If we assuming that the earth is a homogenous sphere (which she is not exactly) the gravitational field intensity may be written as
where r = distance of observation point from the centre of the earth.
The above expression shown that g decreases when we go away from the surface either inward (depth) outward (altitude).
For small height h above the surface
The above discussion shows that g varies at faster rate is going upward than in going inward from the surface of the earth.
As we go upward initially g falls at faster rate but at later distance its rate of fall becomes smaller-smaller whereas when we go inside the earth g goes on decreasing at constant rate becoming zero at the centre.
