If the received frequency is greater than the transmitted frequency, which statement is correct?

• A. Color encoding red, negative Doppler shift
• B. Color encoding blue, negative Doppler shift
• C. Color encoding red, positive Doppler shift
• D. Color encoding blue, positive Doppler shift

Answer: (C)

The key idea is how Doppler shift sign relates to direction and how color Doppler maps that sign to color. If the received frequency is higher than the transmitted frequency, the Doppler shift is positive, which means the target is moving toward the transducer along the line of sight. In color Doppler displays, positive shifts are typically encoded as red, while negative shifts (lower frequency) are encoded as blue to represent motion away. So the statement that color encoding red with a positive Doppler shift matches motion toward the transducer and a higher frequency. The other pairings would either reverse the direction or the color mapping, which doesn’t fit the given condition.