We have surveyed the Earth's surface using gravity anomalies and second-order radial derivatives of the disturbing gravitational potential computed from the gravitational model EGM2008 complete to degree and order 2159 (for selected degrees up to 2190). It corresponds to 5 arcmin resolution on the ground. Over most well known impact crater sites on the Earth we found the second-order derivatives (not available from ordinary gravity surveys) offered finer discrimination of circular features than the gravity anomalies themselves. We also discovered that some of the sites show evidence of double or multiple craters which will need further ground verification. Some of these signatures (in hilly or mountainous terrain) may also need to be corrected for the gravitational effect of topography to sharpen their hidden features., Jaroslav Klokočník, Jan Kostelecký, Pavel Novák and Carl A. Wagner., and Obsahuje bibliografii
During the General Assembly of the European Geosciences Union in April 2008, the new Earth Gravitational Model 2008 (EGM08) was released with fully-normalized coefficients in the spherical harmonic expansion of the Earth's gravitational potential complete to degree and order 2159. EGM08 is based on inverse modeling methods that rely on data observed both on the Earth's surface and in space. Forward modeling equations based on Newtonian integrals can be converted into series forms that are compatible with the spherical harmonic description of the geopotential. Namely gravitational potentials of ocean water (fluid masses below the geoid) and topographical masses (solid masses above the geoid) can be formulated and evaluated numerically through spherical harmonic expansions. The potential constituents as well as their radial derivatives can be used for a step known in geodesy and geophysics as gravity field reduction or stripping. Reducing EGM08 for these constituents can help to analyze the internal structure of the Earth (geophysics) as well as to derive the Earth's gravitational field harmonic outside the geoid (geodesy)., Pavel Novák., and Obsahuje bibliografii