Rainfall Estimation - Introduction
From the radar equation, we can get Z, the radar reflectivity factor. Recall that:
Z depends on the rainfall rate (RR) and the size distribution (SD) of the drops.
So Z = Z(RR,SD) (2)
Since Z is known, but RR and SD are unknown, (2) shows that we have one equation, but two unknowns.
Solution to problem:
Let's assume a specific form of the size distribution - the Marshal Palmer Drop Size Distribution:
Where D is the drop diameter (mm)
N0 is just a constant = 8000/m3mm
l can be expressed in terms of the rainfall rate:
l = 4.1R-0.21 (for rain)
where R is the rainfall rate in mm/hr.
So (3) becomes:
Hence, we can use (4) with a known rainfall rate (R) to calculate the number of drops (Nd) at a given diameter, (D). (see graph above)