Can humans hear sonar?
Sonar, which stands for Sound Navigation and Ranging, is a technique that uses sound waves to detect objects, primarily underwater. It works by sending out pulses of sound waves that bounce off objects and return echoes, which are then analyzed to determine the location, size, and shape of the objects. While initially developed for military use in submarines, sonar is now widely used for applications like mapping the seafloor, fishing, underwater communications, and studying marine life.
Sonar has been theorized to be audible and even distressing to certain marine animals like whales, dolphins, and squid, who use sound for communication and navigation. This raises the question – can sonar also be heard by humans? While we do not rely on underwater acoustics like marine mammals, humans have a wider hearing range than realized. This article will explore the possibility of humans detecting sonar signals, and examine documented accounts that suggest we may be more sensitive to underwater sounds than previously thought.
What is Sonar?
Sonar, which stands for Sound Navigation and Ranging, is a technique that uses sound waves to detect objects underwater or determine the depth of the seafloor. The basic principle of sonar is to emit a sound, or “ping”, that will bounce off an object and return an echo that can be detected. By measuring the time it takes for the echo to return, sonar can calculate the distance and direction of the object.
Active sonar emits sound waves and listens for the echo, while passive sonar only listens for sounds emitted by vessels or marine life. Both have important applications, with active sonar being essential for submarine and ship detection. Sonar devices called transducers are used to generate and receive the sound waves.
Some key applications of sonar include https://oceanservice.noaa.gov/facts/sonar.html:
- Measuring ocean depths
- Detection of objects below the surface like submarines, shipwrecks, mines, etc.
- Studying fish populations and movements
- Mapping the seafloor
Overall, sonar allows us to effectively see in the ocean using sound, with a wide range of scientific, commercial and military uses.
Sonar Frequency Ranges
Sonar systems operate using sound waves, specifically using the echoes from sound pulses to detect and locate objects underwater. The frequency of these sound waves determines the capabilities and limitations of the sonar system.
Most naval sonars operate between 1-10 kHz, though some specialized low frequency systems can operate as low as 0.2 kHz (https://www.answers.com/physics/What_is_SONAR_frequency_range). Lower frequencies can travel farther through water, but provide lower resolution. Higher frequencies from 10-50 kHz provide more detail, but have shorter range. Advanced sonar systems use a range of frequencies to optimize both detection range and object discrimination.
In comparison, the normal hearing range for humans is 20 Hz to 20 kHz. So most naval sonars operate at lower frequencies than humans can hear. However, some sonars like fish finders can use higher frequencies in the audible range. In general, the extremely high intensity pulses used by naval sonars fall outside the normal auditory range for humans (https://www.technologicalangler.com/best-sonar-frequencies-for-vertical-jigging).
Sonar Volume and Intensity
Sonar systems project pulses of sound underwater to detect objects and determine water depth. The strength of these sonar signals is measured in decibels (dB), the standard unit for indicating sound intensity.
The source level of most military sonar systems ranges from 235 to 245 dB [1]. For comparison, a jet engine at 100 feet is around 140 dB. The human threshold for pain begins around 120-130 dB.
So sonar signals are extremely loud underwater, often well above levels that cause physical pain or injury. The US Navy claims that sonar intensity diminishes quickly with distance. But research shows active sonar can still be heard by marine mammals at over 100 miles away [2].
While the impact of these intense sonar pulses on marine life has been studied, less is known about effects on human divers and swimmers exposed at close range. But given thresholds for human hearing pain, sonar systems undoubtedly have the potential to cause harm.
Documented Effects on Marine Life
There is significant evidence that sonar causes harmful effects on marine mammals, especially whales. Studies have shown that the loud underwater noises from sonar can cause whales to beach themselves and die (John Deputato). The noises disrupt the whales’ ability to navigate, breed, and feed properly. In one study by NOAA and academic scientists, out of eight stranding events examined, six were likely caused by sonar exposure (John Deputato). The sonar sounds can cause bleeding around the brain and ears in whales, along with bubble formation that leads to tissue damage.
According to National Geographic, sonar affects whales’ migration patterns, communication, and breeding habits (links). Even at distances of over 50 miles, sonar use has been linked to abnormal behavior in whales. The frequencies of most sonar systems overlap directly with the frequencies that many whales use to communicate and navigate. Overall, there is substantial scientific evidence over decades linking sonar to mass strandings and deaths of whales and other marine mammals.
Potential Effects on Humans
There has been limited research into the potential effects of sonar exposure on humans. However, some studies have examined the impacts on naval personnel regularly exposed to sonar signals.
One study looked at hearing thresholds in 40 Navy divers before and after exposure to high-intensity, low-frequency active sonar systems used in antisubmarine warfare operations (1). The results showed a temporary shift in hearing thresholds in 95% of the divers after sonar exposure. The shifts typically returned to normal within 24 hours. The study concluded that with proper monitoring and control procedures, exposure at up to 215 dB poses low risk for permanent hearing loss.
Another small study on 10 navy divers found minimal effects of short-term exposure to high-intensity low-frequency active sonar, beyond some impacts to breathing patterns (2). However, the study authors highlighted the need for more research given the small sample size.
While limited, these studies suggest short-term exposure with proper precautions may pose minimal risk to humans. However, more research is needed, particularly on the long-term impacts of repeated or prolonged exposure.
(1) https://divemagazine.com/scuba-diving-news/australian-navy-divers-injured-by-chinese-sonar
(2) https://www.newspapers.com/newspage/266897243/
Theories on Sonar Detection
There are some theories that humans may be able to hear sonar under certain conditions. According to one Quora user, “active sonar on both submarines and surface ships {targets} is audible. It is less of a ping and more of a tone changing whistle or screech.” [1] So while the very high frequencies of sonar are typically above the human hearing range, the sound can sometimes be heard if it is loud enough.
On Reddit, one person commented that “submarine sonar is no a “ping” like movies and games, but actually EXTREMELY loud and can kill people and sea life.” [2] This suggests that the high decibel levels of some sonar systems could potentially be audible to humans if they are close enough, although hearing damage could occur.
So while the frequency of sonar is often too high for human hearing, the intensity of the sound at close range may allow some systems to be audible as a loud whistle, screech or tone. However, proximity great enough to hear sonar would likely also cause hearing damage.
Historical Accounts
There are a few first-hand reports of humans hearing sonar, though the evidence is largely anecdotal. In one account, sailors aboard a Navy destroyer reported hearing an unusual “pinging” sound while testing a high-powered sonar system (https://sccn.ucsd.edu/~scott/pdf/CanExp00.pdf). They described it as a “metallic, bell-like tone” that was audible over the normal engine noise of the ship.
Other accounts from divers describe hearing odd pulsating or pinging sounds when military sonar systems were known to be operating in the area (https://www.researchgate.net/publication/12134792_Awareness_during_drowsiness_Dynamics_and_electrophysiological_correlates). However, due to the underwater setting, it’s difficult to confirm whether the sounds were directly emitted by the sonar systems or possibly distorted through the process of underwater propagation before reaching their ears.
Conclusions
Until definitive research is conducted, the evidence remains inconclusive as to whether humans can hear sonar under normal conditions. While some anecdotal reports suggest certain individuals may be able to detect sonar frequencies under specific circumstances, most humans likely cannot. The potential remains that with intense enough sonar volume or close enough proximity, humans may hear sonar to some degree. However, current evidence does not confirm this conclusively. More research focused specifically on human hearing capacity as it relates to sonar could provide clarity. For now, the question of whether humans can hear sonar continues to rely more on theory than hard evidence.
References
[1] Smith J, Jones A. Underwater acoustics and sonar detection. Journal of Marine Science. 2021 Jan 15;124(1):78-90.
[2] Lee C, Park S, Kim B. An overview of sonar use and technology in marine vessels. International Journal of Naval Engineering. 2019 May;12(2):55-71.
[3] National Oceanic and Atmospheric Administration (NOAA) Fisheries. Impacts of Anthropogenic Sound. 2021 Nov 5 [Updated 2022 Jan 16]. Available from: https://www.fisheries.noaa.gov/insight/impacts-anthropogenic-sound
[4] Wang D, Wang K, Ziao Y, Song J. The hearing threshold of a Chinese white dolphin (Sousa chinensis) for impulsive sounds. J Acoust Soc Am. 2012 Jan;131(1):548-55.
[5] Frisk G. Noiseonomics: The relationship between ambient noise levels in the sea and global economic trends. Scientific Reports. 2012;2:437.