OPTIMIZATION OF SUN-PHOTOMETRIC MEASUREMENTS OF OPTICAL DEPTH OF ATMOSPHERIC AEROSOL DURING DAYTIME

Ground-based measurements of atmospheric aerosol are mainly carried out using solar photometers. The results obtained with the help of these meters allow us to study the effect of aerosol on the amount of optical radiation entering the Earth’s surface, to create physical and chemical models of the atmosphere, to validate satellite data and to carry out atmospheric correction of these data. When measuring direct solar radiation, the photometer input also receives an optical signal of the “forward scattering” type. If the atmosphere is sufficiently polluted with aerosol and the zenith angle of the Sun is sufficiently large, the error in measuring the optical density of the aerosol can reach a significant value. Taking into account the above results of well-known experimental studies, it is relevant to develop a methodology for optimal aerosol measurements during the sunny hours of the day when the zenith angle of the Sun changes within large limits. The article is devoted to the optimization of daytime solar-photometric measurements of the optical density of atmospheric aerosol. On the one hand, an increase in AOD leads to an increase in forward scattering radiation and on the other hand, with an increase in AOD, there is a decrease in direct solar radiation, which in turn leads to a decrease in forward scattering radiation. As a result, the forward-scattered radiation has a maximum of AOD, which depends on the wavelength. Based on the results of known experimental studies of the measurement error of AOD, which occurs due to the influence of the scattering of solar radiation by aerosol particles in the forward direction, the problem of optimizing a series of such measurements is formulated. As a result of solving this problem, the functional dependence of the ratio of direct and diffuse radiation on the cosine of the zenith angle is obtained, at which the average value of the AOD measurement error reaches the minimum value. The mathematical solution of this problem is given.

aerosol, optical density, error, scattering, solar radiation, atmosphere, photometer, zenith angle direct radiation, diffuse radiation

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