Earth Gravitational Model 1996Edit
Earth Gravitational Model 1996 (EGM96) is a global representation of the Earth's gravity field, expressed as a potential function expanded in spherical harmonics to describe how gravity varies over the planet. Released in 1996, it became a foundational reference for geodesy, oceanography, and satellite orbit studies, providing a consistent framework for interpreting gravity-related phenomena on a planetary scale. The model represents the gravitational potential as a series of coefficients that encode deviations from a perfectly spherical, uniform Earth and thus enable practical applications in mapping, navigation, and geophysical research. Earth gravitational field geopotential geoid
EGM96 emerged from a collaborative effort among government agencies, research laboratories, and international partners to integrate diverse data sources into a single, coherent description of the gravity field. It combined satellite observations with terrestrial gravity measurements to produce a global set of spherical-harmonic coefficients up to a high degree and order. Among the satellite data contributing to the model were measurements from active and passive tracking of orbiting platforms, while the terrestrial component drew on gravity surveys conducted around the world. Notable programmatic contributors and facilities include LAGEOS and other satellite optoelectronic or laser ranging campaigns, as well as data and analysis efforts coordinated by agencies such as National Geospatial-Intelligence Agency and research centers involved in geodesy. satellite laser ranging TOPEX/Poseidon terrestrial gravity data
From a technical standpoint, EGM96 describes the Earth's gravitational potential using a spherical-harmonic expansion with coefficients commonly denoted as Cnm and Snm. The model extended to relatively high degree and order, providing finer spatial resolution than many previous global gravity representations. This structure allows scientists and practitioners to compute geoid undulations, gravity anomalies, and satellite trajectories with improved consistency. The approach also facilitates integration with other gravity models and geodetic systems, contributing to more accurate reference frames for positioning and navigation. spherical harmonics gravitational potential geoid satellite orbits
Applications and impact of EGM96 span several domains. In geodesy and cartography, the model supported the construction of 보다 accurate global reference surfaces and improved the interpretation of gravity data in terms of height and shape of the geoid. In navigation and space missions, it aided orbit determination and satellite mission design by providing a better representation of the Earth’s gravity field that influences trajectory predictions. In oceanography and geophysics, EGM96 contributed to studies of sea level variation, ocean circulation, and crustal structure by offering a unified, global gravity framework against which regional measurements could be compared. Related topics include Global Positioning System positioning, geoid height analyses, and the interpretation of gravity anomaly data. EGM2008 geophysics oceanography
Controversies and debates surrounding EGM96, as with major scientific models, centered on data coverage, methodological choices, and the evolution of gravity modeling. Because gravity is affected by mass distribution across oceans, continents, and polar regions, regions with sparse gravity data in the 1990s could exhibit larger uncertainties in the corresponding coefficients. Critics and proponents alike discussed the balance between extensive global data integration and region-specific accuracy, as well as the implications of combining surface gravity data with satellite measurements. As newer models were developed—most notably Earth Gravitational Model 2008—the discussion shifted to how best to incorporate time-variable changes in the gravity field and how to reconcile differences between models produced by different institutions or data sets. These debates are a normal part of advancing a field where improved data and methods continually refine our understanding of the planet. gravity data geodesy EGM2008
In the broader arc of gravity modeling, EGM96 is viewed as a milestone that helped standardize global gravity field representation and paved the way for subsequent refinements. It demonstrated the value of bringing together satellite observations and terrestrial surveys under a unified mathematical framework, influencing subsequent programs and datasets in Earth science and related disciplines. The model sits within the lineage of global gravity models that support both scientific inquiry and practical applications in navigation, mapping, and earth system research. LAGEOS satellite altimetry GFZ NASA