Open AccessLight transport with weak angular dependence in fog
Author(s) -
Brian Bentz,
Brian J. Redman,
John D. van der Laan,
Karl Westlake,
Andrew G. Glen,
Andres L. Sanchez,
Jeremy Benjamin Wright
Publication year - 2021
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.422172
Subject(s) - scattering , optics , mie scattering , radiative transfer , heavy traffic approximation , computational physics , mean free path , physics , boltzmann equation , light scattering , path length , absorption (acoustics) , wavelength , atmospheric optics , diffusion , statistics , mathematics , quantum mechanics , thermodynamics
Random scattering and absorption of light by tiny particles in aerosols, like fog, reduce situational awareness and cause unacceptable down-time for critical systems or operations. Computationally efficient light transport models are desired for computational imaging to improve remote sensing capabilities in degraded optical environments. To this end, we have developed a model based on a weak angular dependence approximation to the Boltzmann or radiative transfer equation that appears to be applicable in both the moderate and highly scattering regimes, thereby covering the applicability domain of both the small angle and diffusion approximations. An analytic solution was derived and validated using experimental data acquired at the Sandia National Laboratory Fog Chamber facility. The evolution of the fog particle density and size distribution were measured and used to determine macroscopic absorption and scattering properties using Mie theory. A three-band (0.532, 1.55, and 9.68 µm) transmissometer with lock-in amplifiers enabled changes in fog density of over an order of magnitude to be measured due to the increased transmission at higher wavelengths, covering both the moderate and highly scattering regimes. The meteorological optical range parameter is shown to be about 0.6 times the transport mean free path length, suggesting an improved physical interpretation of this parameter.