中文说明：
使用GPS双频码观测值，通过最小二乘平差估计tec（总电子含量）。电离层在350km高度近似为单层模式，采用局部或全局tec模式。估计卫星/接收机DCB（差分码偏差）以及tec模型系数。
English Description：
Tec (total electron content) is estimated by least square adjustment using GPS dual frequency code observations. The ionosphere is approximately a single-layer model at a height of 350 km, using local or global Tec models. Estimate the satellite / receiver DCB (differential code deviation) and Tec model coefficients