Dear Tejaswi Lakkundi have ...

Dear Tejaswi Lakkundi have you tried the Arithmatic Mean? When the area of the basin is less than 500 km2 this method implies summing up of all the rainfall values from all the raingauging stations and then dividing it by the number of stations in that basin. 

I am listing down some of the widely used rainfall measurement  method here:

1. Standard Rain Gauge

2. Automated Rain Gauge

3. Measuring Precipitation with Weather Radar

4. Measuring Precipitation Using Weather Satellites - this is relatively new methods for the rainfall measurement. 

Also the Tropical Rainfall Measuring Mission (or TRMM) is a NASA satellite that provides more information both to test and to improve climate models. TRMM is particularly devoted to measuring precipitation in the tropics and subtropics of the earth. Among the three primary instruments on TRMM, the most innovative is the Precipitation Radar. The Precipitation Radar, built by the National Space Development Agency (NASDA) of Japan, will be the first spaceborne instrument designed to provide three-dimensional maps of storm structure. The measurements should yield invaluable information on the intensity and distribution of the rain, on the rain type, on the storm depth and on the height at which the snow melts into rain.