An echo from a high speed meteor as it plunges through the upper atmosphere
This radio spectrogram shows the shift in frequency of a meteor that is entering the atmosphere at more than 10 kms-1. This is shown by the Doppler shift of the carrier frequency (the straight line at 1kHz) by more than 1 kHz. The signal then drops by 1 kHz over a period of about one second (characteristic of a type 1 echo), showing that the meteor had suddenly slowed as it was destroyed.
See also 'Leonids 2001 Radio Recording' for a sound recording of the meteor. You can hear the meteor echo (about 2 seconds into the track) as the radio waves reflect off it.