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Rapid growth of geodetic information provided by the Global Positioning System (GPS) and stringent requirements for a precise geoid in ocean areas for ocean circulation models have spurred interest in geoid studies. As a result, the International Geoid Commission was formed to provide a focus for this important geoid research. Determination of the Geoid: Present and Future is the result of the first meeting of the Commission, held at the Instituto di Topografia, Fotogrammetria e Geofisica at the Politecnico di Milano, June 1990. Six major topics are presented: Global Geopotential Models: Present and Future; Role of Topography in Geoid Computations; the Geoid and the Global Positioning System; the State of Computation of National or Regional Geoids; Software and Data Improvements for Geoid Computations; and Recent Developments in the GEOMED (Determination of the Geoid in the Mediterranean) Project.
A world-wide estimate of the gravity field, based on all available gravimetry and extended by Markov analysis using correlation with elevation, was combined with an estimate of the geoid based on astro-geodetic data covering 19% of the earth and with secular and long period variations of the 1957 Beta and 1958 Beta satellite orbits, into a generalization of least-squares adjustments taking correlation into account. The value obtained for the quadratic sum indicated that the estimates of variance and covariance should be increased about 44%. The results obtained include: Equatorial radius, 6378163 + or - 21 m; Flattening, 1/298.24 + or - 0.01; Equatorial gravity, 978043.6 + or - 1.2 milligals (Potsdam system); Datum shifts (with three-dimensional standard deviation) for the Americas system, + or - 35 m; Europe-Africa-Siberia-India system, + or - 38 m; Japan-Korea-Manchuria system, + or - 68 m; Coefficients in the spherical harmonic expression of the gravity field up to the 8th degree; and World-wide geoid heights, with standard deviations varying from + or - 10 m to + or - 22 m. (Author).
Based on an international symposium held in Tokyo, the volume combines papers in the fields of gravity, geoid and marine geodesy. Special emphasis is placed on the use of gravity in modeling tectonic processes and the problems of geophysical inversion. In addition, absolute and relative gravity measurement in static and airborne mode, satellite altimetry, geopotential modeling, and global geodynamics are dealt with. The field of marine geodesy includes contributions on sea level change, seafloor deformation and mapping, sea surface positioning, electronic charting, and datum transformations.
This book will be based on the material of the lecture noties in several International Schools for the Determination and Use of the Geoid, organized by the International Geoid Serivice of the International Association of Geodesy. It consolidates, unifies, and streamlines this material in a unique way not covereed by the few other books that exist on this subjext. More specifically, the book presents (for the first time in a single volume) the theory and methodology of the most common technique used for precise determination of the geoid, including the computation of the marine geoid from satellite altimetry data. These are illustrated by specific examples and actual computations of local geoids. In addition, the book provides the fundamentals of estimating orthometric heights without spirit levelling, by properly combining a geoid with heights from GPS. Besides the geodectic and geophysical uses, this last application has made geoid computation methods very popular in recent years because the entire GPS and GIS user communities are interested in estimating geoid undulations in order to convert GPS heights to physically meaningful orthometric heights (elevations above mean sea level). The overall purpose of the book is, therefore, to provide the user community (academics, graduate students, geophysicists, engineers, oceanographers, GIS and GPS users, researchers) with a self-contained textbook, which will supply them with the complete roadmap of estimating geoid undulations, from the theoretical definitions and formulas to the available numerical methods and their implementation and the test in practice.
This volume discusses recent advances and future prospects in the exploration of the gravity field. Both theoretical and practical aspects, ranging from gravity instrumentation, space and airborne gradiometry, satellite altimetry, the presentation of international measurement campaigns and projects, networks and gravity field-related data bases and software, to geophysical inversion techniques and recent undertakings such as the determination of the geoid in Europe, are dealt with.