中文摘要：

从GPS掩星探测数据中反演的参数可同化入数值天气预报模式.附加相位的计算精度受参考链电离层噪音及L2噪音影响,在L2信号加密情况下噪音影响更为显著.为提高附加相位处理精度,减少一般单差法从参考链传入掩星链的噪音,本文采用改进的单差法（updated single difference,USD）计算大气附加相位.参考链数据采用组合频率LC观测数据,并以一定时间窗口（2s）做平滑处理,逐项考虑天线相位中心改正、相对论效应改正等因素的影响.利用COSMIC掩星观测数据对上述方法进行了验证,上升及下降典型掩星事件分析表明：USD计算的附加相位与COSMIC官方发布的附加相位有很好的一致性;计算了全球分布的440次掩星事件附加相位,结果表明USD法可明显改进附加相位平均偏差与标准差的分布,证明了我们算法的可靠性.USD法可应用于风云三号气象卫星掩星仪器半无码跟踪L2得到的数据处理中.

英文摘要：

The parameters retrieved from GPS occultation data can be assimilated into numerical weather prediction model.The accuracy of excess phase is affected by the noise from ionosphere and L2 frequency,especially,when L2 signal is encrypted.In order to improve the accuracy of excess phase and remove the noise by the single difference method from reference link into occulted link,we use the updated single difference（USD） method to compute atmospheric excess phase.The combined frequency LC data from the reference link are used and smoothed in an interval time window of 2 s.The antenna phase center correction and relativity correction are estimated.The USD method is validated by utilizing COSMIC data.The case analyses of representative rising and setting occultation events indicate that the excess phases from USD and COSMIC are in good agreement.The excess phase of globally distributed 440 occultation events is also computed.The results show that USD method can obviously improve the distribution of mean bias and standard deviation of bias,which demonstrates the reliability of our USD algorithm.The USD method can be applied to the data processing for FY-3 GNOS（GNss Occultation Sounder） occultation mission which uses semi-codeless technique to track L2 signal.