Gravimetern

Gravimeters are instruments designed to measure local gravitational acceleration, known as g. They are used to map the Earth’s gravity field, monitor mass redistribution, and support geodetic and geophysical research. Gravimeters are broadly classified as absolute and relative.

Absolute gravimeters determine g directly by tracking the motion of a test body under gravity. Classical designs release a mass in vacuum and measure its position or velocity over time with laser interferometry to compute acceleration. Modern absolute gravimeters also employ atom interferometry, where the phase shift of matter waves provides a measurement of g with high stability. Absolute gravimeters typically achieve precision at the microgal level (one microgal equals 10^-8 m/s^2).

Relative gravimeters measure gravity differences rather than the absolute value. They rely on a spring-based sensor or a mass that responds to changes in g, outputting a signal proportional to gravity. Relative devices are commonly used for field surveys and long-term monitoring. Well-known examples include spring gravimeters such as the LaCoste & Romberg types, and superconducting gravimeters, which use a levitated superconducting mass for very sensitive, continuous observations.

Applications of gravimetry span geodesy, mineral and groundwater exploration, and monitoring of atmospheric, hydrological, and tectonic processes. Gravimeter data contribute to gravity field models used in satellite gravimetry, navigation, and climate studies. The field continues to advance with advances in laser and atom interferometry, expanding the precision and range of gravity measurements.