Lidar Simulation And Echo Retrival Methods Of Water Vapor Detection

Water vapor, an active component of the atmosphere, is of significant importance inprecipitation, energy transport, process of radiation balance and cloud formation. Besides, italso play an important role in weather and climate monitoring and disaster prediction. Asone of significant positive remote detections, Lidar boasts lots of advantages, such as highspatial resolution, fine accuracy and real-time continuous monitoring. Different applicationplatforms result in different principles. When it comes to water vapor detection at theatmosphere, there are two basic performances, one is ground-based Raman lidar in watervapor, and the other is space-borne range resolved differential absorption Lidar (DIAL).In this paper, system designs on both ground-based Raman lidar and space-borne rangeresolved DIAL were carried out, as well as the relative retrival algorithms. This researchconsists of three parts; firstly, a simulation of Raman lidar with day and night detection onwater vapor at the bottom of tropospheric was completed; secondly, a simulation ofspace-borne range resolved DIAL on water vapor under the bottom of stratosphere wascompleted; thirdly, a study on processing echo signal for the above two systems werefinished.The main innovations of this paper are as follows in detail:1. A simulation of Raman lidar with day and night detection on water vapor at the bottom oftropospheric was completed. According to the low level of the troposphere model, bothecho model and noise model of water vapor Raman scattering lidar, the echo Signal toNoise Ratio(SNR) were calculated with different system parameters, such as thewavelength, pulse energy, the telescope aperture,atmospheric visibility. Besides, theperformance for the designed system was also evaluated by changing the parameters oftransmission, receiver system and the outside atmosphere condition. At last, a ground-basedRaman lidar system for water vapor was designed. Simulation results showed that acontinuous day and nignt detection could be performed, covering0~4km during the dayand0~9km during the night, which represented the detect ability met the lower part of thetropospheric water vapor profiles detection requirements.2. A simulation of space-borne range resolved DIAL on water vapor under the bottom ofstratosphere was completed. According to the standard model of the mid-latitudeatmosphere with atmospheric aerosols, molecules, water vapor distribution, Doppler broadening corrected range resolution DIAL echo model and noise model, the SNR and itsperformace were considered by varying the laser energy and frequency stability, telescopeaperture and FOV, atmospheric environment, and pointing angle of a laser beam.Afterwards, a space-borne range resolved DIAL system for water vapor within15kmaltitude was designed.3. A new thresholding method for de-noising weak lidar echo was mentioned. The newmethod overcame the lackage of the original thresholding methods, such as uncontinuousfor hard threshold function method and missing high frequency information deficiencies forsoft threshold function one. To prove the efficiency of the new method, both computersimulation and actual lidar echo signal were denoised with it. The simulating result showedthat both MSE and the output SNR were higher than the original ones. While the real dataprocessing revealed that the new method worked well for the near-field signal. But whenthe data was huge, complexing with the soft threshold method during the process accordingto the detect range became necessary.4. The relative inversion algorithms of space-borne DIAL for water vapor detection and ofground-based Raman lidar were studied. With the de-noisy method and echo functions,retrievals on simulated signals were done. Comparing with1976U.S. standard atmosphericmodel, the relative error for former was less than20%with an altitude less than5km; forlatter the very error was less than an altitude of15km. These results proved that the designof the two lidar system were valid. What is more, the retrival of simulated DIAL echo wasbased on the new deduced DIAL echo function with Doppler broadening.