Marine geodesy

Summary This discussion only scratches the surface of the subject of marine geodesy. Its sole purpose is to bring into focus some of the problems and the requirements which will arise as a result of the exploration of the sea. It seems clear at least at this time that the geodetic accuracies obtainable over the ocean areas in general will be at least one or two orders of magnitude less than those obtainable on land. But modern science which has produced the atom bomb, artificial satellites, soft landings on the moon, and other highly sophisticated accomplishments, might be expected in the future to provide some means of obtaining much higher geodetic accuracies at sea than can now be foreseen.     

现代大地测量学的进展

经典大地测量学主要研究地球的几何形状、定向及其重力场,并关注在地球上点的定位、重力值。现代大地测量则已超过原来经典的研究内容,将原来所考虑的静态内容,在长距离、大范围、实时和高精度测量的条件下,和时间(历元)这一因素联系起来。此外,现代大地测量学提供和处理了涉及原来是地球动力学、行星学、大气学、海洋学、板块运动学和冰川学等学科所需的信息。现代大地测量学可以并已经涉及多种学科领域,并提供多种学科领域长期以来很难取得的数值和有可能解决它们相应的困惑,事实证明现代大地测量学业已形成了学科交叉意义上的一门科学,它将更大地影响和促进地球科学、环境科学和行星科学的发展。     

Publications of the international association of geodesy

Scientific Informations

Publications of the international association of geodesy     

GGOS和大地测量技术进展

在2005年8月澳大利亚凯恩斯(Cairns)国际大地测量协会(IAG)科学大会上,全球大地测量观测系统(GlobalGeodeticObservingSystem,简为GGOS)作为这次科学大会一个重要议题成为一个热点问题,也成为未来大地测量学科进展的一个风向标。本文较为全面地介绍了GGOS的背景、目标、任务和科学原理等,结合GGOS在全球动力系统观测中的应用构想,说明了GGOS与其他地球观测系统越来越紧密的联系和相互促进的发展趋势。除此之外,本文还简要介绍了这次科学大会其他领域如大地坐标框架和卫星重力等领域的最新进展。     

On a relativistic geodesy

Theoretical formulas for relativistic estimation of geopotential differences are given. The relativistic geoid is defined. A technique for measuring potential differences with high precision clocks (masers or equivalent) is described. The method can operate over arbitrary terrestrial distances. Two clocks are used. The drift between the clocks is estimated by using closed loops. The clocks are used in an operational mode during the whole measuring interval. No satellite links are necessary but VLBI, GPS and ANIK-links can be used in combination with the method.     

月球地形测绘和月球大地测量(1)

从十九世纪六十年代以来的几十年中 ,人类一直试图发射航天器 ,以对月球 ,特别是它的远月面进行探测。美国和前苏联发射了各类月球探测器达七十余个 ,对月球进行探测 ,至今几乎已经完成了对月球重要的地学勘查 ,其中包括对全部月面的地形测绘和月球重力场测定。本节对月球航天探测的主要情况作了介绍 ,对月球的不同起源学说作了简要回顾 ,对月球的几何和物理特征作了介绍     

On the foundation of collocation in physical geodesy

The boundary value problem in physical geodesy is nowadays mostly presented with the use of an advanced stochastic model by Krarup-Moritz. This model includes a primary Gauss-Markov model and an adjoining Wiener-Hopf model. Degenerations of the Wiener-Hopf section are found in thesingular auto-covariance matrix of the residuals. The non-singular inverse of the auto-covariance matrix of the signal is proved to be a generalized inverse of the singular auto-covariance matrix of the residuals. The joint model is given a non-stochastic evaluation for a case with spherical external surface (using a non-singular inverse). These findings will not prevent a successful application of the model, which has important merits, specially when using suitablea priori values for the stochastic parameters in the covariance functions. A method for quadratic unbiased estimation ofa priori variances is presented in an introductory section. It is meant to be of value when using a solution of the boundary value problem with the collocation technique based on the classical Gauss-Markov solution. (Bjerhammar (1963).)     

Polyhedral approximations in physical geodesy

Summary A procedure is derived for the upward continuation of unevenly spaced gravity data. The topographic relief is approximated by a polyhedron with triangular faces and vertices placed at small distances around the surface of a sphere. The usual Fredholm integral equation of the second kind is modified considering the discontinuity of the normal vector. It is solved by successive approximations assuming the unknown function is linear inside each face at every step of the iteration process. An approximate formula to obtain the anomalous potential from the Bouguer anomaly is discussed. The potential of a homogeneous polyhedron is derived and used to compute relief corrections to the geoid undulations. Numerical applications are presented with respect to the Romanian territory.Partially presented at theJoint Symposium of IGC and IGC, Graz, Austria, 11–17 September 1994     

流动卫星激光测距技术在中国的发展

SLR(卫星激光测距)技术是一项应用广泛的空间大地测量技术,本文在介绍其测距原理的基础上,通过与GPS、VLBI技术进行对比,分析了其实现手段和所能达到的精度;根据SLR应用现状提出了在国内建立SLR流动站的思路;并对SLR技术的未来发展作了展望。     

On a four-dimensional integrated geodesy

In contrast to continuous global considerations of time dependent boundary value problems an attempt is made to define4D-linear observation equations in the framework of integrated geodesy for discrete, more or less regional and local applications (deformation analysis) where time variations in position and in the gravity field have to be considered. The derivation is a strict analogue and extension of the3D integrated approach. In addition the construction of time dependent covariance functions is discussed, which are necessary to solve for unknown displacements and changes in the gravity potential in the generalized least squares collocation model.     

On the error of analytical continuation in physical geodesy

Analytical continuation of gravity anomalies and height anomalies is compared with Helmert's second condensation method. Assuming that the density of the terrain is constant and known the latter method can be regarded as correct. All solutions are limited to the second power of H/R, where H is the orthometric height of the terrain and R is mean sea-level radius. We conclude that the prediction of free-air anomalies and height anomalies by analytical continuation with Poisson's formula and Stokes's formula goes without error. Applying the same technique for geoid determination yields an error of the order of H², stemming from the failure of analytical continuation inside the masses of the Earth.     

A numerical experiment of integrated geodesy

The paper has two main targets: to prove by numerical experiment on simulated data (exact solution a priori known) that the integrated approach gives superior results that can’t be achieved neither by pure (“incorrect”) λ.s. adjustment nor by a λ.s. adjustment of observations corrected by some a priori long wave length gravity model; to find among many strategies for approximate solutions, one which preserves most of the features of the exact one, although with a much simpler numerical structure.