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MILITARY TECHNOLOGY (MILTECH) is the world's leading international tri-service defence monthly magazine in the English language. MILITARY TECHNOLOGY is "Required Reading for Defence Professionals". Follow us on Twitter: MILTECH1

21 October 2015

Microflown AVISA Creates Acoustic Awareness

Capable of detecting, localising, identifying and tracking sound sources in 3D space according to Microflown AVISA, the small and lightweight Acoustic Vector Sensor (AVS) is at the heart of all of the company’s sensor systems. MT takes a look at the Dutch companies technology.

Microflown AVISA’s AVS is now a combat proven technology with the company’s Vehicle Mounted Acoustic Multi Mission Sensor (V-AMMS) system being deployed on Netherlands Special Forces ground mobility vehicles in Mali. (All photos via author)

Microflown AVISA’s AVS is now a combat proven technology with the company’s Vehicle Mounted Acoustic Multi Mission Sensor (V-AMMS) system being deployed on Netherlands Special Forces ground mobility vehicles in Mali. Despite V-AMMS being part of a two year innovation project, early findings with the system were so promising that the Dutch military decided to procure nine sets halfway into the WHELAC project, MT learned during a technology demonstration day organised by Microflown AVISA and the Dutch MoD on 25 September.

Delivered to Mali in January, the systems were in operational use for six months by the time the technology demonstrator project ended in mid this year. Capable of localising small arms fire, the acoustic sensors are integrated on the Netherlands Army Special Forces Regiment’s Mercedes Benz G280CDI wheeled offroad vehicles operating in the African country as part of the Dutch contribution to what is called the Multidimensional Integrated Stabilisation Mission in Mali (MINUSMA).

A low SWaP system, an V-AMMS weighs a mere 1.75kg, sizes 30cm in diameter while its power consumption is less than 2W. The AMMS contains a sensor node, electronics, a DSP, a sheet metal housing and a black open foam windcap. The vehicle based system, V-AMMS, puts the AMMS on a customised vehicle mount. Combined with a power and data adapter and a Durabook display unit, the V-AMMS provides information relative to the vehicle. Advanced software routines recognise background noises created by the platform itself, such as doors being slammed or gun boxes rattling, so the likelihood of false alerts has been reduced to zero.

Netherlands Army Special Forces with Microflown AVISA’s Vehicle Mounted Acoustic Multi Mission Sensor (V-AMMS).

The V-AMMS detects the bullet’s shockwave, providing an alert and a 120° sector indication. The detection of the corresponding muzzle blast allows the sensor to give a prompt and accurate shooter location, with an angular accuracy of less than 3° and a range accuracy within 10 percent. During all this, V-AMMS ignores the sound of outgoing fire that might be caused by the 7.62mm and 12.7mm machineguns mounted on the Mercedes Benz G280CDI host vehicle. The V-AMMS system that is currently mounted on the SOF vehicles is a standalone system. However, networked options are also possible. This would enhance V-AMMS’ capabilities turning it into a system that can better deal with urban scenarios and with RPGs for instance. Such an enhanced version would also see grid coordinates of shooter locations being shown on a digital map.

Capable of localising small arms fire,Microflown AVISA’s Vehicle Mounted Acoustic Multi Mission Sensor (V-AMMS) are integrated on the Netherlands Army Special Forces Regiment’s Mercedes Benz G280CDI wheeled offroad vehicles operating in the African country as part of the Dutch contribution to what is called the Multidimensional Integrated Stabilisation Mission in Mali (MINUSMA). 

Patented Technology

Based in Arnhem, the Netherlands, Microflown AVISA uses Micro-Electrical-Mechanical Systems (MEMS) technology and no microphones unlike most of its competitors. As a result, the sensor uses the temperature difference in the cross section of two extremely sensitive heated wires to determine acoustic particle velocity. Three orthogonally placed directional sensors placed together in one single point lead to a compact AVS.

A key benefit of Microflown AVISA’s sensor is that it not only has the ability to locate small arms fire but also the sounds generated by larger projectiles, by helicopters and by fixed wing and rotary wing UAVs. Thus being a broadbanded technology, the AVS has a multi-threat detection/localisation capability unlike omnidirectional microphone setups which are more frequency dependent.

Microflown AVISA also claims that for gunshots the area covered by a single V-AMMS is 10 times larger than existing microphone based arrays. This is because the system is capable of detecting bullet noise at a shot miss distance (or closest point of approach – CPA) of 500m when used in a static mode. This figure is reduced to some 150m when the vehicle is moving (at speeds of up to 60 km per hour) which still allows a drastic reduction in the number of acoustic sensors needed to adequately protect a convoy for instance. In addition to AMMS’ coverage area, direction and range accuracy are also touted as being much better than of competing systems. All this makes AMMS an ideal enabling technology as part of a wider architecture that also has C-RAM and/or C-UAS functionality. However, the V-AMMS system that is now used in Mali is a standalone system which only gives direction and range of any hostile small arms fire that might be detected. For C-RAM purposes a more elaborate system of multiple networked sensors would be needed. Such a networked AMMS system has much better performance, its direction accuracy being given by Microflown AVISA as 0.2° which compares favourably to a stand-alone sensor, accuracy of which is around 1.5 degrees.

A Commercial Success

Over the years, Microflown AVISA has had quite some success with its AVS technology selling V-AMMS to three European countries including the Netherlands, while UAV based systems were sold to a customer in Asia. The Netherlands also uses three ground based systems that are based on AMMS. This includes a networked so-called RAM-SCORE system used on the Army’s artillery live fire training area together with a portable variant that is used at the much frequented Bergen/Munster Süd training area in Germany and elsewhere. Also designed to provide point of impact (POI) and point of origin (POO), a single system is in use as part of the Dutch military’s upgraded Deployable Integrated Sensor for Compound Security (DISCUS) system.

In its previous configuration, DISCUS was used for compound protection in Afghanistan protecting the main base in Tarin Kowt which the Dutch troops used when deployed to Uruzgan province. Featuring Thales’ SQUIRE ground surveillance radar and what appears a TEOSS-350 night vision system, the enhanced DISCUS system was again put to good effect during the 2014 Nuclear Security Summit (NSS 2014) held in the Netherlands.

During the event it was up to Microflown AVISA’s networked acoustic sensors to deal with the risk of sniper fire that might be aimed at harming foreign dignitaries arriving for the summit at Amsterdam Schiphol airport. A new multi-mission radar is apparently being considered for integration on DISCUS too. Also aimed at protecting smaller outposts, Microflown AVISA’s 360° Mobile Force Protection System typically consists of five AMMS and a Panasonic Toughbook based command post with detected sniper positions being reported as grid coordinates. If needed, the threat information can be passed on to a Battlefield Management System (BMS) and/or be used to cue other sensors or to help aim a remote controlled weapon station.

RAVEN lookalike with Acoustic Pointer.

Airborne Applications

Under the ACHOFILO (Acoustic Hostile Fire Locator) project, Microflown AVISA’s acoustic sensor technology has been tested successfully on one of the Dutch Defence Helicopter Command’s Airbus Helicopters AS532U2 COUGAR Mk2 transport helicopter in June 2013 with the helicopter actually being shot at, albeit with some safety margins of course. Notably, most of the casualties with helicopters in Afghanistan and Iraq were caused by low tech weapons such as small arms fire or RPG’s. While chaff and flares do not help in such cases, ACHOFILO not only brings an alert to the crew, but also informs them where the firing came from, allowing a change in doctrine. Until now, such attempts at bringing down a helicopter, which mostly fail, remain unnoticed until the helicopter has returned to its base. With ACHOFILO deployed, the crew can either evade the threat area or return fire, putting a penalty on the attempt.

In the FLACOUSE (Flying Acoustic Seeker) project funded by the Netherlands MoD, the acoustic vector sensor has been incorporated into a daggered shaped windcap that handles the head wind on a fixed wing UAV. This so-called Acoustic Pointer weighs less than 150g and consumes less than 100mW. As the Acoustic Pointer hears in a fully spherical bubble, its use is not only for wide volume acoustic target acquisition, but also Hear and Avoid as required for autonomous flights. Two variants of the Acoustic Pointer have been developed, a networked and a fully autonomous version that simply can be clipped on to the wing of any fixed wing UAV, such as Aerovironment’s RQ-11 RAVEN or WB Electronics’ FLY EYE. In this case, the Acoustic Pointer has its own inertial sensors and reports to a separate ground control station, making the fixed wing a mere “taxi.”

When the UAV operator opens up its own software, Microflown AVISA can provide the read in/read out interface from its Acoustic Pointer. A follow up to the FLACOUSE project will be the installation of two Acoustic Pointers on an interception drone. The so-called Twin Dagger will double the radius of the detection bubble around the platform, increasing its performance, reducing required sensor density to loiter an area.

Perch and Listen sees the ground based AMMS being put on top of a multicopter that carries the sensor across enemy lines. 

Another UAV project, Perch and Listen, sees the ground based AMMS being put on top of a multicopter that carries the sensor across enemy lines. Providing a means for the artillery to replace its active and thus vulnerable weapon location radars by a passive system, the Perch & Listen opens up opportunities to close in on the enemy. Hence the intrinsic disadvantage of acoustic arrays, the slowness of the acoustic propagation, is being addressed. Featuring an advanced autonomous landing system, the 5kg Perch and Listen AMMS system will likely be deployed from a transport box mounted on top of a tactical vehicle. Closing in on enemy activity over a distance 10-14km, Perch and Listen AMMS will step by step improve the accuracy of the grid coordinates being generated of hostile small arms fire and RAM. When combined with other sensors, such a system could also be used for flank protection or to guard a choke point. Flying at 12m per second, the Perch and Listen system has an endurance of 21 minutes according to Microflown AVISA while it can remain at standby for 48 hours. The system’s range is being cited as 7.5 kilometres.


Ongoing Activities

Whereas in WHELAC a single stand-alone AMMS was implemented on open wheeled tactical vehicles, Microflown AVISA is now expanding its applications in the Loose Track project. Under this project, Microflown AVISA aims to integrate V-AMMS onto the new Versatile Expeditionary Commando Tactical Off Road (VECTOR) air transportable vehicle that is being procured for the Royal Netherlands Army’s Special Forces. It has recently emerged that the Army’s 13th Light Brigade which is being transformed into a motorised unit will also receive VECTOR while the new vehicle by Defenture is also said to be the frontrunner in the contest for a new air assault vehicle for the 11th Airmobile Brigade. Not limited to VECTOR, Loose Track also takes into account other wheeled vehicles such as the Dutch Army’s BOXER, FENNEK, and BUSHMASTER. The merits of networked versions, above all for convoy protection scenarios, will also be studied.

V-AMMS Perch and Listen AMMS combo.

Also related to Loose Track, AMMS has also been installed on tracked infantry fighting vehicles (IFV), such as the CV90. Microflown AVISA insists that, acoustically speaking, the self-noise of such a vehicle would be similar to that of a light weight open wheeled vehicle if the metal tracks were to be replaced by a rubber track reducing the self-noise of the vehicle by around 15dB. The upside potential for dismounted soldiers would be large, as the acoustic umbrella provided by the vehicle would provide 3D acoustic situational awareness to the soldiers without themselves having the need for a man wearable system.

This said, as the company’s strategy is to put an AMMS on all sorts of platforms, the needs of the dismounted soldier are currently being addressed in the Walking Ears project that is also being funded by the Dutch MoD.

Part of the Benelux Smart Vest soldier modernisation programme, a helmet mounted version is required, so based on a novel, IP67 compliant sensor node, a miniaturised AMMS has been developed and tested for the very first time in September 2015. Live firing trials including tests in an urban environment with its acoustic reflections have been scheduled for November 2015. Rifle mounted and man-packed throwable versions are meanwhile also being considered. Information provided by these miniature sensors could be used to improve an infantry squad or platoon leader’s situational awareness. This can be done by representing enemy shooter locations on a smartphone like handheld BMS that is part of the Elbit Systems smart vest ensemble about to be introduced into Dutch army service.

In order to keep up its claim that an AMMS can be used to detect, locate and track all sorts of audible threats, Microflown AVISA is currently improving the capabilities of its SKYSENTRY system that is able of handling helicopters and propeller planes. UAVs, be it fixed wing or multicopter, are currently being researched, sponsored by the Dutch Ministry of the Interior. The C-UAS system will be demonstrated in several Western countries in the fall of 2015.

Pieter Bastiaans is a Netherlands based regular contributor to MT.