From Mars to Greenland: Charting Gravity With Space and Airborne Instruments


Book Description

Precise and continuous tracking with multi-satellite systems of aircraft andlow flying satellites, accurate airborne measurement of gravity and gravity gradients, and satellite gradiometry have fundamentally changed our view on the de- termination of the Earth's gravity field. The papers in this volume describe these techniques in detail. The ideas are presentedas complementary, and are used to develop new theoretical concepts of gravity field analysis. Computatio- nal models using these techniques are also discussed and are tested in simulations. The papers presented in this volume are the result of an IAG symposium held during the XX General Assembly of the Inter- national Union of Geodesy and Geophysics in Vienna, Austria, August 11-24, 1991.




Geoid Determination


Book Description

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.




U.S. Land Gravity


Book Description

"Gravity data have many scientific applications, both on the surface of the Earth and in space. The data are used for computing gravitational models, which aid those searching for oil, gas, and minerals. Alone or in combination with other data (such as satellite, astrogeodetic, or geophysical), gravity data are used to calculate deflection of the vertical components, geoidal heights, gravity disturbance components, and datum shifts for orienting local geodetic datums to an Earth-centered world geodetic system. The data are also used for calibrating inertial navigation and guidance systems"--Introduction.




The Effect of Topography on Airborne Gravity Gradiometer Data


Book Description

The reduction and conversion of airborne gravity gradiometer data to ground level estimates of the gravity disturbance vector is currently of considerable interest in support of short wavelength gravity modeling. A pressing problem is the need for an accurate procedure for the downward continuation of data acquired at altitude by the Airborne Gravity Gradiometer Survey System (GGSS). As part of ongoing investigations, a prism method has been used to calculate the effect of topography on the gravity disturbance vector and the five independent second order gravity gradients. Calculations of the contribution of topography to the magnitudes of these gravimetric parameters were made at both surface and elevated points in the Wichita Mountains of Oklahoma. Computations were made utilizing Digital Terrain Elevation Data (DTED) with an assumed constant density of 2.67 grams/cc for the topographic masses. Results are presented which reflect the use of DTED sets of different horizontal extend and grid interval. Keywords: Terrain Effects; Gradiometry.




The Role of the Topography in Gravity Gradiometer Reductions and in the Solution of the Geodetic Boundary Value Problem Using Analytical Downward Continuation


Book Description

The effect of topography on gravity gradient data is considered and the effect of topography on the solution of the geodetic boundary value problem by using analytical downward continuation is also investigated. The validity of solving Molodensky's problem by using the analytical downward continuation is inspected. Even though it has been shown that the analytical downward continuation solution is equivalent to Molodensky's solution which is considered theoretically perfect, a very small topographic effect exists. This effect is trivial and can be neglected in the numerical computations. It is also shown that a spherical harmonic expansion cannot exactly represent the disturbing potential outside the Brillouin sphere and nearby the earth at the same time. If the points are nearby the earth (between the Brillouin sphere and the earth's surface), there is a topographic effect to the geopotential represented by a spherical harmonic expansion whose coefficients are determined by using the gravity anomalies analytically downward continued onto the ellipsoid. This effect is the same as the solving of the Molodensky's problem by using the analytical downward continuation. The convergence problem of the analytical downward continuation is also investigated under planar approximation. It is shown that the downward continuation is convergent almost everywhere, except at the infinite point of the circular frequency omega = infinity. This is important for geopotential modeling. Gradiometers. (edc).










Gravity forward modeling with a tesseroid-based Rock-Water-Ice approach – Theory and applications in the context of the GOCE mission and height system unification


Book Description

Detailed information on the gravitational effect of the Earth's topographic and isostatic masses can be calculated by gravity forward modeling. Within this book, the tesseroid-based Rock-Water-Ice (RWI) approach is developed, which allows a rigorous separate modeling of the Earth's rock, water, and ice masses with variable density values. Besides a discussion and evaluation of the RWI approach, applications in the context of the GOCE satellite mission and height system unification are presented.