The mean and standard deviation of the 500 velocities are computed. In our experience, drop velocities vary with drop diameter and distance from the sprinkler, and don't relate to theoretical terminal velocities at all. Normally a sample of 10,000 drops is collected at each distance from the sprinkler. Drop size tests are done along with a traditional test of the sprinkler application rate as a function of distance from the sprinkler. As noted above, drops cannot be counted if their image shadows the end diode of the array.
Larger drops have decreasing window sizes.
Thus the correction factor for a given size is the ratio of maximum window width to effective window width for that size. The drop size distribution for an entire sprinkler may be arranged as in Table 1. This table provides the full detail needed for research purposes, but is far too massive to be easily interpreted or used by the general irrigation community. So CIT, in consultation with industry members, has developed special drop size parameters to aid in the evaluation of sprinkler performance. These parameters can give an indication of which sprinklers, nozzles and pressures may be susceptible to pattern distortion by the wind, and which may be susceptible to infiltration rate reduction when irrigating bare soil.