Gravity field determination and characteristics : retrospective and prospective

摘要: Gravimetry has had a long history, using pendulums, torsion balances, and static spring gravimeters. Relative accuracy adequate for many geophysical problems was already attained by 1900, but it took another half century to build readily portable Calibration datum definition remained until the 1970s when free-fall absolute gravimeters were developed that now have precision of 10 -3 mGal. The geographic inaccessibility field party costs (notably in areas greatest tectonic interest) are being overcome airborne gravimetry achieved accuracies 1-3 mGal with resolutions 20 km. Satellite techniques best way determine long-wavelength variations gravity field. resolution models steadily improved number satellites observations. current model includes tracking data from more than 30 satellites, satellite altimetry, surface about 290 km (harmonic degree 70) most recent improvements coming Doppler orbitography radiopositioning integrated (DORIS) SPOT 2 laser ranging (SLR), DORIS, Global Positioning System (GPS) TOPEX/POSEIDON satellite. Meanwhile, radar altimetry become dominant technique infer marine geoid tens kilometers or shorter. Similarly, fields Moon, Venus, Mars been determined harmonic degrees 70, 75, 50, respectively, although limitations result spatial resolution. Modeling Earth's abundance precise an increasingly complex task, which development computer capacity kept pace. Contemporary solutions entail 10,000 parameters, them effects other fixed Earth. Temporal arising tides well modeled, nontidal changes identified. improvement gravitational engendered corresponding advances interpretation. Isostatic refined expanded account regional thermal histories. Interpretation mainly terms plate tectonics as manifestation mantle convection. Gravity significant inferring there must be large increase viscosity depth (most strongly, apparent slow sinking subducted slabs). prospects increasing determination rest primarily new measurement systems. Airborne is taking promising steps GPS, global awaits dedicated system, future altimeter missions will do ocean dynamics studies improvement. Advances interpretation occur through data, such seismic tomography, larger-scale modeling