An Optical Instrument to Measure Cloud Liquid Water Content and Droplet Spectra

In fogs, accretion of supercooled water drops is responsible for icing of power lines and structures. In clouds, the same process causes icing on aircraft. In both cases the concentration and size of liquid wate drops, along with their velocity relative to the icing surface, primarily determines the shape and mass of the accreted ice. Better measurements of the concentration and size of water drops in fogs and clouds are needed to improve predictions of ice accretion. In Phase I, we do numerical simulations and perform laboratory tests of a new optical instrument for measurieng liquid water content and drop spectra. The new device makes high-resolution measurmentrs of the angular distribution of diffracted light from an 'ensemble' of water drops. Using weighting functions, liquid water content is computed in software. Using inversion techniques, the same set of measurments are then used to compute drop spectra without a priori assumption of the shape of the spectra. The new instruments works without the need to measure air velocity and temperature. In Phase II, we will build a reggedized, microprocessor-based, field version of the instrument that functions without operator intervention.