Compact, Airborne, Particle-Sizing Sensor

A unique, airborne particle sizing system is proposed to reliably measure the size and number of particles found in the atmosphere from their backscattering off-axis signal. The proposed technique will solve a fundamental problem in optical particle sizing that normally prevents the use of backscattering or near backscattering. Multiple wavelengths from independent laser diode sources will be mixed to produce a laser sheet to illuminate the particles. Light scattered at angles between ninety degrees and backscattering by particles crossing the laser sheet will not have the large Mie scattering oscillations characteristic of monochromatic radiation, but instead will be characterized by a near-monotonic distribution. The feasibility of using two receivers positioned symmetrically to the laser transmitter will be explored to assess the ability of establishing particle asphericity. A backscattering receiver with an interference filter centered at a wavelength of interest to optical air data systems will provide the backscattering distribution. Analyses using five discrete wavelengths near 800 nm show that particles between 0.4 ¿m and 20 ¿m yield a typical measurement error of 5% for known index of refraction. Phase I will include analytical studies and experimental work with particles of known size and composition.