Single‐scattering albedo of smoke retrieved from the sky radiance and solar transmittance measured from ground

Abstract

A method of aerosol single‐scattering albedo retrieval from diffuse radiance measured in the solar almucantar and direct solar measurements is proposed. The aerosol scattering optical thickness is derived from the diffuse radiance by applying a radiative transfer model driven by aerosol microstructure parameters and Mie theory. To improve the accuracy of the scattering optical thickness, the inversion results are acceptable only if the radiance is measured across the total almucantar and is accurately fitted by a theoretical model. The aerosol is assumed as an external mixture of purely scattering particles and soot particles, with the soot approximated as a pure absorber. The criterion for the acceptance of fit is determined from the analysis of the effects of random and systematic errors on the single‐scattering albedo retrieval. The method was applied to measurements conducted during the Smoke, Clouds, and Radiation ‐ Brazil (SCAR‐B) campaign in August and September 1995. Aerosol radiance data were extensively collected by the Aerosol Robotic Network (AERONET) of ground‐based Sun/sky radiometers. The analysis focuses on the studies of the time variability of the biomass burning aerosol in the local Cuiabá area, supplemented by measurements collected in Cuiabá in 1993–1994. The results show reasonable ranges of the aerosol single‐scattering albedo variability (for example, single‐scattering albedo averages 0.87 ±0.08 at 670 nm). The spectral dependence of the single‐scattering albedo has both tendencies: decreasing and increasing with wavelength. The potential reasons causing different spectral behavior are analyzed theoretically.