The meteorological particle sensor works by imaging individual particulates, including rain, snow and hail, and measuring their size. Larger dust particles are also detected. A laser beam is transmitted between the two terminals of the instrument. The shadows of the particles which pass through the beam are imaged onto a photo-diode array in the receiver terminal. The number of elements covered by the shadow the particle gives a measure of the particle size. The instrument is free to rotate on a pivot; a large vane on the side of the instrument orients it with the instantaneous wind direction. Particles between 0.05 and 3.2 mm in diameter are counted in 62 size bins.

The system provides an instant response to the onset of rainfall and changes in rainfall rate and drop size distribution, without any delay such as occurs in raingauges which rely on collecting rain in a funnel. It is sensitive to smaller particles than can be quantified using a disdrometer. Measurements are made continuously.

The meteorological particle sensor was manufactured by Droplet Measurement Technologies, Inc. (USA). It was deployed at Sparsholt College from 2004 to 2007 and has been deployed at Chilbolton since 2009.