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Guiding light: how lasers can inform military operations


Brian Perrett, Security Technology Lead

Ask most people to imagine a laser and what probably comes to mind is a Star Wars-style weapon, a music festival light show, or a cat chasing a little red dot. It’s pretty unlikely that lasers as microphones would feature in the conversation at all, but this lesser-known application has myriad potential uses across a number of industries.

Laser Vibrometry - image showing green laser beams against black background

Laser vibrometry uses directed beams of light to ‘listen’ to sounds. A laser is aimed at a vibrating surface, producing a Doppler shift in the reflected light that can be measured to determine the amplitude and frequency of the vibrations.

The technique is already used in manufacturing and other instances where there is a need to gather accurate vibration data at a safe distance. Take, for example, an engine from a commercial airliner. It is vital to know whether a bearing is failing or a fan blade is damaged, but it’s incredibly expensive and time-consuming to dismantle, inspect and rebuild the engine. Attaching sensors or wires to the engine may be unsafe, inaccurate, or even impossible due to the forces produced by the spinning turbine. A laser vibrometer can not only show that a fault is present, but pinpoint the likely nature of the fault, without making contact.

At QinetiQ, we like to reimagine interesting concepts like these, repurposing them in ways that solve other urgent defence and security problems. Here a few ways in which laser vibrometry might be applied to some of the challenges faced by militaries today:

Detecting and classifying vehicles

The sensors currently used to detect and identify enemy vehicles at long range and from high altitudes leave certain capability gaps. Thermal imaging sensors can detect the presence of an active vehicle, but not identify it or determine its intent. A typical camera cannot identify a vehicle over great distances, due to atmospheric distortion and insufficient image resolution. Both can be fooled by rudimentary camouflaging techniques.

Used in combination with other sensor types, laser vibrometry can confirm the presence and status of an active vehicle, even when camouflaged. It can pick up nuanced variations in the vehicle’s engine noise and other acoustic signatures, offering clues as to whether it is inactive, idling, occupied, ready to deploy, or just a decoy. It may be possible to identify the specific model of vehicle from its unique acoustic signature, and even offer clues about the nature of its cargo, based on the way its load affects vibration at different points.

Laser vibrometry can differentiate between vehicle types at ranges beyond the capability of other existing sensors. At distances of over 20 kilometres it can separate tanks from trucks; military aircraft from commercial jets; or fast attack craft from fishing boats – providing earlier warning of incoming threats and enabling surveillance from high-altitude pseudo-satellite (HAPS).

Seeing through walls

At present, a reconnaissance mission to work out the status of an enemy building may involve spending days or weeks looking and listening for any sign of activity. It’s very hard to figure out what’s inside a building by staring at the outside. Laser vibrometry has great potential to accelerate and improve the process by detecting and classifying movement within the property. Are there footsteps inside? Is the air conditioning on? Is there heavy machinery present that is inconsistent with the building’s stated purpose? This intelligence could help troops to make faster and better-informed decisions about whether or not to enter and the appropriate use of force.

Identifying people in a heartbeat

Pointing lasers at people is not something we do at QinetiQ, even when testing at very low wattage. However, the US Pentagon claims to have a laser vibrometry system that can identify an individual by their heartbeat. Quite how useful this is remains to be seen. The technology reportedly has difficulty taking a reading through thick clothing, and would require the creation of a ‘cardiac signature database’, like the ones that currently exist for fingerprints and DNA, before it could be used to identify strangers. However, there is another potential use (albeit one that most soldiers may prefer not to think about) – battlefield triage. The ability to detect the presence or absence of a heartbeat at standoff distance could aid in the prioritisation of medical assistance, and avoid sending medics into dangerous situations when their patient has zero chance of survival.

Current state-of-the-art

We at QinetiQ are incorporating our laser vibrometry research into a wider programme of laser sensor development to address the future needs of defence and security. Using funding awarded by the Defence and Security Accelerator (DASA) programme, we are developing a software defined multi-function lidar (SDML) payload for air, sea, land and space platforms, unclassified for export. The sensing mode of the payload is wholly defined in software, allowing the user to switch between different Information, Surveillance and Reconnaissance (ISR) modes and a communications mode to conduct multiple tasks in a single mission. The functions include 3D mapping of a scene, such as a building or compound; marking a target in the field; and measuring vehicle velocity, like a very long-range speed camera. By switching to communications mode, the laser can then transmit the collected data back to the ground. Our current focus is readying the payload for deployment on HAPS to enable persistent surveillance over enemy territory at an altitude of over 20 kilometres.

If you would like to learn more about QinetiQ’s novel sensing capabilities, please contact us.