AbstractA passive optical device has been developed for the ground‐basedin situmeasurement of liquid water content,L, in clouds. Light scattered at five, computationally selected, small forward angles is collected and ‐ with the application of appropriate weighting factors ‐ combined to give a response which is linearly proportional toLover the droplet diameter range 1 to 80 μm.Lcan be measured to within ±0.05 gm−3at a frequency of up to 100 Hz, thus permitting fluctuations in the liquid water content of clouds to be examined on spatial scales of less than one metre. A miniaturized version of the device ‐ for airborne usage ‐ is unde