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Atmospheric Composition

Airborne dust particles play an important role in the Earth's climate system through their direct and indirect influences on the radiation budget and hydrological cycle in the earth-atmosphere system. Dust particles are almost exclusively nonspherical particles with complicated morphologies. A number of recent studies have demonstrated that the nonsphercity effect of dust particles on relevant radiative transfer simulations and remote sensing applications cannot be neglected. To use the minimum number of the degree of morphological freedom to account for particle nonsphericity, the simplest model is the spheroid model that involves two degrees of morphological freedom, i.e., particle size and aspect ratio. The optical properties of spheroidal particles are highly sensitive to the aspect ratios of these particles. To accurately quantify dust particle overall shapes in forward scattering and radiative transfer modeling efforts involved in various applications, there is a pressing need to investigate the distribution of dust aspect ratio from a global perspective on the basis of satellite observations. The aerosol polarimetry senor (APS) on the Glory platform will provide an unprecedented opportunity to study the aspect ratio distribution of dust aerosols. With the polarization capability and multi-angle observational features of the APS, we propose to infer the aspect ratio distribution of dust particles and to analyze its seasonal and geographical variations. Once the aspect ratio distribution is derived, we will compute the bulk scattering properties of dust particles as functions of the effective particle size, effective variance and mean aspect ratio for a number of satellite sensor channels including those of APS, MISR and MODIS. The scattering data sets will be made available to the remote sensing community. Since appropriate scattering properties of dust particles are a prerequisite of reliably retrieving dust properties from space observations, the outcome of this effort will directly benefit the Glory mission and NASA's other missions involving dust property retrieval. The major tasks of the proposed tasks are as follows: (1) Use state-of-the-art scattering models to simulate the scattering kernels for individual dust particles at the nine APS spectral bands. (2) The aforementioned scattering kernels will be further integrated with the distributions of particle aspect ratio and size to produce the bulk scattering properties of a polydispersion of dust particles. (3) Integrate a vector radiative transfer model and the aforementioned bulk scattering properties for simulating the Stokes parameters I, Q, and U at the top of the atmosphere. The forward model will properly account for Rayleigh scattering, gaseous absorption, and the bidirectional reflection function of the surface. (4) Identify a number of dusty scenes from APS observations. By minimizing the differences between the ASP observations and model simulations based on various dust particle aspect ratios, we will determine an appropriate value of the aspect ratio for each scene. Two techniques based on the spherical albedo and polarized reflectance pattern will be used to determine appropriate values of the aspect ratio distributions of dust particles. (5) Analyze the seasonal and geographical variations of the aspect ratios of dust particles from a global perspective. (6) Once the proper values of dust aspect ratios are determined for various geolocations and seasons, we will provide the corresponding bulk scattering properties of the dust particles to the remote sensing and radiative transfer communities for research application.

Project PI: Ping Yang/Texas A&M; University

Texas A&M; University Room 906B, O&M; Building Department of Atmospheric Sciences MS 3150 College Station, Texas 77843

Phone: (979)845-4923

Fax: (979)862-4466

Email:  pyang@ariel.met.tamu.edu

http://atmo.tamu.edu/profile/Pyang

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Started: Sep 27, 2010

Last Activity: Jan 04, 2011

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