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Counter-Drone Detection Technology: Pros and Cons [From Sensor Experts]

Counter-Drone Detection Technology: Pros and Cons [From Sensor Experts]

Many sensor systems are available today that can detect drones in flight, but the system performance is usually very localized and is therefore expensive to implement across large areas. We are only discussing detection of drones at this point and no type of countermeasure or mitigation. When reading this article, please keep in mind there are numerous sensor design options within each sensor type that can drastically affect the drone detection performance. We have summarized average, generalized performance for comparison, and we discuss the strengths and weaknesses of each counter-drone sensor type.

Radio Frequency (RF) Detection

RF detection is one of the most common techniques for drone detection since this same sensor can also be used for mitigation in some systems. RF receivers are used to detect the communication between the drone and its controller. This detection can either be the communication uplink from the controller to the drone or the downlink from the drone to the controller.

Drone communications typically occur in the Industrial, Scientific, Medical (ISM) frequency bands. The ISM band is frequently crowded with other signals like cordless phones, Bluetooth devices, WiFi routers, Near Field Communications (NFC), garage door openers, baby monitors, and even microwave ovens. Sophisticated signal processing is required to detect and extract drone signals from all this background noise. The detection range of the system is a function of the antenna gain, receiver hardware, and the signal processing techniques. More expensive hardware components usually yield longer detection ranges.

Pros:

  • High probability of detection with an extremely low false alarm rate.
  • Day/night operations, all weather performance, and 360° coverage using an omnidirectional antenna.
  • Medium Detection ranges of 1-3 km are common.1
  • Simultaneous detection of multiple drones.
  • Pilot geolocation is also an option with the right conditions.
  • Lightweight system with low power requirements. Low-Medium system cost.

Cons:

  • Line of sight obstacles (hills, buildings, and trees) will degrade detection performance.
  • If the drone is not communicating, there will be no detection.

Video Camera Detection

Drone detection using video cameras can be an effective technique and has a relatively low cost. However, it does require sophisticated computer algorithms to process the images and the video data streams.2 The most common approach uses machine learning techniques that require specialized training data to identify drones in the camera’s field of view. The machine learning algorithms need to be trained with multiple drone types (numerous look angles and different levels of zoom) flying across various backgrounds (clear sky, clouds, tree lines, buildings) to be effective. Training against thousands of images yields reasonable detection performance; training with tens of thousands of images increases detection performance even more. These algorithms continue to learn and keep getting better the more they are used operationally.

Pros:

  • High probability of detection with low false alarm rates.
  • Simultaneous detection of multiple drones.
  • Detections are possible even in the absence of drone RF communication.
  • Lightweight system with low power requirements.
  • Low cost.

Cons:

  • Limited to daytime operations only in good weather.
  • The coverage is limited by the Field-of-View (FOV) of the cameras and the number of networked cameras in use.
  • Limited detection ranges due to the size of the drone in the camera image.
  • Detection ranges out to 100m are common, and this can be extended out to 300m with camera zoom capabilities.
  • Line of sight obstacles (hills, buildings, and trees) significantly degrades performance.
  • Pilot geolocation is not an option.

There is no "one best sensor" for drone detection. Each sensor type has pros and cons, and the ultimate drone sensor selection is heavily dependent on the customer’s operational needs, environmental conditions, and budget.

Infrared Camera

Infrared (IR) camera detection is similar to video camera detection, but now night-time operations are also possible. The camera cost is higher and the detection performance is dependent on many IR camera system parameters such as wavelength of operation, Field-of-View (FOV), and the thermal sensitivity of the sensor design.

Pros:

  • Good probability of detection with relatively low false alarm rates.
  • Better detection performance at night than during the day.
  • Simultaneous detection of multiple drones.
  • Detections are possible even in the absence of drone RF communication.
  • Lightweight system with low power requirements.
  • Moderate cost.

Cons:

  • Daytime operations are possible with a more expensive sensor.
  • Inclement weather degrades performance.
  • The coverage is based on the field of view of the cameras and the number of networked cameras in use.
  • Limited detection ranges due to the size of the drone in the camera image.
  • Detection ranges out to 100m are common, and this can be extended out to 300m with camera zoom capabilities.
  • Line-of-sight obstacles (hills, buildings, and trees) significantly degrades performance. Pilot geolocation is not an option.

Radar

The FAA uses radar technology for nationwide Air Traffic Control of commercial and private planes. A radar will typically provide the longest detection range of any sensor type, but this is highly dependent on the size of the antenna array, the power output of the antenna, and the Radar Cross Section (RCS) of the drone (The RCS can be thought of as the electrical size of the drone). A large drone with highly reflective metallic surfaces and components will have a much higher RCS than a small drone made with a lot of plastic and will therefore be much easier to detect at longer ranges with a radar sensor.

Pros:

  • Day/night operations, all weather performance except for heavy rain rates.
  • Longer detection ranges with ranges of 2-5 km common for larger radars.3
  • Detections are possible even in the absence of drone RF communication, such as waypoint flight mode.
  • Simultaneous detection of multiple drones.

Cons:

  • Medium probability of detection with higher false alarm rates.
  • Radar returns from birds are very similar to radar returns from drones, but sophisticated signal processing can help differentiate these targets.
  • Line of sight obstacles (hills, buildings, and trees) will degrade detection performance. 360o coverage is obtained by either using multiple radar units or using a rotating mount for the radar.
  • Pilot geolocation is not an option.
  • Heavier system with higher power requirements.
  • High system cost.

Acoustic Detection

Acoustic technologies can be used to detect any object that produces noise (sound waves). Sophisticated microphone arrays using digital signal processing can detect drones in cluttered areas where RF performance may be at a disadvantage.

Pros:

  • Day/night operations. 360o coverage can be obtained using multiple microphone arrays, but this increases the cost.
  • Detections are possible even in the absence of drone RF communication, such as waypoint flight mode.
  • Simultaneous detection of multiple drones.
  • Small microphone arrays with low power requirements.
  • Low-Medium system cost.

Cons:

  • Medium probability of detection with higher false alarm rates.
  • Shorter detection ranges4from 100-400m depending on obstacles in the area. Line of sight obstacles (hills, buildings, and trees) only slightly degrades detection performance. Pilot geolocation is not an option.

Because there is not a single best sensor for drone detection, a strong detection approach is a multi-layered solution that uses a combination of multiple sensor formats. This approach relies on the strengths of each sensor while mitigating the weaknesses of each.

Our next post will focus on what to do with your new system: Counter-Drone Operations – Am I Breaking the Law?

To learn more about our counter-drone solutions, please reach out to us at: [email protected]

Hawkeye Aerial Defense (HAD) System

Increasing Protection with Drone Detection Analytics, Axis Communications

Elvira Drone Detection Radar, Robin Radar Systems

Detection and tracking of drones using advanced acoustic cameras, Joel Busset, et. al., SPIR Proceedings Volume 9647, Unmanned/Unattended Sensors and Sensor Networks XI, SPIE Security and Defense 2015, Toulouse, France.

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