Lidar Spectrometer of the LITES facility at the University of Hertfordshire: Instrument Setup, Capabilities, and First Measurements

Conventional Raman and high-spectral-resolution lidar are used for deriving profiles of aerosol optical properties. These instruments can also be used for retrieving aerosol microphysical properties through inversion techniques if suitable optical data are available. In the context of the LITES (Lidar Innovations for Technologies and Environmental Sciences) facility, part of the lidar development at the University of Hertfordshire (UH) is centred on exploring the feasibility of using Raman backscatter signals of various target species for obtaining mass concentration profiles of selected chemical compounds of particulate pollution.

This goal marks the logical next step in aerosol profiling with lidar. This step will not only allow for defining aerosol types according to their chemical composition rather than their optical properties. This approach will also allow for identifying aerosol components which usually are used in the modelling of the climate impact of aerosol pollution. Thus, this instrument will for the first time allow for investigating the link between aerosol types that are commonly used for aerosol characterization by aerosol remote sensing techniques and aerosol components which are used for the modelling of, e.g. the radiative impact of atmospheric pollution. This new instrument technology thus will also allow for exploring how we can unify the treatment of aerosol types used in lidar remote sensing and derived from in-situ measurements. The feasibility of the underlying methodology has been proven for the case of measurements of Raman backscattering of silicone dioxide molecules within Asian dust layers that usually are mixed with anthropogenic pollution.

We will provide an overview on the new facility and its capabilities, and present first measurement examples. A high-power Nd:YAG/OPO laser set-up is used to excite Raman backscattering across a wide range of wavelengths. The receiver unit combines a high-performance spectrometer with a 32-channel detector or an ICCD camera to resolve Raman signals of various chemical compounds of particulate pollution. This set-up also allows for daytime detection of rotational-Raman scattering.