Abstract
Abstract. This paper presents a new method for simultaneously retrieving aerosol and surface reflectance properties from combined airborne and ground-based direct and diffuse radiometric measurements. The method is based on the standard Aerosol Robotic Network (AERONET) method for retrieving aerosol size distribution, complex index of refraction, and single scattering albedo, but modified to retrieve aerosol properties in two layers, below and above the aircraft, and parameters on surface optical properties from combined datasets (Cloud Absorption Radiometer (CAR) and AERONET data). A key advantage of this method is the inversion of all available spectral and angular data at the same time, while accounting for the influence of noise in the inversion procedure using statistical optimization. The wide spectral (0.34–2.30 μm) and angular range (180°) of the CAR instrument, combined with observations from an AERONET sunphotometer, provide sufficient measurement constraints for characterizing aerosol and surface properties with minimal assumptions. The robustness of the method was tested on observations made during four different field campaigns: (a) the Southern African Regional Science Initiative 2000 over Mongu, Zambia, (b) the Intercontinental Transport Experiment-Phase B over Mexico City, Mexico (c) Cloud and Land Surface Interaction Campaign over the Atmospheric Radiation Measurement (ARM) Central Facility, Oklahoma, USA, and (d) the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) over Elson Lagoon in Barrow, Alaska, USA. The four areas are dominated by different surface characteristics and aerosol types, and therefore provide good test cases for the new inversion method.
Highlights
The techniques for deriving atmospheric aerosols from solar transmission measurements may be traced back to the very early effort of Bouguer in 1725 on measuring light extinction at different solar elevations in an attempt to discover “a true law” followed by light in its attenuation
It is important to check the performance of the inversion method with different bidirectional reflectance distribution function (BRDF) models, we will demonstrate the performance of the inversion using the Coupled Surface-Atmosphere Reflectance (CSAR) model
The CSAR is a three-parameter semi-empirical model based on a product of three functions: (i) a modified Minnaert function (Minnaert, 1941), which is a combination of the view and illumination zenith angles, (ii) a one-term Henyey-Greenstein term F (g), and (iii) a hot spot function simulated by 1 + R(G)
Summary
The techniques for deriving atmospheric aerosols from solar transmission measurements may be traced back to the very early effort of Bouguer in 1725 on measuring light extinction at different solar elevations in an attempt to discover “a true law” followed by light in its attenuation (cf. Bouguer, 1760). There are a few methods that are used to retrieve aerosol properties over bright surfaces such as arid or unvegetated surfaces by making use of multi-channel, multi-angle, and/or polarimetric satellite observations (cf Hsu et al, 2004; Diner et al, 2008; Deuzeet al., 1993). None of these methods have the ability to retrieve complete sets of aerosol optical properties, and most derive only the total aerosol content assuming aerosol models representative of local conditions.
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