Active vs. Passive sensors

Flashcards detailing the differences between how active and passive sensors work.

Active sensors

Active sensors emit their own energy (usually in the form of radio waves, lasers, or light) and then measure the reflection of that energy off a target.

When can active sensors be used?

Since they work independently of natural light, they can be used at night or in darkness, and in any weather condition.

What systems use active sensors?

They are used in radar, LiDAR, and some satellite imaging systems like Sonar (underwater - emits sound waves).

What is a disadvantage of active sensors?

Active sensors can be more complex and require more power. 

Passive sensors

Passive sensors do not emit any energy themselves. They detect natural energy that is reflected or emitted by objects — usually sunlight or thermal radiation.

When can passive sensors be used?

Since passive sensors rely on ambient light or heat, they cannot function well in darkness (except thermal sensors). They are mainly used during the day.

What systems use passive sensors?

Cameras (optical, RGB), Infrared (IR) sensors, and Radiometers (measure radiation) use passive sensors.

What is an advantage of passive sensors?

Passive sensors can be simpler and more energy-efficient, less prone to interference, and more covert.