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Systems using PRF above 30 kHz function better known as interrupted continuous-wave (ICW) radar because direct velocity can be measured up to 4.5 km/s at L band, but range resolution becomes more difficult. High PRF is limited to systems that require close-in performance, like proximity fuses and law enforcement radar.
The received signals are also compared using the frequency ambiguity resolution process. A blind velocity occurs when Doppler frequency falls close to the PRF. This folds the return signal into the same filter as stationary clutter reflections. Rapidly alternating different PRF while scanning eliminates blind frequencies.
The Nyquist frequency will also change when the PRF is changed. This is explained best using an example with 2 different PRF, although real systems use a different method. In the example, PRF A can detect true speed up to 600MPH and PRF B can detect true speed up to 500MPH.
The difference between the sample numbers where reflection signal is found for these two PRF will be about the same as the number of the ambiguous range intervals between the radar and the reflector (i.e.: if the reflection falls in sample 3 for PRF 1 and in sample 5 for PRF 2, then the reflector is in ambiguous range interval 2=5-3).
Pulse-Doppler typically uses medium pulse repetition frequency (PRF) from about 3 kHz to 30 kHz. The range between transmit pulses is 5 km to 50 km. Range and velocity cannot be measured directly using medium PRF, and ambiguity resolution is required to identify true range and speed.
This is an accepted version of this page This is the latest accepted revision, reviewed on 31 December 2024. Art and practice of creating images by recording light For other uses, see Photography (disambiguation). Photography of Sierra Nevada Photography is the art, application, and practice of creating images by recording light, either electronically by means of an image sensor, or chemically ...