Final answer:
The Nyquist limit for a PW Doppler instrument with a PRF of 16 kHz is 8 kHz.
Step-by-step explanation:
To determine the Nyquist limit for a PW Doppler instrument with a PRF (Pulse Repetition Frequency) of 16 kHz, we can use the Nyquist-Shannon sampling theorem. According to this theorem, the highest frequency that can be accurately measured is half of the PRF. Therefore, the Nyquist limit in this case is 8 kHz. This means that any signal with a frequency above 8 kHz cannot be accurately measured by the instrument.