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What is ELF? Why can it travel through the depths of the ocean and even communicate with submarines?
Ultra-low frequency (ELF) radio waves refer to electromagnetic radiation with frequencies between 3 and 30 Hertz (Hz) and wavelengths ranging from 100,000 to 10,000 kilometers. This special frequency range allows ELF waves to propagate with very low attenuation in nature and to effectively penetrate seawater, making them an ideal medium for communicating with submarines.
Due to their extremely long wavelengths, ELF waves are able to bypass large obstacles and are not blocked by mountains or the horizon.
The properties of ELF waves also allow them to propagate along the curvature of the Earth. This propagation mechanism relies on the waveguide effect between the Earth and the ionosphere, during which ELF waves can also be reflected and circle the Earth several times. This makes it possible for them to communicate over extremely wide distances. Especially for submarines, when they are in the deep sea and cannot receive other high-frequency radio signals, ELF waves play an irreplaceable role.
ELF waves have a very low attenuation rate of just 1 to 2 decibels per 1,000 kilometers, making global communications possible from a single transmitter.
Only a few countries (such as the United States, Russia, India and China) are known to have built ELF communication facilities for communicating with submarines. These facilities typically use grounded radio antennas tens of kilometers long and are driven by transmitters capable of outputting millions of watts. The United States' ELF facility operated from 1985 to 2004 but has now been dismantled.
Natural Generation and Function of ELF Waves
Natural sources of ELF waves mainly come from lightning and natural disturbances in the Earth's magnetic field. In atmospheric science, these waves are studied because they can provide useful data about the Earth's climate and environment. In addition, ELF waves are used in applications such as oil and gas exploration on Earth because they can penetrate seawater. In the medical field, ELF frequencies are also used in some treatment methods, which once again highlights the wide range of uses of these low-frequency radio waves.
Challenges of Submarine Communications
While ELF waves play an important role in submarine communications, their data transmission speed is relatively slow, typically only a few characters per minute. Since submarines cannot be equipped with relatively large antennas, communication is usually carried out by sending an ascent command so that the submarine rises to a shallower water layer to receive higher frequency signals.
Because electromagnetic waves attenuate extremely quickly in seawater, ordinary radio communications are almost impossible for submarines.
Concerns and Controversies in the Scientific Community
Due to the characteristics of the frequency, the impact of ELF waves in ecosystems remains a controversial topic. In fact, the impact of long-term exposure to electromagnetic fields on health is still inconclusive, and issues such as its correlation with leukemia have attracted attention from all walks of life. The World Health Organization organized experts to assess the risks in this regard in 2005, but the results showed insufficient support.
In this context, are there other potential impacts that we don't yet understand, or do these waves have no significant impact on our environment and organisms?
