Through the use of Z-R relationships which relate reflectivity and rainfall rates, weather radars can be used to determine estimates of rainfall. These relationships take the form of Z = ARB where A and B are constants, Z is reflectivity and R is the rainfall rate. Depending on the type of precipitation and the environment in which that precipitation is falling, different Z-R relations are used to estimate the rainfall. These different relations are designed to create more accurate representations of rainfall totals. However other factors go into the accuracy of rainfall estimates as well. The distance between a point and the radar, the radar's power and the radar's beamwidth are some of the factors which can influence radar estimates of rainfall.

Using a combination of Vaisala WXT-510 peizometric rain sensors and tipping bucket mechanisms we measured rainfall over several weeks for different rainfall events and compared the radar estimates of rainfall at sites in West Lafayette, IN from the WSR-88D Doppler radar in Indianapolis, IN with estimates made from the 30” WRT-701C radar operated by WLFI in Lafayette, IN. While the Indianapolis radar is more powerful and has a smaller beamwidth, it is also much farther from West Lafayette. Results comparing the radar estimates of rainfall from the WLFI radar with the National Weather Service radar will be presented. Comparisons of the radar estimates to surface observations from the two types of rain gages, and a report on the consistency of the different measurement techniques will also be shown. We will also examine why one radar may have outperformed the other for a given rainfall event.