Research On The Method Of Maintenance Of Regional Reference Frame Based On GNSS

The high-precision regional reference frame is the basis of the air-space-earth geodetic observation system and the national major infrastructure.The geodetic datum not only provides a unified reference datum for various sensor observations,but also provides a reference datum for earth geometry measurement,earth gravity field and earth dynamic change monitoring.Space geodetic technology is the main means of constructing and maintaining modern reference frame.Among them,Global Navigation Satellite System(GNSS)technology is especially suitable for dynamic monitoring and maintenance of regional reference frame due to its advantages of high precision,all-weather,and real-time performance.However,since the earth is a constantly changing elastic body,various nonlinear signals such as various tectonic signals,earth tidal signals,plate motion signals,local topographic change signals and seasonal change signals are implied in the high-precision GNSS time series information.Therefore,the use of GNSS to monitor and maintain the reference frame must carefully deduct the influence of various system noises,and also invert various types of earth surface and internal motion information,so as to obtain the point coordinate information that can actually characterize the earth reference frame.With that in mind,the paper systematically discusses the spatiotemporal characteristics and nonlinear effects of GNSS observations,and systematically studies the relevant theories and algorithms for the construction and maintenance of China regional reference frame based on the series of observations of Beidou Navigation Satellite System(BDS-3).The content of the experiment was analyzed and verified by taking the mountainous area in complex environment as a demonstration area.The main research work and achievements of the paper include the following aspects:(1)The foundational theory of data processing for establishing and maintaining a GNSS-based regional reference frame is systematically expounded.The paper systematically sorts out key issues such as the parameter estimation method for the establishment and maintenance of the terrestrial reference frame,the definition and implementation of datum,the internal constraint model,and the data processing method of the cumulative solution;The advantages of various spatial observation data fusion modes and methods are analyzed,and the deficiencies in the existing reference frame maintenance strategies and the latest reference frame maintenance strategies are discussed in depth.(2)The inversion scheme of relative motion,spatiotemporal law and nonlinear change law of regional reference frame points is proposed,which suppresses the influence of linear or nonlinear forcing of spatial relationship between frame points in the maintenance of regional reference frame.The covariance model of the random influence of the baseline component and the length direction of the station movement is presented,and the variation rule of the spatial relationship of the frame is objectively described from the random model.(3)A stable reference datum is the key to monitoring the deformation of the regional reference frame.Be aimed at the problem of instability of the reference stations the regional reference frame,which were caused by plate motion,geological structure and other factors,the reference point is unstable,as well as the shortcomings of the traditional global and regional datum methods to analyze the micro-deformation,a local regional reference frame micro-deformation analysis datum considering the coordinate changes characteristics and stability of the reference station is proposed.The experimental results show that the method proposed in this paper takes into account the nonlinear effect,especially the deformation in the vertical direction is more accurate,so as to realize the dynamic correction of the spatial relationship of the regional reference datum.(4)The performance of the regional reference frame based on BDS-3 are discussed in depth,and the optimal weight ratio strategy and maintenance effect between different systems of the regional reference frame established by GNSS are investigated,provide a technical approach for Muti-GNSS Fusion Positioning.The results indicates that BDS-3 is comparable to GPS in constructing a high-precision reference frame,the plane difference is less than±3mm,and the vertical difference is less than ±7mm;the PPP solution based on BDS can rapidly identify the variation of regional reference stations;the regional reference frame maintenance effect of multi-system integration with baseline length accuracy as the initial weight factor is better;the accuracy of BDS/GPS reference frame in N and E directions is increased by 15.04% and 12.65% respectively,especially in U direction,which is increased by 24.03%.(5)The influence of the random parameter constraint method and the minimum constraint method constructed by the similar variation method on the maintenance of the regional reference frame is analyzed,and a regional frame point coordinate calculation method with the minimum constraint of the stable IGS station coordinate correction is proposed,which effectively takes into account the influence of different datum constraint methods on the maintenance of the regional reference frame.The experimental results show that the prior coordinates in the N,E and U directions have deviations of about 2 cm for some stations in China;when the constraints imposed on the IGS stations are of appropriate magnitude,the positioning errors of the IGS stations are significantly reduced;the least constraint method can better weaken the influence of the positioning error of the IGS reference station,and the positioning error in the plane and elevation directions is not more than 1cm.(6)The selection scheme of the optimal minimum constraint frame point in China is proposed.Taking into account the complexity of geological structure and the non-linear and non-isotropic characteristics of plate motion in China,a regional reference frame maintenance strategy for the optimal minimum constraint frame point is proposed,which achieves a high-precision conversion to the ITRF reference frame.The results show that the accuracy of the ITRF reference frame conversion parameters calculated by the frame station with the selected characteristics of plate motion in China is better than that of the global IGS station.The accuracy of translation parameters of frame conversion is better than ±4mm,the accuracy of rotation angle of rotation parameters is better than ±0.0013 mas,and the accuracy of scale parameters is ±0.35ppb(1ppb ≈ 6.3mm).(7)A dynamic maintenance method of CGCS2000 based on the relative motion of plates in regional background field of China is proposed,which solves the local instability problem of regional reference frame maintenance.Using the 6-year observation data of the CMONOC and the optimal frame points to construct the internal constraints,the paper analyzes the transformation parameters time series characteristics and the frame maintenance precision accuracy under the CGCS2000 reference frame.The seven-parameter time series of the single week solution and the long-term solution are stable,the translation parameter in the X direction is less stable,the maximum deviation reaches 5.913 cm,and the translation parameters in the Y and Z directions are highly stable;the absolute value of the rotation parameter is stable at about 0.001″(The resulting error is less than 3 cm);the RMS of the scale parameter is less than 1.2 ppb,and the resulting error does not exceed 8 mm.(8)A rapid monitoring algorithm for GNSS network solution with additional ground point tropospheric delay information correction is proposed and implemented,which effectively suppresses the influence of non-stationary atmospheric changes and poor tropospheric model accuracy adaptability on the coordinate accuracy of frame points in mountainous areas with large altitude differences.The method effectively controls the impact of the inconsistency of the tropospheric delay at both ends of the short-term observation baseline,the external coincidence accuracy of the plane direction monitoring is millimeter level,and the external coincidence accuracy of the vertical direction monitoring is ±1.5cm;the method effectively shortens the observation time,expands the side length of the observation network,and significantly reduce the operation cost;when there are more than 3high-precision ground stations within 100 km around the monitoring point area and the observation time of the monitoring station reaches 1h,the rapid monitoring accuracy of plane millimeter level and elevation ±2cm can be achieved.(9)A GNSS-based regional reference frame maintenance software is developed and applied to the maintenance of mountain reference frames with complex geological structures.The software can reasonably take into account the internal spatial relationship of the region and the tectonic movement characteristics of the mountain block,and automatically select the optimal and minimum constraint frame points in the region to form the constraint conditions,so as to realize the dynamic monitoring and maintenance of the reference frame in the mountainous area,which provides important technical support to the maintenance of regional reference frames.