At times there are military fighter aircraft flying overhead of my location (MiG-21Bis and Su-30MKI).

The first indication of their presence being the sound, that obviously causes one to look up to try and acquire them visually. The sound can be distinctly made out to be changing, as if for a moving object (not sure pure Doppler shift and/or change of source location).

However, almost all the times the aircraft are actually sighted in a totally different location from where the sound 'seems' to indicate them to be (and sometimes not sighted at all)! This seems obvious due to the relatively slow speed of sound and the fast speed of the aircraft.

However, are there are any suggested method(s) to locate such aircraft visually based on the sound?

  • $\begingroup$ It's really not different from any wave-based passive detection like radar, sonar, etc. With a large enough receive aperture and high enough signal to noise ratio you can do it definitely, and has been done. $\endgroup$ Sep 26 '17 at 16:51

From a single spotting location, then yes by training. But for any location, then it's very hard. Our ears get confused when the sound reflects off the surrounding surfaces, e.g., ground, buildings, etc. And when the sound comes from above.

Most mammals are adept at resolving the location of a sound source using interaural time differences and interaural level differences. However, no such time or level differences exist for sounds originating along the circumference of circular conical slices, where the cone's axis lies along the line between the two ears.

Consequently, sound waves originating at any point along a given circumference slant height will have ambiguous perceptual coordinates. That is to say, the listener will be incapable of determining whether the sound originated from the back, front, top, bottom or anywhere else along the circumference at the base of a cone at any given distance from the ear.

Tilting your head might help though.

So much so, airplane spotters in WWII judging only by sound misjudged the direction of Allied bombers and the entire Luftwaffe was sent looking in the wrong direction, only to realize the direction reported was incorrect and they had to land once they started running out of fuel.

Göring freely admitted the laugh was on him, that he had sent the Luftwaffe on a mammoth tour of their own air space.

But with computers it can be done using 3D sound localization. Or good old locators:

enter image description here
(theatlantic.com) Chinese soldiers man a sound detector which directs the firing of 3-inch anti-aircraft guns, around the city of Chongqing, China, on May 2, 1941.

P.S. Same problem arises when trying to figure out where an artillery fire is coming from or going to.

  • $\begingroup$ This interesting video by Smarter Every Day shows how well humans can detect sounds from smaller distances, even from above (and why dogs so tilt theirs heads so much) $\endgroup$
    – Sanchises
    Sep 5 '17 at 6:46

The Problem with localizing air crafts by their sound is: sound is slow.

The speed of sound is roughly 300m per second.

eg.: If an aircraft is 2km away its sound needs about 6 seconds to reach you. During this time an aircraft traveling at 600km/h moves 1km.

It is quite likely that you hear the sound from high flying airfrafts after it passed your position. This likeliness increases with the speed of the aircraft and reaches 100% for supersonic flights.

Furthermore the air craft can do any maneuver within the time its sound travels to you.

This means that you, at best, can estimate an aircrafts position by sound analysis. The accuracy you can get is far to worse to either use it for air traffic controlling or anti air missile guidance.

  • $\begingroup$ I myself wrote in the question due to the relatively slow speed of sound and the fast speed of the aircraft, so I understand this issue... $\endgroup$
    – Kanchu
    Sep 5 '17 at 9:37
  • 1
    $\begingroup$ However, in the first world war, at least the aircraft themselves were slow. rarehistoricalphotos.com/aircraft-detection-radar-1917-1940 $\endgroup$
    – Mackk
    Sep 5 '17 at 9:48

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