Adaption of the MODIS aerosol retrieval algorithm using airborne spectral surface reflectance measurements over urban areas
S.5237-5249 MODIS (MOderate-resolution Imaging Spectroradiometer) retrievals of aerosol optical depth (AOD) are biased over urban areas, primarily because the reflectance characteristics of urban surfaces are different than that assumed by the retrieval algorithm. Specifically, the operational "...
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ftfrauneprints:oai:publica.fraunhofer.de:publica/243245 2024-05-19T07:27:34+00:00 Adaption of the MODIS aerosol retrieval algorithm using airborne spectral surface reflectance measurements over urban areas Jäkel, E. Mey, B. Levy, R. Gu, X. Yu, T. Li, Z. Althausen, D. Heese, B. Wendisch, M. 2015 https://publica.fraunhofer.de/handle/publica/243245 https://doi.org/10.5194/amt-8-5237-2015 en eng Atmospheric Measurement Techniques : AMT JA2023/2-2 doi:10.5194/amt-8-5237-2015 https://publica.fraunhofer.de/handle/publica/243245 journal article 2015 ftfrauneprints https://doi.org/10.5194/amt-8-5237-2015 2024-04-24T00:59:44Z S.5237-5249 MODIS (MOderate-resolution Imaging Spectroradiometer) retrievals of aerosol optical depth (AOD) are biased over urban areas, primarily because the reflectance characteristics of urban surfaces are different than that assumed by the retrieval algorithm. Specifically, the operational "dark-target" retrieval is tuned towards vegetated (dark) surfaces and assumes a spectral relationship to estimate the surface reflectance in blue and red wavelengths. From airborne measurements of surface reflectance over the city of Zhongshan, China, were collected that could replace the assumptions within the MODIS retrieval algorithm. The subsequent impact was tested upon two versions of the operational algorithm, Collections 5 and 6 (C5 and C6). AOD retrieval results of the operational and modified algorithms were compared for a specific case study over Zhongshan to show minor differences between them all. However, the Zhongshan-based spectral surface relationship was applied to a much larger urban sample, specifically to the MODIS data taken over Beijing between 2010 and 2014. These results were compared directly to ground-based AERONET (AErosol RObotic NETwork) measurements of AOD. A significant reduction of the differences between the AOD retrieved by the modified algorithms and AERONET was found, whereby the mean difference decreased from 0.27 +/- 0.14 for the operational C5 and 0.19 +/- 0.12 for the operational C6 to 0.10 +/- 0.15 and -0.02 +/- 0.17 by using the modified C5 and C6 retrievals. Since the modified algorithms assume a higher contribution by the surface to the total measured reflectance from MODIS, consequently the overestimation of AOD by the operational methods is reduced. Furthermore, the sensitivity of the MODIS AOD retrieval with respect to different surface types was investigated. Radiative transfer simulations were performed to model reflectances at top of atmosphere for predefined aerosol properties. The reflectance data were used as input for the retrieval methods. It was shown that the ... Article in Journal/Newspaper Aerosol Robotic Network Publikationsdatenbank der Fraunhofer-Gesellschaft Atmospheric Measurement Techniques 8 12 5237 5249 |
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Publikationsdatenbank der Fraunhofer-Gesellschaft |
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ftfrauneprints |
language |
English |
description |
S.5237-5249 MODIS (MOderate-resolution Imaging Spectroradiometer) retrievals of aerosol optical depth (AOD) are biased over urban areas, primarily because the reflectance characteristics of urban surfaces are different than that assumed by the retrieval algorithm. Specifically, the operational "dark-target" retrieval is tuned towards vegetated (dark) surfaces and assumes a spectral relationship to estimate the surface reflectance in blue and red wavelengths. From airborne measurements of surface reflectance over the city of Zhongshan, China, were collected that could replace the assumptions within the MODIS retrieval algorithm. The subsequent impact was tested upon two versions of the operational algorithm, Collections 5 and 6 (C5 and C6). AOD retrieval results of the operational and modified algorithms were compared for a specific case study over Zhongshan to show minor differences between them all. However, the Zhongshan-based spectral surface relationship was applied to a much larger urban sample, specifically to the MODIS data taken over Beijing between 2010 and 2014. These results were compared directly to ground-based AERONET (AErosol RObotic NETwork) measurements of AOD. A significant reduction of the differences between the AOD retrieved by the modified algorithms and AERONET was found, whereby the mean difference decreased from 0.27 +/- 0.14 for the operational C5 and 0.19 +/- 0.12 for the operational C6 to 0.10 +/- 0.15 and -0.02 +/- 0.17 by using the modified C5 and C6 retrievals. Since the modified algorithms assume a higher contribution by the surface to the total measured reflectance from MODIS, consequently the overestimation of AOD by the operational methods is reduced. Furthermore, the sensitivity of the MODIS AOD retrieval with respect to different surface types was investigated. Radiative transfer simulations were performed to model reflectances at top of atmosphere for predefined aerosol properties. The reflectance data were used as input for the retrieval methods. It was shown that the ... |
format |
Article in Journal/Newspaper |
author |
Jäkel, E. Mey, B. Levy, R. Gu, X. Yu, T. Li, Z. Althausen, D. Heese, B. Wendisch, M. |
spellingShingle |
Jäkel, E. Mey, B. Levy, R. Gu, X. Yu, T. Li, Z. Althausen, D. Heese, B. Wendisch, M. Adaption of the MODIS aerosol retrieval algorithm using airborne spectral surface reflectance measurements over urban areas |
author_facet |
Jäkel, E. Mey, B. Levy, R. Gu, X. Yu, T. Li, Z. Althausen, D. Heese, B. Wendisch, M. |
author_sort |
Jäkel, E. |
title |
Adaption of the MODIS aerosol retrieval algorithm using airborne spectral surface reflectance measurements over urban areas |
title_short |
Adaption of the MODIS aerosol retrieval algorithm using airborne spectral surface reflectance measurements over urban areas |
title_full |
Adaption of the MODIS aerosol retrieval algorithm using airborne spectral surface reflectance measurements over urban areas |
title_fullStr |
Adaption of the MODIS aerosol retrieval algorithm using airborne spectral surface reflectance measurements over urban areas |
title_full_unstemmed |
Adaption of the MODIS aerosol retrieval algorithm using airborne spectral surface reflectance measurements over urban areas |
title_sort |
adaption of the modis aerosol retrieval algorithm using airborne spectral surface reflectance measurements over urban areas |
publishDate |
2015 |
url |
https://publica.fraunhofer.de/handle/publica/243245 https://doi.org/10.5194/amt-8-5237-2015 |
genre |
Aerosol Robotic Network |
genre_facet |
Aerosol Robotic Network |
op_relation |
Atmospheric Measurement Techniques : AMT JA2023/2-2 doi:10.5194/amt-8-5237-2015 https://publica.fraunhofer.de/handle/publica/243245 |
op_doi |
https://doi.org/10.5194/amt-8-5237-2015 |
container_title |
Atmospheric Measurement Techniques |
container_volume |
8 |
container_issue |
12 |
container_start_page |
5237 |
op_container_end_page |
5249 |
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1799482170007355392 |