Remote sensors can be passive or active. Which statement describes active sensing?

• A. Passive sensors require external stimuli
• B. Passive sensors are more accurate in all conditions
• C. Active sensors emit signals and receive them
• D. Active sensors measure temperature only

Answer: (C)

Active sensing involves the sensor sending out energy toward the scene and then detecting the energy that returns. This transmitter–receiver approach lets you measure distance, surface structure, and other properties, and it can work when ambient light is insufficient or conditions are challenging. Examples include radar, which uses microwave signals, and LiDAR, which uses laser pulses.

Passive sensing, by contrast, relies on natural energy like sunlight or thermal emission and does not emit any signal itself. The statement that best describes active sensing is that active sensors emit signals and receive them. The other statements describe aspects of passive sensing, not the defining feature of active sensing, and the idea that active sensors measure only temperature is incorrect because they can capture a variety of properties.