Research On The Theory And Methods Of Dynamic Maintenance Of National Geodetic Reference Frame

The development of national geodetic coordinate system is closely related to that of science and technology. The earliest national geodetic coordinate systems were established on the surface of reference ellipsoid, which belongs to the 2D coordinate system. With the progress of modern space technology, especially, with the rapid establishment and hypergrowth of GNSS (Global Navigation Satellite System), the 2D coordinate systems had been unable to meet the needs of national economic development; it is urgent need to establish geocentric coordinate system which can be compatible with GNSS. Therefore, geocentric coordinate systems, as new generation of national geodetic coordinate systems have been established and used by more and more countries, with updating of the national geodetic coordinate system, national geodetic reference frame, as the implementation of national geodetic coordinate system with which GNSS technology as the observation means, need to maintain high accuracy all the time.As a national geodetic coordinate system, the origin of geocentric coordinate system is located in the center of the whole earth mass which including the oceans and atmosphere, and it is the most suitable coordinate system for description the motion of the earth. A complete national geodetic coordinate system includes not only the definition of coordinate system, the construction of reference frame, continuous refinement and maintenance of the coordinate system is also essential for guaranteeing the precision of coordinates. As the implementation of national geodetic coordinate system, the accuracy and stability of the national geodetic reference frame determines directly represents that of the national geodetic coordinate system. Therefore, according to the basic theory and methods to refine and maintain the national geodetic reference frame would to be researched in this thesis. The main research and contributions are listed in the following:1) the current situation of the development of domestic and foreign reference frames were summarized, the latest advances of ITRF2008, WGS84, IGS08, NAD83 and other reference frame of global and regional (state) were introduced. Meanwhile, as a comparison, our national geodetic coordinate system and its reference frame were analyzed, the basic composition of the national reference frame was summarized from the above information. And then the basic theory and method of national geodetic reference frame refinement and maintenance was given.2) The precise data partition processing method for large GNSS network. Accurate coordinates is the basic element of national geodetic reference frame. The national geodetic reference frame which observations based on GNSS mostly belong to large-scale GNSS network, therefore, in the process of the national geodetic reference frame refinement and maintenance, for such a large-scale GNSS network, processing method and partition strategy adopted in data processing are all the important factors affected the accuracy of the reference frame. Therefore, precision data processing method by choosing suitable reference frame sites and applicable data processing strategy was researched, with the principle for choosing sites and partition method proposed in the thesis, adjustment of CGCS2000 reference frame network was done,and high precision coordinate and velocity field were derived.3) Method for constructing regional plate motion model. Plate motion model is an important part of national geodetic reference frame. With the plate model, the coordinate of a reference frame point in the current epoch can be deducted to the one in its reference epoch. Considering the characteristics of large numbers, large range and the motion is not consistent of national crustal plates, taking our national plates as an example, regional plate modeling methods were analyzed and studied, our national plates were divided into seven first-level ones and twenty second-level ones, plate, first-level and second-level plate motion model which named CPM-CGCS2000 were established using Euler vector, and the plate motion model were evaluated and validated using the CGCS2000, by reduction the frame coordinate in current epoch to results in CGCS2000 were verified, and that CPM-CGCS200 plate model was the most suitable plate model matching CGCS2000 was proved.4) Grid velocity field modeling. The grid velocity field model is one of essential components of national geodetic reference frame. For the distribution density of the national Continuous Operation Reference Stations (CORS) which as main framework of CGCS2000 is not enough to reflect the dynamic characteristics of our national coordinate framework fully, model establishment of Chinese mainland grid velocity field were studied in this thesis, using ten years data of National Geodetic GPS Control Network 2000 from 1999 to 2009, the model of Chinese mainland grid velocity velocity field was established with inverse distance weighted interpolation method, Euler vector method, finite element method and the least squares collocation. The coordinate and velocity of an arbitrary frame point can be derived with the interpolation of grid velocity. Such dynamic maintenance of the reference frame can be implemented.5) Because the precision and the stability of CGCS2000 frame are affected not only by linear motion triggered by geophysical effect, at the same time, the influence of those nonlinear motions also can’t be ignored. In this paper, the analysis of nonlinear motion of CGCS2000 frame stations was studied by adapting singular spectrum a nonlinear modeling method of CGCS2000 reference frame, which can improve the accuracy of CGCS2000 reference frame, was studied and modeled; based on such nonlinear model, the beneficial conclusions were drawn:the maintenance accuracy of the reference frame can be improved, also, the model can provide prediction of the motion of reference frame.6) Summary and outlook. At the end of the thesis, the suggestion for updating national geodetic reference frame was proposed by researching the theory and method of maintaining the national geodetic reference frame.