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Xiaolin Zhu Kwok Huen Leung Wing Sze Li Lek Kin Cheung 《International Journal of Digital Earth》2020,13(8):886-898
ABSTRACT Minqin County in northwestern China is highly affected by desertification. Campaigns have been initiated in recent decades to combat desertification in Minqin. To assess the effectiveness of these campaigns, this study used a dense Landsat time series from 1987 to 2017 to investigate the interannual dynamics of vegetation coverage and greenness over the past 31 years. First, this study applied an advanced technology to reconstruct a high-quality Landsat annual time series. Specifically, one image in the vegetation-peak season was selected as the base image in each year, and then problematic pixels were interpolated by the neighborhood similar pixel interpolator using ancillary images in the same year. Second, the land cover map and the enhanced vegetation index (EVI) were derived from all reconstructed images. Third, the change of vegetation coverage and EVI values over the 31 years were analyzed. The results show that the total vegetation coverage and greenness increased during the 31 years. Linking this change trend to other factors suggests that vegetation in Minqin County is highly affected by agriculture and groundwater supply rather than by climate. To mitigate desertification in a sustainable way, agriculture should be well managed to avoid overconsumption of natural resources such as underground water. 相似文献
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The Space Telescope Imaging Spectrograph (STIS) on HST provides the first ultraviolet data that are of sufficient spectral and temporal resolution to generate Doppler tomograms of X‐ray binaries.We show both optical and ultraviolet maps constructed for the intermediate mass system Hercules X‐1/HZ Her and the massive wind‐fed system SMC X‐1/SK160. We have used the maps and corresponding lightcurves as diagnostics with which to test the validity of published models for Hercules X‐1. We find that although the models are mostly able to explain the light curves they are not consistent with the full phase maps. We present simulations of Doppler maps of X‐ray lines that will be possible with the spectral and temporal resolution and substantial effective area of the next major X‐ray mission, Con‐X. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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