Bayesian aerosol retrieval algorithm for MODIS AOD retrieval over land

We have developed a Bayesian aerosol retrieval (BAR) algorithm for the retrieval of aerosol optical depth (AOD) over land from the Moderate Resolution Imaging Spectroradiometer (MODIS). In the BAR algorithm, we simultaneously retrieve all dark land pixels in a granule, utilize spatial correlation mo...

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Bibliographic Details
Published in:Atmospheric Measurement Techniques
Main Authors: Lipponen, Antti, Mielonen, Tero, Pitkänen, Mikko R. A., Levy, Robert C., Sawyer, Virginia R., Romakkaniemi, Sami, Kolehmainen, Ville, Arola, Antti
Format: Article in Journal/Newspaper
Language:English
Published: Copernicus Publications 2018
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article
Verlagsveröffentlichung
Aerosol Robotic Network
Online Access:https://doi.org/10.5194/amt-11-1529-2018
https://noa.gwlb.de/receive/cop_mods_00006987
https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00006944/amt-11-1529-2018.pdf
https://amt.copernicus.org/articles/11/1529/2018/amt-11-1529-2018.pdf
Description
Summary:We have developed a Bayesian aerosol retrieval (BAR) algorithm for the retrieval of aerosol optical depth (AOD) over land from the Moderate Resolution Imaging Spectroradiometer (MODIS). In the BAR algorithm, we simultaneously retrieve all dark land pixels in a granule, utilize spatial correlation models for the unknown aerosol parameters, use a statistical prior model for the surface reflectance, and take into account the uncertainties due to fixed aerosol models. The retrieved parameters are total AOD at 0.55 µm, fine-mode fraction (FMF), and surface reflectances at four different wavelengths (0.47, 0.55, 0.64, and 2.1 µm). The accuracy of the new algorithm is evaluated by comparing the AOD retrievals to Aerosol Robotic Network (AERONET) AOD. The results show that the BAR significantly improves the accuracy of AOD retrievals over the operational Dark Target (DT) algorithm. A reduction of about 29 % in the AOD root mean square error and decrease of about 80 % in the median bias of AOD were found globally when the BAR was used instead of the DT algorithm. Furthermore, the fraction of AOD retrievals inside the ±(0.05+15%) expected error envelope increased from 55 to 76 %. In addition to retrieving the values of AOD, FMF, and surface reflectance, the BAR also gives pixel-level posterior uncertainty estimates for the retrieved parameters. The BAR algorithm always results in physical, non-negative AOD values, and the average computation time for a single granule was less than a minute on a modern personal computer.

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