequency bands 

ranging from 300 to 5,000 Hertz (Hz). These low frequencies 

are required for radio waves to achieve significant penetration 

through the mine overburden. With TTE communications, there 

is a single, direct wireless link between the underground and 

surface transceivers. TTE radios are commonly half-duplex 

devices, able to communicate in only one direction at a time. 

Evaluating Through-the-Earth Performance 

As shown in Figure 1, the transmit antenna is typically a 

loop(s) of wire oriented in the horizontal plane. 

Figure 1. An example of through-the-earth (TTE) 

communications depicted at a mine site.

To achieve 

successful communication, TTE signals must penetrate the 

layers of the earth above the mine. For the strongest signal, the 

surface transceiver should be directly above the subsurface TTE 

transceiver. Although these systems are fairly tolerant of some 

misalignment, at some point the signal falls off. This is a known 

issue, but each location is unique and can be tested ahead of 

time. Obtaining an adequate surface location requires that the 

mine have knowledge of the location and depth of the 

subsurface unit and access to the surface above it. Because 

permissible TTE systems are not very mobile, a system would 

likely be installed prior to an emergency and accurately marked 

on a mine map which could be overlaid on a map of the surface. 
There are many surface and underground considerations 

when communicating through the overburden depth and the 

constituents in the strata. Underground coal mines can vary 

dramatically in depth at different locations. The overburden can 

also contain mined-out seams or aquifers that may limit the 

distance TTE signals can propagate. Generally, the lower the 

frequency of TTE signals, the less the attenuation and the 

greater the allowable separation of the transmitter and receiver. 

However, lowering the TTE frequency will reduce the amount 

of information that can be sent in a given period of time 

(sometimes referred to as system bandwidth). Due to this 

limited bandwidth, some TTE systems use text messaging 

instead of voice communications to further reduce the time it 

takes to transfer a message. Electromagnetic noise from sources 

such as large motors and power lines on the surface or

underground can affect TTE performance. TTE systems should 

be installed away from potential noise sources as the effects 

from noise drop off quickly with increasing separation distance. 

The size of the antennas limits the locations for transmission 

of TTE messages. Some TTE systems can achieve greater 

depths by using a larger transmit loop on the surface, but in the 

underground environment the loop must be placed around a coal 

pillar to maximize the area within the antenna as there are few 

locations wide enough in the mine to deploy such a large 

antenna. This may not be possible in some locations within the 

mine thereby limiting where or how the antenna can be 

deployed. 

Increasing power levels in the transmit antennas both on the 

surface and underground can improve TTE performance. 

However, the amount of power used underground is limited by 

permissibility requirements. This factor limits the distance 

underground TTE systems can transmit back to the surface even 

though the surface unit can operate at much higher power. 

Available Through-the-Earth Technology 

Since 2006, NIOSH has sponsored the development of 

several different TTE technologies through a series of 

competitive contracts and awards via Broad Agency 

Announcements (BAAs). Several prototype TTE systems have 

been tested at various underground coal mines. It was observed 

that some TTE prototypes could receive voice messages through 

approximately 1,000 ft of overburden. Text messages could be 

received from even farther distances—through overburdens of 

about 2,000 ft. Other tests have shown that a system could reach 

as far as 5,000 ft; however, these tests were taken point-to-point 

horizontally in a mine and not directly through overburden. 

Results such as these may vary from mine to mine or even at 

different locations within the mine itself. 

Of the five systems selected for BAA contracts, the 

MagneLink® Magnetic Communications System (MSC) 

(Figure 2) developed by Lockheed Martin is the only one that 

has received Mine Safety and Health Administration (MSHA) 

permissibility approval. 

Figure 2. MagneLink® Magnetic Communications System.

This system contains a transmit antenna 

which is a length of wire that could be deployed around a coal 

pillar. The 3-axis orthogonal receive antenna and other receive 

electronics are in a separate housing (box on the left in Figure 

2). The backup batteries and computer control are in an 

explosion-proof box which is about 3 x 3 x 2 ft in size.

This underground system was designed to be installed in a fixed 

location perhaps near a refuge alternative or other strategic 

location underground. 

Currently, Magnelink® is the only MSHA approved TTE 

communication system available to the underground coal 

mining industry. It has been tested at ranges up to 1,500 ft for 

voice and approximately 2,000 ft for text. The technology 

described in this article is available from Lockheed Martin 

(http://www.lockheedmartin.com). 

For More Information 

For more information on this technology and its use, contact 

Nick Damiano (ndamiano@cdc.gov) or the Health 

Communications Coordinator (OMSHR@cdc.gov), NIOSH 

Office of Mine Safety and Health Research, P.O. Box 18070, 

Pittsburgh, PA 15236-0070. 

To receive NIOSH documents or for more information 

about occupational safety and health topics, contact: 1-800-

CDC-INFO (1-800-232-4636), 1-888-232-6348 (TTY), e-mail: 

cdcinfo@cdc.gov, or visit the NIOSH web site at 

http://www.cdc.gov/niosh. 

Mention of any company name, website or product 

does not constitute endorsement by the National 

Institute for Occupational Safety and Health. 

DHHS (NIOSH) Publication No. 2013–105