Research For WAAS Ionospheric Delay Estimation Based On Kriging Algorithm

Ionospheric delay as one of the main sources of error in the Global Navigation Satellite System(GNSS),and ther are many methods applied to reduce the error of ionospheric delay.First,the methods(planar and kriging)of the ionospheric delay estimation based on the thin-shell model which are used by the Wide Area Augmentation System(WAAS)are designed and realized by the experimental data.At the same time,the ionospheric tomography technique and tomography combined with kriging method are used to refine and evaluate the algorithm,and then the applicability of different methods which aer used to estimated the ionospheric delay of WAAS grid point is studied.The main contents and results are as follows:In order to realize the near real-time estimation of the ionospheric delay for WAAS grid points in the study area when ionosphere status is static,the GPS broadcast ephemeris data and four estimation methods are used to estimate the ionospheric delay.The results show that the errors estimated by the planar method,kriging method,tomography method,and tomography combined with kriging method decrease in sequence,and the estimation results of the kriging method based on thin shell model are similar to those of the two methods based on ionospheric tomography;Next,in order to study the possible impact of different ephemeris data on the tomography results,GPS broadcast ephemeris data and precision ephemeris data are used to study respectively.The results show that the tomography results based on precise ephemeris data are superior to that of the broadcast ephemeris data,indicating that the accuracy of the experimental data is related to the tomographic results.In order to further study the ionospheric delay estimation of different methods for WAAS grid point under static and disturbed conditions,firstly,comparing the tomography results based on different empirical orthogonal functions(EOF)with the ionosonde data,and then select the appropriate EOF for tomography method under different ionospheric conditions.The results show that the tomography inversion results based on iriEOF are better than those of modelEOF when under the static conditions,and the tomography inversion results based on modelEOF are better than those of iriEOF when under disturbed conditions.Then to estimate the ionospheric delay of grid points when under the static and disturbed conditions by the GPS precise ephemeris data,and the results show that no matter whether the ionosphere status is static or disturbed,the estimation result based on planar method is the worst.Under static conditions,the errors estimated by the kriging method,tomography method,and tomography combined with kriging method decrease in sequence,and the estimation results of the kriging method based on the thin shell model are similar to those of the two methods based on ionospheric tomography,when under disturbed conditions,compared with the two methods based on the thin shell model,the ionospheric tomography method can obtain a more accurate estimation results for WAAS grid point during the study area.and compared with the tomography method,the estimation results of tomography combined with kriging method for WAAS grid point is not much improved.