DROPLET SIZE AND TRANSMITTANCE SPECTRA OF MECHANICALLY GENERATED WATER FOGS

The concept of using commercially available water fog generators to si mulate natural fogs and military obscurants is investigated. Results o btained with a high-pressure direct impaction system developed for agr icultural and environmental control applications are reported. Experim ents verify that such systems can produce optically dense ''artificial fogs'' similar in appearance to natural fogs under favorable meteorol ogical conditions. Measurements of the droplet mass distribution funct ion indicate a broad spectrum in the lower size region (0.3-1.5 mu m) and a marked peak in the upper region at a diameter of about 17 mu m. Experiments show that droplet size can be partially controlled with co mmon surfactants and inhibitors. The artificially generated fogs are g ood broadband obscurants, exhibiting a nearly flat transmittance spect rum in the visible through mid-infrared regions with a broad peak in t he far infrared region. The measured extinction spectrum is similar to natural fogs, being in between the advective and radiative cases.