Gps Monitoring Of Ionospheric And Applied Research

Ionospheric delay is one of the key error sources for GPS navigating and positioningapplications. One method to correct the ionospheric delay is to use the broadcasted Klobucharionosphere model of GPS system. Usually, Klobuchar ionosphere model can only achieve 50%of the ionospheric effect because of the following two factors: using the fixed phase and a constantionosperic delay at night time (9ns, based on L1 frequency). In actual case, the daily ionospeficdelay of night and the phase vary with time and latitude. For regional GPS navigating andpositioning applications, it's necessary to modify the former Klobuchar ionosphere model so as toimprove the precision for single frequency users.On the other hand, it's a good way to correct ionospheric delay in GNSS by usingdual-frequency observations. However, the dual-frequency GPS receivers are much expensivethan the single-frequency GPS receivers. So, it's necessary to find out some useful way to usesingle-frequency observations to solve the problem about Ionospheric delay.Considering above reasons, the main work and content of this paper is read as following:1. To analyze the disadvantages of the former Klobuchar model of GPS and to develop animproved Klobuchar model. The phase of trigonometric function and the night delay areconsidered as variables with geographic latitude. In the model, we have increased the number ofthe original model parameters from 8 to 14. To accomplish the modeling algorithm, theparameters are firstly estimated to describe the diurnal variation of ionosphere (includingperiod, amplitude, initial phase, the average VTEC value in night) using the least RMS; then,the Least Square method is applied to calculate the final 14 parameters of Klobuchar model. Afteranalyzing, we have written out all codes for the new improved Klobuchar model using computerlanguages such as C, FORTRAN and C-shell. The codes are installed and run under LINUXsystem. The improved Klobuchar model will be used in Chinese regional GNSS system, whichis being developed step by step.2. In this paper, a method for estimating VTEC is proposed and carded out which takesadvantage of real-time pseudo random code and carrier phase observation data obtained by asingle-frequency GPS receiver. Preliminary results of VTEC and the VTEC-derivative will bepresented and compared with results from dual-frequency GPS observations estimates. Theproposed method in this paper may benefit the satellite-to-satellite occultation experiment in thejoint martian exploration (YH-1 and PG-1) between China and Russia.