From time to time helicopters pass over our home in Escondido, CA, US. We can hear them coming and hear them leave. I caught several infrasonic tracks of these events, showing incoming and outgoing rotor noise doppler effects. I have attached one for your review. All comments welcome!
David Drake
R2C1C
Hello David, and welcome to our community!
Definitely a great recording of a helicopter pass, the doppler effect is clearly visible, and this is a good example of what other Shakers can look for if they hear choppers around their homes!
Only advice I can give is to zoom back a little more so that the entire waveform/spectrogram can be seen.
Thanks for posting it!
If the helicopter passes pretty much directly overhead, you can calculate its speed from the frequency shift.
I have a small PDF file which describes the derivation of the formula … if you are not interested in how the formula is arrived at, all you need is the result, at the end.
doppler.pdf (76.0 KB)
Very nice model! Thank you.
