Answer: amount of precipitation reaching the ground
Explanation:
A Doppler radar uses the Doppler effect when measuring return echoes after having sent a signal (in this specific case microwaves).
In the case of weather radars, a microwave signal is sent to a target and then reflected, so that the radar system measures this difference between the sent signal and the reflected signal.
So, a Doppler radar is is useful to determine the intensity of the precipitation and its location, by calculating its motion, and estimating its type (for example: rain or snow, among others). In addition, this type of radar is able to determine the height and the structure of storms by detecting the motion of rain droplets.
However, weather radars are not capable to determine the amount of precipitation reaching the ground.
