On Fri, 13 Feb 2004 02:15:11 +0000 (UTC), Eric Baird
wrote:

Hello!
I've been looking in modern physics textbooks for a reference to
the acoustic transverse Doppler effect.

In other words, the Doppler shift that you'd expect to hear if the
source was stationary wrt the air, and you were moving past at v m/s,
and pointed your rifle mic out at 90 degrees to your direction of
motion ... when you hear a quick burst of signal entering your
directional mic, what sort of frequency shift should it have?

Anyone know of a good reference source that gives the "official"
equation for this shift?



PS: I know what =I= think it ought to be, but I can't find the damned
thing in print.
PPS: If modern physics people don't know about the effect, can I lay a
claim to it? grin


=Erk= (Eric Baird)

Assume a set of axes, the vertical of which is represented by the
direction from the source to the microphone and draw on them a vector
representing the speed and direction of travel of the source. The
length of the Y (cosine) portion of this vector represents the net
speed of the source towards (or away from) the microphone at that
instant. Add (or subtract when moving away) this to the speed of sound
to get the ratio of perceived to actual frequency.

Once you have this clear in your head, just derive the actual equation
relating angle, velocity and frequency.

d

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