ESTIMATION OF THE TRANSMITTER AND RECEIVER DIFFERENTIAL BIASES AND THE IONOSPHERIC TOTAL ELECTRON-CONTENT FROM GLOBAL POSITIONING SYSTEM OBSERVATIONS

In the estimation of the ionospheric total electron content from the G lobal Positioning System (GPS) observables, various instrumental syste matic effects such as the biases in the GPS satellites and receivers m ust be modeled. This paper describes a procedure, based on a Kalman fi ltering approach, for estimating these instrumental biases as well as the total electron content at each GPS station, using dual GPS data. T he method is applied to six data sets, of 48 hours each, spanning one year, from the Deep Space Network with GPS stations in Australia, Spai n, and the United States. The formal errors for the estimated satellit e biases and for the total electron content at each station are about 0.07 ns and 0.2 x 10(16) el/m2, respectively. The variation in time of the satellite biases (relative to the mean of all of them) estimated in different epochs during 1-year period, is below 1 ns.