Counter-drone technology works in two steps by detecting and then defeating a drone. Today I’ll be looking at how rogue drones are detected thanks to a recent factbook by Australian counter-drone company DroneShield.

As drones have become more present worldwide, there has also been an increase in illegal and dangerous drone activity. This has resulted in the need for counter-drone solutions to keep them out of sensitive airspace.

DroneShield is one of the companies leading the counter-drone race with its line up of drone detection and defeating products, including the famous drone-destroying gun.

How drones are detected

Radio frequency (RF)

RF scanners are used to scan a known range of frequencies commonly used by drones to operate. The sensors can stay up to date with the latest drones, thanks to an updated database with all the drones. The RF system is passive, meaning it doesn’t transmit anything. It just receives signals from the drones in the area.

An RF system can pick up a drone’s signal and then sniff out the controller’s signal and approximate location. It can also tag and filter out false alarms that can be caused by Wi-Fi scanners and sniffers. This also means the system improves over time as it learns more about the signals being received.

DroneShield’s RfOne MK 2 system uses radio frequencies to detect nearby drones. The system best works when two or more RF sensors are used, as this allows the drone to be located by calculating various angles and using math to find the drone in 3D space.

There are essentially 5 categories of UAS RF communications globally:

  • Remote Control (RC) hobbyist drones, licensed for control in traditional shared hobbyist frequency bands. These bands are not designated for use outside of low baud rate telemetry control
  • ISM (Industrial Scientific and Industrial) band hobbyist UAS that are essentially license-free but regulated in terms of applications, output power, and spectral purity
  • Commercial drones, operational as compliant within allocated bands by the respective country’s civil regulator
  • Military drones, not regulated by civil regulators who use traditional military communication bands, details of which are normally classified
Two RF sensors used to triangulate the location of the drone.

Radar

The second method is radar. Radar can accurately track a drone moving through the airspace. Most radars are made to detect planes and helicopters, not carbon fiber drones. Recently, companies have been working on radars to detect DJI-type drones flying more than one kilometer away.

Radar is best used in open areas as trees and other ground objects can show up on the radar, creating false readings. Many radar systems today have a vertical detection range of about 10 to 30 degrees, which is not enough when trying to detect drones flying at all sorts of heights.

There are three types of radar used to detect drones. Pulse sends out an intermittent pulse that detects drones in the area. The shorter the pulse means, the higher the resolution is of the radar, making it easier to pinpoint the drone’s location.

Continuous radar constantly sends out a signal to actively track the location and speed of the drone. To ensure that the distance measurement can be accurately detected, a timing reference number must be included every time the radar receives a signal back. Some of the market’s radar systems today are so sensitive that they can detect the direction a propeller is moving due to the difference in frequency of the air being compressed and decompressed.

Radar detecting a drone

Acoustic

A much simpler method of detecting drones is to use a microphone. There is currently two main acoustic methods that includes using a single microphone or an array of microphones to detect and locate the drone.

The acoustic detection system removes all of the background noise made by the drone’s propellers and motors to focus on the drone’s noise signature. The sound is compared to a database of sound signatures that allows the operator to know the drone’s make and model.

Due to the recent drones being made smaller and quieter, acoustic detection systems have a harder time detecting drones, making them more useful when used alongside other methods. The DroneShield FarAlert Acoustic Sensor Installation takes advantage of microphones to detect drones.

DroneShield FarAlert Acoustic Sensor Installation

Optics

One of the most talked-about drone detection methods is using various cameras to detect drones in the sky visually. These visual systems often use electro-optical (EO) and infrared cameras to see drones. Pairing the system with an updated database and AI also allows the system to name the exact drone.

Due to the limitations in resolution and field of view, optical systems are often used in combination with others and an extra layer confirmation.

Two Mavic Airs being detected and tagged

Multi-sensor systems

The final and best solution is a mix of the above-mentioned systems. It uses all of the systems to accurately detect and track hundreds of drones at the same time. By combining them all into one system, you can get the benefits from all to outweigh the negatives many have when used by themselves.

DroneShield’s DroneSentry system uses a combination of detection methods to provide customers with a one-stop counter-drone solution. It has a range of 8 kilometers and can be scaled up or down depending on the requirements. The company has also come out with an X variant of the system that can be equipped on vehicles.

Photo: DroneShield

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