A thesis submitted in partial fulfilment of the requirements for the degree of Master of Engineering of the Asian Institute of Technology, Bangkok, Thailand .

Thesis (M.Eng.) - Asian Institute of Technology, 1973

An investigation of the drop size distribution of rainfall at various intensities was made. The flour pellet technique of sampling raindrops was employed for this purpose. A rain sampling machine for automatic sampling near the ground level at any pre-determined intensity was designed. With the help of this machine, several samples at intensities varying from 1 in./hr. to 5 in./hr. were taken for analysis. A rain-intensity switch with provisions for instantaneous recording of any variation of intensity during the sampling period was also designed. The analysis of the results shows that drop size distribution of rainfall follows a definite pattern with the variation of intensity. The modal value of drop diameter is found to increase with intensity up to a certain rate of precipitation in between 2.5 in./hr. and 3.5 in./hr., after which it starts decreasing. It is found that the median volume drop diameter of rain does not go on increasing indefinitely as intensity increases. As in the case of modal drop diameter, it increases with intensity up to a certain value of probably 4 in./hr. and then a reversal of the trend starts for further increase in intensity.