Which correction accounts for the mass of material lying between the observation point and the elevation datum using a uniform slab approximation?

• A. Bouguer correction
• B. Free-air correction
• C. Eötvös correction
• D. Instrument drift correction

Answer: (A)

The main idea is isolating the gravity effect of the crustal material between the observation point and the reference surface by modeling that intervening mass as a uniform density slab. This is the Bouguer correction, which removes the gravitational attraction of the mass lying between the observation height and the datum so you can compare gravity values at different elevations. In practice you assume a crustal density and a slab thickness equal to the height difference, and apply the Bouguer term (often conceptually 2πGρh). This distinguishes it from the free-air correction, which only accounts for height change assuming no intervening mass; the Eötvös correction, which handles rotation/velocity effects; and instrument drift corrections, which address sensor bias.