free-air anomaly


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free-air anomaly

[′frē ‚er ə′näm·ə·lē]
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However, the overlying positive EGM-96 free-air anomaly suggests that the crustal model may not be completely compensated.
Free-air anomaly is defined as the difference between the actual gravity (measured on the ground) and the normal gravity [gamma], whereas the latter is related to the normal height H (counted from the reference ellipsoid) of the survey point.
Free-air anomaly, [DELTA]g, which in a modern context (proposed in Molodenskij 1945) is defined as the difference between the actual gravity measured on the topographic surface g([r.sub.T], [OMEGA]) and the normal gravity y([r.sub.T], [OMEGA]):
The free-air anomaly is known to be highly correlated with the heights of the topographic masses, so, if there is rough topography in the computation area, the free-air anomalies will be rough as well.
(6) becomes -0.11187H Hence, the Bouguer anomaly can be calculated via free-air anomaly and height:
Recall that the simple Bouguer anomaly field is much smoother than that of the free-air anomaly, therefore the former is more appropriate for the interpolation.
Free-air anomaly, [DELTA][g.sub.F] which in a modern context (proposed in Molodensky 1945) is referred to the ground level, is defined as the difference between the actual gravity measured on the ground [g.sub.P] and the normal gravity [[gamma].sub.Q]:
(2) and the topographic density [rho] set to 2.67 g [cm.sup.-3], the Bouguer anomaly can be calculated via free-air anomaly and height:
The free-air anomaly is known to be more sensitive to the topography, so, if there are rough topographic masses in the computation area, the free-air anomalies will be rough and that is why the interpolation cannot always be successful.