Gravity readings observed at a gravity station after corrections for instrument drift and Earth tides are called what?

• A. observed gravity
• B. normal gravity
• C. free-air gravity
• D. Bouguer gravity

Answer: (A)

Observations of gravity taken at a station, after removing instrumental drift and Earth tides, are called observed gravity. This value represents the actual gravity at the site as recorded by the instrument, stripped of those instrumental and tidal influences. It serves as the baseline for further corrections: normal gravity is the theoretical value from a reference ellipsoid, while free-air gravity and Bouguer gravity apply additional adjustments for elevation and the mass between the measurement level and the reference surface. So the term that matches readings after drift and tide corrections is observed gravity.