Lidar probes atmosphere above Swiss Alps

Oct. 1, 2000
A research group at the Swiss Federal Institute of Technology in Lausanne, Switzerland (EPFL) has installed a laser-based probe system in a high-altitude Alpine station that provides a unique site for Earth-based atmospheric observations.

A research group at the Swiss Federal Institute of Technology in Lausanne, Switzerland (EPFL) has installed a laser-based probe system in a high-altitude Alpine station that provides a unique site for Earth-based atmospheric observations. For most of the time, the Jungfraujoch station is located in the free troposphere at an altitude of 3600 m (11,811 ft) above sea level. It forms part of the Network for Detection of Stratospheric Change, and for several decades its instruments have provided information essential for global observation.

The new lidar system will make range-resolved measurements up to the high stratosphere. This will provide, for the first time, detailed information on aerosol and water-vapor concentration profiles and on temperature profiles. The aerosol lidar is part of the European lidar network EARLINET, which will monitor aerosols across Europe on a regular basis.

The EPFL research group has developed a lidar system based on a 40-W Nd:YAG laser emitting at 355, 532, and 1064 nm, with a repetition rate continuously adjustable up to 100 Hz. It is installed in what was previously an observatory and uses its 76-cm telescope as a primary telescope. An additional 20-cm telescope is installed for low-altitude observation, thus enabling measurements over a total altitude range of a few hundred to 10 km above sea level. Information on aerosols can be gathered by looking at elastically scattered light, while Raman scattering will be used to investigate water vapor.

The new lidar station will retrieve atmospheric aerosol parameters in both the troposphere and the stratosphere, water-vapor profiles in the troposphere, and temperature profiles in the stratosphere and mesosphere. The data generated will be analyzed together with those of the other instruments on site; trace-gas column measurements are obtained on a regular basis using Fourier-transform infrared spectroscopy. Additional range-resolved ozone and chlorine oxygen profiles come from a passive microwave instrument, and column measurements of ozone and water vapor are performed by a 14-channel sun spectrophotometer.

Project managers Philippe Quaglia and Bertrand Calpini, reporting on progress to date, said, "Our first measurements have been made on aerosols using the 20-cm telescope; we are currently commissioning the 76-cm telescope. We recently obtained the first Raman water-vapor profile with an altitude resolution of less than 100 m in the free troposphere. Soon we will have the complete use of the lidar capabilities, so we can retrieve the aerosol, water-vapor, and temperature profiles."

For more information contact Bertrand Calpini, [email protected].

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