free-air correction

free-air correction

(frē′âr′)
n.
A compensation factor used in gravitational surveys that takes into account the decrease in the force of gravity with increasing altitude, assuming that only air intervenes between the observation point and sea level. It is equal to -0.3086 milligals per meter above sea level.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.