Can I change Free Air anomaly to gravity disturbance? #91
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Hi I became curious after reading the "Should geophysicists use the gravity disturbance or the anomaly?" article. The picture below is what I organized after reading the article. There was a difference in the gravitational effect between gravity disturbance and Free Air anomaly as much as the geoid height. If I calibrate the gravitational effect corresponding to the height of the geoid to Free Air Anomaly, can I make a gravity disturbance and use it? The data I'm using is Free Air Anomaly from Geoid, so I'm asking you to use gravity disturbance Thank you. |
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Hi @prince-Ha. Thanks for opening this question. Your derivations seems right, so using that last equation you could get from the free-air anomaly to an approximation of the gravity disturbance. I say approximation because the expression you have for the gravity disturbance in equation 1 is an approximation: The term between parenthesis is actually a first order Taylor approximation of the normal gravity on the point p. This approximation is actually not needed, Li and Gotze (2001) present a closed-form formula to compute the normal gravity on any external point. We have this formula implemented in Boule. If you have details of how the free-air anomaly was applied to your data you can "undo" it and recover the observed gravity values And then you can compute the gravity disturbance using the analytical solution we have in Boule. Does it make sense? |
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They are actually two different quantities. I think you mean that people still use free-air anomaly as if they were gravity disturbances. If that so, chill out, it's not your country only, it's a worldwide issue 😅
I'm pretty certain that that is free-air anomaly and not gravity disturbance. But if you need …