Impact of MODIS-derived cloud cover on aerosol optical depth measured with a sun photometer: a case study from Nanjing, China

• Published in: International journal of remote sensing Vol. 34; no. 23; pp. 8534 - 8548
• Main Authors: Zha, Yong, Zhang, Jiahua, Gao, Jay, He, Junliang
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 10.12.2013
• Subjects: Aerosols; air; Animal, plant and microbial ecology; Applied geophysics; Argon oxygen decarburizing; Biological and medical sciences; case studies; China; Cloud cover; Clouds; correlation; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General aspects. Techniques; Internal geophysics; moderate resolution imaging spectroradiometer; MODIS; Photometers; Photometry; remote sensing; Sun; Teledetection and vegetation maps; Far East; Asia; China; China, People's Rep., Jiangsu Prov., Nanjing; China, People's Rep; atmosphere; data; aerosols; accuracy; Index; air; case studies; clouds; Research; photometry; Result; Cloudiness; correlation coefficient; detection; Space remote sensing; Satellite observation; indicators; monitoring; Acquisition; Sun; in situ; contamination; depth; Correlation analysis; Environment
• ISSN: 0143-1161; 1366-5901; 1366-5901
• DOI: 10.1080/01431161.2013.843807

Sun photometers have been used increasingly to monitor the atmospheric environment by measuring indicators such as aerosol optical depth (AOD). However, ground-measured AOD results are subject to the presence of clouds in the air. When cloud cover is not extensive, it is still possible to use sun photometry to determine AOD, even though accuracy is reduced by cloud contamination. This research aims to detect cloud cover from Moderate Resolution Imaging Spectroradiometer (MODIS) data and then assess its impact on in situ-measured AOD. Normalized difference cloud index (NDCI) and linear spectral unmixing (LSU) were used to detect cloud cover from MODIS data. AOD at the time of acquisition of MODIS data was measured on the ground by sun photometry within 20 min of satellite overpasses (10 min before and 10 min after). Correlation analysis of NDCI- and LSU-derived cloud cover with in situ-measured AOD data demonstrates that LSU has a higher correlation coefficient with AOD than with NDCI. At 550 nm, a unit of cloud cover (e.g. 1%) raises ground-observed AOD by 0.0157. The findings of this study can be used to modify ground-derived AOD results to improve their reliability.