Wenbo Sun, Bruce Wielicki, David Young, and Constantine Lukashin 1.Introduction 2.Objective 3.Effect of anisotropic air molecules on radiation polarization 4.Depolarization of linearly polarized light by aerosols 5.Height of GSLC site on laser depolarization at TOA 6.Conclusion Depolarization of polarized light by atmospheric molecules and aerosols Wenbo Sun, Bruce Wielicki, David Young, and Constantine Lukashin CLARREO Science Definition Team Meeting, Hampton, VA, April 10-12, 2012

E1E1 E 10 E1E1 E2E2 For single scattering, if particle shape is symmetric to the incidence direction, the scattered light is not depolarized; but multiple scattering can cause depolarization for any particle shapes. The depolarization of the linearly polarized light by atmospheric components will incur uncertainty in the calibration of space-borne sensors for polarization with ground to space laser calibration (GSLC) system. Polarized light is depolarized by atmospheric components Introduction

1.In this study, we firstly examine the effect of molecular anisotropy on the polarization of Earth-atmosphere solar radiation. 2.We also calculated the depolarization of light by small sphere aggregates and irregular Gaussian-shaped particles, to reveal the effect of aerosols on the depolarization of linearly polarized light. 3.By doing these, we aim to achieve an accurate modeling of polarized radiation for CLARREO PDM and GSLC applications. Objective

For randomly oriented anisotropic molecule Rayleigh scattering (Hansen and Travis 1974) Effect of anisotropic air molecules on radiation polarization For isotropic molecule Rayleigh scattering (Chandraskhar 1950) For air How does the air molecule depolarization affect the polarization of upward radiation?

Wenbo Sun, Bruce Wielicki, David Young, and Constantine Lukashin WL = 490 nm SZA = deg

Wenbo Sun, Bruce Wielicki, David Young, and Constantine Lukashin WL = 490 nm SZA = deg

Wenbo Sun, Bruce Wielicki, David Young, and Constantine Lukashin WL = 532 nm SZA = deg

Wenbo Sun, Bruce Wielicki, David Young, and Constantine Lukashin WL = 532 nm SZA = deg

Wenbo Sun, Bruce Wielicki, David Young, and Constantine Lukashin Comparison of Pristine-sky DOP and reflectance at 490 nm and 532 nm, SZA = deg

Wenbo Sun, Bruce Wielicki, David Young, and Constantine Lukashin Comparison of Pristine-sky DOP and reflectance at 490 nm and 532 nm, SZA = deg

CALIPSO-measured depolarization ratios of different aerosols Depolarization of linearly polarized light by aerosols

We define I 1 and I 2 as parallel and perpendicular intensity of scattered light; I 01 and I 02 as parallel and perpendicular intensity of incident light, respectively. For linearly polarized incidence, in a proper coordinate system, we can have For any light scattered by any particles For linearly polarized light scattered by randomly oriented particles Depolarization ratio for linearly polarized incidence is Note: This is only for scattered light. For total field, we must add the transmitted light. Calculation of the depolarization of linearly polarized light by aerosol particles In this study, depolarization ratios of 3 particle habits are calculated. Refractive index of smoke aerosol ( i) is used.

. UPML Inner surface for wave source Incident + scattered field Scattered field only Incidence The FDTD is a direct numerical solution of the source-free Maxwell’s equations discretized both spatially and temporarily Phase matrix elements of irregular aerosols are calculated by the 3D UPML FDTD light scattering model

Comparison of phase matrix elements from Mie theory and the FDTD Validation of the light scattering model

Randomly Oriented Randomly Oriented Depolarization ratio at 532 nm as function of scattering angle for sphere aggregates of smoke particles Depolarization ratios of irregular aerosols have common features

Depolarization ratio at 532 nm as function of scattering angle for Gaussian-shaped aerosol particles

Phase matrix elements of Gaussian particles Why do depolarization ratios of irregular aerosols have common features?

Height of GSLC site on laser depolarization at TOA 532 nm DOP and normalized forward-scattered radiance at TOA for GSLC site at 0 km and 3 km altitude (AOT = 0.1 below 3 km only) 3 km AOT = 0.1 AOT = 0.0 Received = Direct + Forward-Scattered

Conclusion 1.Aerosol is the primary component of clear atmosphere to depolarize light. Air molecules are secondary issue. 2.Randomly oriented small irregular particles have some common depolarization properties as functions of scattering angle and size parameter. 3.Depolarization ratio of scattered light in the forward-scattering direction is very small, generally smaller than ~0.3% for aerosols. 4.Lager particles result in smaller forward-scattering depolarization ratio but larger backscattering depolarization ratio. 5.Over mountain > 3km, linearly polarized laser beam is little depolarized by the atmosphere. The laser intensity is also little affected by the atmosphere.