In Situ Cloud Characterization Instrument for Small Aerial Platforms -- a Feasibility Study

Description

A compact and inexpensive optical imaging technology is being developed for fast in situ characterization of cloud droplets, including measurement of droplet size distribution function and droplet number concentration. The targeted droplet diameter range is 10–1000 micrometer (um). The proposed method is based on analysis of scattered light images acquired by a two-camera imaging system from droplets illuminated by a pulsed light source. Results of two SBIR Phase I feasibility studies are reported. The first study includes experimental justification of the sensitivity and development of image processing software that involves identifying the droplet images in camera frames, determining the 3D coordinates and integral scattering signal for each droplet, and building an integral scattering intensity distribution function histogram, which can be re-binned to the droplet size distribution function histogram. The second study extends the proposed method to mixed phase cloud measurement applications. It adds the capability of polarization resolved imaging that allows discrimination between water droplets and non-spherical ice particles and also improves the sensitivity down to the droplet diameter of 2–3 um. In addition, an initial version of in situ particle imager is demonstrated, which provides optical resolution of about 3 um and can be used to determine the size and habit of ice particles. This work was supported by DOE SBIR Phase I Grants No. DE-SC0015095 and DE-SC0017149.