Satellite gravimetry: Methods, products, applications, and future trends

The gravitational field of the Earth reflects Earth's surface mass redistribution and its inner structure and dynamics. Satellite gravimetry techniques have been used to observe the Earth's external gravitational field and its temporal variations on a global scale. The global gravitational models from satellite gravimetry, typically in terms of spherical harmonic coefficients, are crucial in geodetic, geodynamic, geophysical, hydrological, glaciological, oceanographic, and many other geoscience applications. In this paper, we provide a comprehensive overview of theoretical definitions describing relationships between the spherical harmonic coefficients and different satellite gravimetry observables such as orbital perturbations in terms of satellite positions, velocities, and accelerations; satellite-to-satellite range rates; and gravitational gradients. Products and applications of the Earth's static global gravitational models are presented and discussed in the context of determination of the gravimetric geoid and physical heights, gravimetric and isostatic crustal thickness, bathymetric depths, glacier bedrock relief, sediment thickness, geostrophic and eddy currents, Earth's inertia tensor and dipole, precession and nutation parameters of the Earth's rotation, and prediction of the satellite orbital geometry. Furthermore, applications and advances of the Earth's time-variable gravitational models for monitoring large earthquakes, hydrological mass transport, Earth's rotation parameters, and vertical crustal motions (due to the glacial isostatic adjustment and other phenomena) are presented. Finally, future trends and prospects in the satellite gravimetry are discussed.