High-resolution radar can detect individual raindrops

A high-resolution Doppler radar has the ability to detect individual hydrometeors, such as atmospheric raindrops, over 0.5 mm in diameter research led by the Naval Research Laboratory has revealed. The discovery should further understanding of the structure and behavior of clouds, and could lead to more accurate forecasting of severe weather.

A Doppler radar sends focused microwave signals towards a target and listens for the reflection. By analyzing the doppler effect, the changes in frequency of the reflected microwaves, the radar is able to ascertain the target’s velocity.

Though the principle is identical to that used by a police speed gun, the technology that comprises the high-resolution radar is rather more powerful. The 3 MW radar emits microwaves with a 0.22-degree beam-width, which allows it to interrogate a 14 cubic-meter (500 cubic foot) volume of cloud for individual raindrops from a range of 2 km (1.25 miles) at a “world’s best” resolution of 0.5 m (1.6 ft). The radar was previously put to use tracking debris coming away from NASA space shuttles during launch.

The detection of raindrops is in part made possible due to the fact that these larger drops are highly reflective but occur in much lower concentrations than the much smaller particles from which clouds are mainly comprised. Cloud droplets are on average only 10-15 micrometers in diameter.

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