Dictionary:Free-air correction

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{{#category_index:F|free-air correction}} 1. A correction for the elevation of a gravity measurement required because the measurement was made at a different distance from the center of the Earth than the datum. The correction is 0.308 768–0.000 440sin2λ–0.000 000 1442h mGal/m, where λ is the latitude and h is elevation above the ellipsoid. Usually only the first term is used, 0.3086 mGal/m or 0.09406 mGal/ft. See Figure G-7. 2. In Turam, normalizing a ratio of successive measurements by dividing by the calculated free-space vertical magnetic field. Compare normal correction.