Nephelometer optical response model for the interpretation of atmospheric aerosol measurements

High-efficiency aerosol scatterometer that uses an integrating sphere for the calibration of multiwavelength lidar data

For the purpose of calibrating multiwavelength lidar data, we developed a scatterometer to measure the aerosol scattering coefficient at the ground level. The system is based on an integrating sphere, cw lasers (532 and 633 nm), and a controlled flow of the ambient air, including aerosol particles. The simulation study and experimental results indicate that the detection efficiency of this instrument is approximately 10%-40% better than that of an integrating nephelometer, because of the wider acceptance angle of the scattered light. The scattering coefficients measured at the two wavelengths, as well as the resulting value of the angstrom exponent, show good correlation with the results simultaneously measured with an integrating nephelometer and an optical particle counter.

Toward an ideal integrating nephelometer

The Integrating Sphere Integrating Nephelometer is a novel and unique reciprocal nephelometer that uses an integrating sphere with attached truncation-reduction tubes to contain the sample volume and to integrate the scattered light. Its main advantage compared with current integrating nephelometers is a sevenfold reduction in truncation angle, which reduces errors in measured scattering from large particles. Additional features include improved sampling efficiency for large particles and a well-defined operating wavelength.

Evidence for particle-shape sensitivity in the correlation between polarization states of light scattering

The cross correlation between polarization states of scattered laser speckle as a function of scattering angle is observed for a range of spherical and nonspherical particle suspensions. A variation in the degree of correlation between polarization states is observed, and this information is indicative of the particle shape. A comparison with a theoretical model for small particles is made, suggesting that variations in polarization correlation with angle originate from the nonisotropic polarizability of nonspheres. Experiments are also performed on large spheroids and random-shaped polydispersions, and the results indicate that the measurement method has significant potential for nonsphere detection and characterization.