Research On Atmospheric Water Vapor Detection System Based On Software Defined Radio Technology

Due to the aggravation of greenhouse effect and the increase of extreme weather in the world,it has a great impact on human survival.Therefore,high-precision and real-time atmospheric water vapor monitoring and forecasting of disastrous weather is particularly important for all of us.Since the 1990s,with the development of GPS meteorology,new water vapor detection methods have been derived,which can not only improve the shortcomings of traditional water vapor detection methods,but also meet the requirements of high timeliness and high precision.In this paper,the Software-Defined Radio(SDR)technology with the advantages of open,universal and reconfigurable are used to construct the atmospheric water vapor detection system,which is divided into GPS data receiving part and data processing part.The feasibility and accuracy of the detection system in the calculation of Perceptible Water Vapor(PWV)are verified by the combination of the two parts.Finally,the optimal scheme of water vapor detection system is proposed.The main contents of this paper are as follows:(1)This paper introduces the principles and thoughts of GPS meteorology in detail.Based on these principles,the whole system selects GNU radio,a software platform in software radio,and USRP,a hardware platform,as the experimental platform,and takes the GPS signal receiving as an example to analyze the theoretical basis involved in the receiving process.This paper discusses the irrelevant error,ionospheric delay,introduces the tropospheric delay correction model in detail and compares the correction effects of various models,selects the dual-frequency correction method to eliminate the ionospheric delay,and designs the receiving part to use GPS L1 and L2 signals for subsequent experiments based on that.(2)The data processing part of the system is designed,the whole water vapor inversion part of the process design is mainly introduced,and GAMIT is chosen to solve the problem.A dual-frequency receiver is introduced to form a short baseline to receive GPS data for later calculation.Based on the idea of numerical integration and the data of sounding station,the weighted average temperature Tm of atmosphere at UTC=12 in July to September 2019 in Nanchang area is calculated.The higher the accuracy of Tm,the better the inversion of Precipitable Water Vapor(PWV).Three kinds of tropospheric delay models that are suitable for Nanchang area are introduced and compared with the actual Tm according to the three models,and the Tm model with the best accuracy and stability is selected.(3)In the process of data receiving,it is found that the receiving stability is not enough.So,the GNSS SDR based on GNU Radio is introduced into this system,to complete the module configuration file corresponding to the system receiving requirements,and the received data is imported into Google earth to verify the accuracy of the positioning.Mainly introduces the input and output files and settings of GAMIT,compares and evaluates the errors of GPS/PWV and radio/PWV of high precision sounding station,and obtains the Bias=0.6422,RMSE=2.4730,correlation coefficient R=0.9698,which verifies the feasibility of the system to retrieve the PWV.Finally,the calculating errors are analyzed,and the errors of different tropospheric models are emphatically expounded.By comparing the errors of Black model and Hopfield model with the data of Saastamoinen model selected in the above experiments,the three models can effectively reflect the PWV trend,and the Saastamoinen model is more suitable for water vapor calculation in Nanchang area.(4)After completing the above water vapor detection system research and based on the existing cases,the subsequent optimization scheme of the detection system is proposed.The water vapor detection in the two directions of "horizontal+vertical" can be realized by using the SDR technology,and a system can possibly be formed to improve the water vapor inversion accuracy and monitoring capability.Briefly introduces the principle of horizontal detection,then carries out preliminary experiments,and lists several improvement measures after analyzing the current difficulties.