Weathering heights

European scientists and engineers plan to monitor the Earth’s climate more efficiently by mounting sensor technology on a fleet of modified commercial aircraft. Jon Excell reports.

By investigating the upper reaches of our planet’s atmosphere we can learn much about the earth’s climate and our impact on it.

The problem is that the equipment for monitoring this extreme environment — from balloons, to satellites, to specialised research aircraft — is often expensive, sometimes unreliable, and simply unable to carry out the sort of continuous analysis that’s required for truly accurate climate models.

The answer, according to a group of European scientists and engineers, is to tap into a resource that has been staring us in the face — or, to be more accurate, flying above our heads — for the past 50 years.

The team, an alliance of academics and engineers from industry giants Airbus, Lufthansa and BA is investigating the possibility of using existing commercial aircraft to create a global sensing network that will probe the troposphere and stratosphere with unprecedented regularity.

Dubbed IAGOS (Integration of routine Aircraft measurements into a Global Observing System) the EU-funded project is the continuation of an earlier initiative named MOZAIC, (Measurement of Ozone and Water vapour by Airbus In-service aircraft) which equipped a small fleet of passenger aircraft with a package of ozone, water vapour, carbon monoxide and nitrogen oxide sensors.

The project’s leader, Dr Andreas Volz-Thomas of Germany’s Juelich research centre, explained that the aim of IAGOS is to expand on this with a slimmed down, more advanced sensor package that will be deployed on a larger number of aircraft.

The initial plan is to install the payload on a fleet of 10 to 20 Airbus A340s for which the group has a so-called Supplemental Type Certificate (STC) authorising it to make particular modifications. Volz-Thomas said he hopes soon to gain a similar certificate for A330s which are typically flown on shorter routes and can therefore provide a more detailed vertical profile of the atmosphere.

Weighing around 220lbs (100kg), compared to the 180kg of the MOZAIC payload, the sensor package will be installed in the avionic compartment beneath the cockpit. A340s are particularly well-suited to the project as this compartment contains a handy bit of free space which is designed to accommodate a rarely used optional refrigeration system.

As for the nature of the payload, as well as the ozone, CO and NOx instruments from MOZAIC, IAGOS will contain a number of new instruments.

One of these, a cloud particle sensor, is currently under development by a Manchester University team.

The device weighs around 2kg and consists of a tiny laser, which will fire a beam through a small window in the avionic compartment, and a small telescope for retrieving the backscattered light. Volz-Thomas said the data acquired by this system could lead to big improvements in climate models. ‘You need to know the particle distribution to do the radiative transport model to feed into climate models and to understand cloud formation,’ he said.

The Manchester team is also working alongside scientists at the German Aerospace Centre (DLR) on the development of optical particle counters that, mounted inside the aircraft, will be able to measure the full range of particles in the air.

The MOZAIC system’s plate on the exterior of a Lufthansa A340 showing the ozone, carbon monoxide and water vapour sensing inlets (above left) and the device’s instrument rack, power supply and data system (above right)

Volz-Thomas is particularly excited about the opportunities the project will provide for studying the tropopause; the boundary between the troposphere — which is where the weather happens — and the stratosphere. The tropopause is where jet planes fly and is of great interest to climate scientists because it effectively acts as an invisible barrier to rising air, and plays a major role in cloud formation and weather.

Volz-Thomas said that aircraft flying through the tropopause have distinct advantages over the satellite and ground-based sensing techniques that are currently used. ‘Satellites cannot resolve the sharp gradients between the troposphere and the stratosphere because they don’t have the height resolution, and the same holds for remote sensing from ground — these measurements usually give you vertical columns or some very coarse height resolution. Passenger aircraft represent a very cheap way to collect a huge amount of data in the region around the tropopause and will fill a big gap in understanding.’

The only instruments that have so far been capable of analysing the tropopause in any kind of detail are those mounted on board specially-designed research aircraft such as the National Environmental Research Council’s (NERC) BAe146, but this, said Volz-Thomas, is expensive. ‘You can put a lot more complicated equipment into such aircraft, but they cost around £3,000 an hour so you cannot do monitoring from these for more than a couple of times a year on very special objectives,’ he said.

Putting a lower cost — albeit less sophisticated — system in the air with the frequency of passenger flights will, he said, provide a far clearer picture of the tropopause and the vertical structure of the troposphere.

This improved understanding could ultimately help mitigate some of the worst effects of aviation. For instance, high saturations of aircraft travelling repeatedly along the same flight-paths often cause persistent con-trails, which can become Cirrus clouds, which in turn reflect infrared radiation from the earth and contribute to atmospheric warming. Through real-time monitoring Volz-Thomas said it should be possible to avert the formation of con-trails by subtly altering the flight paths of aircraft travelling through problem areas.

Another potential application of the IAGOS system will be monitoring the effect on the climate of the growing sources of air pollution in the far east and South America. Again, Volz-Thomas believes that an aircraft-based monitoring system will fill an important blank. ‘we see extremely high CO concentrations over Asia at flight levels — at altitudes between six and seven miles (10 and 12km) — but current global models don’t put it there and the satellites didn’t show it.’

Early next year, the new system will go into trials on a Lufthansa aircraft, and following that will be rolled out on around 20 passenger planes. So far, Lufthansa, Air France, China Airlines and Cathay Pacific have all signed up to the initiative. BA is also said to be extremely interested, but the STC, which is a pretty expensive document, doesn’t currently run to Boeings.

Ultimately Volz-Thomas hopes to sign up enough partners to make the reach of IAGOs truly global, ‘An important part missing from MoZaic was that we had only European airlines,’ he said. ‘if we can get more partners outside Europe this may become a global observing system. One of the important goals of Iagos is to extend the coverage to the Pacific and the southern hemisphere — so we have to find partners in these regions.’

The chances of this happening seem fairly high. Although it must agree to fly the devices for free, the civil aviation industry is said to be extremely enthusiastic about the project. Under increasing pressure to improve their environmental credentials, Volz-Thomas said IAGOS gives aircraft manufacturers a gilt-edged opportunity ‘to put some green paint on their planes.’