The absolute acceleration of the Earth’s gravity field as opposed to relative gravity such as measured by conventional gravimeters. Absolute gravity can be measured using a corner-cube reflector falling in a small vacuum chamber, the position of the reflector being measured with a laser interferometer. Portable absolute gravimeters are now in experimental exploration use. They can be operated in sets coupled by fiber optics to measure absolute gravity gradients directly. See Niebauer et al. (1995) and Brown et al. (2000).