RADA radar is integrated on the US Army IM-SHORAD
Pulse-Doppler, multi-mission, AESA radar have been a common technology introduced for the detection and tracking of the UAS. It is particularly suited to picking up moving targets, as well as, propellers and rotors. Here the RADA radar is integrated on the US Army IM-SHORAD intended forward air defence. (GDLS)

Small unmanned systems are often difficult for engaged ground forces to detect – but help is at hand.

As we have seen in the UAV section of this issue, the increasing presence of unmanned systems on the battlefield and their widening combat use has necessitated attention to countering them. Unmanned aerial systems (UAS) have grown from a handful of expensive dedicated reconnaissance platforms employed by upper echelons to relatively inexpensive systems suitable for tactical use down to the squad. Unmanned systems in the form of the UAS have already demonstrated their potential to alter the conditions of the battlefield. Their successful use against the Saudi oil facilities at Abqaiq and Khurais, in the eastern Ukraine, and against Armenian forces in Nagorno-Karabakh has emphasised the necessity of developing and deploying effective countering systems.

Tactical UAS offer particularly unique challenges. Those referred to as Group 1 and 2 being under 121 pounds (55 kilograms) and operating below 3,500 feet (1,066 metres) above ground level represent a new and unconventional threat. Operating from dispersed locations, in close proximity to the battle, under direct control and often hidden by the clutter of the surroundings they are more difficult to detect and counter using traditional air defence techniques and systems. In fact, simply the difficulty of being able to determine if a UAS is actually present is both a major advantage of the drone and a principle challenge for ground forces.

Tactical UAS

The nature of the Tactical UAS (TUAS) complicates the process of detecting and defeating them. This is especially true for units forward on the battlefield. Even individual combat vehicles have limited means for addressing a TUAS if encountered and supporting systems like command and logistics have virtually none. Exacerbating this is that there are few forward air defence units capable of engaging the TUAS and it is likely that they will be committed to protecting more critical assets. This leaves much of the battlefield force vulnerable to attention by enemy unmanned systems without means to deter them. In itself, this further encourages their use and enhances their effectiveness. A Ukrainian soldier reflected to a correspondent covering the fighting in the east of the country that “the constant presence or even the possibility that a UAS could be watching one’s every move quickly becomes a constant concern. One begins to assume that every action may be known and act accordingly. It becomes a physiological burden.”

Detecting UAS has become even more difficult as the fixed wing UAS has been increasingly replaced by vertical take-off and landing (VTOL) UAS. Their relative flight path unpredictability is a particular problem. VTOL UAS, like the US Marine Corps InstantEye also have the implicit advantage of being able to operate without need for either a separate launcher or large open area as they can be launched from more restricted and less conspicuous sites. Recognising this increased flexibility UAS developers are introducing hybrid designs which combine fixed wing and helicopter like rotor blades. Systems like the Russian VTOL ZALA 421-16EV have both rotor blades and fixed wings. This allows vertical take-off, yet higher air speed and range, factors which combine to make detection more difficult.

Armed UAS or loitering munitions, also referred to as Kamikaze drones, were also used during the Armenian conflict. Equipped with an explosive payload, IAI Harop drones were essentially flown into their target by Azerbaijani operators. Their effectiveness was facilitated by the lack of any counter-UAS (C-UAS) capability by the Armenian army.

Russia’s Zhukovsky Air Force Academy, together with Autonomous Aerospace Systems – GeoService and Group Kronstadt presented FLOCK-95 at Moscow’s Interpolitex-2019 security exhibition. Samuel Bendett, a fellow in Russia studies at the American Foreign Policy Council declared: “Russians think that this swarm will be an effective weapon against high-tech adversaries based on what they have seen and learned in Syria”. The number of drones and the possibility that coordinated attacks could be received simultaneously from multiple directions further complicates the C-UAS challenge.

Portable detection radar such as the Retinar FAR-AD, developed by Meteksan Defense
Portable detection radar such as the Retinar FAR-AD, developed by Meteksan Defense, are optimised for tactical use against mini/micro unmanned aerial vehicles and threats from land. (Meteksan Defense)

Detection

Detecting a tactical UAS is not simple as their small profile, relatively quiet flight, and ability to remain hidden by surrounding terrain, vegetation and buildings makes unaided visual detection difficult. Radar offers the best practical solution, with AESA (active electronically scanned array) having proven the most effective. Lee Dingman, president and COO at Ascent Vision, explained: “Systems like our RADA Multi-mission Hemispherical Radar reliably provides an umbrella surveillance coverage out to 5-6km (3-4 miles) both while stationary and on-the-move. Plus, they are compact and energy efficient to be compatible for integration on mobile platforms.” In fact, such systems have been preferred in dedicated C-UAS currently being introduced such as the MADIS (Marine Air Defence Integrated System) and US Army IM-SHORAD from Leonardo DRS.

Doppler radars are well suited to detecting UAS as they are able to track moving objects and can discard static objects which could be false targets. Systems like the EVIRA, a Frequency Modulated Continuous Wave (FMCW) from Robin Radar Systems in the Netherlands are mini-doppler radars. These are able to specifically detect speed differences among moving objects which is particularly relevant to UAS that use some version of propellors. In addition, as the radar is always sending and receiving, it offers accurate and fast tracking with quick update rates, all critical to finding and tracking an agile target like a UAS that is able to quickly drop out of sight.

Acoustic detection, determining the presence and bearing of a UAS by its sound signature, is being introduced as well. This capability may be included as an added feature in ‘shot’ or gunfire detection systems on vehicles. Where a number of acoustic detection and alerting systems are present within a unit or around a site they can be networked. Comparing the bearing of the detection from several systems allows triangulation thereby providing the precise location of the UAS. The microphone arrays do not depend on the size of the drone, but rather on the sound of the propeller. This means that they can effectively offer both detection and recognition, determining whether it is drone or not, and then track it. The latter may be refined through accessing a digital library of UAS acoustic signatures to even identify the specific type. This information then offers details on the capabilities of the threatening UAS, allowing a determination as to the capabilities and best counter to each UAS.

The use of optical systems, including both high resolution colour and thermal heat sensing infra-red cameras, are already a component of many counter-UAS systems. They are integrated to provide a positive identification of the target detected by another search medium. An optical sight is generally also the preferred aiming method for engaging hostile UAS. For these applications, the optical devices by necessity have greater magnification and limited field-of-view (FOV).

Infra-red Search and Track (IRST) which continuously scan and detect heat-signatures have also shown promise, certainly as a surveillance and search system, and increasingly for recognition and identification as well.

IRST systems like the HBH Infrared Systems Spynel-X series have already been successfully demonstrated in perimeter surveillance conditions. These continuously rotate around 360 degrees scanning a vertical FOV of between 5-20 degrees depending on the model. The mid-wave IR focal plan array detects the heat signatures of everything in its FOV. Comparing the scene of each rotation, which can be as fast as two scans per second, the system is able to detect new heat signatures. Repeated sensings provide a track and through signature filters a confirmation of a potential threat. Once alerted, the operator can access the video image to verify that it is a UAS or other intrusion requiring further action. The advantage of infra-red systems such as Spynel is that they is fully passive, of compact size, and provide alerting and targeting for a range of threats, not just UAS.

The SPYNEL thermal imaging technology by HBH
The SPYNEL thermal imaging technology by HBH provides panoramic detection, identification and tracking of multi-target airborne threats like UAS simultaneously. (HBH)

RF (radio frequency) detection and signal direction finding has proven an effective passive detection approach for fixed or stationary sites, such as airfields, where RF receivers can installed. Dr. Jon Bradley, vice president sales at CRFS, a leader in RF detection systems explained: “Our RFeye uses three or more receivers connected to omnidirectional antenna placed in spatially separated network. Using TDOA or Time Difference Of Arrival it is able geolocate in 3-dimensions RF transmissions.” This allows not just the accurate locating of the drone but potentially the drone control station as well. The later is invaluable in offering an additional, and particularly effective additional option in defeating the UAS.   Identifying where the operator of the UAS may be located in combat situations allows the site to be engaged by either indirect or indirect fires. In a more benign environment, it could open the opportunity to physically capture the operator and their equipment. Both cases offer greater return than simply downing the UAS platform itself.

RF detection and ranging, previously less practical for tactical use, is feasible as CRFS provides a system with man-portable or vehicle mounted common sensors. Bradley explained: “Four or more sensors networked will detect, track (including altitude and speed) and identify (including target type) in 3D and do so entirely passively.” As RFeye collects from a broad RF spectrum, analysis of its collected data could also have other signals related applications such as counter-artillery, C2 location, SigInt, and electronic warfare.

RFEye detects radio frequencies
RFEye detects radio frequencies up to 8/18 & 40GHz utilising four or more networked nodes which then uses its 3DTDOA direction finding technology to deliver precise latitude, longitude & altitude of any emitting targets including unmanned drones. (CRFS)

Classification and Identification

Detection of a ‘sighting’ then requires confirmation that it is in fact a valid potential target. Referred to as Classification and Identification, the focus is on determining that the object is in fact a UAS and not a false alarm. Although the advanced nature of detection filters are quite efficient in eliminating naturally occurring false targets like birds there is always the need to determine ‘friend or foe’ or simply confirm what response is needed or best. In a tactical scenario, this is currently undertaken through visual identification using day and/or thermal imaging systems. Having an accurate bearing or location facilitates acquiring the potential target since generally positive identification can require higher magnification meaning a narrower field-of-view. For vehicle mounted C-UAS, the hand-off between detection and acquisition can be automated allowing more rapid execution of the target identification. For dismounted, particularly handheld C-UAS, acquisition and identification can be hampered by the complexity of the view of the surroundings and limits of handheld optics. Field experience has shown that positive identification of a small UAS by the unaided eye at a sufficient distance where action can be taken is questionable at best. Even high resolution optical systems are challenged given the necessary high magnification ;thereby limiting the FOV. As CRFS’s Dr. Bradley shared: “a successful C-UAS effort requires detection and reliable target confirmation at as great a distance as possible to provide sufficient time to effectively respond.” The ideal C-UAS incorporates detection, identification, and both aerial platform and its controller location and does so rapidly, thus, allowing for selection and execution of the most appropriate defeat action.

by Stephen W. Miller