Derivation Of GPS-TEC And Instrumental Biases In The Equatorial Anomaly Region

The research on the ionosphere in the equatorial anomaly region plays an important role in studying the global characteristics of ionosphere. At present, Ionospheric Total Electron Content (TEC) derived from GPS observation is an important parameter to study the ionosphere. This thesis first introduces the basic principle of deriving TEC from GPS observational data, and shows that the main sources of error during the deriving process are the satellite and receiver biases, which are often referred to as instrumental biases. Based on the least-square technique, the thesis presents a method of deriving GPS-TEC and instrumental biases in the equatorial anomaly region. The data used in the paper is from a GPS observational chain in the equatorial anomaly region including four dual frequency GPS receivers located at Fuzhou, Xiamen, Guangzhou and Nanning respectively, which are set by Center for Space Science and Applied Research, Chinese Academy of Sciences. Applying the method to the data from the GPS chain in 2006, the TEC with 15 min resolution is obtained for 48 meshes with size of 3°×1°in longitude and latitude covering an area of (20～28°N,105～123°E). The biases of the GPS satellites and the four GPS receivers are derived as well. The derived TEC and the instrumental biases during the geomagnetic quiet days, a geomagnetic storm and the whole year of 2006 are analyzed respectively. The derived satellite biases are compared to those published by Center for Orbit Determination in Europe (CODE). The result shows that the derived satellite biases in 2006 are close to those of CODE relatively. The mean of the differences is 0.24ns and the standard deviation of the differences is 1.17ns. The receiver biases are stable in the whole year and the mean of the standard deviation is 0.83ns. By analyzing the derived TEC in 2006, the thesis also investigates the morphological characteristics of the ionosphere in the equatorial anomaly region. The day-to-day and daily variations of TEC are remarkable. Seasonal variations also manifested in TEC. The maximum values of TEC in spring and autumn are larger than those in winter and summer; and the maximum value of TEC in spring is the largest. There is a trend that the maximum value in winter is larger than that in summer, but this character seems to weaken with the increasing of the latitude. Moreover, the maximum value of TEC appears at 14:00 local time in winter while it appears at 16:00 local time in summer.