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Abstract
Small portable 1.5um Doppler lidars have recently become available which can operate in all weathers and are reasonably priced. These lidars detect backscatter from the aerosol particles in the boundary layer and the vertical motion of the air in the boundary layer can be inferred from the Doppler shift. However interpreting the lidar backscatter in terms of the aerosol is ambiguous if the aerosol size spectrum is not known. We report results from a field campaign in April 2008 at Chilbolton (Hampshire) where we observed the backscatter profile from three ground based lidars operating at 355nm, 905nm and 1.55um, the aerosol size spectra and the humidity measured with an in-situ balloon, together with the aerosol size spectrum and chemical characteristics at a range of humidities measured at the ground.
During most days the Doppler lidar observations indicate that the boundary layer is well mixed. On these occasions we find that the lidar backscatter profiles at three wavelengths predicted from the ground aerosol measurements and the observed humidity profile agreed well with those observed with the three lidars. These results imply that a ground-based aerosol instrument provides a good sample of the aerosols in the well mixed boundary layer, while the lidar provides an estimate of the vertical extent and the vertical motions of the air in the boundary layer. We also report on a method of inferring the dissipation rate of turbulent kinetic energy from the lidar and its validation using an in-situ sonic anemometer mounted on the balloon.