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Journal of Applied Remote Sensing • Open Access

Algorithms for Moderate Resolution Imaging Spectroradiometer cloud-free image compositing
Author(s): Hai-bing Xiang; Jin-song Liu; Chun-xiang Cao; Min Xu

Paper Abstract

The presence of clouds is the biggest obstacle in the investigation of land cover, and many techniques have been developed to detect clouds. However, few indicators have been proposed for the detection of cloud-free conditions. To address this, we propose two indicators for use in compositing 8-day cloud-free images: the B 1/7 ratio is the ratio of the band 1 reflectance to the band 7 reflectance of Terra surface reflectance images (MOD09GA), and saturation refers to the color saturation of these images. Here, we describe the principles underlying these two indicators and analyze their characteristics for vegetation, water, urban, and nonvegetation pixels under cloud-free, cloud shadow, and cloudy conditions using MOD09GA from October 16 to 23, 2007, in North China (sample A) and using data published by the U.S. Geological Survey (USGS). We found that the B 1/7 ratio and saturation are suitable for extracting cloud-free pixels over land and water, respectively; therefore, we combined these two indicators to develop a single-unified model. In particular, our results demonstrate that the pixels exhibiting the lowest B 1/7 ratios should be adopted as cloud-free pixels over land when the value of B 1/7 for land surfaces is between 0 and 1, and the surface reflectance of Moderate Resolution Imaging Spectroradiometer band 1 is less than 0.3. Otherwise, the pixels exhibiting the greatest saturation values should be adopted. We used our model to composite cloud-free images for two additional regions in China: the Tarim basin (sample B) from October 2 to 9, 2012, and the coastal areas of southeastern China (sample C) from April 15 to 23, 2013. We compared the cloud-free images of these regions with the 8-day surface reflectance product (MOD09A1) with respect to clouds, cloud shadow, and cirrus clouds, and we found that our proposed cloud-free image compositing approach can accurately eliminate both clouds and cirrus clouds. Specifically, the percentage of residual cloud pixels in sample C was found to be less than that in MOD09A1. Moreover, in the cloud-free images obtained using our newly developed method, cloud-free pixels are typically associated with greater sensor zenith angles and smaller scatter angles than those in MOD09A1. However, our method retains some limitations. In particular, 9.68, 33.22, and 33.00% of cloud-shadow pixels remain in the cloud-free images for samples A, B, and C, respectively.

Paper Details

Date Published: 5 November 2013
PDF: 18 pages
J. Appl. Rem. Sens. 7(1) 073486 doi: 10.1117/1.JRS.7.073486
Published in: Journal of Applied Remote Sensing Volume 7, Issue 1
Show Author Affiliations
Hai-bing Xiang, Institute of Remote Sensing and Digital Earth (China)
Jin-song Liu, Hebei Normal Univ. (China)
Chun-xiang Cao, Institute of Remote Sensing and Digital Earth (China)
Min Xu, Institute of Remote Sensing and Digital Earth (China)

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