Aircraft

New sensor measures aircraft velocity by bouncing lasers off air molecules

New sensor measures aircraft v...
Known as the Laser Air Speed Sensing Instrument (LASSI), the new system was developed by scientists in Chelmsford in the UK
Known as the Laser Air Speed Sensing Instrument (LASSI), the new system was developed by scientists in Chelmsford in the UK
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Known as the Laser Air Speed Sensing Instrument (LASSI), the new system was developed by scientists in Chelmsford in the UK
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Known as the Laser Air Speed Sensing Instrument (LASSI), the new system was developed by scientists in Chelmsford in the UK

British defense and aerospace company BAE Systems has come up with some interesting technology over the years, including armored vehicles that used Formula 1 suspension tech, and army helmets that use bone conduction for comms. Now, it's looking to improve how we measure airspeed, replacing conventional, air-pressure-based systems with tech that bounces around ultraviolet lasers to get the job done.

Conventional air speed sensors take the form of small tubes, known as pitot tubes, that protrude from aircraft. These are combined with small holes positioned at right-angles to the direction of flight, positioned either somewhere on the pitot tubes themselves, or elsewhere on the aircraft.

The conditions inside the right-angle holes describe the normal conditions outside the aircraft, something that's known as "static" air pressure, while those inside the pitot tubes, which are positioned towards the direction of flight, detail the pressure created by the forward motion of the aircraft. The difference between the two observed pressures is used to indicate airspeed.

Pitot tubes usually have heating apparatus built in, but they're still prone to icing up under really cold conditions. By their very nature, they're also vulnerable to collisions with birds, and they're not particularly accurate at low speeds.

The new system, known as the Laser Air Speed Sensing Instrument (LASSI), was developed by BAE Systems scientists working in Chelmsford in the UK. Instead of relying on air pressure, the new technology makes use of an ultraviolet laser.

The laser is used to bounce light off the surrounding air molecules, and the change in the color of the reflected beam, as caused by the Doppler Effect, is measured.

This can be thought of in a similar way to the classic police siren example of the Doppler Effect. Just as the sound of the approaching object is altered as the frequency of the wave changes when the object moves closer and then further away, the frequency of the laser light (and therefore its color) is also altered depending on the relative velocity of the air molecules reflecting the light back to the detector.

The ultraviolet light is invisible to the human eye, but tiny changes in its color can be picked up by the system's detector. Essentially, the larger the degree of color change in the reflected light, the faster air molecules are moving relative to the craft, and therefore the faster the vehicle is moving.

BAE has already conducted ground vehicle and wind tunnel testing of LASSI, and the team is now looking to scale down the system, targeting use in aircraft within the next five years. Overall, the it could provide a big upgrade over current methods.

"LASSI can be located completely inside the aircraft and is accurate at low airspeeds." said BAE Systems' Dr Leslie Laycock. "These features should ensure that the equipment is robust against damage, requires less maintenance and be easier to operate at lower airspeeds."

Source: BAE Systems

8 comments
physics314
It would be interesting to know how the system handles Doppler broadening caused by the thermal motion of air molecules, at speeds that are on average higher than the corresponding speed of sound. That's a lot of noise to get rid of!
nicho
and they don't use GPS because ???
windykites
Why not use inertial guidance to detect acceleration/time?
Captain Danger
@Spacewalker I think they mean a commercially viable system in 5 years.
SpeedBird2014
I cannot imagine this (valuble) technology would be remotely relevent to the GA community. Any technology that enhances safety and performance is appluaded. Lets push to make viable air transportion to the many instead of the few...progress is certainly being made but limited...push hard and forward!
CharlieSeattle
...YAWN, Using lasers and radar to find air displacement vortexes is used by the Russians to detect Stealth aircraft.
CharlieSeattle
This reminds me of a deadly flaw in the stealth aircraft design. For example, lets say a B2 is flying in air that is being scanned by Doppler Radar: While the B2 itself cannot be seen by regular radar, the air displacement is clearly seen by Doppler Radar. That makes the B2 a very expensive slow moving target. As a result, the Doppler Radar can pick up enough on the Air Displacement for an accurate location as to the stealth's position. If that can be relayed to anti-Air Defenses in Real Time the Stealth can be shot down easily! National Weather radars travel at 750,000 watts with a beam width of 0.88 to 0.96. The radar is so advanced it can detect dust! What's worse is that this technology has been developed in China back in 2004! F-15's use this system of radar now. The United States should admit it has a flawed gem that can not be used effectively without first jamming, locating and knocking out enemy radar sites using Boeing EA-18G Growler electronic attack aircraft or the Northrop Grumman E-2D Advanced Hawkeye to guide stand off missile attacks, thus blowing most of the element of surprise.