The aureole technique is a method developed for estimating columnar optical and physical properties of atmospheric aerosols. It consists of measuring both direct solar irradiance and diffuse sky radiance by means of ground-based Sun-sky radiometers. Measurements are taken at different wavelengths in the UV-VIS-NIR bands, and selected within atmospheric windows in order to minimize the absorption of atmospheric gases (such as ozone, water vapor, NO2 or CO2).
The direct solar irradiance is measured by pointing the sensor normal to the sun direct direction.
The sky radiance measurements are taken in two different geometries:
Both direct and diffuse radiance measurements are analyzed by inversion algorithms (Nakajima et al., 1983, 1996; Dubovik et al., 2000) that solve the radiative transfer equation by taking into account the multiple scattering. Columnar optical and physical parameters retrieved by the aureole technique are: aerosol optical depth, Angström coefficient, single scattering albedo, scattering phase function, asymmetry factor, complex refractive index and size distribution.
O. Dubovik and M. D. King. "A flexible inversion algorithm for retrieval of aerosol optical properties from sun and sky radiance measurements," J. Geophys. Res. 105, 20673-20696, 2000.
T. Nakajima, M. Tanaka and T. Yamauchi. Retrieval of the optical properties of aerosols from the aureole and extinction data. App. Opt. No.22, pp.2951-2959, 1983
T. Nakajima, G. Tonna, R. Rao, P. Boi. Y. Kaufman and B. Holben, Use of sky brightness measurements from ground for remote sensing of particulate polydispersions. App. Opt. vol.35,No.15, pp.2672-2686, 1996