GNSS Tidal Measurement And Establishment Of Marine Vertical Datum Model

Tide level is the instantaneous absolute initial surface of sounding.Ocean vertical datum is derived from tide level,which is a reference for ocean surveying and mapping results and an important part of ocean geodetic survey.High-precision positioning technology such as GNSS is widely used in ocean surveying and mapping,but an important bottleneck problem restricting the expression and application of its results is how to convert geodetic height measured with GNSS into normal height or chart height based on depth datum.At present,the problem has not been solved well either in estuary or offshore.To this end,this paper studies the theories and methods of GNSS tide level measurement and ocean seamless vertical datum model construction.The main work and innovation of the paper are as follows:1.Traditional methods for tidal measurement and determination of vertical datumFive tidal measurement methods and four tidal correction methods are introduced,and the advantages and disadvantages of each method are discussed;It is considered that the residual water level correction method can significantly improve the tide level prediction accuracy of the tide model;According to the length of the tide level sequence,the determination and transmission method of the mean sea level(MSL)and the depth datum(L)are respectively given;Considering the consistency of the tide properties and the relationship between the vertical datum at the tide station,the unified method of different starting surfaces of the regional tide station is given taking the CGCS2000 ellipsoid as the reference surface;2.Long-distance,high-precision GNSS tide level measurementAiming at the difficulty of tide level acquisition under far-shore and special hydrological conditions,and the insufficiency of accuracy and efficiency of traditional fixed-point tidal level measurement methods,the GNSS tidal level measurement method was studied,and the long-distance,high-precision GNSS anchoring/sailing tidal level measurement method and the tidal level dynamic extraction method is given,and the implementation process is given as well.(1)GNSS anchor/sailing,tidal measurement of full sea area method is given.(2)The data processing method of GNSS roving/static tide level measurement is proposed,and the data processing model and the specific implementation flow are given.(3)Through theoretical analysis and practice,the two methods determining the cutoff period(Tc)for GNSS tidal extraction in different hydrological environments are given respectively,namely the spectrum analysis and the minimum tidal component.The former determines Tc at the inflection point of spectrum characteristic curve of watersuface height series,while the later chooses the period of minimum tidal component of whole main tidal components as Tc.(4)The GNSS RTK/PPK/PPP tide level measurement experiment was carried out in different areas and the tide level measurement accuracy better than 10 cm was achieved whether anchored or voyaging,the correctness of the proposed GNSS tide level measurement method,data processing method and cut-off period determination method is verified.At the same time,it overcomes the shortcomings of traditional tide level measurement methods and provides a new way for tide level acquisition.3.Ocean vertical datum transfer combining station tide level and GNSS tide levelAiming at the problem of offshore vertical reference determination and the construction of local seamless vertical datum model,the method of marine vertical datum transfer based on GNSS anchor tide level is studied,three kinds of marine vertical datum transfer models are proposed,and a local marine seamless vertical datum transfer model is constructed,and the conversion from GNSS measured geodetic height to the chart height taking the local mean sea level or local depth datum as starting datum is implemented.(1)The relationship between the CGCS2000 ellipsoid,the local mean sea level and the local depth datum is given.The influence of the radius of curvature of the ellipsoid on the transmission of the ocean vertical datum is analyzed.And it is considered that when the tolerance is 0.1m,the range of vertical datum transmission using GNSS tide level is preferably limited within 90 km.(2)Three mean sea levels and depth datum transfer methods are proposed: the same station tide level comparison method and MSL and L transfer,the MSL and L integrated transfer method under the same reference,and the MSL and L transfer methods under different reference.The above three methods have achieved that the average sea level and depth datum with accuracy better than 10 cm when the PPK baseline length is less than 100 km.It solves the high-precision acquisition problem of long-distance depth datum and mean sea level,and provides a new way to determine the depth datum of the offshore waters.(3)Considering the tolerance of tide level model,the influence of ellipsoid curvature radius and the consistency of local tide properties,the geometric construction methods of local seamless depth datum model,local transformation model of seamless vertical datum is given,achieving the conversion of GNSS measurements from the region to the local mean sea level and depth datum.This study solves the problem of offshore vertical datum determination and the seamless transformation of local GNSS measurement4.Theory and method for constructing marine seamless vertical plane model in estuary basinConsidering the characteristics of strips in the estuary basin,dense tide stations,single tidal changes,and small elevation anomalies varies,the problem of seamless vertical datum model construction is studied.For the first time,a set of theories and methods for constructing a marine seamless vertical datum model suitable for the estuary basin was proposed.The accuracy of the quasi-geoid model better than 5 cm and the seamless depth datum model better than 6cm were obtained in the waters of the Yangtze River estuary,solving the problem of seamless conversion from GNSS measured geodetic height to normal height and chart height in the estuary watershed.(1)The relationships between the ellipsoidal surface,the quasi-geoid surface and the depth datum are clarified,and the basis for constructing the seamless vertical datum model of the estuary basin with the ellipsoidal surface as the seamless vertical reference datum is given.(2)Combined with the characteristics of estuarine basin,the geometric modeling method,EGM2008 model modifying method and the local quasi-geoid model refining method are presented,which are suitable for the construction of quasi-geoid model in estuarine basin.(3)Aiming at the discrete,hopping and discontinuity of depth datum in estuary basin,the method of seamless depth datum model is studied systematically.Five geometric modeling methods such as the nearest principle method,inverse distance weighting method,triangular interpolation method,curve/surface segmentation fitting method and surface spline fitting method are given.The curve/surface segmentation modeling method is superior;Two kinds of physical modeling methods,such as tidal ranging method and method of tidal harmonic constant interpolation,which are considered to take into account the characteristics of tidal waves changes,and the tidal harmonic constant interpolation method is superior;Based on the characteristics of geometric modeling and physical modeling methods,a combined modeling method is proposed,which adopts the curve/surface segmentation modeling method in the depth datum changing slowly waters,and the tide harmonic constant interpolation method in the complex waters.(4)Based on the connotation of seamless vertical datum model,a two-step method and a one-step method for the transition from geodetic height to chart height with ellipsoid as the vertical reference datum were proposed,which solved the problem of seamless transition between normal height,geodetic height and chart height in estuary basin.(5)According to the characteristics of tidal stations,elevation anomalies and depth datum changes in the Yangtze river estuary,this paper divided the Yangtze river estuary into different sections.The quasi-geoid model of each section was constructed by geometric method and EGM2008 model correcting method respectively.It was considered that the accuracy of the two methods was close,but the accuracy of geometric method was slightly higher.Finally,the quasi-geoid model of the Yangtze river estuary was constructed using geometric method with a precision higher than 5cm;The combined modeling method formed by quadric surface fitting and tidal harmonic constant interpolation modeling method was used to construct the Yangtze river estuary seamless depth datum model,and the modeling accuracy was better than 6.0cm;Finally,based on the above two models,the seamless vertical datum conversion model of the Yangtze estuary is formed,which solves the problem of the Marine vertical datum conversion in the Yangtze estuary.5.Theory and method of building offshore seamless vertical datum modelFor the sparse distribution of the near-shore tide stations and the discrete/hopping/discontinuity of the depth datum,the problem of constructing the offshore vertical datum model is systematically studied.The global tidal model optimization method,constituent optimization method for global tidal models,the local optimal tidal model reconstruction method based on the preferred tidal model,and the remodeling model refining method considering the distribution characteristics of the offshore tide stations are proposed,forming a set of theories and methods for constructing offshore seamless vertical datum model based on global tidal model and global mean sea level model.(1)The depth datum L model and the ground height model are constructed based on the global tide model.(2)A method for selecting the optimal tidal components of the global tidal model is proposed based on the results of tidal level calculations of several global tidal models and the consistency of tidal components and harmonic constant.(3)A global tidal model reconstructing method based on optimal tidal separation is proposed.(4)In this paper,two kinds of near-shore refining methods for global tidal models are proposed,namely,the tidal ratio refining method based on tidal cluster reconstructing model and the seamless difference correcting method of tidal harmonic constant considering tidal station distribution.(5)The strategy and implementation process of the global tide model are given.This study solves the problem of building a seamless vertical datum model for large area offshore,and achieves the seamless conversion of GNSS measurement results to the chart height based on depth datum.6.Construction of seamless vertical datum model for Chinese offshore seaCombined with 5 global tidal models,2 global mean sea level models and 51 tide stations' data,the Marine seamless depth datum L model and geodetic height model of China offshore and adjacent waters were constructed,and the modeling accuracy was better than 10 cm,solving the conversion problem of GNSS vertical solution of China offshore and adjacent waters.(1)Using tidal data,the nearshore optimal tidal components are selected from five global tidal models.According to the consistency of tidal components' contribution in the global tidal model,the optimal tidal components are optimized.(2)Based on the optimized tidal components,a new tidal model which is suitable for China offshore was constructed by reconstruction.Compared with the original global tidal model,the accuracy of the tidal model level has been more than doubled.(3)Based on the tidal level data of 51 tide stations in the nearshore,the reconstructed tidal model is refined by the proposed tidal range refining method and the tidal harmonic constant seamless differential correcting method considering the distributions of tide stations.The station's tidal harmonic constant differential correcting method is significantly better than the tidal range method.The refined model has almost the same accuracy as the tide stations observation measured.(4)Based on the refined tidal model,the seamless depth datum L model and the geodetic height model of China's coastal and adjacent waters with a precision better than 10 cm are constructed.