An optical sensor for the measurement of microphysical and optical properties of aerosol and cloud particles

Droplet Measurement Technologies proposes to build a compact, lightweight optical sensor that measures the size, concentration, refractive index and phase of cloud and aerosol particles in the diameter range from 0.2 - 80 micrometers. The sensor uses a unique combination of optics that detects light scattered from individual particles in both forward and backward directions with respect to the incident laser beam. Comparison of the forward and back scattered components provides an estimate of particle refractive index and whether it is liquid or solid. The sum of these two scattering components is used to determine the particle size from Mie theory. The information is processed within the probe and sent in compressed form over a standard RS-232 serial line. Phase I of this proposal will demonstrate the forward and backward measurement and analysis technique and the ability of the digital signal processor to handle the quantity and speed of information. Phase II will take the laboratory demonstration model from Phase II and package it in a housing that will be installed on an aircraft for further testing and eventual research missions. The uniqueness of the proposed instrument is it 1) covers a size range that currently requires two commercially available sensors, 2) provides a measure of refractive index, 3) provides the data in a preprocessed form easily interfaced to computer communication ports 4) samples isokinetically, and 5) provides auxillary measurements of airspeed, temperature and instrument performance parameters.