Total Ionospheric Electron Content Calibration Using SERIES GPS Satellite Data

This article describes the current status of the Deep Space Network advanced systems research into ionospheric calibration techniques, based on Global Positioning System (GPS) data. A GPS-based calibration system is planned to replace the currently used Faraday rotation method by 1989. The SERIES receiver system used in this research determines the differential group delay of signals transmitted at two different carrier frequencies. This differential delay includes an ionospheric component and a GPS transmitter offset. The transmitter offsets are different for each GPS satellite. Tests have been conducted to assess the effect of the offsets on the ionospheric calibration accuracy. From the obtained data, the total electron content and GPS transmitter offsets are calculated by a least-squares estimation method employing a local model of total ionospheric electron content. The end product is an estimation of the total ionospheric content for an arbitrary line-of-sight direction. For the presented polynomial fitting technique, the systematic error due to mismodeling is estimated to be _6 X 1016 el/m 2, while the formal error is _2 X 1016 el/m 2. The final goal is an error of 3 X 1016 el/m 2 (_0. 7 ns at 2.3 GHz ).