Which PRF type provides unambiguous Doppler responses for velocity measurement?

Which PRF type provides unambiguous Doppler responses for velocity measurement?

• A. Low PRF
• B. Medium PRF
• C. High PRF
• D. Ultra-High PRF

Answer: (C)

The key idea is that velocity measurement with Doppler is limited by how often you sample the returning signal, i.e., the pulse repetition frequency (PRF). The Doppler frequency shift f_d you observe is proportional to velocity (f_d = 2v/λ). When f_d exceeds half the PRF, the shift can alias and appear as a wrong velocity. So the unambiguous velocity range is up to v_max = (PRF × λ) / 4. Increasing PRF raises this limit, allowing higher speeds to be measured without ambiguity. Therefore, using a higher PRF type gives unambiguous Doppler responses for velocity measurement. Lower PRF would alias at lower speeds, while higher PRF is the standard way to avoid that ambiguity.

The key idea is that velocity measurement with Doppler is limited by how often you sample the returning signal, i.e., the pulse repetition frequency (PRF). The Doppler frequency shift f_d you observe is proportional to velocity (f_d = 2v/λ). When f_d exceeds half the PRF, the shift can alias and appear as a wrong velocity. So the unambiguous velocity range is up to v_max = (PRF × λ) / 4. Increasing PRF raises this limit, allowing higher speeds to be measured without ambiguity. Therefore, using a higher PRF type gives unambiguous Doppler responses for velocity measurement. Lower PRF would alias at lower speeds, while higher PRF is the standard way to avoid that ambiguity.