Chapter 23 The Establishment and Precision Analysis of Global Ionospheric Model of COMPASS System

摘要

Ionospheric delay is one of the main error sources affecting the positioning and timing precision of satellite navigation system for single frequency users. China's regional satellite navigation system uses ionospheric puncture point data of monitoring stations to fit the 8 parameters of klobuchar model in geographic coordinate system,and broadcasts them to users through the navigation message which is valid for 2 h. Long-term monitoring shows that this model can correct the ionospheric delay up to 74 % in service area around China. Due to the lack of ionospheric measured data in the southern hemisphere and high latitudes of the northern hemisphere, this model can not guarantee the correction accuracy in equatorial belt and high latitudes. This paper improves the klobuchar model expressed in the form of 9 parameters. Not only this model can keep the ionospheric double-peak characteristic but also ensure global fitting precision. In order to obtain real-time ionospheric data outside regional monitoring network, this paper examines the precision of forecasting model based on ionosphere spherical harmonic coefficient. According to the results of compari-son,the model in this paper can correct the ionospheric delay for the next 24 h up to 72 % in China. Globally, the correction accuracy reaches 70 % in the north hemisphere, while 69 % in the south hemisphere. As a result, the correction precision of the model is better than the model broadcasted by GPS.