利用GPS观测和精密星历，采用多项式或球谐函数模型的方法进行建模，能够同时估计接收和卫星DCB，在此基础山计算电离层TEC,为导航单位提供电离层延迟改正-Using GPS observation and precise ephemeris, or methods using spherical harmonic polynomial function model to model, simultaneously estimates the reception and satellite DCB

Estimate tec (total electron content) by least-sqaure adjustment using GPS dual-frequency code observables. Ionosphere is approximated as the single- layer model at the height of 350km with local or global tec model. Satellite/receiver dcbs (diffe