A pair of near-infrared lidars are operated continuously at Chilbolton. The new 1.5 micron HALO Doppler lidar points vertically and measures backscatter and mean Doppler velocity profiles from liquid cloud droplets, ice crystals and aerosols every 30s. The 905nm Ceilometer is oriented 4 degrees off vertical to avoid specular reflection from aligned plate crystals in ice clouds, and also records backscatter profiles every 30s.
The combined backscatter information from the two lidars together can be used to identify regions of liquid water, specularly reflecting plate-like ice crystals. The different absorption properties of ice at 905nm and 1.5 microns allows us to gain some information about the shape and size of ice particles. Similarly the different sensitivities of the lidars to aerosols, and may allow us to make measurements of aerosol swelling.
The Doppler information is very valuable, and allows the estimation of the vertical air motion in aerosols, providing us with data about the up and down drafts in the boundary layer. In ice clouds, the lidar Doppler velocity may combined with radar Doppler measurements and spectra to obtain information about the shape & size distribution of ice particles.
Turbulence may also be identified and eddy dissipation rates calculated by estimating the variability in the mean doppler velocity. This technique has been applied for radar data (Bouniol et al. 2003) but this new lidar technique will provide a cross-check in ice cloud, as well as allowing estimates in aerosol and liquid clouds.
Quicklooks for the lidars are available in real-time.
Doppler Lidar Specifications
Wavelength: 1.5 microns
Range resolution: 36 m
Integration time: 30 s
Maximum range: 10 km
Maximum Doppler velocity: 10 m/s
Doppler accuracy: 0.05 m/s (SNR dependent)
Antenna: monostatic optic-fibre coupled