AERONET inversion code provides aerosol optical properties in the total atmospheric column derived from the direct and diffuse radiation measured by AERONET

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AEROSOL ROBOTIC NETWORK (AERONET) DOCUMENT 1 AERONET Inversion Products AERONET i nversion code provides aerosol optical properties in the total atmospheric column derived from the direct and diffuse radiation measured by AERONET Cimel sun/sky -radiometers. AERONET inversion development and research activities are described in the papers by Dubovik and King, [2000], Dubovik et al. [2000], Dubovik et al. [2002a], Dubovik et al. [2002b], Dubovik et al., [2006 ], Siny uk et al. [2007]. The Version 2 (V2) inversion (or retrieval) products are summarized b elow. These products are available through the internal analysis system fidemonstratfl and the AERONET website. A detailed description of V2 AERONET retrieval will be provided in the paper by Holben et al., [2006 ]. 1. Operational Protocol: РThe AERON ET code inverts sky radiances simultaneously at all available wavelengths for the complete solar almucantar scenario or princip al plane scenario (~2.0 < ) together with measurements of aerosol optical depth () at the same wavelengths . Depending on the model of Cimel radiometer , the measurements may be taken on all or some of the following spectral channels: 0.34, 0.38, 0.44 , 0.5, 0.675, 0.87, 1.02 and 1.64 m. 2. Inversion assumptions: - Aerosol particles are assumed to be partitioned into two components : spherical and non -spherical. The s pherical component is modeled by an ensemble of polydisperse , homogeneous spheres ( complex index of refraction is the same for particles of all sizes). The n on-spherical component is a mixture of polydisperse , randomly -oriented homogeneous spheroids [e.g. Mishchenko et al. 1997]. The spheroid aspect ratio distribution is fixed to one retrieved by Dubovik et al. [2 006] and fit to the entire scattering matrix of mineral dust (Feldspar) measured in laboratory by Volten et al. [2001]. The importance of using refined surface reflectance properties in the retrieval and possible improvements in retrieved aerosol propertie s are described by Sinyuk et al. [ 2007]. - Atmosphere is assumed plane -parallel. - Vertical distribution of aerosol is assumed homogeneous in the almucantar inversion and bi -layered for the princip al plane inversion. - Surface Reflectance is approxima ted by BRDF: Cox -Mun k model for over water of Cox and Munk [1954a] and by Lie -Ross model over land of Lucht and Roujean [2000] . The BRDF parameters for land sites are adopted from MODIS Ecotype PAGE - 2 ============ AEROSOL ROBOTIC NETWORK (AERONET) DOCUMENT 2 generic BRDF models (courtesy of Feng Gao). The BRDF models ar e mixed according to Eco type map of Moody et al. [2005], NISE SSM/I snow and ice extent by Nolin et al. [1998] and MO DIS snow cover map by Hall et al. [2002]. Cox -Munk calculations use wind speed from NCEP/NCAR Reanalysis data , which are acquired from the NOAA National Weather Service NOMADS NCEP server . - The statistically optimized inversion and corresponding retrieval error estimates are obtain ed under the assumption of uncorrelated log -normally distributed errors. Th is optimization accounts for differe nt levels of accurac y in the measurements (e.g. the standard deviation for error in () is assumed 0.01, the standard deviation for error in sky radiance measurements is assumed 5%). The details see in Dubovik and King [2000], Dubovik [2004] and Dubovik e t al. [2006b]. 3. Inversion results: The V2 AERONET retrieval provides wide number of parameters and characteristics that are important for the comprehensive interpretation of the aerosol retrieval. The output include s both retrieved aerosol parameters ( i.e., size distribution, complex refractive index and partition of spherical/non -spherical particles) and calculated on the basis of the retrieved aerosol properties (e.g. phase function, single scattering albedo, spectral and broad -band fluxes, etc.). In addition, the output provides many values that can be helpful for assessment of the retrieval quality. Namely, the output provides estimates for both random and possible systematic (resulted from possible biases in measurements) errors for most of the retr ieved characteristics. According to those estimates, 68% confidence interval intervals are presented for most retrieved characteristics. Also, for convenience of data analysis, the retrieval code groups the output based on measured characteristics and thei r fit. 3.1 Microphysics The volume particle size distribution dV(r)/dlnr (m3/m2) is retrieved for 22 logarithmically equidistant discrete points ( ri) in the range of sizes 0.05 m. The real n() n( k() parts of the complex refractive k( radiance measurements. The retrieval provides the percentage of spherical particles in the observed aerosol [Dubovik et al., 2006 ]. In addition to the det ailed size distribution , the retrieval provides the following standard parameters for total (t), fine (f) and course (c) aerosol modes: (*) -the definitions of each parameter are given in the Appendix below. Cv Π(m3/m2) volume concentration (t, f, c); rv- volume median radius (t, f, c); - standard deviation (t, f, c); reff - effective radius (t, f, c); PAGE - 3 ============ AEROSOL ROBOTIC NETWORK (AERONET) DOCUMENT 3 Fine and coarse mode separation : The inversion code finds the minimum within the size interval from 0.439 to 0. 992 m. This minimum is used as a separa tion point between fine and coarse mode particles. Using that separation , the code simulate s optical thickness, phase function and single scattering albedo of fine and coarse mode separately. Furthermore, the retrieval provides estimates of Effective Radiu s reff , Volume Median Radius reff , Standard Deviation and Volume concentrations Cv (m3/m2) for both fine and coarse modes of the retrieved size distribution. NOTE: The fine and coarse modes of single scattering albedo are technically estimated, however, it is not advised to use these values for the phys ical interpretation because the retrieval is implemented under assumption that complex refractive index is the same for all particle sizes. NOTE: These parameters characterize generally a size distribution of any shape. Therefore, they can still be usefu l even if the size distribution is not bi -modal. 3.2 Radiative properties 0() - single scattering albedo at wavelengths corresponding to sky radiance measurements; P(; ) - phase function for 83 scattering angles at wavelengths corresponding to sky radiance measurements; Рasymmetry parameter for each phase func tion; Spectral fluxes (W/m 2) at the wavelengths corresponding to sky radiance measurements: FTOA () and F BOA () Рdown ward flux FTOA () and F BOA () Рupward ward flux (TOA Рtop of atmosphere and BOA Рbottom of atmosphere) The detailed retrieved aerosol properties are used for calculating broad -band fluxes in spectral range from 0.2 to 4.0 m. The flux simulation rel ies on the retrieved n() and k(). The spectral integration uses n() and k() that are interpolated/extrapolated from the values n() and k() retrieved at AERONET wavelengths. Similarly, spectral dependence of surface reflectance is interpolated/extrapolated from surface albedo values assumed in the retrieval on the wavelengths of sun/sky -radiometer. The gaseous absorption is account ed using radiative transfer model GAME (Global Atmospheric ModEl) [Dubuisson et al., 1996]. This model performs spectral integration using correlated -k distribution based on line by line simulations [Scott, 1974].

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AEROSOL ROBOTIC NETWORK (AERONET) DOCUMENT 4 Broadband fluxes (W/m 2): FTOA and FBOA – down ward flux FTOA and F BOA – upward ward flux Radiative forcing (W/m 2): FTOA = F0TOA – FTOA FBOA = FBOA – F0BOA where F0TOA and F0BOA are fluxes calculated with no aerosol Radiative forcing efficiency (W/m 2): Feff TOA = FTOA / m) Feff BOA = FBOA / m) Appendix: The formulas for calculating standard parameters of the particle size distribution. Effective radius : reff r3dNrdlnrdlnrrmin rmax r2dNrdlnrdlnrrmin rmax (1) We retrieve the aerosol size distribution of the partic le volume dV(r)/dlnr. It relates to the distribution of particle number as follows: . rdrdNrrdrdNrVrdrdVln34lnln3 (2)

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AEROSOL ROBOTIC NETWORK (AERONET) DOCUMENT 5 Volume median radius (mean logarithm of radius): lnrvlnrdVrdlnrdlnrrmin rmax dVrdlnrdlnrrmin rmax . (3) Standard deviation from volume median radius (mean logarithm of radius): vlnrlnrv2dVrdlnrdlnrrmin rmax dVrdlnrdlnrrmin rmax . (4) Volume concentration (m3/m2): CvdVrdlnrrmin rmax dlnr. (5) Optical Residual (Error) f* values are measured sky radiance (or AOD ). f values are fit by the model for sky radiance (or AOD) . For sky error, N represents the number of sky radiance measurements for a spe cific wavelength. For sun error, N represents the number of wavelengths for AOD. Using logarithms: [ln ln ]2=1100 =% (6) The spectral sky error average is provided as the sky error of the retrieval.

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AEROSOL ROBOTIC NETWORK (AERONET) DOCUMENT 6 References. Cox, C., and W. Munk, 1 954a: The measurements of the roughness of the sea surface from photographs of the sun’s glitter. J. Opt. Soc. Am. , 44, 838-850 Dubovik, O. and M. D. King, fiA flexible inversion algorithm for retrieval of aerosol optical properties from Sun and sky radiance measurementsfl, J. Geophys. Res., 105, 20,673-20,696, 2000. Dubovik, O., A. Smirnov, B.N. Holben, M.D. King, Y. J. Kaufman, T.F . Eck and I. Slutsker, Accuracy assessment of aerosol optical properties retrieval from AERONET sun and sky radiance measurements, J. Geophys. Res ,105, 9791-9806, 2000. Dubovik, O., B. N. Holben, T. Lapyonok, A. Sinyuk, M. I. Mishchenko, P. Yang and I. Slutsker, Non -spherical aerosol retrieval method employing light scattering by spheroids, Geophys. Res. Lett ., 10, 10.1029/2001GL014506, 2002a. Dubovik, O., B. N. Holben, T. F. Eck, A. Smirnov, Y. J. Kaufman, M. D. King, D. Tanré, and I. Slutsker, fiVariabili ty of absorption and optical properties of key aerosol types observed in worldwide locationsfl, J. Atmos. Sci ., 59, 590 -608, 2002b. Dubovik, O., fiOptimization of Numerical Inversion in Photopolarimetric Remote Sensingfl, in Photopolarimetry in Remote Sensing (G. Videen, Y. Yatskiv and M. Mish -chenko, Eds.), Kluwer Academic Publishers, Dordrecht, Netherlands, 65 -106, 2004. Dubovik, O., A. Sinyuk, T. Lapyonok, B. N. Holben, M. Mishchenko, P. Yang, T. F. Eck, H. Volten, O. Munoz, B. Veihelmann, van der Zander, M Sorokin, and I. Slut -sker, Application of light scattering by spheroids for accounting for particle non – sphericity in remote sensing of desert dust, J. Geophys. Res ., 111, doi:10.1029/2005JD006619. Dubuisson, P., J.C. Buriez and Y. Fouquart, High Spectral Resolution Solar Radiative Transfer in Absorbing and Scattering media, application to the satellite simul ation, J. Quant. Spectros. Radiat. Transfer , Vol. 55, No 1, pp. 103 -126, 1996 Hall, D.K., G.A. Riggs, and V.V. Salomonson. 2002, updated daily. MODIS/Terra Snow Cover Daily L3 Global 0.05Deg CMG V004 , February 2000 to Present. Boulder, CO, USA: National S now and Ice Data Center. Digital media. Hall, D.K., G.A. Riggs, and V.V. Salomonson. 2003, updated daily. MODIS/Aqua Snow Cover Daily L3 Global 0.05Deg CMG V004 , July 2002 to Present . Boulder, CO, USA: National Snow and Ice Data Center. Digital media. Holben, B. N., T. F. Eck, I. Slutsker, A. Smirnov, A Sinyuk, J. Schafer, D. Giles, O. Dubovik , 2006: Aeronet ™s Version 2.0 quality assurance criteria, Proc. SPIE 6408, Remote Sensing of the Atmosphere and Clouds, 6 4080Q, doi:10.1117/12.706524. Luch t, W., and Roujean, J. L. (2000), Consideration in parametric modeling of BRDF and albedo from multi -angular satellite sensors observations. Remote Sensing Reviews, 18, 343 -379. Moody, E., G., M. D. King, S. Platnik, C. B. Schaaf, and F. Gao, Spatially com plete global spectral surface albedos: Value -added datasets derived from terra MODIS land products, IEEE Trans. Geosci. Remote Sens., 43 (1): 144 -158, 2005.

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AEROSOL ROBOTIC NETWORK (AERONET) DOCUMENT 8 Corrections /Updates Correction (4/8/2010): Updated Fine and Coarse Mode separation range from 0.194 to 0.576um to 0.439 to 0.992um Correction (2/1 9/2014): Updated size dist ribution description to state that retrievals are performed for discrete points ( ri) and not calculated for bins. Update (8/28/2014): Added description of the calculation of the optical residual to the Appendix. Correction (8/24/2015) Fixed typographical error in TOA radiative forcing calculation description Update (12/5/2016) Updated reference section to remove Dubovik et al. 2006 fiin press fl Modified Dubovi k et al. 2006b to Holben et al. 2006 Updated Sinyuk et al. 2006 ( under review ) to 2007

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