Which of the following are considered active sensors?

Active sensors are systems that emit their own energy to gather information about a target, rather than relying solely on ambient energy reflected from that target. Radar (Radio Detection and Ranging) and LiDAR (Light Detection and Ranging) are prime examples of active sensors as they actively send out signals—radar uses radio waves and LiDAR uses laser pulses—and then measure the energy that is reflected back after interacting with objects.

This characteristic of emitting energy distinguishes active sensors from passive sensors, which only detect the energy that is naturally available in the environment, such as sunlight or thermal radiation. For instance, optical sensors, passive infrared sensors, and thermal sensors primarily rely on ambient energy, making them passive in nature. Therefore, the identification of radar and LiDAR as active sensors is accurate and highlights their role in not just observing, but also illuminating targets to gather data effectively.