3 results on '"Li, Changchun"'
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2. Mapping Winter Wheat with Optical and SAR Images Based on Google Earth Engine in Henan Province, China.
- Author
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Li, Changchun, Chen, Weinan, Wang, Yilin, Wang, Yu, Ma, Chunyan, Li, Yacong, Li, Jingbo, and Zhai, Weiguang
- Subjects
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WINTER wheat , *SYNTHETIC aperture radar , *OPTICAL images , *NORMALIZED difference vegetation index , *RANDOM forest algorithms - Abstract
The timely and accurate acquisition of winter wheat acreage is crucial for food security. This study investigated the feasibility of extracting the spatial distribution map of winter wheat in Henan Province by using synthetic aperture radar (SAR, Sentinel-1A) and optical (Sentinel-2) images. Firstly, the SAR images were aggregated based on the growth period of winter wheat, and the optical images were aggregated based on the moderate resolution imaging spectroradiometer normalized difference vegetation index (MODIS-NDVI) curve. Then, five spectral features, two polarization features, and four texture features were selected as feature variables. Finally, the Google Earth Engine (GEE) cloud platform was employed to extract winter wheat acreage through the random forest (RF) algorithm. The results show that: (1) aggregated images based on the growth period of winter wheat and sensor characteristics can improve the mapping accuracy and efficiency; (2) the extraction accuracy of using only SAR images was improved with the accumulation of growth period. The extraction accuracy of using the SAR images in the full growth period reached 80.1%; and (3) the identification effect of integrated images was relatively good, which makes up for the shortcomings of SAR and optical images and improves the extraction accuracy of winter wheat. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
3. Overridingly increasing vegetation sensitivity to vapor pressure deficit over the recent two decades in China.
- Author
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Liu, Miao, Yang, Guijun, Yuan, Wenping, Li, Zhenhong, Gao, Meiling, Yang, Yun, Long, Huiling, Meng, Yang, Li, Changchun, Hu, Haitang, Li, Heli, and Yuan, Zhanliang
- Subjects
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VAPOR pressure , *BROADLEAF forests , *CLIMATE change , *ARID regions , *DECIDUOUS forests , *CLIMATIC zones - Abstract
• The increasing trend of vapor pressure deficit (VPD) change in 1997–2020 is ten times higher than in 1981–1996. • Increasing VPD promoted cropland and grassland growth in Arid, while inhibited the growth of shrubland. • Significant positive or negative difference in the sensitivity to VPD for the same vegetation under different climatic zones. • The vast majority of vegetation showed a significant increase in the inter-annual trend of the sensitivity to VPD. • The relationship of higher sensitivity with lower VPD is not stable under different vegetation and climatic zones. Vapor pressure deficit (VPD) shows significant spatial and temporal variability in the context of global climate change, which is important for studying the implications of climate change on the structure and function of ecosystems to analyze the effects of VPD on vegetation dynamics. Spatial patterns of vegetation sensitivity to VPD have been recently investigated, however, the feedback of different vegetation types to VPD may vary depending on physiological characteristics, it is unclear how different types influence the sensitivity to VPD. In this study, the ERA5-Land reanalysis time-series dataset was used to analyze the spatial and temporal trends of VPD under different vegetation types. It was found that VPD showed an increasing trend in vegetated areas over the past 20 years with large spatial heterogeneity, generally increasing with drying conditions. On this basis, the spatial patterns of vegetation sensitivity to VPD and temporal trends in sensitivity were evaluated over the past 20 years in China using the enhanced vegetation index (EVI) and near-infrared reflectance of vegetation (NIRv) which can describe vegetation dynamics. The results show that the sensitivities under the two indices have high spatial consistency, with northeastern and central China showing positive sensitivities and southern China showing negative sensitivities, respectively. The positive sensitivities are relatively high for Deciduous Broadleaf Forests (DBF), Deciduous Needleleaf Forests (DNF), Grasslands (GL), and Croplands (CL) types, while the negative sensitivities are larger for Shrublands (SL) and Savannas (SA) types. Under different climatic zones, the sensitivity of CL and GL are independent of climatic zones (both showing positive), while the sensitivity of SL is negative in the Humid zone and positive in the Semi-Arid zone. Temporally, the sensitivity showed a slow increasing trend over the last 20 years. In terms of vegetation types, sensitivities of Evergreen Broadleaf Forests (EBF), DBF, GL and CL types showed a significant increasing trend (p < 0.05), except for the SL type, which showed a significant decreasing trend (p < 0.05). The trends of sensitivity are not affected by the differences in vegetation types (all of them show an increasing trend) under arid and semi-arid conditions, while dry sub-humid and humid have a greater impact on sensitivity trends. The finding of an overall increase in sensitivity suggests a mechanism of erratic change in vegetation growth under climate change. Notably, the increased sensitivity of certain vegetation types (especially GL and CL) suggests that these may become progressively vulnerable to increased VPD as global climate change persists, with the risk of moving from facilitation to inhibition of photosynthesis. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
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