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# Gravity method

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### Transcript

• 1. Gravity Method By Dr. Amin E. Khalil
• 2. 2 21 r MM GF
• 3. gMF 2 21 2 r MM GgM 2 r M Gg
• 4. R = radius of the earth Earth is considered as sphere and hence radius is constant.
• 5. Earth is not sphere and hence radius is not constant. Hence correction must be applied
• 6. Because many factors affect the value of g. As an example: &#x2022;Earth flattening. &#x2022;Surface relief. &#x2022; anomalous masses inside the earth
• 7. What is geoid? It is equipotential surface where the g is always constant. The equipotential surface is usually taken as the sea level. However, due to some heterogeneity in the earth Geoid may differ slightly from Sea level.
• 8. Reduction is carried out to correct for: &#x2022;Latitude &#x2022;Elevation &#x2022;Excess mass &#x2022;Terrain &#x2022;Drift &#x2022;Isostacy &#x2022;Earth&#x2019;s rotation
• 9. The earth is flattened, i.e the radius at the equator is longer than at the poles. gn = 978031.85 (1.0 + 0.005278895 sin2(lat) + 0.000023462 sin4(lat)) (mGal)
• 10. geoid
• 11. gb = gobs - gn + 0.3086h - 0.04193r h (mGal)