Weather radars are used to measure the location and intensity of precipitation – including rain, snow and hail

Weather radars are the most effective way to collect real-time rainfall information. This data is used directly by weather forecasting services, for example by weather applications you might have on your mobile phone. It’s also used by scientists to analyse extreme weather and flooding events. This benefits the public through improved monitoring and forecasting of heavy rainfall.
Weather radars use an electromagnetic pulse to detect precipitation. The radar sends out electromagnetic pulses into the atmosphere, 1000 every second, and if there are precipitation particles in the air some of the energy will be reflected back towards the radar, where it is received and measured. The time delay between the transmitted and received pulses enables the range of the object to be determined. In the case of precipitation, the magnitude of the reflected signal is proportional to the size and number of raindrops.

The wavelength of the pulse depends on the size of the particles being measured. The NCAS X-band radar operates at a frequency of 9.4 Ghz, which is equivalent to a wavelength of 3cm, useful for detecting small particles with a high degree of sensitivity. Under certain conditions, and in the absence of precipitation, the radar is sometimes able to detect insects, which are known as clear-air echoes. The radar also measures the velocity of the targets through the Doppler effect.

Scientists have been developing weather radar for over 50 years. Soon after radar was developed for detecting aircraft in the 1930s, scientists realised it could be used to identify the location and intensity of rain droplets too.