Temperature Measurements In Mid-Lower Atmosphere Based On Pure Rotational Raman-Rayleigh Lidar

Temperature is an important parameter for describing the atmospheric state. Lidar (Lidar detection and ranging) provides a comprehensive understanding of the atmospheric dynamics and thermodynamics by making large-scale temperature profile measurements with high temporal and vertical resolution. Continuous temperature measurements throughout different atmospheric layers are essential to monitor the vertical propagation and energy transport in the atmosphere, and are also significant to study the impact on the environment due to anthropogenic behaviors.This thesis focuses on the atmospheric temperature measurements in mid-lower atmosphere. A combined rotational Raman-Rayleigh lidar, developed by Wuhan Institute of Physics and Mathematics (WIPM), was constructed for high-precision temperature measurements from 5 to 80 km over Wuhan, China (30.5 oN,114.5oE). By processing the observational data, a new calibration and inversion method was put forward, and characteristics of the thermal structure and temperature pertutbations were analyzed as well. The main research contents are as follows:(1) In this dissertation, a set of lidar system that combines two different mechanisms of rotational Raman (RR) and Rayleigh is developed for atmospheric temperature measurements. A frequency-doubled and injection-seeded Nd:YAG laser is employed as a source to emit light at 532.106 nm with an average pulse energy of-300 mJ. Molecular iodine frequency stabilization technology is used for simultaneous measurements of the temperature and wind field in the lower and middle atmosphere. In the receiving unit, a 1-m Cassegrain telescope is applied to collect the laser backscattered light from the atmosphere. Exact matching of laser transmitting and light receiving and optimum design of optical spectroscopic parameters are adopted to improve the light receiving efficiency. Besides, synchronous trigger control by mechanical chopper and weak signal detection technology for different channels are used to improve the detection precision.(2) Connective temperature measuremnets in mid-lower atmosphere are realized based on this combined lidar system. Temperatures covering over 5-40 km are achieved by RR technique, and at the same time temperatures over 30-60 km and 50-80 km based on Rayleigh-integration technique are obtained by RayL and RayH channels, respectively. By using a data merge method, complete temperature profiles covering widely from 5 km to 80 km are obtained for observation of the thermal structure and perturbations from the troposphere up to the mesosphere. The statistical uncertainty of the nightly-mean (hourly-mean) RR temperature is about 0.1K (0.3 K) at 10 km and increases to ～0.7 K (1.8 K) up to 30 km. From 30-50 km, the nightly-mean (hourly-mean) RayL temperature uncertainty varies from 0.15 K (0.4 K) to 1.1 K (2.7 K). And for the RayH temperature (50-80 km), the uncertainty increases from 0.4 K (1.0 K) to 3.4 K (8.8 K). The lidar-observed temperatures over 5-80 km are also compared with the temperature from the local radiosondes, NRLMSISE-00 model and satellite TIMED/SABER. The good consistency validates the reliability of the lidar syatem.(3) Simulation of the RR and Rayleigh temperature inversion methods as well as the data processing of the two techniques are presented in this dissertation. For RR temperature inversion method, this paper mainly analyzes the optimal selection of the filter parameters and calibration functions. The influence of changes of the system parameters (e.g. laser wavelength, line width, and angle of the filters) on the calibration and temperature inversion results is discussed as well. According to the observation data, RR temperature detecting precision with different spatial and temporal resolutions, characteristics of the temperature structure near the tropopause and in different seasons are analyzed, respectively. For the Rayleigh temperature inversion method, this paper mainly discusses the influence of the reference value and aerosol content on the atmospheric density and the temperature inversion results. According to the observation data from RayL and RayH channels, density, temperature and the corresponding perturbations are analyzed, respectively. Both the RR and Rayleigh temperature perturbations show obvious periodic wave chatacteristics for different height range of the atmosphere.(4) Based on the overlapping-region (30-40 km) data obtained from this combined RR-Rayleigh lidar system, we develop a self-calibration method for the determination of the system-dependent constants for RR temperature retrieval. Compared with the conventional radiosonde calibration method, the self-calibration obtained in the overlap region of both lidar temperature measurement techniques can be extrapolated to the lower temperatures in the tropopause region by using the simpler two-constant calibration function, Q=exp(a+b/T). With this new calibration method, the combined lidar system is capable to perform independent and accurate atmospheric temperature measurements when a coincident (in time and space) radiosonde is not available, as it is often the case. This combined RR-Rayleigh lidar thus has the potential for long-term studies of atmospheric thermal structure and associate perturbations.(5) Based on the self-calibration approach, one-night (August 4-5,2014) lidar temperature profiles are presented for case study of the wave avtivities. Some interesting temperature characteristics have been present for studies of waves propagating from near ground level into the mesosphere. Temperature perturbations are found to increase exponentially with a scale height of-10 km. The wavy structure shows minimal perturbations (’nodes’) at some altitudes of 39,52,64 and 73 km. Dominant wavelengths and temperature variations are also analyzed at different time and altitudes. By comparison of the temperature and associate perturbations from the tropopause up to the stratopause, different amplitudes, phase fronts and vertical wavelengths are discovered as well. These discoveries indicate that some waves may originate in the lower atmosphere and propagate upward with decreasing static stability.