undergraduate gravity lecture

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:
•Earth flattening.
•Surface relief.
• 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:
•Latitude
•Elevation
•Excess mass
•Terrain
•Drift
•Isostacy
•Earth’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)