With so many different anti-drone methods jostling for attention, understanding drone detection and neutralization can be an intimidating task. All the same, a handful of technologies have gradually risen above the rest and been adopted by the majority of airspace security providers. How do you choose the drone detection system that’s right for your airspace? The first step is knowing what’s out there. Let’s take a closer look in our two-part series.
Radio Frequency or “RF” technology analyses the RF spectrum within the protected area searching for any form of communication between a drone and its remote control. In some cases, RF can even identify the drone make and model as well as the MAC address of WiFi drones.
The vast majority of COTS (“Commercial Off The Shelf”) drones are connected to their remote controls over specific frequencies of the radio frequency spectrum. This means that the drones “talk” to their controllers in regular intervals – around 30 times per second – transmitting information such as altitude and position, battery life and video feeds. The remote “answers” back with pilot commands like “Go left”, “Go right”, “Accelerate”, etc.
The advantage of this style is that the signature or protocol of COTS drones is relatively distinct from other communications taking place on the same frequencies. This means that even in a busy urban environment with an enormous number of different signals flying through the air from laptops, smartphones and other devices, drone communication stands out as distinct “peaks” on a spectrum chart.
In a radio frequency-based drone detection set-up a passive radio frequency sensor captures activity on select frequencies of the RF spectrum and relays it to a computer where specialized algorithms compare it to a database of drone protocols. The computer detects and matches the telltale frequency peaks of drone/remote communication with a high amount of accuracy, sounding the alert as soon as the drone and its remote are activated. Given that different drones have different protocols, a good radio frequency detection system can in some cases even identify the flying device’s make and model.
What about more than one drone? Recent reports out of Syria and Iraq have raised concerns over “drone swarms” or groups of drones steered by a single pilot. With radio frequency detection, even if multiple drones intrude into airspace at a given moment, they can all be detected and tracked as long as they communicate with their pilot over the RF spectrum – which is the case with nearly every consumer-grade drone.
A particular advantage of RF technology is that certain sensor configurations allow an administrator to discover and track the location of both the drone and its pilot. Given the restrictions placed on drone interception methods, apprehension of the pilot is probably the safest, least complicated and most effective method of neutralizing drone threats at their source.
Despite all the advantages of a radio frequency anti-drone solution, like any technology it has its limitations. Autonomous drones pose perhaps the biggest challenge to an RF-based system since an utter lack of communication between the drone and its controller would eliminate all opportunities to detect it on the spectrum.
But a truly autonomous attack – involving a drone able to navigate by GNSS without even sending back its video stream or telemetry information, spontaneously adapting to changes in the environment and avoiding unexpected obstacles – is extremely complex to orchestrate and therefore unlikely. Barring any sudden technological breakthroughs, RF-piloted drones are likely to remain the device of choice for the majority of operators for the foreseeable future.
Radar can provide effective detection of drone presence over a long range. It can be successfully paired with other technologies, such as RF or optics, to provide more thorough coverage if desired.
A radar system has a transmitter that emits radio waves called radar signals that are either reflected back or scattered by objects they encounter. The distorted waves bounce back to the radar receiver where algorithms convert them into a visual on-screen format that gives an idea of encountered object’s shape, size and density.
Most airports use a mix of radars on the Long Range or “L” band and Short Range or S” band in their air traffic control operations. But since drones are far smaller than any airplane or helicopter, they require a different approach. K and X Band radars are often used for low aerial surveillance, including drone detection, with X being preferable as its shorter wavelengths (8.0 to 12.0 GHz) provide higher level visibility and are more adapted to detecting small targets.
An object moving closer or farther away from the radar transmitter creates a “Doppler Effect” – a distortion or bend in the radio wave. A Pulse-Doppler radar drone detection system emits periodic bursts of radio waves and measures the bends in the returning radar signal to estimate the distance, speed and characteristics of a detected object.
Drones however are mostly made of plastic which is invisible to radar and only their metal cameras, batteries and motors provide a platform for the radar signals to bounce off of. Here’s where Micro-Pulse Doppler, an even more precise system, comes in – emitting a series of pulses very close together to get a more accurate picture of the monitored target, a necessary feature when attempting to identify objects as tiny as a drone camera or motor (4)(5).
Drones are smaller than manned aircraft and tend to fly close to the ground which makes them very difficult for all but the most specialized radar to detect (6). Such systems do exist, but they often present additional issues such as cost, high-false alarm rate and potential interference (7):
– Cost – The most effective drone detection radar systems are more specialized X band Micro-Pulse Doppler models. The initial outlay can be quite costly for a security administrator. But other costs are a result of the very nature of radar. Since it is an “active” or emitting detection technology, the only way for it to work is to be constantly on. Thus, it consumes considerably more energy than a passive system. This also means that radar coverage can knocked out completely if its power supply is disabled by weather, sabotage or malfunction.
– False Alarm Rates – Due to their comparable size and flying patterns, birds tend to create a lot of false alarms when entering the radar coverage.
Potential Interference – Radar’s active nature and the fact that some communications use the same frequencies may mean unintended interference with local broadcasts and the need to obtain a license to operate the system
Optics allow visual and/or infrared thermal imaging detection and characterization of approaching drones and drone payloads. Like radar, optics can be successfully combined with RF technology to provide more thorough coverage.
Optic detection uses cameras to spot intruding drones. The cameras can be divided into several types including standard visual security cameras, but Electro-Optic Infrared Thermal Imaging (EO/IR) cameras are the most commonly employed for CUAS. They work by using mid-wave Infrared Radiation (MWIR) or long-wave Infrared Radiation (LW IR)) to scan the protected space and specialized algorithms to spot heat differences between drones and their environment.
The plastic casing protecting a drone’s inner workings is not a heat conductor and the drone’s motor produces far less heat than one might imagine. However, the lithium battery that powers most consumer UAS generates a sufficient amount of heat to be spotted by a human operator using an infrared camera. Infrared cameras are useful from the moment there’s a difference in temperature and can “see” in total darkness without supplemental illumination, which makes them ideal to use at night or in missions where staying inconspicuous is imperative.
The chief issues confronting an optic anti-drone system are high false alarm rates and weather-related issues. Cameras employing visual scans have shown consistent issues with false alarms due to the difficulty of differentiating between COTS drones and similarly sized airborne objects like birds, or even leaves. To avoid this, a very large database against which the algorithm can compare the detected object is necessary along with heavy processing power.
Some of these challenges may be mitigated by the complementary use of infrared thermal technology to ferret out drones by detecting their heat signatures. But thermal drone detection can be adversely affected by weather conditions. High humidity, rain or dense fog can severely reduce the effectiveness of infrared thermal drone detection as the infrared radiation is scattered by water particles in the air.
In one study, at a Fog Level of III (“visual detection at <300m” using the International Civil Aviation Organization (ICAO) scale) both MWIR and LWIR hardly were virtually no better than visual detection alone. Thus, infrared thermal drone detection becomes problematic in Summer/Winter seasons in Temperate climates and practically year-round in Tropical, Oceanic or Subarctic climates which present high levels of ambient humidity and/or precipitation.
Acoustic UAV detection sensors pick up vibrations made by the propellers and motors of drones and can match them to a database of drone acoustic signatures.
It works by capturing vibrations which drone propellers and motors emit during flight, on a preset noise frequency band. Composed of arrays of multiple microphones, the acoustic drone detection sensors transmit the vibration to a database which uses algorithms to calculate azimuth, thus locating the sector in which the drone is operating and sometimes even the make and model of the drone. If the system is fitted with a large enough and regularly updated database, a large majority of drone models on the market can be identified.
Acoustic technology is lightweight, easy to install and can be used in mountainous or highly urbanized areas where the presence of hillsides or tall buildings might block some other detection methods. It is entirely passive and thus doesn’t interfere with ambient communications and uses little in the way of electric power.
While acoustic detection technology’s advantages: lightweight, low power use and passive nature, make it an attractive option, it’s reliance on acoustic signatures is actually its biggest flaw. Drones are becoming ever more silent as the technology evolves and market pressures demand a quieter device (4). And a homemade drone, constructed from spare parts, may not show up at all since it might not match anything in the database.
In addition, acoustic sensors can often detect drones, particularly in noisy environments, only at relatively close distances (less than 1KM in many instances) (2), which isn’t enough to avert an attack or collision. Given these flaws, an acoustic system might be better suited as a backup to more reliable radiofrequency-based technologies like RF or Radar detection.
Each technology has pros and cons and our experience has taught us that there is no single “foolproof” choice. Nevertheless, it is possible to find an extremely effective solution and set-up adapted to your particular situation, particularly if you opt to mix complementary primary technologies (i.e. radio frequency for detection/geolocation and radar to detect autonomous drones) to assure maximum coverage and if the budget permits, secondary technologies (optic and acoustic) to fill in any potential gaps.
As a stand-alone option, nothing beats the effectiveness and cost-to-benefit ratio of radio frequency, which remains the solid foundation of the vast majority of drone detection solutions and for good reasons.
In the next article in this two-part series, CerbAir will explore the often complicated and sometimes surprising world of drone neutralization.
The playing field for anti-drone technology is crowded and choosing the right system might seem impossibly intimidating. CerbAir has produced a white paper on the subject, complete with descriptions of drone detection and neutralization systems and a convenient checklist to help security administrators determine the best choice for their airspace. Download your copy of The Beginner’s Guide to Securing Sensitive Airspace with Anti-Drone Technology today to learn more.
Additionally, check out our article on qualities to look for in an anti-drone security provider here.