This project aims to develop an instrument to measure rain drop size distributions over integration periods of one second. These instruments, and the measurements made with them, have immediate and highly-valuable application in a range of radio network engineering problems. Measurements of drop size distributions, and the derived rain rates, at temporal scales of one second, provide valuable information on the interaction between atmospheric turbulence and rain formation. Rapid variation of rain drop kinetic energy distributions is also a viatl input into models aiming to understand erosion processes such as infiltation, rill formation and runoff.This project proposes to design and build a novel disdrometer based on analysis of the sound of individual raindrops hitting the surface of a tank of water. The water tank will have a catchment area at least an order of magnitude larger than other disdrometers. The proposed disdrometer is unique in that it will use multiple hydrophones to measure the characteristics of individual drops and to distinguish cases where more than one drop arrives almost simultaneously.Rain drops generate sound by several mechanisms when they impact on a water surface. Initially an intense compression wave is generated by the impact. The energy of this wave is proportional to the rain drop kinetic energy. In many cases, air bubbles are forced into the water by the impact and these oscillate. The sound generated by these bubbles is loud, protracted and highly variable. If surfactant is added to the water to reduce the surface tension, the production of entrained air bubbles can be suppressed. In this case, only the very short, 10 to 50 microseconds, impact wave is produced.The proposed disdrometer will use a water tank with surfactant. Four hydrophones within the tank will detect and measure the amplitude of impact waves caused by individual drop impacts. The use of multiple hydrophones allows the identification of cases where the impact waves from different drop impacts coincide at up to three hydrophones. The delay between impact wave arrival at the four hydrophones allows the position of the drop impact to be calculated. Knowledge of the drop impact position and the amplitude of the impact wave at the four hydrophones allows the drop kinetic energy, and hence the drop size, to be calculated. A disdrometer with the optimal catchment area is capable of measuring 400 drops per second for rain rates between 5 and 100 mm/hr.The project requires the design and construction of a water tank that is anechoic from 10 to 100 kHz. A data acquisition system needs to be built that will determine the arrival time and amplitude of impact waves at the four hydrophones. A data analysis system is required to calculate drop information from impact wave measurements. A disdrometer will be designed and built and tested with artificial rain drops at the University. When ready the disdrometer will be sited at Chilbolton observatory where it will be tested in natural rain and validated against a suite of rain gauges and standard disdrometers.