Scattering Matrices Of Fire Smoke: Measurement, Modeling And Inversion For Particle Size Distribution And Refractive Index

Smoke is one of the basic characteristics of most fires. Scattering matrix is a key parameter to fully describe the light scattering properties of scatterers. Through investigation of scattering matrices of fire smoke particles, all light scattering characteristics and information about scatterers'properties (morphology and composition) can be obtained. Knowledge of the scattering matrices of fire smoke particles is of critical importance in fire detection, pollution control, interpretation of remote sensing data, as well as radar recognition.Smoke particles generated by five different test fires. were analyzed by SEM. Smoke from flaming fires displays fractal morphology. Fractal morphology parameters, including fractal dimension and prefactor, were derived using digital image process for smoke from flaming fire of polyurethane. Morphology of smoke from two smoldering fires is found to be different from of that of smoke from flaming fires. A method to obtain the size distribution information of smoke from smoldering fires based on SEM and AFM analysis were proposed. The elemental composition study shows that the carbon content of smoke from smoldering fires is obviously different from that of smoke from flaming fires. Based on SEM/AFM analysis and composition study, fractal aggregate shape model and spherical shape model were developed for smoke particles from flaming fires and smoldering fires, respectively. Modeling of scattering matrices of smoke particles were presented, aiming to investigate the influence of different shape models on light scattering properties.Through theoretical study of electro-optic modulation, upgrade of key optical and electrical devices, the earlier developed apparatus for scattering matrices measurement were improved. The accuracy of the apparatus was tested by water droplets. Measured scattering matrices as functions of the scattering angle at wavelength of 532 nm for smoke particles from five test fires were presented. We investigate the effects of difference in morphology and composition on the light scattering properties. In particular, comparison between smoke particles from smoldering fires and smoke from flaming fires were carried out. Application of simulated annealing for simultaneous retrieval of particle size distribution and refractive index were studied. Particle size distribution and refractive index of smoke from two smoldering fires were inferred from scattering matrices measurements results using the develop technique. We find that the scattering of smoke from smoldering fires can be well described by Lorenz-Mie theory, which indicated that the shape of smoke from smoldering is spherical. Evaluation of the accuracy of Lorenz-Mie theory to describe the scattering of smoke from flaming fires was also discussed.