中文摘要：

在基于GPS数据提取电离层总电子含量（TEC）的过程中，电离层薄壳高度的选择对解算电离层垂直TEC的精度有很大的影响．但由于不可能获得一个真实的从电离层D层到GPS卫星高度的电子密度剖面，关于电离层薄壳高度的选择一直是基于GPS数据解算电离层TEC方法中关注的一个问题．本文利用等离子体GCPM模型，对太阳活动高年（2002）和太阳活动低年（2008）情况下电离层有效薄壳高度的选择进行了仿真计算．结果表明，最佳的薄壳高度在2002年为560km，而在2008年为695km．通过对全球八个具有代表性地点的仿真计算，揭示了有效薄壳高度更复杂的变化特点．在白天，最佳薄壳的高度变化不大（500km至750km）；但在夜晚，最佳薄壳高度变化范围很大，甚至可以超过2000km．此外，本文还对不同卫星仰角的情况下斜向TEC转换为垂直TEC的误差进行了分析，结果表明：随着卫星仰角的增加，薄壳模型带来的转换误差基本上是单调减少的．因而，在实际应用中，尽可能地采用大仰角的卫星数据有助于提高解算的电离层垂直TEC的精度．最后，对全球不同地点的电离层TEC的仿真研究表明，在电子密度水平梯度较大的地区，应用电离层薄壳模型时会导致电子密度较高处的TEC被高估，而电子密度较低处的TEC被低估，在分析基于GPS数据提取的电离层TEC空间变化时要认识到这一点．

英文摘要：

In the process to derive total electron content （TEC） from GPS observations, ionospheric shell height is one key parameter in the conversion from slant TEC to vertical TEC. Because it is impossible to obtain the real distribution of electron content from D region to the height of GPS orbit, the selection of effective shell height is always an open issue in the TEC derivation method based on GPS data. In this paper, the Global Core Plasma Model （GCPM） is adopted to simulate the ionospheric effective shell height in solar maximum （2002） and solar minimum （2008）. Based on the results of the simulated shell heights at eight representative points selected according to the spatial distribution of global TEC map, the variation of theeffective shell height is studied. During the day-time, the effective shell height is relatively stable （about 500~750 km）, while at night it can change from several hundreds to about two thousands km. In addition, the relative errors in converting the vertical TEC from slant TEC at different elevation angles are analyzed. The result shows that the error decreases when the elevation angle increases. Also, in the regions of the larger spatial gradient of TEC, the shell model can overestimate the TEC where the electron density is high, and underestimate the TEC where the density is low. This problem should be noticed when GPS-derived TEC is used to analyze the variability of ionosphere. Finally, based on the simulated results of effective shell height at different locations of Earth, the most optimized shell height is investigated statistically; the most optimized shell height is 560 km in 2002 and 695 km in 2008 on the global average.