Occasionally, the question arises, “What is the difference between passive and active drone detection?” In some cases, there is a misunderstanding of the meaning of the terms.

The term “active drone detection” is sometimes mistakenly believed to refer to a system that can “read” the content of radio signals between the drone and its control station. This process is more commonly referred to as “decoding.” Decoding an RF signal is a complex process involving receiving the signal, demodulating it to retrieve the baseband signal, and further processing it to extract the originally transmitted information. The exact steps and methods depend on the modulation type and the nature of the transmitted data.

Similarly, “passive drone detection” is sometimes mistakenly believed to refer to a system that does not read the content of the radio signals between the drone and its control station.

Both terms, including a general definition and examples of each, are included below for further reference.

Active Drone Detection

Active drone detection involves emitting signals to detect the presence of drones. Systems transmit radio waves or light pulses, which reflect off objects and return to the sensor, providing information about the object’s location and movement.

According to NASA, “Active sensors send out a pulse of energy and detect the changes in the return signal.”

Examples of active drone detection methods:

  • Radars emit radio waves that bounce off objects and return to the sensor, providing information about the objects’ location and movement.
  • LiDARs emit light pulses that reflect off objects and return to the sensor, providing information about the objects’ location and movement.

Active drone detection methods carry risks in military operations, as they emit signals that can be detected by adversaries.

Passive Drone Detection

Passive drone detection involves using methods to detect the drone and/or its controller without emitting any signals.

NASA states on its website, “Passive sensors detect energy emitted or reflected from an object.”

Examples of passive drone detection methods:

  • RF drone detection systems receive and analyze the communication signals between the drone and its controller.
  • Acoustic sensors receive and analyze the sounds emitted by drone motors and propellers.
  • Cameras detect drones by capturing and, in some cases, analyzing images or videos of the surrounding area. These can be standard optical cameras and/or more advanced systems, such as infrared cameras for night vision.
  • Passive radar systems detect and analyze reflected signals from other electromagnetic sources. They provide information on the location and movement of objects without emitting their own signals.