Key Technigue Study On Rotational Raman Lidar For Atmospheric Temperature Profiles

Atmospheric temperature is one of the important meteorological parameters in study of atmospheric physics, weather forecast and environmental monitoring. Measurement of atmospheric temperature profile in real time is meaningful for studying the solar radiation, explaining the phenomena of the global climate warming and improving the accuracy of weather forecast, especially investigating the phenomena of the urban heat island. The Raman scattering lidar, which has the high space-time resolution, can measure the atmospheric temperature in real time by using the dependence relation between the atmospheric temperature and the intensity of the rotational Raman scattering lines caused by atmospheric molecules. The rotational Raman lidar technique is a novel remote sensing technique of temperature and is more effective than other existing detection tools in continuous monitoring and measurement accuracy.In this paper, a lidar system for measuring the atmospheric temperature through the rotational Raman scattering is designed base on the comparison and analysis of the existing temperature remote sensing techniques, and the theoretical simulation and measurement experiments are made to verify the feasibility of the rotational Raman lidar system for atmospheric temperature. A high-spectral-resolution spectroscope filter constructed with a high resolution grating and two narrow bandpass interference filters separates the weaker rotational Raman scattering signal from stronger elastic scattering light, including Mie scattering and Rayleigh scattering, because the rotational Raman scattering signal is small than about 3～4 orders magnitude compared with elastic scattering.A tripled Nd:YAG pulsed laser and a 250-mm-diameter Cassegrainian telescope are employed as transmitter and receiver respectively. The high-resolution grating with a pinhole is composed of a filter to block the major solar background and elastic scattering spatially. Another spectroscopic filter composing of four narrow bandpass interference filters is used to separate two rotational Raman scattering signals, which have a central wavelength of 353.9nm and 352.5nm respectively. The suppression ratio towards Mie scattering and Rayleigh scattering is up to 7 orders magnitude and the daytime measurement is achieved.The result of a series of experiments taken under the different air conditions for detecting the atmospheric temperature in Xi'an by Raman lidar system shows that the system has the capability of measuring atmospheric temperature with temperature errors of less than 1K up to a height of 1km in condition of 250mJ laser power and 8min integration time.