{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,1]],"date-time":"2026-04-01T20:55:43Z","timestamp":1775076943496,"version":"3.50.1"},"reference-count":46,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2019,2,27]],"date-time":"2019-02-27T00:00:00Z","timestamp":1551225600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100012166","name":"National Key Research and Development Program of China","doi-asserted-by":"publisher","award":["No.2016YFC1400904"],"award-info":[{"award-number":["No.2016YFC1400904"]}],"id":[{"id":"10.13039\/501100012166","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Startup Foundation for Introduction Talent of NUIST","award":["2017r107"],"award-info":[{"award-number":["2017r107"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>In this study, Terra-MODIS (Moderate Resolution Imaging Spectroradiometer) Collections 6 and 6.1 (C6 &amp; C6.1) aerosol optical depth (AOD) retrievals with the recommended high-quality flag (QF = 3) were retrieved from Dark-Target (DT), Deep-Blue (DB) and merged DT and DB (DTB) level\u20132 AOD products for verification against Aerosol Robotic Network (AERONET) Version 3 Level 2.0 AOD data obtained from 2004\u20132014 for three sites located in the Beijing-Tianjin-Hebei (BTH) region. These are: Beijing, located over mixed bright urban surfaces, XiangHe located over suburban surfaces, and Xinglong located over hilly and vegetated surfaces. The AOD retrievals were also validated over different land-cover types defined by static monthly NDVI (Normalized Difference Vegetation Index) values obtained from the Terra-MODIS level-3 product (MOD13A3). These include non-vegetated surfaces (NVS, NDVI &lt; 0.2), partially vegetated surfaces (PVS, 0.2 \u2264 NDVI \u2264 0.3), moderately vegetated surfaces (MVS, 0.3 &lt; NDVI &lt; 0.5) and densely vegetated surfaces (DVS, NDVI \u2265 0.5). Results show that the DT, DB, and DTB-collocated retrievals achieve a high correlation coefficient of ~ 0.90\u20130.97, 0.89\u20130.95, and 0.86\u20130.95, respectively, with AERONET AOD. The DT C6 and C6.1 collocated retrievals were comparable at XiangHe and Xinglong, whereas at Beijing, the percentage of collocated retrievals within the expected error (\u2194EE) increased from 21.4% to 35.5%, the root mean square error (RMSE) decreased from 0.37 to 0.24, and the relative percent mean error (RPME) decreased from 49% to 27%. These results suggest significant relative improvement in the DT C6.1 product. The percentage of DB-collocated AOD retrievals \u2194EE was greater than 70% at Beijing and Xinglong, whereas less than 66% was observed at XiangHe. Similar to DT AOD, DTB AOD retrievals performed well at XiangHe and Xinglong compared with Beijing. Regionally, DB C6 and C6.1-collocated retrievals performed better than DT and DTB in terms of good quality retrievals and relatively small errors. For diverse vegetated surfaces, DT-collocated retrievals reported small errors and good quality retrievals only for NVS and DVS, whereas larger errors were reported for PVS. MVS. DB contains good quality AOD retrievals over PVS, MVS, and DVS compared with NVS. DTB C6.1 collocated retrievals were better than C6 over NVS, PVS, and DVS. C6.1 is substantially improved overall, compared with C6 at local and regional scales, and over diverse vegetated surfaces.<\/jats:p>","DOI":"10.3390\/rs11050486","type":"journal-article","created":{"date-parts":[[2019,2,27]],"date-time":"2019-02-27T11:41:03Z","timestamp":1551267663000},"page":"486","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":48,"title":["Evaluation of Terra-MODIS C6 and C6.1 Aerosol Products against Beijing, XiangHe, and Xinglong AERONET Sites in China during 2004-2014"],"prefix":"10.3390","volume":"11","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-1022-3999","authenticated-orcid":false,"given":"Muhammad","family":"Bilal","sequence":"first","affiliation":[{"name":"School of Marine Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7631-1599","authenticated-orcid":false,"given":"Majid","family":"Nazeer","sequence":"additional","affiliation":[{"name":"Key Laboratory of Digital Land and Resources, East China University of Technology, Nanchang 330013, China"},{"name":"Earth and Atmospheric Remote Sensing Lab (EARL), Department of Meteorology, COMSATS University Islamabad, Islamabad 45550, Pakistan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Janet","family":"Nichol","sequence":"additional","affiliation":[{"name":"Department of Geography, School of Global Studies, University of Sussex, Brighton BN19RH, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1167-3991","authenticated-orcid":false,"given":"Zhongfeng","family":"Qiu","sequence":"additional","affiliation":[{"name":"School of Marine Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7783-5725","authenticated-orcid":false,"given":"Lunche","family":"Wang","sequence":"additional","affiliation":[{"name":"Department of Geography, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Max P.","family":"Bleiweiss","sequence":"additional","affiliation":[{"name":"Department of Entomology, Plant Pathology and Weed Science, New Mexico State University (NMSU), Las Cruces, NM 88003, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xiaojing","family":"Shen","sequence":"additional","affiliation":[{"name":"School of Atmospheric Science at Nanjing University of Information Science and Technology, Nanjing 210044, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0251-4550","authenticated-orcid":false,"given":"James R.","family":"Campbell","sequence":"additional","affiliation":[{"name":"Naval Research Laboratory, Monterey, CA 93943, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6111-152X","authenticated-orcid":false,"given":"Simone","family":"Lolli","sequence":"additional","affiliation":[{"name":"Institute of Methodologies for Environmental Analysis, CNR, 85050 Tito Scalo (PZ), Italy"},{"name":"Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, MD 21221, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2019,2,27]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"215","DOI":"10.1038\/nature01091","article-title":"A satellite view of aerosols in the climate system","volume":"419","author":"Kaufman","year":"2002","journal-title":"Nature"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"376","DOI":"10.1056\/NEJMsa0805646","article-title":"Fine-particulate air pollution and life expectancy in the United States","volume":"360","author":"Pope","year":"2009","journal-title":"N. 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