Vertical profile of polarization over Vladivostok using horizon shadowing: Clues to understanding the altitude variation of reflectance of aerosol particles

• Published in: Journal of quantitative spectroscopy & radiative transfer 2018-01, Vol.204, p.94-102
• Main Authors: Pavlov, Andrey N., Zubko, Evgenij, Konstantinov, Oleg G., Shmirko, Konstantin, Mayor, Alexander Yu, Videen, Gorden
• Format: Article
• Language: English
• Subjects: Aerosol particles; Geometric albedo; Passive remote sensing; Polarization; Umov effect
• ISSN: 0022-4073; 1879-1352
• DOI: 10.1016/j.jqsrt.2017.08.024

•We measure degree of linear polarization of atmospheric aerosols over Vladivostok.•In twilight we measure polarization of aerosols at different altitude (0–17 km).•Umov law – inverse correlation of reflectance and polarization of scattered light.•Using the Umov law we estimate reflectance in aerosol particles.•Conclusions drawn with polarimetric technique are compared vs. lidar approach. We report polarimetric measurements of atmospheric aerosol in evening and morning twilight over Vladivostok (Russia) in late winter–early spring of 2017 using a horizon-shadowing technique. Motion of the Sun beneath the horizon changes the altitude of the boundary of the shadowed atmosphere h, making it possible to constrain the altitude of aerosol particles contributing to the polarimetric response. We investigate the degree of linear polarization P in aerosol particles at different altitudes, ranging from 0 km up to 17 km. In two out of four experiments we found significant variations of the polarimetric response (ΔP ∼ 10%) with altitude; whereas, in the other measurements, the polarization appeared nearly the same (ΔP ∼ 2–3%) throughout the entire range of the studied altitude. Polarization P was measured in the zenith direction with the scattering angle being θ ∼ 90° At such a scattering angle, the polarization is near its maximum value Pmax. We analyze our measurements using the Umov effect that describes an inverse correlation between Pmax and the geometric albedo A. On 2017-02-21, we estimate A ≈ 0.0120 ± 0.0004 at h = 0 km and A ≈ 0.0154 ± 0.0026 at h = 10 km. On 2017-02-27, we find the opposite trend, A ≈ 0.0108 ± 0.0003 (h = 0 km) and A ≈ 0.0084 ± 0.0006 (h = 10 km). On 2017-03-02 and 2017-03-03 we find A ≈ 0.0084 ± 0.0009 and A ≈ 0.0090 ± 0.0010, respectively. Conclusions drawn from polarimetric measurements appear in qualitative accordance with results of remote sensing with a three-wavelength lidar.