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Aerosol optical depth (AOD) is a basic parameter of total aerosol content, which plays an important role in the study of atmospheric air quality. In order to explore the impact of different types of AOD on air quality, this paper proposes two adaptive AOD prediction methods based on GNSS PWV. The proposed method considers the temporal autocorrelation of AOD between adjacent epochs, and the model coefficients can be updated adaptively. One method is to model the 550 nm AOD directly based on GNSS PWV, which is called TAF (total AOD forecast) model. Another AOD modeling method takes into account the sensitivity of five different types of AOD to PWV, referred to it simply as FTAF(five type based AOD forecast) model. The model first establishes the functional relationship between PWV and five types of AOD. Secondly, according to the relationship between 550 nm AOD and five types of AOD, the weight of different types of AOD in 550 nm AOD was determined. Finally, PWV is used to predict five types of AOD, and the final 550 nm AOD is obtained by weighted average. 16 GNSS stations in Beijing, Tianjin, Hebei region are selected to verify the accuracy of the proposed model. The results show that the two 550 nm AOD prediction models have high accuracy, and the FTAF model is better than the TAF model. The AOD prediction model proposed in this paper can effectively apply the tropospheric parameters retrieved from GNSS to remote sensing monitoring of atmospheric environment, which provides a new idea for the study of atmospheric environmental quality.

GNSS three-dimensional water vapor tomography technology is used to obtain all-weather atmospheric water vapor distribution information with high spatial and temporal resolution. At present, the observation data of the tomographic model considering only the top signal have low utilization rate and large grid space rate, and the vertical constraint equation adopted is less consistent with the actual water vapor distribution. This paper based on the function fitted with sounding information to establish a vertical constraints, designs and implements a tomographic method considering boundary signals, uses the observation data of Hong Kong CORS network and radio sounding products. The improvement of the results of water vapor tomography by introducing boundary signals and for vertical constraint equation are analyzed in detail. The results show that the addition of boundary signals increases the observation equation by 51.9%, decreases the grid space rate significantly, and reduces the root-mean-square error of the solution results by 12.1%. Compared with the traditional constraint equation based on the exponential decline characteristic in the vertical direction, the root-mean-square error of the vertical constraint solution adopted in this paper is reduced by 5.7%.

The ionospheric scintillation, as one of the astronomical disasters occurring frequently in Arctic regions, poses great challenges to GNSS positioning navigation and timing (PNT) services. This calls for an urgent need in studying and effectively monitoring the scintillation to overcome its adverse impact. With the capability of high frequency sampling, ionospheric scintillation monitoring receivers (ISMR) are usually required to monitor the ionospheric scintillation, but the distribution of ISMR restricts the comprehensive monitoring in larger areas (such as the Arctic region). Therefore, based on GNSS observations with 1 Hz sampling, this paper studies the relevant empirical parameters and methods of extracting the ionospheric scintillation signal from the carrier phase observations by using geodetic detrending, precise point positioning and wavelet transform techniques, to construct a new phase scintillation index, which can be used to monitor the ionospheric scintillation. Its effectiveness and accuracy are verified by 188-day observations from 11 stations provided by the Canadian High Arctic Ionospheric Network (CHAIN). The results show that, compared with the commonly used ROTI index, both the scintillation index proposed in this paper and ROTI can effectively detect the occurrence of ionospheric scintillation, but the scintillation index proposed in this paper has a better correlation with the phase scintillation index given by ISMR, especially during periods with strong ionospheric scintillation, indicating that the proposed scintillation index has better ionospheric scintillation monitoring capability.

With the increasing number of high orbit spacecraft, the use of high orbit GNSS technology to a certain extent avoids the limitations of traditional ground-based measurement and orbit determination, reduces the operation burden and maintenance cost of ground-based measurement and communication, and improves the autonomous navigation ability and orbit measurement accuracy of the satellite platform. Therefore, GNSS technology has significant research significance and application value for high earth orbit spacecraft. In this paper, the technology development of GNSS used in high orbit spacecraft is reviewed. Compared with low orbit spacecraft, the characteristics of GNSS in high orbit space are analyzed. From the three aspects of high orbit GNSS availability, on orbit technology verification and high sensitive receiver technology, the characteristics and development of high orbit GNSS autonomous navigation technology are summarized. The new tasks of high orbit post precise orbit determination and formation satellite relative navigation are analyzed. From the perspective of the future development of high orbit spacecraft, the future research prospect of high orbit GNSS technology is given.