Dr. Alexander P. Vasilkov Profile

Dr. Alexander P. Vasilkov

Senior Staff Scientist at Science Systems and Applications Inc

SPIE Involvement:

Author

Publications (13)

SPIE Journal Paper | 1 April 2005

Aerosol ultraviolet absorption experiment (2002 to 2004), part 2: absorption optical thickness, refractive index, and single scattering albedo

Nickolay Krotkov, Pawan Bhartia, Jay Herman, James Slusser, Gwendolyn Scott, Gordon Labow, Alexander Vasilkov, Tom Eck, Oleg Doubovik, Brent Holben

OE, Vol. 44, Issue 04, 041005, (April 2005) https://doi.org/10.1117/12.10.1117/1.1886819

KEYWORDS: Aerosols, Ultraviolet radiation, Absorption, Refractive index, Atmospheric modeling, Ozone, Atmospheric particles, Calibration, Visible radiation, Scattering

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Proceedings Article | 14 October 2004 Paper

Measuring aerosol UV absorption optical thickness by combining use of shadowband and almucantar techniques

Nickolay Krotkov, Pawan Bhartia, Jay Herman, James Slusser, Gwen Scott, Gordon Labow, Alexander Vasilkov, Thomas Eck, Oleg Dubovik, Brent Holben

Proceedings Volume 5545, (2004) https://doi.org/10.1117/12.559557

KEYWORDS: Aerosols, Ultraviolet radiation, Absorption, Refractive index, Visible radiation, Scattering, Ozone, Radiometry, Calibration, Atmospheric modeling

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We report final results of an aerosol UV absorption closure experiment where a UV-shadow-band radiometer (UV-MFRSR, USDA UVB Monitoring and Research Network) and 4 rotating sun-sky radiometers (CIMEL, NASA AERONET network) were run side-by-side continuously for 17 months at NASA/GSFC site in Greenbelt, MD. The aerosol extinction optical thickness τ_ext, was measured by the CIMEL direct-sun technique in the visible and at two UV wavelengths 340 and 380 nm. These results were used for UV-MFRSR daily on-site calibration and 3-min measurements of τ_ext at 325nm, 332nm and 368nm. The τ_ext measurements were used as input to the radiative transfer model along with AERONET retrievals of the column-integrated particle size distribution (PSD)to infer an effective imaginary part of the UV aerosol refractive index, k, by fitting MFRSR measured voltage ratios. Using all cases for cloud-free days, we derive diurnal and seasonal dependence of the aerosol absorption optical thickness, τ_abs with an uncertainty 0.01-0.02. At our site τ_abs follows pronounced seasonal dependence with maximum values ~0.07 at 368nm (~0.15 at 325nm) occurring in summer hazy conditions and <0.02 in winter-fall seasons, when aerosol loadings are small. Inferred values of k allow calculation of the single scattering albedo, ω, in UVA and comparisons with AERONET almucantar ω₄₄₀ retrievals at 440nm. Overall, ω was slightly lower in UV than in the visible: case average <ω₃₆₈>=0.93 compared to <ω₄₄₀>=0.95. However, the differences (<ω₄₄₀ - ω₃₆₈> ~0.02, rms difference ~0.016) are smaller than uncertainties of both retrievals (δω~0.03). Low <ω₃₆₈> values are consistent with higher values for imaginary refractive index, k: <k₃₆₈> ~0.01 compare to <k₄₄₀> ~0.006. However, mean differences in k (<k₃₆₈-k₄₄₀>~0.004) were only slightly larger than AERONET retrieval uncertainty δk ~0.003²⁷. We also found that ω decreases with decrease in τ_ext, suggesting different aerosol composition in summer and winter months. So far, our results do not allow explaining the causes of apparent larger aerosol absorption in UV. Continuing co-located measurements at GFSC is important to improve the comparison statistics, but conducting aerosol absorption measurements at different sites with varying conditions is also desirable.

Proceedings Article | 4 November 2003 Paper

A model for the assessment of UV penetration into ocean waters from space-based measurements and full radiative transfer calculations

Alexander Vasilkov, Jay Herman, Ziauddin Ahmad, B. Mitchell, Mati Kahru

Proceedings Volume 5156, (2003) https://doi.org/10.1117/12.506030

KEYWORDS: Atmospheric modeling, Ultraviolet radiation, Absorption, Data modeling, Reflectivity, Signal attenuation, Water, Clouds, Scattering, Radiative transfer

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Proceedings Article | 4 November 2003 Paper

Seasonal variation of UV radiation in the ocean under clear and cloudy conditions

Ziauddin Ahmad, Jay Herman, Alexander Vasilkov, Maria Tzortziou, B. Mitchell, Mati Kahru

Proceedings Volume 5156, (2003) https://doi.org/10.1117/12.505298

KEYWORDS: Clouds, Ozone, Ultraviolet radiation, Absorption, Aerosols, Reflectivity, Atmospheric particles, Radiative transfer, Ocean optics, Scattering

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Proceedings Article | 4 November 2003 Paper

Goddard UV aerosol absorption closure experiment (2002-03)

Nickolay Krotkov, Pawan Bhartia, Jay Herman, James Slusser, Gwendolyn Scott, Gordon Labow, Alexander Vasilkov, Tom Eck, Oleg Dubovik, Brent Holben

Proceedings Volume 5156, (2003) https://doi.org/10.1117/12.508967

KEYWORDS: Aerosols, Ultraviolet radiation, Refractive index, Clouds, Absorption, Atmospheric modeling, Scattering, Calibration, Atmospheric particles, Radiometry

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SPIE Journal Paper | 1 December 2002

Problems in assessment of the ultraviolet penetration into natural waters from space-based measurements

Alexander Vasilkov, Jay Herman, Nickolay Krotkov, Mati Kahru, Brian Mitchell, Christina Hsu

OE, Vol. 41, Issue 12, (December 2002) https://doi.org/10.1117/12.10.1117/1.1516822

KEYWORDS: Ultraviolet radiation, Absorption, Atmospheric modeling, Clouds, Aerosols, Data modeling, Visible radiation, Satellites, Optical properties, Water

Proceedings Article | 17 January 2002 Paper

Problems in assessment of the UV penetration into natural waters from space-based measurements

Alexander Vassilkov, Jay Herman, Nickolay Krotkov, B. Greg Mitchell, Mati Kahru

Proceedings Volume 4482, (2002) https://doi.org/10.1117/12.452912

KEYWORDS: Ultraviolet radiation, Absorption, Atmospheric modeling, Clouds, Satellites, Data modeling, Visible radiation, Radiative transfer, Optical properties, Water

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Proceedings Article | 11 August 1997 Paper

Remote control of natural waters with use of space optoelectronic systems

Timofei Kondranin, Alexander Vasilkov, Alexey Romanov, Andrei Shcherbakov

Proceedings Volume 3200, (1997) https://doi.org/10.1117/12.284738

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Proceedings Article | 26 October 1994 Paper

Solar ultraviolet radiation penetration and photochemical effect on colored dissolved organic matter in coastal waters

Alexander Vasilkov

Proceedings Volume 2258, (1994) https://doi.org/10.1117/12.190072

KEYWORDS: Absorption, Ultraviolet radiation, Ozone, Water, Ions, Optical properties, Atmospheric modeling, Scattering, Solar radiation, Ocean optics

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Proceedings Article | 10 December 1993 Paper

Estimation of the uncertainties of the retrieved seawater parameters

Igor Geogdzhaev, Timofei Kondranin, N. Krotkov, Alexander Vasilkov

Proceedings Volume 2048, (1993) https://doi.org/10.1117/12.165496

KEYWORDS: Scattering, Reflectivity, Error analysis, Absorption, Water, Particles, Optical testing, In situ metrology, Mass attenuation coefficient, Inverse problems

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Proceedings Article | 2 November 1993 Paper

Ultraviolet radiation in the atmosphere-ocean system: a model study

Nickolay Krotkov, Alexander Vasilkov

Proceedings Volume 2049, (1993) https://doi.org/10.1117/12.163517

KEYWORDS: Ozone, Atmospheric modeling, Ultraviolet radiation, Water, Absorption, Atmospheric optics, Atmospheric particles, Ocean optics, Aerosols, Ions

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Proceedings Article | 15 October 1993 Paper

Airborne lidar remote sensing of vertical distribution of sea water scattering coefficient

Alexander Vasilkov, Yuri Goldin, Boris Gureev

Proceedings Volume 1936, (1993) https://doi.org/10.1117/12.157108

KEYWORDS: LIDAR, Polarization, Scattering, Signal attenuation, Laser applications, Laser scattering, Water, Remote sensing, Light scattering, Ions

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Proceedings Article | 8 December 1992 Paper

Optimization of the polarization remote-sensing techniques of the ocean

Nickolay Krotkov, Timofei Kondranin, Alexander Vasilkov

Proceedings Volume 1747, (1992) https://doi.org/10.1117/12.138836

KEYWORDS: Polarization, Remote sensing, Atmospheric modeling, Atmospheric particles, Polarizers, Atmospheric optics, Ocean optics, Scattering, Solar radiation, Aerosols

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Showing 5 of 13 publications

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