Effect of the Aerosol Type Selection for the Retrieval of Shortwave Ground Net Radiation: Case Study Using Landsat 8 Data

Cristiana Bassani,Ciro Manzo,Ashraf Zakey,Emilio Cuevas-Agulló

doi:10.3390/atmos7090111

Abstract

This paper discusses the aerosol radiative effects involved in the accuracy of shortwave net radiation, R n . s w , with s w ∈ (400–900) nm, retrieved by the Operational Land Imager (OLI), the new generation sensor of the Landsat mission. Net radiation is a key parameter for the energy exchange between the land and atmosphere; thus, R n . s w retrieval from space is under investigation by exploiting the increased spatial resolution of the visible and near-infrared OLI data. We adopted the latest version of the Second Simulation of a Satellite Signal in the Solar Spectrum (6SV) atmospheric radiative transfer model implemented in the atmospheric correction algorithm (OLI Atmospherically-Corrected Reflectance Imagery (OLI@CRI)) developed specifically for OLI data. The values of R n . s w were obtained by varying the microphysical properties of the aerosol during the OLI@CRI retrieval of both the OLI surface reflectance, ρ p x l o l i , and the incoming solar irradiance at the surface. The analysis of the aerosol effects on the R n . s w was carried out on a spectrally-homogeneous desert area located in the southwestern Nile Delta. The results reveal that the R n . s w available for energy exchange between the land and atmosphere reduces the accuracy (NRMSE ≃ 14%) when the local aerosol microphysical properties are not considered during the processing of space data. Consequently, these findings suggest that the aerosol type should be considered for variables retrieved by satellite observations concerning the energy exchange in the natural ecosystems, such as Photosynthetically-Active Radiation (PAR). This will also improve the accuracy of land monitoring and of solar energy for power generation when space data are used.

Highlights

Natural and anthropogenic aerosols directly affect the energy exchange in the Earth-atmosphere coupled system by scattering and absorbing the solar radiation and indirectly by changing the lifetime and the microphysical properties of the clouds [1,2,3]
We investigated the influence of the aerosol types with the default exponential vertical aerosol profile of the 6SVmodel, on the shortwave net radiation from Operational Land Imager (OLI) data by considering the OLI image atmospherically corrected with aerosol dust-like component as the benchmark, after validation with the reflectance Moderate Resolution Imaging Spectroradiometer (MODIS) product, ρmodis
These atmospheric parameters were changed to the direct products of the AERONET station only when the OLI@CRI algorithm was applied to the OLI image with El Farafra atmospheric conditions

Summary

Introduction

Natural and anthropogenic aerosols directly affect the energy exchange in the Earth-atmosphere coupled system by scattering and absorbing the solar radiation and indirectly by changing the lifetime and the microphysical properties of the clouds [1,2,3]. There are still uncertainties regarding the radiative effects of the atmospheric aerosol, and many efforts are underway to overcome the resulting errors on the energy exchange in natural ecosystems [4]. Concerning the direct effect, aerosols determine the direct and diffuse components of the radiation available at the surface for land-atmosphere energy exchange. A key parameter for energy exchange studies is the net radiation, Rn , which is defined by the difference between the incoming and the outgoing irradiance, which in turn depend on surface. The Rn.sw depends on the capability of the surface to reflect solar radiation (surface albedo), while the Rn.lw depends on the temperature and emissivity of the surface [5]

Methods

Results

Conclusion