Extended validation and evaluation of the OLCI–SLSTR SYNERGY aerosol product (SY_2_AOD) on Sentinel-3

Sogacheva, Larisa; Denisselle, Matthieu; Kolmonen, Pekka; Virtanen, Timo H.; North, Peter; Henocq, Claire; Scifoni, Silvia; Dransfeld, Steffen

doi:10.5194/amt-15-5289-2022

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Extended validation and evaluation of the OLCI–SLSTR SYNERGY aerosol product (SY_2_AOD) on Sentinel-3

Larisa Sogacheva, Matthieu Denisselle, Pekka Kolmonen, Timo H. Virtanen, Peter North

, Claire Henocq, Silvia Scifoni, Steffen Dransfeld

Atmospheric Measurement Techniques, Volume: 15, Issue: 18, Pages: 5289 - 5322

Swansea University Author: Peter North

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DOI (Published version): 10.5194/amt-15-5289-2022

Abstract

We present the first extended validation of a new SYNERGY global aerosol product (SY_2_AOD), which is based on synergistic use of data from the Ocean and Land Color Instrument (OLCI) and the Sea and Land Surface Temperature Radiometer (SLSTR) sensors aboard the Copernicus Sentinel-3A (S3A) and Senti...

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Published in:	Atmospheric Measurement Techniques
ISSN:	1867-8548
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fullrecord	<?xml version="1.0"?><rfc1807><datestamp>2022-11-28T14:29:35.6671093</datestamp><bib-version>v2</bib-version><id>61813</id><entry>2022-11-08</entry><title>Extended validation and evaluation of the OLCI–SLSTR SYNERGY aerosol product (SY_2_AOD) on Sentinel-3</title><swanseaauthors><author><sid>fc45a0cb36c24d6cf35313a8c808652f</sid><ORCID>0000-0001-9933-6935</ORCID><firstname>Peter</firstname><surname>North</surname><name>Peter North</name><active>true</active><ethesisStudent>false</ethesisStudent></author></swanseaauthors><date>2022-11-08</date><deptcode>SGE</deptcode><abstract>We present the first extended validation of a new SYNERGY global aerosol product (SY_2_AOD), which is based on synergistic use of data from the Ocean and Land Color Instrument (OLCI) and the Sea and Land Surface Temperature Radiometer (SLSTR) sensors aboard the Copernicus Sentinel-3A (S3A) and Sentinel-3B (S3B) satellites. Validation covers period from 14 January 2020 to 30 September 2021. Several approaches, including statistical analysis, time series analysis, and comparison with similar aerosol products from the other spaceborne sensor, the Moderate Resolution Imaging Spectroradiometer (MODIS), were applied for validation and evaluation of S3A and S3B SY_2 aerosol products, including aerosol optical depth (AOD) provided at different wavelengths, AOD pixel-level uncertainties, fine-mode AOD, and Angström exponent.Over ocean, the performance of SY_2 AOD (syAOD) retrieved at 550 nm is good: for S3A and S3B, Pearson correlation coefficients with the Maritime Aerosol Network (MAN) component of the AErosol RObotic NETwork (AERONET) are 0.88 and 0.85, respectively; 88.6 % and 89.5 % of pixels fit into the MODIS error envelope (EE) of ±0.05 ± 0.2 × AOD.Over land, correlation coefficients with AERONET AOD (aAOD) are 0.60 and 0.63 for S3A and S3B, respectively; 51.4 % and 57.9 % of pixels fit into MODIS EE. Reduced performance over land is expected since the surface reflectance and angular distribution of scattering are higher and more difficult to predict over land than over ocean. The results are affected by a large number of outliers.Evaluation of the per-retrieval uncertainty with the χ2 test indicates that syAOD prognostic uncertainties (PU) are slightly underestimated (χ2 = 3.1); if outliers are removed, PU describes the syAOD error well (χ2 = 1.6).The regional analysis of the Angström exponent, which relates to the aerosol size distribution, shows spatial correlation with expected sources. For 40 % of the matchups with AERONET in the Northern Hemisphere (NH) and for 60 % of the matchups in the Southern Hemisphere (SH), which fit into the AE size range of [1, 1.8], an offset between SY_2 AE (syAE) and AERONET AE (aAE) is within ±0.25. General overestimation of low (< 0.5) syAE and underestimation of high (> 1.8) syAE results in high (0.94, globally) overall bias.Good agreement (bias < 0.03) was observed between Sy_2 fine-mode AOD (syFMAOD) and AERONET fine-mode AOD (aFMAOD) for aFMAOD < 1. At aFMAOD > 1, syFMAOD is considerably underestimated (by 0.3–0.5 in different aFMAOD ranges) in the NH. In the SH, only a few aFMAOD values above 1 are measured. The fine-mode fraction (FMF) in the SY_2 AOD product (syFMF) in the range of [0, 0.7] is overestimated; the positive offset of 0.3–0.5 for low (< 0.25) FMF gradually decreases.Differences between the annual and seasonal AOD values from SY_2 and MODIS (mod) Dark Target and Deep Blue products are within 0.02 for the study area (30∘ S–60∘ N, 80∘ W–45∘ E). The agreement is better over ocean; however, a difference up to 0.6 exists between syFMF and modFMF. Over bright land surface (Saharan desert) the difference in AOD between the two products is highest (up to 0.11); the sign of the difference varies over time and space.For both S3A and S3B AOD products, validation statistics are often slightly better in the Southern Hemisphere. In general, the performance of S3B is slightly better.</abstract><type>Journal Article</type><journal>Atmospheric Measurement Techniques</journal><volume>15</volume><journalNumber>18</journalNumber><paginationStart>5289</paginationStart><paginationEnd>5322</paginationEnd><publisher>Copernicus GmbH</publisher><placeOfPublication/><isbnPrint/><isbnElectronic/><issnPrint/><issnElectronic>1867-8548</issnElectronic><keywords/><publishedDay>19</publishedDay><publishedMonth>9</publishedMonth><publishedYear>2022</publishedYear><publishedDate>2022-09-19</publishedDate><doi>10.5194/amt-15-5289-2022</doi><url/><notes>Data availability:The SY_2_AOD product is available upon subscription at https://scihub.copernicus.eu/dhus/#/home (last access: 13 March 2022; S3 Production Service-ACRI, 2022; S3 Production Service-SERCO, 2022). The SY_2_AOD product validation matchups are available upon subscription at https://law.acri-st.fr/home (last access: 10 January 2022; LAW consortium, 2022).</notes><college>COLLEGE NANME</college><department>Geography</department><CollegeCode>COLLEGE CODE</CollegeCode><DepartmentCode>SGE</DepartmentCode><institution>Swansea University</institution><apcterm/><funders>This research has been supported by the EU Copernicus program (project LAW, grant no. 4000129877/20/I-BG; project OPT-MPC, grant no. 4000136252/21/I-Bgi) and ESA.</funders><projectreference/><lastEdited>2022-11-28T14:29:35.6671093</lastEdited><Created>2022-11-08T11:28:36.8560949</Created><path><level id="1">Faculty of Science and Engineering</level><level id="2">School of Biosciences, Geography and Physics - Geography</level></path><authors><author><firstname>Larisa</firstname><surname>Sogacheva</surname><order>1</order></author><author><firstname>Matthieu</firstname><surname>Denisselle</surname><order>2</order></author><author><firstname>Pekka</firstname><surname>Kolmonen</surname><order>3</order></author><author><firstname>Timo H.</firstname><surname>Virtanen</surname><order>4</order></author><author><firstname>Peter</firstname><surname>North</surname><orcid>0000-0001-9933-6935</orcid><order>5</order></author><author><firstname>Claire</firstname><surname>Henocq</surname><order>6</order></author><author><firstname>Silvia</firstname><surname>Scifoni</surname><order>7</order></author><author><firstname>Steffen</firstname><surname>Dransfeld</surname><order>8</order></author></authors><documents><document><filename>61813__25936__4faa373fdc8e4d38a7dcac493192a924.pdf</filename><originalFilename>61813.pdf</originalFilename><uploaded>2022-11-28T14:26:20.8003587</uploaded><type>Output</type><contentLength>45782042</contentLength><contentType>application/pdf</contentType><version>Version of Record</version><cronfaStatus>true</cronfaStatus><documentNotes>© Author(s) 2022. 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spelling	2022-11-28T14:29:35.6671093 v2 61813 2022-11-08 Extended validation and evaluation of the OLCI–SLSTR SYNERGY aerosol product (SY_2_AOD) on Sentinel-3 fc45a0cb36c24d6cf35313a8c808652f 0000-0001-9933-6935 Peter North Peter North true false 2022-11-08 SGE We present the first extended validation of a new SYNERGY global aerosol product (SY_2_AOD), which is based on synergistic use of data from the Ocean and Land Color Instrument (OLCI) and the Sea and Land Surface Temperature Radiometer (SLSTR) sensors aboard the Copernicus Sentinel-3A (S3A) and Sentinel-3B (S3B) satellites. Validation covers period from 14 January 2020 to 30 September 2021. Several approaches, including statistical analysis, time series analysis, and comparison with similar aerosol products from the other spaceborne sensor, the Moderate Resolution Imaging Spectroradiometer (MODIS), were applied for validation and evaluation of S3A and S3B SY_2 aerosol products, including aerosol optical depth (AOD) provided at different wavelengths, AOD pixel-level uncertainties, fine-mode AOD, and Angström exponent.Over ocean, the performance of SY_2 AOD (syAOD) retrieved at 550 nm is good: for S3A and S3B, Pearson correlation coefficients with the Maritime Aerosol Network (MAN) component of the AErosol RObotic NETwork (AERONET) are 0.88 and 0.85, respectively; 88.6 % and 89.5 % of pixels fit into the MODIS error envelope (EE) of ±0.05 ± 0.2 × AOD.Over land, correlation coefficients with AERONET AOD (aAOD) are 0.60 and 0.63 for S3A and S3B, respectively; 51.4 % and 57.9 % of pixels fit into MODIS EE. Reduced performance over land is expected since the surface reflectance and angular distribution of scattering are higher and more difficult to predict over land than over ocean. The results are affected by a large number of outliers.Evaluation of the per-retrieval uncertainty with the χ2 test indicates that syAOD prognostic uncertainties (PU) are slightly underestimated (χ2 = 3.1); if outliers are removed, PU describes the syAOD error well (χ2 = 1.6).The regional analysis of the Angström exponent, which relates to the aerosol size distribution, shows spatial correlation with expected sources. For 40 % of the matchups with AERONET in the Northern Hemisphere (NH) and for 60 % of the matchups in the Southern Hemisphere (SH), which fit into the AE size range of [1, 1.8], an offset between SY_2 AE (syAE) and AERONET AE (aAE) is within ±0.25. General overestimation of low (< 0.5) syAE and underestimation of high (> 1.8) syAE results in high (0.94, globally) overall bias.Good agreement (bias < 0.03) was observed between Sy_2 fine-mode AOD (syFMAOD) and AERONET fine-mode AOD (aFMAOD) for aFMAOD < 1. At aFMAOD > 1, syFMAOD is considerably underestimated (by 0.3–0.5 in different aFMAOD ranges) in the NH. In the SH, only a few aFMAOD values above 1 are measured. The fine-mode fraction (FMF) in the SY_2 AOD product (syFMF) in the range of [0, 0.7] is overestimated; the positive offset of 0.3–0.5 for low (< 0.25) FMF gradually decreases.Differences between the annual and seasonal AOD values from SY_2 and MODIS (mod) Dark Target and Deep Blue products are within 0.02 for the study area (30∘ S–60∘ N, 80∘ W–45∘ E). The agreement is better over ocean; however, a difference up to 0.6 exists between syFMF and modFMF. Over bright land surface (Saharan desert) the difference in AOD between the two products is highest (up to 0.11); the sign of the difference varies over time and space.For both S3A and S3B AOD products, validation statistics are often slightly better in the Southern Hemisphere. In general, the performance of S3B is slightly better. Journal Article Atmospheric Measurement Techniques 15 18 5289 5322 Copernicus GmbH 1867-8548 19 9 2022 2022-09-19 10.5194/amt-15-5289-2022 Data availability:The SY_2_AOD product is available upon subscription at https://scihub.copernicus.eu/dhus/#/home (last access: 13 March 2022; S3 Production Service-ACRI, 2022; S3 Production Service-SERCO, 2022). The SY_2_AOD product validation matchups are available upon subscription at https://law.acri-st.fr/home (last access: 10 January 2022; LAW consortium, 2022). COLLEGE NANME Geography COLLEGE CODE SGE Swansea University This research has been supported by the EU Copernicus program (project LAW, grant no. 4000129877/20/I-BG; project OPT-MPC, grant no. 4000136252/21/I-Bgi) and ESA. 2022-11-28T14:29:35.6671093 2022-11-08T11:28:36.8560949 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Geography Larisa Sogacheva 1 Matthieu Denisselle 2 Pekka Kolmonen 3 Timo H. Virtanen 4 Peter North 0000-0001-9933-6935 5 Claire Henocq 6 Silvia Scifoni 7 Steffen Dransfeld 8 61813__25936__4faa373fdc8e4d38a7dcac493192a924.pdf 61813.pdf 2022-11-28T14:26:20.8003587 Output 45782042 application/pdf Version of Record true © Author(s) 2022. This work is distributed under the Creative Commons Attribution 4.0 License. true eng https://creativecommons.org/licenses/by/4.0/
title	Extended validation and evaluation of the OLCI–SLSTR SYNERGY aerosol product (SY_2_AOD) on Sentinel-3
spellingShingle	Extended validation and evaluation of the OLCI–SLSTR SYNERGY aerosol product (SY_2_AOD) on Sentinel-3 Peter North
title_short	Extended validation and evaluation of the OLCI–SLSTR SYNERGY aerosol product (SY_2_AOD) on Sentinel-3
title_full	Extended validation and evaluation of the OLCI–SLSTR SYNERGY aerosol product (SY_2_AOD) on Sentinel-3
title_fullStr	Extended validation and evaluation of the OLCI–SLSTR SYNERGY aerosol product (SY_2_AOD) on Sentinel-3
title_full_unstemmed	Extended validation and evaluation of the OLCI–SLSTR SYNERGY aerosol product (SY_2_AOD) on Sentinel-3
title_sort	Extended validation and evaluation of the OLCI–SLSTR SYNERGY aerosol product (SY_2_AOD) on Sentinel-3
author_id_str_mv	fc45a0cb36c24d6cf35313a8c808652f
author_id_fullname_str_mv	fc45a0cb36c24d6cf35313a8c808652f_***_Peter North
author	Peter North
author2	Larisa Sogacheva Matthieu Denisselle Pekka Kolmonen Timo H. Virtanen Peter North Claire Henocq Silvia Scifoni Steffen Dransfeld
format	Journal article
container_title	Atmospheric Measurement Techniques
container_volume	15
container_issue	18
container_start_page	5289
publishDate	2022
institution	Swansea University
issn	1867-8548
doi_str_mv	10.5194/amt-15-5289-2022
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college_str	Faculty of Science and Engineering
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description	We present the first extended validation of a new SYNERGY global aerosol product (SY_2_AOD), which is based on synergistic use of data from the Ocean and Land Color Instrument (OLCI) and the Sea and Land Surface Temperature Radiometer (SLSTR) sensors aboard the Copernicus Sentinel-3A (S3A) and Sentinel-3B (S3B) satellites. Validation covers period from 14 January 2020 to 30 September 2021. Several approaches, including statistical analysis, time series analysis, and comparison with similar aerosol products from the other spaceborne sensor, the Moderate Resolution Imaging Spectroradiometer (MODIS), were applied for validation and evaluation of S3A and S3B SY_2 aerosol products, including aerosol optical depth (AOD) provided at different wavelengths, AOD pixel-level uncertainties, fine-mode AOD, and Angström exponent.Over ocean, the performance of SY_2 AOD (syAOD) retrieved at 550 nm is good: for S3A and S3B, Pearson correlation coefficients with the Maritime Aerosol Network (MAN) component of the AErosol RObotic NETwork (AERONET) are 0.88 and 0.85, respectively; 88.6 % and 89.5 % of pixels fit into the MODIS error envelope (EE) of ±0.05 ± 0.2 × AOD.Over land, correlation coefficients with AERONET AOD (aAOD) are 0.60 and 0.63 for S3A and S3B, respectively; 51.4 % and 57.9 % of pixels fit into MODIS EE. Reduced performance over land is expected since the surface reflectance and angular distribution of scattering are higher and more difficult to predict over land than over ocean. The results are affected by a large number of outliers.Evaluation of the per-retrieval uncertainty with the χ2 test indicates that syAOD prognostic uncertainties (PU) are slightly underestimated (χ2 = 3.1); if outliers are removed, PU describes the syAOD error well (χ2 = 1.6).The regional analysis of the Angström exponent, which relates to the aerosol size distribution, shows spatial correlation with expected sources. For 40 % of the matchups with AERONET in the Northern Hemisphere (NH) and for 60 % of the matchups in the Southern Hemisphere (SH), which fit into the AE size range of [1, 1.8], an offset between SY_2 AE (syAE) and AERONET AE (aAE) is within ±0.25. General overestimation of low (< 0.5) syAE and underestimation of high (> 1.8) syAE results in high (0.94, globally) overall bias.Good agreement (bias < 0.03) was observed between Sy_2 fine-mode AOD (syFMAOD) and AERONET fine-mode AOD (aFMAOD) for aFMAOD < 1. At aFMAOD > 1, syFMAOD is considerably underestimated (by 0.3–0.5 in different aFMAOD ranges) in the NH. In the SH, only a few aFMAOD values above 1 are measured. The fine-mode fraction (FMF) in the SY_2 AOD product (syFMF) in the range of [0, 0.7] is overestimated; the positive offset of 0.3–0.5 for low (< 0.25) FMF gradually decreases.Differences between the annual and seasonal AOD values from SY_2 and MODIS (mod) Dark Target and Deep Blue products are within 0.02 for the study area (30∘ S–60∘ N, 80∘ W–45∘ E). The agreement is better over ocean; however, a difference up to 0.6 exists between syFMF and modFMF. Over bright land surface (Saharan desert) the difference in AOD between the two products is highest (up to 0.11); the sign of the difference varies over time and space.For both S3A and S3B AOD products, validation statistics are often slightly better in the Southern Hemisphere. In general, the performance of S3B is slightly better.
published_date	2022-09-19T04:20:55Z
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Extended validation and evaluation of the OLCI–SLSTR SYNERGY aerosol product (SY_2_AOD) on Sentinel-3

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