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Targeting and monitoring island reefs have important strategic significance in safeguarding our national interests. But high-precision positioning of island reefs with satellite imagery often lack controls and fails to achieve its target; thus, the important research value of realizing island reefs targeting under scarce control conditions. In the paper, a Mapping Satellite-1(TH-1) image was taken as the research object. A strict imaging model was established for TH-1 satellite images and TH-1 satellite image island reef positioning was proposed and implemented without controls, based on orbit extrapolation and scarce control of TH-1 island reef satellite image positioning based on orbit extrapolation. An Experimental, analysis tested the feasibility of improving TH-1 geometric positioning of island reefs by orbit extrapolation techniques without controls and with scarce controls. The results demonstrated that the methods without control positioning technology based on orbit extrapolation and scarce control positioning based on orbit extrapolation were the best ways for targeting positioning of island reefs. These approaches can greatly improve positioning accuracy for key sea targets with no controls or under scarce conditions. [ABSTRACT FROM AUTHOR]

In this paper, the traditional objective function, the quadratic of difference of float ambiguity and integer ambiguity, is replaced by a modified function called sum of Li and L2 pure carrier phase residua squares when searching for a correct integer ambiguity. The integer ambiguities search space is obtained by a floating transformation and building observation model with DD (double difference) C/A code range and wide lane carrier phase. The calculation results from 18-hour static GPS data indicate that the modified is better than the traditional objective function for reliability and usability with a higher success rate [ABSTRACT FROM AUTHOR]

Based on 138 evenly distributed IGS coordinate time series spanning more than 10 years, site-to-site coefficents in large scale GPS network were analyzed. Their site-to-site coefficients indicate significant corelationship even when the between-site distance more than 5 000 km. Therefore, this paper proposes a new method introducing coefficients as weight factor to calculate common mode error, and it improved the correlation-based spatial filtering technique. Time series from global and regional networks were used to verify this new method. The results show that this improved coefficient-based spatial filtering technique overcomes the spatial scale limit and effectively extracts common mode error of GPS coordinates time series. [ABSTRACT FROM AUTHOR]

A new GNSS time synchronization system is designed and presented in this paper, the new system place hydrogen maser on the GEO satellite, establishing a high-precision inter-satellite link between the GEO satellites to maintain a high-precision time. The proposed two scenarios were simulated and compared, simulation results show that the proposed new system is feasible and can significantly enhance the accuracy of time synchronization, especially the accuracy of independent time synchronization. And the relationship of time synchronization accuracy with the clock and ISLs is analyzed. The simulation results show that the accuracy of ISLs is more important. [ABSTRACT FROM AUTHOR]

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