Sound Propagation & Wind Effects
Sound is a powerful discriminator — but only if you understand how distance, altitude, wind, and temperature warp what reaches your ears.
The Inverse Square Law & Atmospheric Absorption
Sound intensity drops with the square of the distance, but the atmosphere also absorbs higher frequencies disproportionately. A jet engine at 10 km loses its high-pitched whine and arrives as a low, diffuse rumble. At 15+ km, even large aircraft become inaudible to most observers. Turboprops and piston aircraft are inaudible beyond ~5–8 km in still air.
Audibility range by aircraft type — still air, low ambient noise
Wind Effects on Sound
Wind does not simply "carry" or "blow away" sound — it refracts sound waves by creating a velocity gradient. Sound travelling downwind bends toward the ground (increasing range). Sound travelling upwind bends upward, away from the listener (creating a shadow zone where the source becomes inaudible far sooner than expected).
Wind refraction of sound — downwind range extends dramatically; upwind creates an acoustic shadow
Sound Delay
Sound travels at ~343 m/s at sea level. At 5 km distance, the sound arrives ~15 seconds after the visual event. At 10 km: ~30 seconds. This means the sound you associate with an aircraft's current position actually corresponds to where the aircraft was half a minute ago. For fast jets, the aircraft may have moved 4+ km in that time.
| Source | Audible range (still air) | Sound character |
|---|---|---|
| Jet (A320, B737) | 15–25 km | Low rumble, no distinct frequency |
| Turboprop (ATR, Dash-8) | 5–10 km | Buzzing drone, rhythmic propeller beat |
| Helicopter | 5–12 km | Distinctive thwap-thwap blade slap |
| Piston aircraft (Cessna) | 2–5 km | High-pitched engine whine |
| Consumer drone | 200–500 m | High-pitched buzzing/whining |
| Large commercial drone | 500 m – 1.5 km | Deeper buzz, multi-rotor harmonic |
| Satellite | 0 m — always silent | — |
| Meteor | Rare sonic boom only for large bolides | Delayed crack or rumble (minutes after visual) |
Analyst tip: If you hear nothing but see a light within 5 km and below 2,000 ft — it's almost certainly not a powered aircraft. Consider satellite, planet, tower, or drone (drones at >300 m become hard to hear). If it's a bright silent light at high elevation, it's very likely a celestial object.
Cross-reference your sky observation against live ADS-B data, satellite passes, and weather.
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