Which radar system is primarily used for detecting moving objects by measuring frequency shifts?

Correct option is B

​$$\textbf{Doppler radar} \text{ is a specialized radar system that uses the Doppler effect to detect moving objects and measure their velocity by analyzing the frequency shift (or phase shift) of the returned signal.} \\[10pt]\bullet \ \text{When a target moves towards the radar, the frequency of the reflected signal is higher than the transmitted signal (positive Doppler shift).} \\[6pt]\bullet \ \text{When a target moves away from the radar, the frequency of the reflected signal is lower (negative Doppler shift).} \\[6pt]\bullet \ \text{By measuring this frequency difference (Doppler shift), the radar can accurately determine the radial speed and direction of the moving object.}$$​​