| Continuous operational reference system (CORS) is the most important part of spatial data infrastructure. As the basic facilities of a new generation of services based on location and time, CORS can not only monitor both transient long-term, regional and even global, crustal movement and climate changes, but also provide a variety of high precision positioning services and diversified information services according user requirements. At present, CORS also plays an important role in establishing and maintaining regional and global coordinate reference frame. The well-known International Earth Rotation Service as well as many other countries and regions use CORS as an effective method to establish regional and global coordinate reference frame.This paper systematically elaborated the geodetic standard and criterion of the CORS network establishment based on GPS reference stations in regional areas. The paper deeply investigated GPS data processing strategies and the impact of the ionospheric delay and mass loading include non-tidal ocean loading and atmospheric loading and analyzed the impact of these corrections on GPS coordinate time series. Using CORS, the paper successfully established reliable GPS coordinates time series and velocities time series on the ITRF08by the results of a comprehensive study and achieve the goal of establishing and maintaining regional coordinate reference frame. Based on the above, utilizing the results of leveling survey, we quantitatively analyzed the motion of Wuhan regional plate and brought up the method of unclassified7-parameter transformation and the idea of a seamless real-time coordinate transformation. The main results of the paper are as follows:1) The paper systematically illustrated the theory and methods of establishing and maintaining the International Terrestrial Reference frame and elaborated the basic characteristics, principles of the establishment, technologies adopted and methods of maintenance for a regional coordinate reference frame.2) Then paper deeply investigated the standards and the establishment of the regional coordinate reference frame. Based on the standards, implementation methods and principles of regional datum, the paper systematically discuss the constrains and principles of station selection when using GNSS techniques to establish and maintain the terrestrial reference frame and further evaluate the current status and future development of using CORS to establish and maintain the regional reference frame.3) The paper developed methods of establishing and maintaining regional reference frame using CORS and brought up a method of establishing an independent regional coordinate system based on CGCS2000. The paper also brought up an automatic real-time coordinate transformation method and the "spurious"7-parameter coordinate transformation method, which achieve the goal of unifying the datum of CORS systems.4) The paper analyzed the magnitude of the impacts of different tropospheric projection functions on regional datum and the characteristics of their spatial distributions, and calculated respectively the RMS of regional displacement time series in ITRF08using three models, which are VMF1, GPT2and GMF, and compared the results. By adopting tropospheric projection function VMF1, RMS of n component of the station coordinate time series is the smallest, with an average of2.65mm, and the RMS of E component is smaller than that of U component, with averages respectively of3.81mm and8.76mm.5) By processing the data of WHCORS and CMONOC, the paper quantitatively analyzed the impact of environmental mass loading on the coordinate time series of regional CORS reference stations. The results indicate that the RMS of environmental mass loading time series reflect significant regional characteristics which show consistency and have large magnitude in Northeast, North and Central part of China, relatively larger than the other areas of China. The RMS variation of N and E components are not significant which are all less than lmm. The environmental mass loading correction can improve the coordinate time series of most stations but the magnitude varies in different components. The percentages of stations whose diffrms values improve significant in E and U component stay roughly equivalent, which remain70%, but it is not significant in N component. The maximum diff_rms of U component can reach1.5mm which indicates that the environmental mass loading correction should be taken into serious consideration in GNSS precise positioning and the establishment of regional reference frame.6) The paper quantitatively analyzed the impact of S1-S2atmospheric tide and higher order ionospheric delay on the average annual amplitudes, phases and velocity of the selected stations. The spatial distribution characteristics of S1-S2atmospheric tide are also studied in the paper. The results illustrate that most of the increase of the annual amplitudes remain in0.1mm when applied in S1-S2atmospheric tide correction. The velocity of the reference stations affected by the S1-S2atmospheric tide decreases in general after the correction and the S1-S2atmospheric tide correction in coastal regions works better than in the plateau areas and the mainland. Meanwhile, higher-order ionospheric delay has certain impacts on the linear velocity of regional stations, with E,U components both affected by over50%and N component no more than50%, as a result, in high precision data processing, its impact should be taken into consideration. Velocity of all stations are less than0.1mm/a, but higher-order ionospheric delay will cause variation of WRMS for station in China, especially those of N, E components.7) The paper established Wuhan regional coordinate reference frame’using methods mentioned in the paper and achieve parameters transformations of several existing coordinate systems in Wuhan. Based on time series of stations provided by WHCORS, the paper discussed the maintenance of the regional coordinate reference frame and brought up a method of maintain Wuhan regional coordinate reference frame.8) Combining the results of precise leveling and data of WHCORS, the paper reasonably explained the characteristic of the crustal movement in Wuhan and its variations, and set up the velocity field of Wuhan regional accurately.The results indicate that with the junction of the Han River and the Yangtze River as the boundary, the area near the north side of Yangtze River mainly shows subsidence trends, and other areas near the Yangtze River mainly have the uplifting trends with a uplifting trend for most of the rest of areas accompanied by subsidence trends for a few areas. However, WHKC station in Hankou mainly shows a subsidence trend. The rate of planar motion (in the mainland of China) is roughly2.58-4.88mm/a in Wuhan. Meanwhile, there are two rotation areas in Wuhan, which are respectively clockwise rotation in the west, from west to east to southeast, and a counterclockwise rotation in the east, from northwest to south to southeast, both with the value from2.58to4.88mm/a. The active areas of crustal deformation mainly distributed in urban areas. With extensional movements mainly in the east of the main urban areas, and these areas are mostly in the south of Yangtze River, though with a exception in the north of Yangtze River, Tianxin Bay. The value of these extensions in main direction decreases in the counterclockwise direction. |
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