Investigation Of Martian Atmospheric Wind Speed Detecting,Mach-zehnder Interferometer Based Doppler Lidar

The Martian atmospheric environment research is an important part of the Mars exploration missions in many countries.The Doppler wind lidar based on the Mach-Zehnder interferometer can simultaneously detect the wind field and aerosol distribution in the Martian atmospheric boundary layer.This paper focuses on the scientific issues and the key technology involved,the research summarizes the theoretical model of the simultaneous detection of wind field and aerosol by the Mach-Zehnder interferometer,and proposes the design method of the field-widen technology of the Mach-Zehnder interferometer when large field of view beam is incident.When use low bandwidth photodetection circuit to receive the high-bandwidth emit signal,wind speed inversion still works.Finally,a 1064 nm Doppler wind lidar laser radar experimental system based on the Mach-Zehnder interferometer is built and verified by experiments,it's performance on mars was sumulated then.This thesis mainly includes the following aspects:(1)The wind speed inversion algorithm of Doppler wind lidar based on Mach-Zehnder interferometer is systematically studied.The lidar backscatter ratio,aerosol extinction coefficient and molecular extinction coefficient inversion method are given.The theoretical model of wind speed detection accuracy as a function of signal-to-noise ratio is analyzed.The effect of spectral broadening due to molecular thermal motion on the interference contrast is analyzed.The results show that long-wavelength lasers rather than short-wavelength lasers on the Earth's ground is better,the interference contrast of the echo signal is higher overall when use long-wavelength,and the wind speed detection accuracy is higher.(2)The design method of the field-widen of the Mach-Zehnder interferometer is studied.The respective theories of the prism field-widen scheme and the‘cat's eye'optical system field-widen scheme are analyzed and compared.The theoretical analysis prove that the change of optical path difference is limited to the magnitude of?~4 with the incident field of view?.It is difficult for the“cat's eye”optical system to analyze and express its field-widen capability when the oblique incident light is entered into the“cat's eye”optical system.The optical path difference model is calculated to give a numerically solution.The results show that the field-widen capability of the"cat's eye"optical system is not as good as that of the prism.The optical path difference scaning method with the piezoelectric interferometer is proposed,this scheme of obtaining its transmission spectrum is more flexible and faster than the temperature scanning scheme.The Mach-Zehnder interferometer field-widened with prism is designed and realized.The interference contrast is up to0.93 when the incident field of view is 11 mrad,this result meed the demand for wind detection of Doppler lidar.(3)The Mars atmospheric aerosol inversion method was studied.The extinction coefficient profile of Mars was retrieved based on the data collected by the“Phoenix”lander Mie-lidar.To tackle with the nonlinear effect of the photon counting signal in the near field data,a dead-time correction method is used to splicing the analog detection signal and the far field's photon counting signal,and the spliced signal is used to invert aerosol extinction coefficient.The atmospheric aerosol extinction coefficient profile is corrected and the overlap factor is corrected,and the aerosol distribution information in the range of 0-20 km on the surface of Mars is obtained.According to the aerosol extinction coefficient profile on the surface of Mars,the return power of the designed lidar system working on the surface of Mars is simulated and the return signal-to-noise ratio is calculated.Take the range where signal-to-noise ratio is 100 as the effective wind detect range,we analysed how the effective wind detect range on mars change with average times,laser pulse energy and system optical efficiency.(4)A Doppler wind lidar system based on the Mach-Zehnder interferometer was set up.The earth's atmospheric wind speed and aerosol were observed experimentally on the surface of the earth.An optical transceiver system was developed to receive laser radar return signals using a self-developed data acquisition system.The experimental results show that when the laser energy is 169 mJ and the average number of times is 32,the scattering return signal of 4 km can be received.The effective wind speed detection distance is about 1340 m,and the wind speed detection accuracy is 2 m/s when the SNR is 100,and 0.2 m/s when the SNR is 1000.The influence of interferometer's interference contrast on the accuracy of wind speed detection is analyzed.The results show that the interference contrast of interferometer has little effect on the accuracy of wind speed detection in the range of 0.6-1,but the accuracy is greatly affected when contrast is less than 0.5.The influence of room temperature changes on the system performance was analyzed,it was found that the detection error when using the Mach-Zehnder interferometer was not sensitive to room temperature changes.