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Abstract:
IGS ionosphere products have been widely used for positioning, navigation, timing and monitoring the Earth’s ionosphere. However, the accuracy of these products is restricted by traditional STEC calculation method and degraded by mapping to VTEC. These products can not meet the requirement of small scale ionospheric disturbances monitoring and fast ambiguity resolution of PPP-RTK. With the development of ambiguity-fixed PPP, un-differenced and un-combined PPP can be used to estimate high precision STEC. In this contribution, we firstly introduced STEC calculation method based on ambiguity-fixed PPP solution. Secondly, we used zero/short baseline method to evaluate the accuracy of STEC from different methods. Thirdly, we generated the high precision STEC product from IGS network stations. Finally, we demonstrated its applications including ionosphere modeling, ionospheric disturbance monitoring, and PPP-RTK initialization as well. In this investigation, we found that PPP ambiguity fixing is a state-of-the-art method to compute precise STECs from IGS network. The accuracy of STEC can be improve from 8-10 TECU to 0.5 TECU by using ambiguity-fixed PPP instead of the CCL method. The single frequency PPP experiment demonstrates that the STEC derived from ambiguity-fixed PPP solution is the best in terms of convergence speed, accuracy. Our STEC products including information of epoch, PRN, ionospheric pierce point (IPP) position, elevation, azimuth, and STEC values were routinely generated at Wuhan University for public users，which are very convenient to use for monitoring ionospheric disturbances and can also reduce PPP-RTK initialization time significantly.
