A difference between observed gravity and a specified reference field after stated reductions. Free-air, Bouguer and isostatic anomalies remove different modeled effects; they are not interchangeable raw measurements.
A spectral transfer estimate . Its wavelength dependence constrains compensation, density structure and support, but one transfer curve does not uniquely determine them.
For cross-spectrum and autospectra , squared coherence is . It measures the fraction of spectral association between gravity and topography. Low coherence can signal uncorrelated internal loading, noise or shortcomings of a simple surface-load model; interpreting it as elastic thickness requires a loading model.
For a surface load above a uniform-density crust over a denser substrate, a simple lithospheric flexure model gives the indicated gravity-topography admittance, with . The surface mass contributes positive gravity; downward displacement of the density interface contributes a compensating negative signal attenuated by . Hence at long wavelength and at short wavelength. Here is the interface depth, not automatically the effective elastic thickness.
A gravity anomaly after removing an approximate topographic mass contribution, often an infinite slab , in addition to free-air reduction. Terrain and spherical-curvature corrections refine the slab model.
A correction for the difference between real surrounding relief and the assumed simple topographic slab. Its computation needs terrain geometry and an assumed density, and can matter in rough surface topography.
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A gravity anomaly is a measurement of the difference between the observed gravitational field of the Earth at a specific location and the expected gravitational field, which is typically calculated based on a model of the Earth's shape and mass distribution. Gravity anomalies can provide valuable insights into geological structures and variations in subsurface density. They are instrumental in fields like geophysics, geology, and natural resource exploration.