Weight Reduction
The gravity obtained at the time of data collection is the value of gravity from the measurement
results on the earth's surface. In order to change the size gravity value to the gravity value in the
reference field, a reduction process is needed by calculating the influence value of the
topographical mass, namely the rock mass located between the topographical mass and the
geoid. The geoid is the reference plane used for gravity calculations. There are 3 kinds of gravity
reduction namely
1. Free reduction – Water
This reduction assumes that below the point of gravity on the earth's surface until
it reaches the geoid plane it is considered non-existent so that changes in the value of
gravity are caused by changes in the distance from the surface of the earth to the center of
gravity or differences in the value of surface gravity in the geoid are influenced by the
height factor.
If Me is the mass of the earth and R is the radius of the earth then the gravity on the geoid
(go) and on the surface (g) is
With a series approach the value of the gravity on the surface can be written
The equation for the Free – Air reduction is:
If the average gravity of the earth is used, which is 980.629 gal and the average radius of
the earth is 6.367 x 10 8 cm, the reduction in free air can be written
The gravity obtained at the time of data collection is the value of gravity from the measurement
results on the earth's surface. In order to change the size gravity value to the gravity value in the
reference field, a reduction process is needed by calculating the influence value of the
topographical mass, namely the rock mass located between the topographical mass and the
geoid. The geoid is the reference plane used for gravity calculations. There are 3 kinds of gravity
reduction namely
1. Free reduction – Water
This reduction assumes that below the point of gravity on the earth's surface until
it reaches the geoid plane it is considered non-existent so that changes in the value of
gravity are caused by changes in the distance from the surface of the earth to the center of
gravity or differences in the value of surface gravity in the geoid are influenced by the
height factor.
If Me is the mass of the earth and R is the radius of the earth then the gravity on the geoid
(go) and on the surface (g) is
With a series approach the value of the gravity on the surface can be written
The equation for the Free – Air reduction is:
If the average gravity of the earth is used, which is 980.629 gal and the average radius of
the earth is 6.367 x 10 8 cm, the reduction in free air can be written
