Monitoring and modelling Hong Kong ionosphere using regional GPS networks

Abstract

The ionosphere is the region from 90km to 2000km altitude, where the solar radiation produces partially ionized plasma of different gas components. Knowledge of ionospheric electronic density and its variation is essential for a wide range of applications, such as radio and telecommunications, satellite tracking, earth observation from space, and satellite navigation. This research aims at monitoring detailed low latitude structures of the ionosphere using Hong Kong GPS network. In this study, we have researched on the distribution characteristics of ionospheric TEC and disturbances. It is shown that in Hong Kong, there is a two-dimensional peak along local solar time and latitude for the TEC distribution due to the solar radiation and equatorial ionospheric anomaly. The peak values appear around latitude 22o north and local solar time 2pm. On both sides of the peak, there exist large TEC slopes. Therefore, even with short baselines (i.e. <10km), ionospheric delays cannot be eliminated by double difference technique. Ionospheric disturbances happen frequently in Hong Kong, with the severe ones mainly concentrating at latitude 22o north and local solar time 10pm. Both ionospheric TEC values and disturbances reach their seasonal maximum around the equinoxes. A new ionospheric model is proposed for precise ionospheric TEC modeling for low latitude regions. The numerical results demonstrate that the new model is better than traditional ionospheric models and is able to support GPS precise positioning in Hong Kong. Ionospheric disturbances have strong effects on GPS receiver performances. During periods of ionospheric disturbances, GPS measurement noise level (both pseudorange and carrier phase) increases dramatically and the receivers frequently loss satellite signal lock, which have significant impacts on GPS applications in low latitudes.