Geodesy (Q5891652)

The origin of the present work goes back to a textbook on ``Geodäsie'' written by W.\ Torge and published in 1975 by Walter de Gruyter and Co. A revised edition followed in 1991, and an extended textbook was published in [Geodesy. 3rd completely revised and extended ed. Berlin: De Gruyter. (2001; Zbl 1244.86003)]. Translations were issued in English, Spanish, Chinese, and Greek. Ten years later, again an extensive revision was necessary in the chapters dealing with reference systems, methods of measurement and modeling, and geodetic contributions to recent geodynamic research.NEWLINENEWLINEIn this volume geodesy is treated in the more restrictive sense excluding plain surveying, focusing on global geodesy as well as geodetic surveys, and limiting to the Earth - i.e.\ considering no applications for other planets or moons. Thus the objective of geodesy is ``to determine the figure and external gravity field of the Earth, as well as its orientation in space, as a function of time, from measurements on and exterior to the Earth's surface'' (page 2). This means, the topic of geodesy contains geometric and physical parts which are closely related. So, the physical surface of the Earth, the geometry, is the border between the solid or fluid masses and the atmosphere. It is determined by the gravity field. Further, the ocean floor is included into the discussion of geodesy of the book, as the boundary between the solid terrestrial body and the oceanic water masses. It should be noted that the ocean contributes to about 70 \% of the total surface of the Earth.NEWLINENEWLINEThe ``Introduction'' of the present work contains the definitions and an overview of about 2000 years of history of geodesy, emphasizing the current change to a four-dimensional spacial-temporal concept, and the strong connections to astronomy, physics, and the other geosciences (geophysics including oceanography, hydrology and meteorology, geology, petrology, mineralogy, geochemistry etc.). Chapter 2 on ``Reference Systems and Reference Frames'' has been revised thoroughly. It includes the recent basic units and definitions of geodesy, as well as the realizations of celestial and terrestrial reference systems, and it points up the fundamental role of Earth's rotation. The fundamental quantities gravitation and gravity, as well as their corresponding potentials, are introduced in chap.\ 3 on ``The Gravity Field of the Earth''. Local gravity fields and the spherical harmonic expansion of the gravitational potential are discussed. The geoid, as a physically defined figure of the Earth and reference surface for heights, and gravity variations with time (e.g.\ tidal effects) are of interest. The updating of chap.\ 3 is concentrated on the geoid and mean sea level, with discussion of the manifold problems at realizing these surfaces. Only minor changes were necessary in chap.\ 4 on ``The Geodetic Earth Model'', introducing the so-called level-ellipsoid. Chapter 4 now also contains some definitions and parameters for optimum Earth models. The chapters 5 and 6 on ``Methods of Measurement'' and ``Methods of Positioning and Gravity Field Modeling'' again comprise the core of the book, and required extensive revision and completion. This was due to the overwhelming contribution of geodetic space methods in solving the three basic problems of geodesy, i.e.\ the determination of the surface, the gravity field, and the rotation of the Earth. Chapter 5 is divided into sections dealing with geometric methods of measurements relying primarily on electromagnetic waves, satellite observations employing artificial satellites as targets, geodetic astronomy performing observations to fixed stars and extragalactic radio sources, gravimetry doing terrestrial gravity and gravity gradient measurements, and terrestrial geodetic measurements determining coordinate differences between points on the Earth's surface. Effects disturbing the measurement process are explained. Geodetic evaluation methods may be divided into positioning and gravity field determination, as positioning requires only an approximate knowledge of the gravity field, and gravity field modeling needs only approximate positions. The linearization of the gravity field is always necessary, and it permits a statistical field description described in chap.\ 6. Nowadays, positioning is based on three-dimensional models, while classical strategies distinguish between horizontal positioning and height determination. It is shown that gravity field modeling uses all kinds of gravity field related observables. It can be formulated in the form of boundary-value problems of a potential theory. Local and global gravity field models, as well as the least-squares collocation are presented in chap.\ 5, In the chapters 5 and 6 sufficient space has been given to the description of Global Navigation Satellite Systems like GPS and to sophisticated space systems such as laser ranging and Very Long Baseline Interferometry. Recent successful gravity space missions are also explained in more detail. The present state of terrestrial positioning and gravimetry is discussed intensively, as these methods still play an important role on a local scale, and serve for densification and validation of satellite-derived results. The progress in gravity field modeling is demonstrated by some examples of recent global and local gravity field models, including GRACE- and GOCE-based satellite models, the Earth Gravitational Model EGM2008, and gravimetric geoid models for the USA and for Europe. The transition from classical geodetic control networks to three-dimensional reference frames embedded in the global terrestrial reference system is treated in chap.\ 7 on ``Geodetic and Gravimetric Networks''. Here the impact of absolute gravimetry on the establishment of gravity networks also becomes visible. The final chap.\ 9 on ``Structure and Dynamics of the Earth'' had also to be extended significantly, in order to consider adequately the geodetic contribution to the investigation and modeling of geodynamc processes of global to local scale. The present state of research is shown by several case studies, referring to, e.g., sea level change, glacial isostatic adjustment, plate tectonics, seismic and volcanic activity, hydrological circulation, and Earth tides.NEWLINENEWLINEThe text of the present work is supported by numerous figures. The book's revision led to an increase of about 25 \ The book is mainly intended as an introductory textbook for graduate students, but it may also be used as a reference for scientists and engineers in the fields of geodesy, geophysics, surveying engineering, and geomatics.