Raman lidar measurements
10 Mar 2011
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Examples of measurements using the Chilbolton UV Raman lidar

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These plots show examples of the types of measurements of elastic backscattering and water vapour mixing ratio that can be made with the Chilbolton UV Raman lidar. Time is shown on the x-axis and height on the y-axis. The lidar remains vertically pointing through the measurement, sampling the changing conditions that move through its field of view.

Water vapour mixing ratio
 
 

The upper two plots show measurements from the elastic scattering channel, which gives information on scattering from molecules and aerosols, including cloud droplets and ice crystals. On 23 March 2006 a warm front was approaching, as indicated by the slowly decreasing cloud base, from 6 km to 2km over the course of the measurements. On 12 December 2007 a very tenuous layer of sub-visible cirrus is seen at 10 -11 km. A few cumulus clouds are also seen at around 1 km. As is normal with lidar measurements, no signal can be retrieved from above the cloud layers. Below the clouds a signal which slowly decreases with altitude is seen. This results from Rayleigh scattering from atmospheric molecules. Rayleigh scattering has a (wavelength)-4 dependence and so is most prevalent in lidar systems such as this which transmit an ultraviolet beam.

The lower two plots show water vapour mixing ratio measurements, recorded using the water vapour and nitrogen Raman scattering measurements. On both days measurements continued until after dark. The resulting reduction in the noise level (which results from solar radiation) is seen at altitudes greater than about 2 km towards the end of the plot. Both water vapour plots show a relatively complex variation in water vapour mixing ratio with height.

Volcanic ash measurements from the 2010 Eyjafjallajokull eruption using lidar.

Earlier results also showing examples of radio refractivity measurements.​

Contact: Jeffery, Judith (STFC,RAL,RALSP)