gravimeter

A gravimeter is a scientific instrument designed to measure the local gravitational acceleration, g, which is the acceleration imparted by the Earth's gravity field at a specific location. Gravimeters are used to detect very small vertical accelerations caused by variations in mass distribution near the instrument, topographic features, and temporal changes in the gravity field. They play a key role in geodesy, geophysics, and metrology by providing precise gravity data for maps, models, and calibration tasks.

Absolute gravimeters determine the value of g at a point by tracking the motion of a test body in free fall or by measuring the phase shift of light or matter waves as the body falls. In common laboratory implementations, a corner-cube reflector falls in vacuum while a laser interferometer records position versus time; the data yield g after applying corrections for air, tides, and instrument biases. Absolute gravimeters can achieve sensitivities on the order of a few microgals, where 1 gal equals 1 cm/s^2 and 1 microgal equals 10^-8 m/s^2.

Relative gravimeters measure gravity changes rather than the absolute value. They use a suspended mass on a spring or a superconducting system, and readings reflect variations in g between locations or over time. Relative gravimeters are widely used for gravity surveys in mineral and hydrocarbon exploration, environmental monitoring, and long-term gravity networks because they are robust and comparatively inexpensive, though they require drift corrections and careful calibration.

Applications of gravimetry include constructing gravity maps for geodesy, monitoring groundwater or ice mass changes, detecting subsurface density contrasts associated with ore bodies or faults, and contributing to studies of Earth tides, crustal deformation, and atmospheric or hydrological loading.