Improving ionospheric corrections in the Asia Pacific Region

One of the goals of SBAS (Space Based Augmentation System) is to correct the ionospheric delay which contributes the largest and most unpredictable error to GPS users' range measurements. SBAS works well under the quite ionosphere and the moderate ionospheric storm. However, SBAS is susceptible to local ionospheric disturbances and severe ionospheric storms. This will be more challenging task for an SBAS in Asia Pacific region to provide a good ionosphere model, because most of the Asia Pacific Region is in the low latitude region in comparison with the U.S., and the ionospheric scintillations and the severe ionospheric storms happen more often in the low altitude regions. Therefore, this paper will investigate and evaluate the SBAS ionosphere model developed in the U.S. for this region. To that end, this paper uses the Southeast Asia GPS Networks in Scripps Orbit and Permanent Array Center (SOPAC) database. This paper first selects few stations from SOPAC to act as the SBAS reference stations to collect dual-frequency GPS measurements, and then these measurements will be used to generate the ionospheric measurements in the Southeast Asia. These ionospheric measurements include the GPS satellite hardware group delays (TGD) and the GPS receiver Inter-Frequency Bias (IFB). Thus, this paper uses a software calibration method to calibrate the hardware group delays to generate the clean ionospheric delay measurements. This paper then use these clean ionospheric delay measurements to develop the standard SBAS thin-shell ionospheric delay model. The developed SBAS ionospheric model will be evaluated by the dual-frequency GPS measurements collected in the same region. This paper will also change some of the parameters used in the SBAS ionospheric model to gain possible improvement in the availability of SBAS in Asia Pacific region.