Research On Atmospheric Water Vapor Retrieval Methods Based On Ground-Based GNSS

As an important greenhouse gas,water vapor is also the one of component in the atmosphere that can change in three phases under natural conditions,which is accompanied by energy transfer in the process of phase transition and hydrological cycle.It has a significant impact on the energy balance of the atmosphere and plays a very important role in promoting the movement of the bottom atmosphere.The activity of water vapor is high,and the change of time and space is relatively rapid.The conventional detection method of atmospheric water vapor is limited by the relatively low resolution of observation time and space and the relatively high cost of observation,so it is unable to make timely,effective and sensitive response to the change of water vapor in the atmosphere.Therefore,as a key problem in meteorological research and practical application,atmospheric water vapor detection puts forward higher requirements on the accuracy and efficiency of quantitative remote sensing.In recent years,with the rapid development of global navigation satellite system,GNSS technology has the advantages of high spatial-temporal resolution,high precision,low cost and so on,which is an important innovation of meteorological observation technology.This not only improves the ability of small and medium scale numerical weather observation and prediction,but also makes up the limitation of conventional atmospheric water vapor detection technology.It makes GNSS meteorology grow into a multi field integration discipline with high application potential.After combing and summarizing the theories and methods of water vapor inversion at home and abroad,and synthesizing various available meteorological observation data,this paper uses GNSS double difference phase observation technology to carry out the theoretical verification,water vapor solution experiment and water vapor detection performance analysis of Beidou satellite navigation system.The main research contents are as follows:(1)According to the basic theory and method of ground-based GNSS retrieval of Precipitable Water Vapor,three kinds of precise ephemeris products issued by Wuhan University are integrated to carry out the water vapor retrieval experiment of BDS,and the water vapor detection performance of Beidou satellite navigation system is analyzed and verified by combining the GPS water vapor detection results,ERA-5 reanalysis data products and radiosonde data.the result shows that the water vapor detection results of BDS compared with GPS,The RMS is nearly 2 mm,the linear fitting correlation coefficient more than 0.98.the water vapor detection results of BDS compared with GPS,ERA-5 reanalysis data and sounding station data respectively,The RMS is 3.44 mm and 4.39 mm,the linear fitting correlation coefficient are higher than 0.95.(2)Based on the unique orbit composition of "MEO+IGSO+GEO" constellation in BDS,this paper analyzes the influence of Beidou GEO satellite on the accuracy of water vapor detection.The results show that compared with IGSO and MEO satellites,the influence of the orbit error of Beidou GEO satellite on the accuracy of water vapor detection must be considered.After the solution strategy of "MEO+IGSO" is adopted,the number of outliers in the water vapor detection results is significantly reduced.Compared with the strategy of "MEO+IGSO+GEO",RMS is reduced by 31.2 %,and RMSE is reduced by 37.8 % compared with the strategy of "MEO+IGSO+GEO".In practical application,the method of weight reduction or elimination for the observation of GEO satellite and the method of multi constellation system fusion observation can be adopted,so as to reduce the impact of low precision satellite orbit on water vapor detection and improve the overall water vapor detection accuracy.(3)Based on the basic theory of ground-based GNSS inversion of Precipitable Water Vapor,the difference of water vapor detection accuracy between BDS-3 and BDS-2 is studied.Based on the observation data of 12 MGEX stations around the world and the results of GPS water vapor detection,the water vapor detection performance of Beidou satellite navigation system is analyzed.The experimental results show that the water vapor detection results of BDS-2 compared with GPS,the RMS is 2.94 mm,the linear fitting correlation coefficient more than 0.96.the Water vapor detection results of BDS-3 compared with GPS,the RMS is 1.93 mm,the linear fitting correlation coefficient more than 0.98.Compared with the RMS and thelinear fitting correlation coefficient increased respectively 43.3 % and 2 %.After BDS-2 and BDS-3 are jointly solvedhuode,Std and RMS are increased by 16.2 % and 16.5 % respectively compared with BDS-3 single system,which makes the water vapor detection accuracy of Beidou system reach the same level as GPS,and greatly improves the water vapor detection and application ability of Beidou satellite navigation system in China.