Researchers revolutionize climate observation

New method allows for the first time global measurement of propellant gases

LEO LEO microwave occultation (LMO) and infrared laser occultation (LIO) form the basis of Low Earth Orbit (LEO) at altitudes of 500 to 600 km: Microwave and infrared laser signals traverse the atmosphere and become refracted and absorption influenced. From this, vertical profiles of greenhouse gases and other climate variables such as temperature and wind can be derived. © Uni Graz / WegCenter
Read out

A revolution in the measurement of greenhouse gases has succeeded Grazer researchers. They have developed a method that for the first time allows greenhouse gas concentrations in the free atmosphere to be measured over the long term and extremely accurately worldwide. At the same time, the system also supplies exact data on temperature, pressure, humidity and wind.

The new method could become the reference method for monitoring the climate change in the free atmosphere in the 21st century, the researchers write in the online edition of the journal "Geophysical Research Letters".

Characteristic absorption lines

The method is based on measurements with the help of microwave and infrared laser signals. In so-called microwave and infrared laser occultation, own transmitter satellites emit signals that are picked up by receiver satellites. On their way through the atmosphere, the signals are broken and partially absorbed, so that they arrive muffled at the receiver.

And here, the researchers led by Professor Gottfried Kirchengast from the Wegener Center of the University of Graz make use of invariable quantum mechanical properties of gases: "The various greenhouse gases - such as carbon dioxide (CO2), methane, nitrous oxide, ozone and water vapor - absorb the infrared laser signals to a very specific level Wavelengths strong and almost not at all. Each gas has very characteristic absorption lines, "explains Kirchengast.

From the idea to reality

By choosing the right lines for absorption signals, the respective concentration of gases and wind force can be determined. Data on temperature, pressure and humidity are obtained via the signals of microwave occultation, in the development of which the Graz researchers also play a leading international role. "All of this data has a quality that is difficult to reach even selected ground stations with purely local measurement, " says Kirchengast. display

Church guests already had the idea at the end of 2004 - initially only a fascinating hypothesis. Since then, he has been leading research in an ever-expanding international team. Susanne Schweitzer, for example, played a key role in the implementation of the idea of ​​a feasible method in the context of her dissertation. Among other things, the young researcher has discovered which absorption lines are suitable for infrared laser occultation. "There are over a hundred thousand lines in the possible range of short-wave infrared, but only a few dozen were ultimately suitable, " says Schweitzer.

Global Climate Monitoring

Climate monitoring of the whole earth is possible only with the help of satellites. So far, in the free atmosphere, which begins about two to three kilometers above the surface, only temperature and pressure could be measured with comparable quality, using GPS radio occultation. However, there was no suitable system for the worldwide observation of other climatic conditions and, above all, of greenhouse gases. Currently, data are based on spot measurements from balloons or aircraft, as well as model calculations and comparatively inaccurate satellite data.

Microwave and infrared laser occultation, according to the researchers, gives hope for far-reaching new insights into climate change through the possibility of highly accurate and model-independent observation. (Geophysical Research Letters, 2011; doi: 10.1029 / 2011GL047617)

(University Graz, 07.07.2011 - DLO)