Investigation of the Spatial and Temporal Variation of Temperature and Water Vapor in Lower Troposphere Using the Combined Backward Raman Scattering LiDAR and Lateral Scanning Raman Scattering LiDAR

A novel Raman scattering LiDAR is proposed to achieve accurate measurements of atmospheric temperature and water vapor from the ground to the concerned height, in which a lateral scanning receiver is constructed to collect the lateral rotational and vibrational Raman scattering signals excited by the transmitted laser pulses from the backward Raman scattering LiDAR (BWRSL). The major advantages of the combined lateral scanning Raman scattering LiDAR (LSRSL) and BWRSL are the sharing of the transmitted laser and the measurements of temperature and water vapor without the effect of geometrical overlap function. To simplify the mechanical mounting and offer the commonality configuration, both polychromators in the LSRSL and BWRSL utilize the modular design with narrow-band interference filters to extract the high- and low-quantum-number transitions of the pure rotational Raman scattering signals and the vibrational Raman scattering signals of N2 and H2O. Different with the BWRSL in the profiling of Raman scattering signal in its dependence on the time elapsed after the transmission of the laser pulse, the profiling of the LSRSL is realized by the elevation angle scanning of the lateral receiver, in which four horizontally aligned telescopes mounted on a steerable frame are spatially separated to look at the vertical laser beam at a certain distance. The experimental measurements of both LSRSL system and BWRSL system are carried out with the temporal resolution of 16 min and the spatial resolution of 36 m. The retrieval results after data gluing shows that the combined BWRSL and LSRSL system can realize the detection of atmospheric temperature and water vapor from the ground to the height of 4.00 km. The error analysis shows that both deviation and statistical error of the atmospheric temperature are less than 1 K, and both deviation and statistical error of the water vapor mixing ratio are less than 0.5 g/kg within the detection height interval of 0–4.00 km.