Abstract
Aerosol properties over the Arctic snow-covered regions are sparsely provided by temporal and spatially limited in situ measurements or active Lidar observations. This introduces large uncertainties for the understanding of aerosol effects on Arctic climate change. In this paper, aerosol optical depth (AOD) is derived using the advanced along-track scanning radiometer (AATSR) instrument. The basic idea is to utilize the dual-viewing observation capability of AATSR to reduce the impacts of AOD uncertainties introduced by the absolute wavelength-dependent error on surface reflectance estimation. AOD is derived assuming that the satellite observed surface reflectance ratio can be well characterized by a snow bidirectional reflectance distribution function (BRDF) model with a certain correction direct from satellite top of the atmosphere (TOA) observation. The aerosol types include an Arctic haze aerosol obtained from campaign measurement and Arctic background aerosol (maritime aerosol) types. The proper aerosol type is selected during the iteration step based on the minimization residual. The algorithm has been used over Spitsbergen for the spring period (April–May) and the AOD spatial distribution indicates that the retrieval AOD can capture the Arctic haze event. The comparison with AERONET observations shows promising results, with a correlation coefficient R = 0.70. The time series analysis shows no systematical biases between AATSR retrieved AOD and AERONET observed ones.
Highlights
Aerosols exert a variety of effects on both the climate and the environment, directly through scattering, and indirectly through their effects on cloud formation and the microphysical properties of clouds, which in turn influences cloud albedo and precipitation [1,2]
The pure snow bidirectional reflectance distribution function (BRDF) model has been corrected by the snow fraction estimation from the normalized-difference snow index (NDSI)
This paper aims to provide an attempt to derive aerosol optical depth (AOD) over the Arctic regions
Summary
Aerosols exert a variety of effects on both the climate and the environment, directly through scattering (e.g., cooling of the atmosphere–surface system and absorption of incoming solar radiation that cools the surface but warms the atmosphere), and indirectly through their effects on cloud formation and the microphysical properties of clouds, which in turn influences cloud albedo and precipitation [1,2]. Aerosol optical depth (AOD) retrieval over the Arctic region from satellite is an important but challenging task. Existing aerosol retrieval algorithms for passive remote sensing focus mainly on those snow/ice and cloud free regions. Especially a multi-angle imaging spectro-radiometer (MIRS), show potential capabilities for aerosol retrieval over snow and ice and has been investigated [8]. Istomina et al tried to use a dual-view method with visible wavelengths [9] and infrared [12] spectral regions to retrieve AOD over the Arctic regions using advanced along-track scanning radiometer (AATSR) data. Mei et al have used a similar idea to retrieve AOD over the Arctic regions using both AATSR [10] and MODIS [11].
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