On the measurement of the Rayleigh-Brillouin spectrum and atmospheric temperature using a coherent Doppler lidar

We present a Doppler lidar designed to detect the molecular spectrum characteristics, which are attributed to the Rayleigh-Brillouin scattering, in the atmospheric boundary layer. The suggested system is a continuous-wave, infrared Doppler lidar based on a bi-static transceiver and a coherent in-phase/quadrature detection scheme. For the detection of the features of the Rayleigh-Brillouin spectrum we use fiber-coupled, balanced photodetectors and a digitizer with a 1.6 GHz bandwidth. This broad bandwidth is necessary for the detection of Doppler shifts not only at frequencies of atmospheric winds, but also of the ones corresponding to molecular and acoustic speed that extend over several hundred megahertz. We demonstrate that using this configuration it is possible to detect the molecular Rayleigh-Brillouin spectrum over 30-minute time periods. The observational range of this system is focused on the lower part of the atmosphere (< 200 m) and the objective is to investigate if the resolved features of the Rayleigh-Brillouin spectrum can be related to the temperature, which could lead to the development of a novel vertical profiler of atmospheric temperature.