Optical Properties Of Lower Atmosphere Derived From Lidar Measurement

In this work, firstly, the Mie scattering lidar system is built and introduced. The dye laser is the transmitter, working at the wavelength of560nm. The Cassegrain telescope is taken as the signal receiver. In order to improve the SNR, a ray bar is used to limit the field of view. The photo detector is a low-noise, high grain photomultiplier tube. The operational-amplifier circuit is taken as the output mode of the signal detection part, and a TDS5104B oscilloscope is used to displayed and stored the data. By the system, the detection of the lower atmosphere in northern suburbs of Nanjing is achieved, and the obtained echo shows the real atmospheric conditions.As the experimental lidar using non-coaxial mode, the geometrical form factor should be calibrated. The theoretical calculation of geometrical form factor is complex, so a simple exponential form, whose geometrical meaning is clear, is assumed. Make it done the least squares fitting with the theoretical calculation to determine the relevant parameters, and the result is ideal,which shows the theoretical calculation approximate to the exponential trend. To solve the problems that the theoretical calculation is not practical and experimental operation is inconvenient, a simple calibration is proposed based on the near-field correction of relevant scholars. Using the linear fitting of near-field and quadratic fitting of far-field, make the original echo signal devised with near-field signals according to the lidar equation, and the geometrical form factor is gained.Klett inversion algorithm, which requires a reference height and extinction value, is used widely and successfully. A new calibration based on fitting for reference value is presented in this paper. The echo signal is directly corrected through the geometrical form factor. The least squares method is used to fit the maximum range of atmospheric echo signals, then the reference value is gained. Using the calibration, the lower atmosphere echo signals of the northern suburb of Nanjing are inversed, and the good results are got.