The PRF is the frequency of pulses that are emitted from a Doppler radar. A higher PRF means the radar is sending out more pulses per unit time. A lower PRF means the radar is sending out less pulses per unit time. When the PRF is high the radar has less time to sample the atmosphere between pulses. If the radar has less time to sense, it can not detect objects further away from the radar as compared to a low PRF. Thus, a high PRF has a smaller unambiguous range as compared to a low PRF. The Doppler dilemma states there is an inverse relationship between the unambiguous range and the unambiguous velocity. When PRF is low----unambiguous range is high---but that results in a low velocity range When PRF is high----unambiguous range is low---but that results in a high velocity range Example: Suppose a radar can sense up to 250 miles from the location of the radar (unambiguous range) and can detect velocities of up to 30 m/s before velocity folding occurs (a.k.a. velocity aliasing). If the PRF was increased, the unambiguous range will drop to say 200 miles but the unambiguous velocity will increase to say 35 m/s. |