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In the past few years, precise point positioning (PPP) has become an important positioning method for many practical applications. It is based on ionosphere-free carrier phase combination measurements, in which only first-order ionospheric error is removed. Past research has shown that high-order ionospheric effect can affect PPP performance. In this study, the effect of high-order ionospheric error, the second-order one, on PPP has been evaluated in Hong Kong, a low latitude area. First, a method regarding how to calculate second-order ionospheric error is introduced and the evaluation method is also discussed. After that, the numerical results are shown. Based on the results, it is found that the effect of the second-order ionospheric error on ionosphere-free carrier phase combination measurements reached up to the cm level in 2001 and the effect of the second-order ionospheric error on both kinematic and static PPP also reached the cm level. Further, it is also demonstrated that the effect of second-order ionospheric error on PPP is closely related to solar activity. [ABSTRACT FROM AUTHOR]

Abstract: This research is aiming for cycle slip detection and correction in case of ionospheric scintillation. Different from the normally discussed situation without ionospheric scintillation, ionospheric delay cannot be neglected due to abrupt ionosphere change. In this case, ionosphere-free testing quantities for cycle slip detection and correction have to be used. In the past research, several geometry-free and ionosphere-free testing quantities have been proposed and in every of them, code measurements are involved. So these geometry-free and ionosphere-free testing quantities are sensitive to code observation noise and multipath. In this research, non-geometry-free and ionosphere-free testing quantities are proposed. Different from previously proposed, the code measurements are not longer involved. Detailed discussion on cycle slip detection and correction in case of ionospheric scintillation are given and method using the new proposed non-geometry-free testing quantities in combination with one previously proposed geometry-free & ionosphere-free wide-lane testing quantity is described. The cycle slip detection and correction performance may not be very reliable with the new proposed method. But it is expected that this research will benefit for future work in this aspect. [Copyright &y& Elsevier]

New GNSS systems (i.e. GPS modernization, BeiDou, and Galileo) will provide multiple navigation signals for reliable navigation services. The triple or even multiple frequency signals are expected to bring great benefits to the ambiguity resolution (AR) over long-range baselines, which is always regarded as a huge challenge. Another issue in the long baseline AR is the unmodeled ionospheric delay, which is one of the major errors in ranging signals. A new triple-frequency, ionosphere-free technique for ambiguity resolution of long-range baseline is developed in this study. In this technique, the optimal observation combinations are chosen considering the effect of ionospheric delay. At the same time, using this technique, the double difference (DD) ionospheric delay is nullified in the ambiguity search process. The performance of the new technique is examined using the simulated GPS triple frequency data as well as the real BDS observation. Results show that the ambiguity can be fixed within 10 min for GPS and BDS long-range baselines with this new technique. [ABSTRACT FROM AUTHOR]

Abstract: Plasma bubble is one of the important weather events of the ionosphere. In past research, many studies on its occurrence characteristics have been done based on various observations, such as ionosondes, topside sounders, radio scintillations and in situ measurements by satellites. In recent years, GPS has become an important tool for the studies in this aspect. In this research, a study is made on occurrence characteristics of plasma bubbles with the GPS observations collected by the Hong Kong local GPS network for about 12years. [Copyright &y& Elsevier]

Abstract: The ionosphere is an important part of the atmosphere and it is the largest error source of GNSS positioning for single-frequency users. So establishing a precise ionosphere model is one of the critical steps for satellite navigation and also for ionospheric research. Our targeted area of our research is a low latitude area – Hong Kong. Though some ionospheric models have been established in the past research, they are not fit for the Hong Kong area for various reasons. In this research, we are trying to establish a 2-dimensional model fit for the Hong Kong area based on the local GPS network and the model should be able to be used to predict VTEC for GPS navigation. [Copyright &y& Elsevier]