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The RALMO system is deployed at the aerological station of Payerne (46.82°N, 6.95°E, 491 m) and is operated by the Federal Office of Meteorology and Climatology MeteoSwiss. Payerne is a NDACC site providing ozone profiles from radiosoundings since 1966, ozone profiles from a microwave radiometer since 2004 and water vapour profiles from Raman lidar since 2008. At the same time, Payerne is recognized as a GRUAN station and as a CIMO test bed and a variety of high quality measurements at the surface and in the free atmosphere are performed operationally and on campaign basis.

Instrument Description

RALMO is a Raman lidar for day and nighttime water vapour measurements. It has a tripled Nd:YAG laser emitting 300 mJ per pulse at 355 nm with a repetition rate of 30 Hz. The system measures the Raman backscatter signals from nitrogen (387 nm) and from water vapour (407 nm) for water vapour measurements. Additionally, the elastic and two pure rotational Raman backscatter signals close to the laser wavelength are measured for the retrieval of aerosol and temperature profiles. The system uses the narrow field of view and narrow bandwidth technique to achieve good daytime performance. A near range fiber improves the signal to noise ratio close to the instrument and extends the lower boundary of the measured water vapor profile to 100 m above ground level.

Instrument History

The instrument was built by the Federal School of Technology in Lausanne (EPFL) in a joint project with MeteoSwiss. After first test measurements in Lausanne the instrument has been moved to Payerne by the end of 2007. After a test period the system became operational by the end of 2008 providing routine water vapour measurements in real-time. The system is fully automatic and is one of the few lidar systems that runs 24/7.

Measurement Frequency

The RALMO system is an operational system of MeteoSwiss. It is fully automated and water vapor measurements are performed whenever the meteorological conditions are favorable (no precipitation, cloud base higher than 2000 m). The standard water vapour product is derived from raw data averaged over 30 minutes resulting in an altitude coverage from 0.1 to 9 km during the night and 0.1 to 4 km during day-time.

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