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'Star Wars' laser experiment improves understanding of Earth's atmosphere

Posted on 9 December 2011

York chemists are part of an international research team exploring novel ‘Star Wars’ techniques to improve our understanding of the Earth’s atmosphere and of global change.

As part of a project funded by the European Space Agency (ESA) and led by the University of York’s Department of Chemistry, researchers recently took part in a two-week experiment designed to test the feasibility of using new techniques on future space missions.

The experiment involved firing laser pulses between two astronomical observatories on the Canary Islands to test the practicality of continuous monitoring of greenhouse gases. During the two weeks, laser beams lit up the sky over the Atlantic Ocean with green pulses of light, creating a Star Wars film effect.

The experiment was designed to demonstrate the concept of using infrared differential absorption spectroscopy as a way of making extremely accurate measurements of the concentrations in the atmosphere of trace gases such as carbon dioxide and methane.

The approach we were testing is revolutionary in that it uses shortwave laser pulses

Dr Barry Thomas

The new approach will involve linking two satellites orbiting Earth; one acting as a transmitter and the other as a receiver, with the atmospheric composition being probed as the beam travels between them.

To test this concept, the scientists used ESA’s optical ground station on Tenerife, part of the Observatorio del Teide run by the Instituto de Astrofisica de Casarias, as the receiving site. The transmitter was installed at a second facility, the Observatorio del Roque de los Muchachos, on the top of a similarly high peak on La Palma. Separated by 144 km, there is an unobstructed path between the two facilities, making it an ideal location for the experiment.

Dr Barry Thomas, who manages the the ESA project, said: “Radio occultation, which tracks signals from satellites as they rise or set behind Earth, is a well-established method of sensing the atmosphere using microwave signals. However the approach we were testing is revolutionary in that it uses shortwave laser pulses. Since building and launching satellites is an expensive business, before going to that stage, ESA required that the practicality of the concept be demonstrated

“Individual chemical components in the atmosphere aborb at specific wavelengths and the absorption affects the beam intensity. From the variation in intensity we can calculate concentrations of trace gases and also wind speed.”

Laser beam leaving La Palma

The core team of scientists involved in the experiment were from the Universities of York and Manchester, the University of Graz in Austria and the University of Jena, Germany. Together they successfully recorded the first data of this kind despite having to modify the equipment on site, hit a target 3 m in size at a distance of 144 km and cope with sand storms blowing from the Sahara!

The infrared beams are invisible to the naked eye, but an impressive green laser was used for alignment purposes and to record atmospheric turbulence, creating a spectacular effect.

Armin Löscher, from ESA’s Future Mission Division, said: “It was a challenging experiment to coordinate, but a real pleasure to work with the motivated teams of renowned scientists and young academics.”

The experiment was carried out within ESA’s Earth Observation Support to Science Element.