Spectral discrimination of coarse and fine mode optical depth

By Norman T. O'Neill, Thomas F. Eck, Alexander Smirnov, Brent N. Holben, S. Thulasiraman. 2003

706 citations recorded by the source corpus.

[1] The recognition that the aerosol particle size distribution (PSD) is effectively bimodal permits the extraction of the fine and coarse mode optical depths (tf and tc) from the spectral shape of the total aerosol optical depth (ta = tf + tc). This purely optical technique avoids intermediate computations of the PSD and yields a direct optical output that is commensurate in complexity with the spectral information content of ta. The separation into tf and tc is a robust process and yields aerosol optical statistics, which are more intrinsic than those, obtained from a generic analysis of ta. Partial (optical) validation is provided by (1) demonstrating the physical coherence of the simple model employed, (2) demonstrating that tc variation is coherent with photographic evidence of thin cloud events and that tf variation is coherent with photographic evidence of clear sky and haze events, and (3) showing that the retrieved values of tf and tc are wellcorrelated, if weakly biased, relative to formal inversions of combined solar extinction and sky radiance data. The spectral inversion technique permitted a closer scrutiny of a standard (temporally based) cloud-screening algorithm. Perturbations of monthly or longer-term statistics associated with passive or active shortcomings of operational cloud screening were inferred to be small to occasionally moderate over a sampling of cases. Diurnal illustrations were given where it was clear that such shortcomings can have a significant impact on the interpretation of specific events; (1) commission errors in tf due to the exclusion of excessively high-frequency fine mode events and (2) omission errors in tc due to the inclusion of insufficiently high-frequency thin homogeneous cloud events. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 4801 Oceanography: Biological and Chemical: Aerosols (0305); KEYWORDS: Sun photometry, aerosol, optical depth, fine mode, coarse mode, cloud screening

Subfields: Atmospheric Science, Global and Planetary Change

View Paper: https://www.semanticscholar.org/paper/0160755a003153be07628482c38ff9efe2193c93

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Citations in the corpus

Angstrom exponent and bimodal aerosol size distributions (2006, background): “…with wavelength, and a more precise empirical relationship between aerosol extinction and wavelength is obtained with a 2nd-order polynomial [King and Byrne, 1976; Eck et al., 1999; Eck. et al., 2001a, b, 2003; Kaufman, 1993; O’Neill et al., 2001a, 2003]: ln τ(λi) = a0 + a1 ln λi + a2(ln λi) 2.”
Second‐generation operational algorithm: Retrieval of aerosol properties over land from inversion of Moderate Resolution Imaging Spectroradiometer spectral reflectance (2007, methodology): “O’Neill et al. [2003] developed a method for retreiving h from the direct Sun measurements of spectral t.”
Global Monitoring and Forecasting of Biomass-Burning Smoke: Description of and Lessons From the Fire Locating and Modeling of Burning Emissions (FLAMBE) Program (2009, methodology): “Table IV contains regressions of FLAMBE smoke AOD to fine mode optical depths as derived from a spectral deconvolution method [68].”