Doppler shift is the frequency change caused by relative motion. What is its primary role in radar?

• A. To calibrate radar temperature
• B. To calculate the radial velocity of targets
• C. To measure target size
• D. To determine hull color

Answer: (B)

Doppler shift in radar is used to measure motion along the line of sight. When a target moves toward or away from the radar, the frequency of the reflected signal changes—the Doppler shift. This shift is proportional to the radial velocity, the component of the target’s speed along the line of sight. In simple terms, the faster the target moves directly toward or away, the larger the frequency shift observed. From that shift, the radar calculates the target’s radial velocity, which is central for tracking and distinguishing moving targets from stationary clutter. This doesn’t tell you target size, hull color, or temperature, and motion perpendicular to the line of sight doesn’t change the Doppler frequency.