The laser frequency stabilization is crucial to the measurement accuracy of wind speed in a Doppler wind lidar. In this thesis, a molecular iodine absorption cell was used to conduct the laser frequency stabilization. Before adding a frequency stabilization system, the seed injection Nd: YAG laser frequency was changed about 1.5GHz within 4h; after adding the frequency stabilization system, the maximum excursion of the frequency was less than 40MHz within 2.5h. Generally speaking, most of the frequency points were controlled within ±20MHz. The standard deviation was 9.54MHz. Such a way greatly improved laser frequency stability.
Raman-Mie scattering lidar is widely used to monitor atmospheric aerosols, but there are still some errors in the detection of bottom echo signals. Fernald method is one of the most widely used methods to calculate atmospheric aerosols, but it is difficult to determine the atmosphere its boundary value. The boundary value of backscattering coefficient can be calculated better by using scattering method than by iteration method, but there are still some errors. By combining the Fernald method with the optimization of the laser radar constant and the optimization of the iteration algorithm, an optimization method for selecting the calibration value is proposed without loss of accuracy. The new extinction profile is retrieved and its noise is analyzed. The relative error and defects of this method are proposed, which provides a reference for the calculation of extinction coefficient in the future.
Cloud and aerosol play a very important role in the Earth's atmospheric system,the accurate data of the three- dimensional information of optical characteristic of cloud and aerosol are of great significance to the climate change research.The new scanning coaxial Mie lidar system (SCML lidar) has been developed,which is mainly used for automatic continuous measurement of temporal and spatial variation of optical characteristics of aerosol and cloud. The axes of the emergent bean and the telescope of the coaxial lidar system remain in the same line by the collimation system.With the elevation and azimuth motors,the SCML lidar can take the horizontal,vertical and conial scans of the atmosphere.This paper discusses the structure,technical parameters,detection principle and modes of the SCML lidar and its results.According to the relationship between the boundary value and the range corrected signal is derived from the lidar equation,the new extinction coefficient iterative method is proposed to obtain the accurate boundary value of extinction coefficient of cloud and aerosol at lower elevation angle.The observational results show that the SCML lidar can provide the three-dimensional information of the extinction coefficient of aerosol and cloud.It is helpful to locate the sources of pollution aerosol in urban area and the smoke of straw burning in suburb,to determinate the height of planetary boundary layer(PBL),to improve the measurement accuracy of the lower atmosphere,and to track and monitor the aerosol plume and its transportation process.
A Vehicle-mounted Mie lidar is developed. The structure and data processing method of the lidar system are introduced. Based on the traditional Fernald method,the inverse astigmatic aerosol extinction coefficient is proposed by using the fixed scattering ratio method. Using the lidar system, the temporal and spatial distribution of aerosols over hefei was detected, and the extinction coefficient profile of aerosols in the vertical direction and the spatial distribution of aerosols in the 45° azimuth Angle were obtained, which is of great significance for the realization of large-scale aerosol detection.
The Fabry-Parot etalon can be widely used in the lidar for Doppler wind measurement and aerosol detection. Due to the very wide application of the FP etalon, the standard transmission curve of the F-P is a very important parameter. The general FP etalon measures the transmittance curve by tuning the wavelength of the laser source or tuning the angle of incident light. The FP etalon generally measures the transmittance curve of the etalon by tuning the wavelength of the laser source or use the frequency comb source. Moreover, the tuning of the wavelength and the angle of incident light are nonlinear, and the measurement accuracy is insufficient, and the frequency comb source is very expensive. This paper proposes a new method for testing the transmittance curve of a FP etalon using a similar frequency comb source. The whispering gallery mode is a typical similar frequency comb laser source which has multiple frequency components, but not equal intervals. The spacing of the frequency of the whispering gallery mode is not equal, but the spacing of the frequency can be determined. So, the transmittance curve of the FP etalon can be measured at one time. And the frequency interval and spectral range are tunable easily. This new method greatly reduces the cost of measuring transmission curve, improve measurement accuracy and effectiveness and has great theoretical and practical value.
As the increasing demands of the environmental protection, meteorological monitoring, ecological detection and other fields, lidars are needed to simultaneously measure a variety of atmospheric parameters (especially simultaneous measurement of various pollutants, such as volatile organic solvent VOCs). Multi-wavelength Raman lidar, differential absorption lidar (DIAL) and high spectrum resolution lidar (HSRL) can be implemented these fields. But either technique needs multiple laser sources to meet their requirements. This paper proposes a new lidar based on Frequency Comb Light Source, which can provide multiple frequency components through a single light source for simultaneously measuring various multiple atmospheric parameters. The frequency comb laser light source is used to emit seed light of frequency ωc from the seed laser, and then after passing through the frequency comb laser, a series of equally spaced spectral frequency components are emitted centered on ωc; then emitted into the atmosphere, and the laser reacts with the atmosphere. The echo signal enters the receiving optical path through the telescope, and is sent through the beam splitter or the discriminator to detect by the detector. Based on different pollutants have different absorption cross sections, similar differential absorption lidar(DIAL), the λon and λoff can be determined. The lidar using the frequency comb light source can be easy designed into a compact structure, which is convenient to carry and maintain. It’s also a very advantageous for the lidar miniaturization and industrialization with a wide application prospect.
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