Final answer:
The described technique measures the velocity of a reflector by using the principle of Doppler shift, which creates a beat frequency that is easy to measure and interpret in the audible range.
Step-by-step explanation:
The technique described utilizes the principle of Doppler shift in echoes to measure the velocity of a reflector such as a medical imaging device. By comparing the frequency of the echoed sound (f1) with the broadcast frequency (f2), a beat frequency (FB) is produced, which is the absolute value of the difference between f1 and f2 (FB = |f1 - f2|).
This beat frequency is directly proportional to the Doppler shift and the reflector's velocity. The measurement of the beat frequency is advantageous because it does not require the high accuracy that would be needed to measure the Doppler shift directly, especially given that the Doppler shift can be small.
Additionally, the beat frequency falls within the audible range and can be easily amplified and interpreted by a medical observer. An example of similar technology is found in radar dish antennas used for space exploration, like the C-band radar dish at Kennedy Space Center which tracks launch vehicles with high-definition imagery.