How can weather radar detect the difference between rain and freezing rain?

Dear Tom,
How can weather radar detect the difference between rain and freezing rain since freezing rain doesn’t become freezing until it falls to the Earth’s surface?

Ann Borsuk,
Clarendon Hills

Dear Ann,
Weather radar cannot tell the difference between rain and freezing rain. The radar beam reflects back to the transmitter a portion of the energy transmitted when it strikes objects like raindrops, and this returned energy is converted into an image on the radar scope. Whether raindrops in the air become rain or freezing rain upon striking the ground depends entirely on the temperature of the surface and surface-based objects. The radar cannot tell the difference because radar is not temperature-sensitive. However, computer algorithms enhance radar images and differentiate between rain, freezing rain, sleet and snow.