中文摘要：

对于GPS单频用户而言，电离层延迟是最重要的误差来源之一。GPS系统使用Klobuchar模型对电离层延迟进行改正，其改正数从370组常数中选取。目前全球分布的GPS测站可以获得高精度的全球电离层监测结果，GPS为什么不发播采用实测数据计算得到的Klobuchar模型参数呢？本文针对这一问题进行分析。首先，对欧洲定轨中心CODE提供的全球电离层图GIM预报COPG电离层进行精度评估，然后根据COPG电离层进行Klobuchar模型参数拟合，并利用IGS提供的事后高精度电离层图进行精度分析，最后将不同的电离层模型参数应用于单点定位以评估其对单频用户的影响。分析结果表明，采用全球实测数据计算的电离层模型参数与导航电文中发播的电离层模型参数精度相当，为55％左右。而仅采用地磁纬度45°S以北的数据拟合得到的模型参数，其电离层改正精度有明显提升，可达65％左右，但其对单频用户定位精度改善不明显。

英文摘要：

To GPS single‐frequency users ,the ionospheric delay is one of the most important sources of errors .GPS uses Klobuchar model ,whose corrections come from 370 groups of constants derived from empirical models and historical data ,to correct the ionospheric delay currently stations distributed all over the world can provide ionosphere monitoring results with high precision , why GPS doesn’ t broadcast Klobuchar model parameters calculated with observed data？This article focuses on this question .Firstly , the precision of predicted global ionosphere maps ,COPG ,provided by center for orbit determination in Europe （CODE） is estimated .Secondly ,the Klobuchar model parameters are fitted with COPG .Then the parameters’ precision is assessed with global ionosphere maps provided by IGS .Finally single point positioning is done using different Klobuchar parameters to evaluate their influences on GPS single‐frequency users .Results show that restricted by Klobuchar model with 8 parameters , precision of parameters fitted using global observed data is just equal with GPS broadcast parameters ,both around 55% .On the other hand ,precision of model parameters fitted using data on the north of geomagnetic latitude 45°S is much higher ,which arrives about 65% ,but it performs no better in positioning of single‐frequency users .