Remote sensing of atmospheric aerosol properties
Document ID: 207
Philbrick, C. Russell1
Hallen, Hans D.1
Snyder, Michelle Grace1
Brown, Andrea M.2
1 North Carolina State University, Raleigh, NC, U.S.A.
2 Johns Hopkins University, Applied Physics Laboratory, Laurel, MD, U.S.A.
Presented: 91st American Meteorological Society Annual Meeting, 13th Conference on Atmospheric Chemistry
Seattle, Washington, January 22-27, 2011
Introduction
Ambient aerosol properties and distributions are still one of least understood features of the lower atmosphere. A new technique has been developed that promises to help fill the voids in this knowledge during the next several years. Based on ideas we considered in the mid-1980s, several doctoral students have developed and applied the capabilities of using the polarization ratio of the optical scattering phase function to determine the properties of atmospheric aerosols. Bistatic and multistatic lidar measurements use the polarization ratio of the scattering phase function to calculate profiles of the aerosol number density, size distribution, and type. These parameters can be determined for spherical particles in the size range between about 20 nm and 20 μm using UV-VIS-NIR wavelengths. Analysis of the aerosol concentration and size distribution requires adopting a mathematical shape function, usually a log-normal distribution of spherical particles. Information on aerosol type can be roughly determined based on the refractive index of the scatterers and depolarization of the scattered radiation as a function of wavelength. Measurements have been used to investigate vertical profiles of layered haze and determine the properties, and horizontal measurements have been used to characterize the aerosols for different types of fog. One project has studied the cases of relatively dense fogs, where multiple scattering dominates. Laser remote sensing techniques provide important tools to determine most of the characteristics of aerosols, including their physical and chemical properties. Spatial and temporal distributions of aerosols are then available to investigate the sources, processes of formation, growth rate, and the roles aerosols play in establishing the planetary albedo and radiative transfer into space.
Laser remote sensing techniques can now provide tools for investigations of most of the properties of aerosols, including their physical and chemical characteristics. Examples from several data sets are selected to show the types of information contained in the optical scattering signatures. These measurements improve our understanding of the distribution of aerosols, their sources, and processes controlling their formation and growth are needed for a detail understanding of their contributions to the planetary albedo and their influence on radiative transfer.
Several laser remote sensing techniques are used to characterize the properties of aerosols. The various techniques include: the Rayleigh lidar profiles of relative backscatter coefficient, profiles of optical extinction using Raman scatter, and bistatic-multistatic scattering using the polarization ratio of the scattering phase function. In addition, the Raman lidar can provide simultaneous profiles of water vapor and temperature so that the growth of hydroscopic aerosols can be examined. Bistatic and multistatic lidar measurements of the polarization ratio are used to determine the number density, size, and size distribution, under the assumption of spherical scatterers. The measurements can sometimes be used to describe other aerosol characteristics; properties such as aerosol type based upon approximate refractive index, and departures from spherical shape particles, can be determined when several wavelengths and multiple angles are available in simultaneous data sets, and when the aerosol environment is not too complex in containing several overlapping size distributions.
| Citation: | "Remote sensing of atmospheric aerosol properties", Philbrick, C. R., H. D. Hallen, M. G. Snyder, A. M. Brown, Proceedings of 13th Conference on Atmospheric Chemistry, Vol. J11.3, American Meteorological Society, 2011, pp. 1 - 13 |