Experimental Research On Atmospheric Probing Using Coherent Doppler Lidar

Coherent Doppler Lidar has important scientific and social significance for its high spacial resolution and speed resolution and the ability to detect low-altitude atmospheric wind field under clear sky conditions. This paper focuses on the method of Coherent Doppler Lidar atmospheric detection and can be divided into four parts.First, the research process of domestic and international Coherent Doppler Lidar is discussed in detail. Through the analysis of the development of CDL at home and abroad, 1.55μm CDL is the best choice with the development of space and value in use. Aiming at the issue of limited detecting range, this paper proposes the program of improving the noise to signal ratio by coherent and incoherent accumulation.Secondly, this paper introduces the basic detecting theory of Coherent Doppler Lidar. The basic principles and methods of coherent and incoherent accumulation on Coherent Doppler Lidar is analyzed. So this paper also analyzes the performance of the Fourier transform, including the form of the Fourier transform of signal and noise, the improvement in SNR of Fourier transform and the theory of spectral leakage.Thirdly, in order to study the speed measuring capability of CDL, combining the comparative analysis of domestic and foreign velocity measurement, proposes the CDL speed measuring experimental program by servo. This paper establishes the speed-detecting device in the core of the servo, the maximum likelihood discrete spectral peaks estimation method is used to estimate the frequency of the echo signals.. Determine the speed of the servo by the speed range of the CDL and carry out the velocity measuring experiments of 16 speeds. The echo signals don’t need to be accumulated since the power of the echo signals are pretty high. So the echo signals can be spectrum estimated directly. Compare the speed of the servo and the measurements of the system and calculates the speed precision, the mean square of the measurement is 0.26m/s. analyze the influence of servo structure, reasons why the signal can’t be accumulated coherently.Finally, carry out the fixed target and atmospheric sounding experiments of CDL. Respectively uses the Optical Circulator and the space Circulator to accumulate the fixed target echo signals of 100 m and 500 m coherently. This paper efficiently enhances the SNR of the echo signals by 20 dB, and verifies the possibility of coherent accumulation on echo signals of fixed target. Through the comparative analysis of the advantages and disadvantages of Optical Circulator and the space Circulator, verifies the limit of coherent accumulation using Optical Circulator. This paper also measures the power of the background noise. Through detecting the atmospheric wind field, corrects the signal in the frequency domain. By comparison with the background signal with the strong shearing wind field near the hard target, qualitative verifies the system’s frequency response of the atmospheric wind field.