Why Sky Sounds Point the Wrong Way

Introduction

Many reports of unexplained “UFO noises” include a striking claim: the sound seemed to come from directly overhead, from somewhere in the sky, or from no identifiable direction at all. Witnesses often describe being certain about where the noise was located even when they could not see a source. Yet outdoor acoustics is full of situations where that certainty can be misleading.

Human hearing is good at locating nearby, visible sounds in familiar environments. It is much less reliable when sounds travel long distances through changing layers of air, reflect from terrain or buildings, or arrive after atmospheric refraction has bent their path. Under those conditions, ordinary ground-based sounds can appear detached from their true origin and seem airborne. Acoustic researchers have long studied these effects because they affect everything from aircraft-noise monitoring to military detection systems and environmental sound modelling. [Acoustics Today]acousticstoday.orgIf the speed changes from one pointAcoustics Todayrefraction of sound in the atmosphereJune 22, 2017 — by TB Gabrielson · Cited by 18 — The speed at which a sound wave trav…Published: June 22, 2017 [ResearchGate]researchgate.netResearchGate(PDF) Sound Propagation in the AtmospherePropagation of sound close to the ground outdoors involves geometric spreading, air…

How Humans Judge Sound Direction

People locate sounds by comparing what reaches each ear. The brain uses several cues at once:

• Interaural time difference (ITD): a sound reaches one ear slightly before the other.
• Interaural level difference (ILD): a sound is louder in one ear than the other.
• Spectral cues: the shape of the head and outer ears subtly alters frequencies depending on where a sound originates.
• Movement cues: small head movements help resolve ambiguities. [Acoustics Lab]acousticslab.orgAcoustics Lab Fundamentals of SoundFundamentals of Sound - Module 07The term auditory localization describes judgments on the location (orientation & distance), movement, a… [PMC]pmc.ncbi.nlm.nih.govPMCThe Encoding of Sound Source Elevation in the HumanPMCby R Trapeau · 2018 · Cited by 28 — Sound localization is achieved by extracting spatial cues from the acoustic signal that arise from… [NeurIPS Papers]papers.neurips.ccNeurIPS PapersSpectral Cues in Human Sound Localizationby CT Jin · Cited by 20 — The differential contribution of the monaural and intera…

Under ideal conditions, these cues work remarkably well. However, they were not evolved for interpreting distant industrial sounds refracted through kilometres of atmosphere. Researchers in psychoacoustics have shown that localisation becomes less reliable when sounds are low-frequency, broadband, prolonged, heavily reflected, or stripped of the sharp transients that normally help the brain pinpoint a source. [Variety Of Sound]varietyofsound.wordpress.comVariety Of Soundthe world of sound localization according to psychoacousticsApril 11, 2023 — 11 Apr 2023 — Sound localization refers to the ability of the human auditory system to determine the location of a sound…Published: April 11, 2023 [PMC]pmc.ncbi.nlm.nih.govPMCThe Encoding of Sound Source Elevation in the HumanPMCby R Trapeau · 2018 · Cited by 28 — Sound localization is achieved by extracting spatial cues from the acoustic signal that arise from…

This matters because many reported sky noises are described as deep hums, drones, rumbles or metallic groans. Those characteristics are precisely the kinds of sounds that are difficult to place accurately in open environments.

Why “Overhead” Is Harder Than People Realise

Humans are generally better at judging left-versus-right position than elevation. Determining whether a sound is above, below, in front of or behind relies heavily on subtle frequency filtering by the outer ear. These cues are weaker and more vulnerable to distortion than horizontal localisation cues. [PMC]pmc.ncbi.nlm.nih.govPMCThe Encoding of Sound Source Elevation in the HumanPMCby R Trapeau · 2018 · Cited by 28 — Sound localization is achieved by extracting spatial cues from the acoustic signal that arise from… [NeurIPS Papers]papers.neurips.ccNeurIPS PapersSpectral Cues in Human Sound Localizationby CT Jin · Cited by 20 — The differential contribution of the monaural and intera…

Researchers describe a phenomenon known as the cone of confusion, in which multiple source positions produce similar timing and loudness differences between the ears. Without additional cues, the brain can confuse front with back or misjudge elevation. Small head movements normally help resolve this problem, but when a distant sound arrives from multiple refracted or reflected paths, the extra information can remain ambiguous. [NeurIPS Papers]papers.neurips.ccNeurIPS PapersSpectral Cues in Human Sound Localizationby CT Jin · Cited by 20 — The differential contribution of the monaural and intera…

As a result, listeners may honestly perceive a sound as suspended overhead even when the physical source is near the horizon.

How the Atmosphere Disrupts Location Cues

The atmosphere does not merely change how far sound travels. It can also alter the apparent direction from which the sound arrives.

Temperature gradients and wind gradients change the speed of sound through different layers of air. As a sound wave moves through these layers, it bends through refraction. Under temperature inversions—common during calm evenings, nights and early mornings—sound that would normally disperse upward can curve back toward the ground. [STUDENTS]students.aip.orgphysics puzzler sound reasons the answersSTUDENTSPhysics Puzzler: Sound Reasons: The Answers1 Feb 2016 — Various atmospheric conditions can cause a temperature inversion, with ai… [Acentech]acentech.comCold Snaps and Sound Waves: Atmospheric AcousticsAcentechCold Snaps and Sound Waves: Atmospheric AcousticsFebruary 15, 2022 — 15 Feb 2022 — In a temperature inversion, the sound from far…Published: February 15, 2022 [Acoustics]acoustics.org.nzAcoustical Society of New ZealandWind and Temperature Effects on Sound PropagationMarch 1, 2012 — As discussed in the previous article, w…Published: March 1, 2012 at Penn State

To a listener, the sound may seem disconnected from its source because the wave reaching the ear has not travelled in a straight line.

Environmental acoustics literature repeatedly notes that wind and temperature gradients can significantly alter propagation paths and perceived source locations over large distances. Modern drone-detection and sound-localisation systems must account for these effects because atmospheric refraction can distort direction-of-arrival estimates. [Acoustical Society of New Zealand]acoustics.org.nzAcoustical Society of New ZealandWind and Temperature Effects on Sound PropagationMarch 1, 2012 — As discussed in the previous article, w…Published: March 1, 2012 [Acta Acustica]acta-acustica.edpsciences.orgActa AcusticaPassive acoustic detection and localization of drones using…by Z Ghouli · 2026 — Wind and temperature gradients can also…

A witness standing several kilometres from a motorway, railway line or industrial site may therefore hear sound arriving from an angle that does not obviously point back to the real source.

Wind Can Create Acoustic Misdirection

Wind affects sound in a more complicated way than many people assume.

At different heights above the ground, wind speed often changes. This wind shear bends sound waves, much like a lens bends light. Downwind propagation can carry sound farther and concentrate acoustic energy in unexpected locations. Upwind propagation can create shadow zones where the same source becomes difficult to hear. [Acoustical Society of New Zealand]acoustics.org.nzAcoustical Society of New ZealandWind and Temperature Effects on Sound PropagationMarch 1, 2012 — As discussed in the previous article, w…Published: March 1, 2012 ResearchGate When combined with temperature inversion layers [researchgate.net]researchgate.netResearchGate(PDF) Sound Propagation in the AtmospherePropagation of sound close to the ground outdoors involves geometric spreading, air…, wind can produce situations in which a listener receives a strong sound signal while having very poor directional information. The sound feels present and close, but its origin remains difficult to identify.

That mismatch between loudness and localisation is important in many sky-noise accounts. People often assume that a loud sound should also be easy to locate. Outdoor acoustics shows that the opposite can occur.

Reflections Can Make Ground Sources Seem Airborne

Refraction is not the only mechanism that distorts direction.

Large surfaces reflect sound. Hillsides, cliffs, cloud bases, water surfaces, building façades and industrial structures can all redirect acoustic energy. The listener may hear a mixture of direct and reflected sound arriving from different angles. [European Acoustics Association]euracoustics.orgNear and far fields of sound sources and directivity. PageEuropean Acoustics AssociationAcoustics in PracticeOctober 28, 2013 — interference, reflection, refraction, and application to sound prop…Published: October 28, 2013

The brain generally assumes that the earliest strong arrival points toward the source. When reflections become unusually prominent, that assumption can fail.

Several conditions increase the risk:

• Valleys and enclosed landscapes that channel sound.
• Urban environments with large reflective structures.
• Calm nights when atmospheric conditions preserve reflected energy.
• Low-frequency sounds, which travel efficiently and diffract around obstacles. [ResearchGate]researchgate.netResearchGate(PDF) Sound Propagation in the AtmospherePropagation of sound close to the ground outdoors involves geometric spreading, air… [European Acoustics Association]euracoustics.orgNear and far fields of sound sources and directivity. PageEuropean Acoustics AssociationAcoustics in PracticeOctober 28, 2013 — interference, reflection, refraction, and application to sound prop…Published: October 28, 2013

A factory drone, distant train or aircraft noise may therefore seem to hover over a neighbourhood rather than originate from a recognisable point on the horizon.

The Problem of Multiple Arrival Paths

One reason witnesses sometimes struggle to describe a sound’s location is that there may not be a single arrival path.

A listener can receive:

These arrivals reach the ears with slightly different timing and frequency content. Instead of producing a clear directional cue, they can create a diffuse acoustic image. The result is a sound that seems everywhere and nowhere at once. [ResearchGate]researchgate.netResearchGate(PDF) Sound Propagation in the AtmospherePropagation of sound close to the ground outdoors involves geometric spreading, air…

Descriptions such as “the whole sky was humming” or “it sounded like it was above the entire town” fit this pattern better than they fit the behaviour of a compact object directly overhead.

Why Witnesses May Hear the Sky

The most important point is not that witnesses are mistaken about hearing a sound. It is that hearing a sound and correctly locating it are separate tasks.

People naturally trust directional hearing because it usually works well in daily life. In unusual atmospheric conditions, however, the auditory system can be working with incomplete or distorted information. A sound may be real, loud and genuinely unusual while still being mislocated.

This helps explain a recurring feature of sky-noise reports:

• No visible source is found.
• The sound seems elevated or overhead.
• Multiple listeners disagree about direction.
• The event occurs at night or during calm weather.
• The noise appears to drift or move without an obvious source. [Acentech]acentech.comCold Snaps and Sound Waves: Atmospheric AcousticsAcentechCold Snaps and Sound Waves: Atmospheric AcousticsFebruary 15, 2022 — 15 Feb 2022 — In a temperature inversion, the sound from far…Published: February 15, 2022 [The Natural Navigator]naturalnavigator.comsounds during a temperature inversionThe Natural NavigatorSounds during a temperature inversion7 Jan 2019 — When there is a temperature inversion it creates a 'sandwich effec…

Those features do not automatically identify a conventional explanation, but they do match known acoustic situations in which atmospheric propagation and localisation errors become significant.

The Main Risk in UFO-Noise Interpretation

The strongest lesson from atmospheric acoustics is that directional certainty is often overstated.

A witness may accurately report what was heard while unintentionally misreporting where it came from. In investigations of unexplained sky sounds, the location estimate is frequently treated as evidence that the source was airborne. Yet acoustics research shows that direction, elevation and distance judgments can become unreliable when sound travels through complex outdoor environments. [Acta Acustica]acta-acustica.edpsciences.orgActa AcusticaPassive acoustic detection and localization of drones using…by Z Ghouli · 2026 — Wind and temperature gradients can also… [PMC]pmc.ncbi.nlm.nih.govPMCThe Encoding of Sound Source Elevation in the HumanPMCby R Trapeau · 2018 · Cited by 28 — Sound localization is achieved by extracting spatial cues from the acoustic signal that arise from… [NeurIPS Papers]papers.neurips.ccNeurIPS PapersSpectral Cues in Human Sound Localizationby CT Jin · Cited by 20 — The differential contribution of the monaural and intera…

For that reason, reports that place a mysterious sound “in the sky” are not necessarily evidence that the source was actually in the sky. They may instead reflect the way atmospheric refraction, wind gradients and reflections scramble the cues that people normally use to navigate the acoustic world.

Amazon book picks

Further Reading

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Endnotes

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2. Source: pmc.ncbi.nlm.nih.gov
   Title: PMCThe Encoding of Sound Source Elevation in the Human
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   PMCby R Trapeau · 2018 · Cited by 28 — Sound localization is achieved by extracting spatial cues from the acoustic signal that arise from...

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   Published: February 15, 2022

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   Title: physics puzzler sound reasons the answers
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6. Source: researchgate.net
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