Geoid Determination Theory and Methods
Knowledge of the Earth’s gravity field is an essential component for understanding the physical system of the Earth. Inside the masses, the field interacts with many other fields, according to complicated processes of physical and chemical nature; the stu
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Global Gravitational Models Nikolaos K. Pavlis
6.1 Outline of the Chapter This chapter discusses the development and use of Global Gravitational Models (GGMs), specifically those GGMs that are represented in the form of spherical (and/or ellipsoidal) harmonic coefficients. With the mathematical details having been presented in Chap. 3 of Part I of this book, the focus here is on the main concepts and considerations involved in the design and in the choice of alternative techniques and strategies that can be used to develop GGMs. Recent advances in geodetic techniques, in particular the availability of dedicated geopotential mapping missions on one hand and the availability of very high resolution GGMs on the other, provide the natural setting for the discussion that follows. Section 6.2 provides an introductory overview of the main concepts and distinguishes between Global and Regional (or Local) models, the latter being discussed in subsequent chapters within this part of the book. Section 6.3 discusses the aspects involved with the representation of GGMs and the characteristics of the data that are used to create the GGMs. Section 6.4 discusses the new satellite missions that are dedicated to the mapping of the gravitational field from space, and the advances and challenges that these missions introduce to GGM developments. Section 6.5 discusses the combination of the gravitational information obtained from satellites with the information obtained from surface data, which permit the development of very high resolution GGMs like EGM2008. Sections 6.2–6.5 provide the main concepts underlying the development of GGMs, omitting intentionally the mathematical and numerical details. In contrast, Sect. 6.6 discusses in some detail the specific mathematical and numerical procedures that may be used for the development of GGMs. For this purpose, two models are used as representative examples in Sect. 6.6 – EGM96, which represents the state-of-the-art before the availability of data from CHAMP and GRACE, and EGM2008, which represents currently the global model with the highest accuracy (developed prior to the availability of data from GOCE) and also the highest resolution. Section 6.7 discusses briefly the data requirements and the availability of the data necessary to develop GGMs. Section 6.8 deals with several F. Sans`o and M.G. Sideris (eds.), Geoid Determination, Lecture Notes in Earth System Sciences 110, DOI 10.1007/978-3-540-74700-0 6, © Springer-Verlag Berlin Heidelberg 2013
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6 Global Gravitational Models
aspects related to the use of a GGM and its by-products. The focus here is on the computation of the geoid, especially with regards to the treatment of permanent tide effects and the computation of height anomalies and geoid undulations referring to some specified ellipsoid of revolution and its normal gravity potential. Section 6.9 briefly discusses temporal (non-tidal) variations of the gravitational potential arising from the redistribution of mass within the Earth system, and the very recent advan
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