Research On Correction And Application Of Tropospheric Delay In Southwestern Yunnan

Tropospheric delay is one of the main factors affecting GNSS positioning.It is important to study how to weaken its influence on navigation positioning.The tropospheric delay can also invert the atmospheric water vapor,which is also of great significance for weather forecasting and disaster prediction.This paper introduces the principle of GPS positioning and the basic theory of CORS system,introduces the characteristics of neutral atmosphere and its influence on GNSS signals,and elaborates the tropospheric delay correction model and mapping function.Based on the GPS data of the southwestern region with large height difference,the spatial-temporal variation of the mapping function in the region and its applicability are analyzed.The accuracy of the regional tropospheric interpolation and fitting model are studied,and the Tengchong sounding data are used to discuss the application of tropospheric delay correction in predictable water vapor content inversion.The research content of this paper mainly includes the following aspects:(1)Three commonly used mapping functions including NMF,VMF1 and GMF,are compared and studied.The values of the three models' dry mapping functions are large in winter and small in summer,showing cosine changes.Compared with the values of VMF1 and GMF,the NMF value is obviously systematically large,and its value of wet mapping function remains unchanged throughout the year,indicating that the NMF model also does not reflect the annual variation of the wet delay com-mendably.In the GAMIT solution,the NRMS of three mapping functions have no signifi-cant difference,and the level precision of the baseline using the three mapping functions is higher than the vertical precision.However for the baseline repetition rate,the VMF1 model has the best effect in the NEU directions,and the GMF model is the second,which is superior to the NMF model.It is recommended to use a 10° cutoff height angle when solving GPS data in southwestern Yunnan.(2)The high-precision zenith tropospheric delay is obtained by GAMIT software,and the correlation of tropospheric delays of each station in southwestern Yunnan is analyzed.It shows that with time changes,the daily tropospheric delay of each station will be different,but the trends of the stations are similar.The zenith delay of the station has no obvious regularity with the change of the meridian and latitude,but has a strong correlation with the height,and decreases with the increase of the height,which changes roughly linearly.(3)Interpolation models and fitting models was studied using the zenith tropospheric delay of the regional station.From the study of the interpolation model,it is found that the interpolation error of the Yunnan's southwestern region with large height difference is large,and the interpolation accuracy of the three interpolation models is best up to 5cm.For the YINJ station,the error is as high as 20 cm or more.Because the zenith delay of the station has a strong correlation with the elevation,the projection and extension method is used to correct it,and good results are obtained.The IDW interpolation method has the best correction effect,and the four experimental station errors are within 2 cm.Then the H1QX1,H1QX2 and H1QM3 models are obtained by the least square method,and its are compared with the corrected IDW interpolation method.It is found that the H1QM3 model has good accuracy and the daily average error is less than 1.5cm.(4)The GPS/PWV of the zenith direction of the TENC station based on the tropospheric delay correction inversion is compared with the Radio/PWV detected by the radiosonde.The results show that: GPS/PWV of TENC station based on tropospheric delay correction inversion and Radio/PWV has a very good consistency in the overall trend of change.The correlation coefficient is 0.98,the mean deviation is 3.86 mm,and the root mean square error is 4.06 mm.This can be shown that the PWV based on tropospheric delay correction inversion is comparable to the PWV detected by the radiosonde and can be used for water vapor monitoring and prediction studies in the region.