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As one of the key parameters for characterizing crop canopy structure, Leaf Area Index (LAI) has great significance in monitoring the crop growth and estimating the yield. However, due to the nonlinearity and spatial heterogeneity of LAI inversion model, there exists scale error in LAI inversion result, which limits the application of LAI product from different remote sensing data. Therefore, it is necessary to conduct studies on scale effect. This study was based on the Heihe Oasis, Zhangye city, Gansu province, China and the following works were carried out: Airborne hyperspectral CASI (Compact Airborne Spectrographic Imager) image and LAI statistic models were adopted in muti-scale LAI inversion. The overall difference of muti-scale LAI inversion was analyzed in an all-round way. This was based on two aspects, “first inversion and then integration” and “first integration and then inversion”, and on scale difference characteristics of three scale transformation methods. The generation mechanism of scale effect was refined, and the optimal LAI inversion model was expanded by Taylor expansion. By doing so, it quantitatively analyzed the contribution of various inversion processes to scale effect. It was found that the cubic polynomial regression model based on NDVI (940.7 nm, 712 nm) was the optimal model, where its coefficient of determination R2 and the correlation coefficient of test samples R reached 0.72 and 0.936, respectively. Combined with Taylor expansion, it analyzed the scale error generated by LAI inversion model. After the scale effect correction of one-dimensional and two-dimensional variables, the correlation coefficient of CCD-LAI (China Environment Satellite HJ/CCD images) and CASI-LAI products (Compact Airborne Spectro graphic Imager products) increased from 0.793 to 0.875 and 0.901, respectively. The mean value, standard deviation, and relative true value of the two went consistent. Compared with one-dimensional variable correction method, the two-dimensional method had a better correction result. This research used the effective information in hyperspectral data as sub-pixels and adopted Taylor expansion to correct the scale error in large-scale and low-resolution LAI product, achieving large-scale and high-precision LAI monitoring.
Xiao-Ai Dai; Chao Liu; Nai-Wen Li; Mei-Lian Wang; Yu-Wei Yang; Xing-Ping Yang; Shi-Qi Zhang; Xu-Wei He; Zheng-Li Yang; Heng Lu; Jing-Zhong Li; Ze-Kun Wang. LAI scale effect research based on compact airborne spectrographic imager data in the Heihe Oasis. Journal of Mountain Science 2021, 18, 1630 -1645.
AMA StyleXiao-Ai Dai, Chao Liu, Nai-Wen Li, Mei-Lian Wang, Yu-Wei Yang, Xing-Ping Yang, Shi-Qi Zhang, Xu-Wei He, Zheng-Li Yang, Heng Lu, Jing-Zhong Li, Ze-Kun Wang. LAI scale effect research based on compact airborne spectrographic imager data in the Heihe Oasis. Journal of Mountain Science. 2021; 18 (6):1630-1645.
Chicago/Turabian StyleXiao-Ai Dai; Chao Liu; Nai-Wen Li; Mei-Lian Wang; Yu-Wei Yang; Xing-Ping Yang; Shi-Qi Zhang; Xu-Wei He; Zheng-Li Yang; Heng Lu; Jing-Zhong Li; Ze-Kun Wang. 2021. "LAI scale effect research based on compact airborne spectrographic imager data in the Heihe Oasis." Journal of Mountain Science 18, no. 6: 1630-1645.
With the emergence of new types of data (e.g. social media data) and cutting-edge computer technology (e.g. Natural Language Processing), the shortcomings of traditional methods (subjective and objective ways) for detecting urban livability can be overcome by an integrated approach. This study aims to develop a comprehensive approach to measure urban livability based on statistic data, geo-data (e.g. points of interest), questionnaires survey, and social media data (Instagram), from both objective and subjective angles. Hong Kong, as a city with a high level of urbanization and contrasting urban environments, is chosen as the study area in this research. Through this study, the question “which area of Hong Kong is more suitable for living” is answered by the visualization of GIS-based analysis. Also, the correlation between livability scores and individuals’ sentiment scores are explored. Specifically, the results show that central areas of Hong Kong with a higher level of urbanization are relatively more livable than suburban regions. However, through sentiment analysis, individuals who post Instagram in suburban areas of Hong Kong usually express more positive content and happier emotion than those who post Instagram in central urban areas. The study could offer useful information for the policy action of authorities as well as the residential location choices of citizens.
Jianxiao Liu; Han Bi; Meilian Wang. Using multi-source data to assess livability in Hong Kong at the community-based level: A combined subjective-objective approach. Geography and Sustainability 2020, 1, 284 -294.
AMA StyleJianxiao Liu, Han Bi, Meilian Wang. Using multi-source data to assess livability in Hong Kong at the community-based level: A combined subjective-objective approach. Geography and Sustainability. 2020; 1 (4):284-294.
Chicago/Turabian StyleJianxiao Liu; Han Bi; Meilian Wang. 2020. "Using multi-source data to assess livability in Hong Kong at the community-based level: A combined subjective-objective approach." Geography and Sustainability 1, no. 4: 284-294.
Landscape ecological risk assessment (LERA) evaluates different types of potential environmental impacts and their cumulative effects, thereby providing policy insights for sustainable regional land-use and ecosystem management. In a departure from existing literature that heavily relies on low-resolution land-use data for LERA at provincial or municipal scales, this study applies high-resolution land-use data to a relatively small research area (county). In addition, this study modifies the evaluation units of LERA from equal-sized grids to watersheds and refines the ecological vulnerability weight on the basis of finer-resolution data. The main findings are summarized as follows: (1) In 2011–2013, nearly 866 ha of land use in Xiapu County changed; moreover, the construction land, which was mainly concentrated in Songgang Street and Xinan Town, increased the most (340 ha). (2) Landscape ecological risk (LER) was roughly maintained, and areas of high ecological risk were mainly concentrated along the coast. (3) The spatial distribution of LER maintained a relatively aggregated pattern, with no trend toward more aggregated or more dispersed change. This study further discusses the relationship between local LER and land-use change and how to balance global and local LER in planning practices.
Jianxiao Liu; Meilian Wang; Linchuan Yang. Assessing Landscape Ecological Risk Induced by Land-Use/Cover Change in a County in China: A GIS- and Landscape-Metric-Based Approach. Sustainability 2020, 12, 9037 .
AMA StyleJianxiao Liu, Meilian Wang, Linchuan Yang. Assessing Landscape Ecological Risk Induced by Land-Use/Cover Change in a County in China: A GIS- and Landscape-Metric-Based Approach. Sustainability. 2020; 12 (21):9037.
Chicago/Turabian StyleJianxiao Liu; Meilian Wang; Linchuan Yang. 2020. "Assessing Landscape Ecological Risk Induced by Land-Use/Cover Change in a County in China: A GIS- and Landscape-Metric-Based Approach." Sustainability 12, no. 21: 9037.
The widely distributed lakes, as one of the major components of the inland water system, are the primary available freshwater resources on the earth and are sensitive to accelerated climate change and extensive human activities. Lakes play an important role in the terrestrial water cycle and biogeochemical cycle and substantially influence the health of humans living in the surrounding areas. Given the importance of lakes in the ecosystem, long-term monitoring of dynamic changes has important theoretical and practical significance. Here, we extracted water body information and monitored the long-term dynamics of Bosten Lake, which is the largest inland lake in China. We quantified the meteorological factors of the study area from the observation data of meteorological stations between 1988 and 2018. The characteristics of climate change and its correlation with the change of area in the Bosten Lake Basin in the past 30 years were analyzed. The major contributions of this study are as follows: (1) The initial water body was segmented based on the water index model Normalized Difference Water Index (NDWI) and Modified Normalized Difference Water Index (MNDWI) with a pre-assigned threshold value. The results were evaluated with the area extracted through artificial visual interpretation. Then we conducted mathematical morphology operators, opening and closing operations, and median filter to eliminate noise to ensure the accuracy of water body information extraction from the Bosten Lake. A long-term water surface area database of the Bosten Lake was established from high-resolution remote sensing images during 1988–2018. (2) Due to the seasonal difference of snow, ice content, and other objects on images, the areadynamics of Bosten Lake in the recent 30 years were analyzed separately in dry season and rainy season. The water surface area of Bosten Lake showed large inter-annual variations between 1988–2018. (3) Based on the assumption that climatic change has more direct effects on lake than human activities, six meteorological factors were selected to analyze the impacts of climate change on the annual mean lake surface area. The result indicated that in the past 30 years, climate conditions in the Bosten Lake Basin fluctuated greatly. We conducted correlations analysis between the areal dynamics of the Bosten Lake and the meteorological factors. Here, the annual average evaporation had the highest correlation with the areal dynamics of Bosten Lake followed by air temperature, precipitation, sunshine hours, and relative humidity, while the annual average wind speed had the weakest correlation.
Xiaoai Dai; Xingping Yang; Meilian Wang; Yu Gao; Senhao Liu; Junmin Zhang. The Dynamic Change of Bosten Lake Area in Response to Climate in the Past 30 Years. Water 2019, 12, 4 .
AMA StyleXiaoai Dai, Xingping Yang, Meilian Wang, Yu Gao, Senhao Liu, Junmin Zhang. The Dynamic Change of Bosten Lake Area in Response to Climate in the Past 30 Years. Water. 2019; 12 (1):4.
Chicago/Turabian StyleXiaoai Dai; Xingping Yang; Meilian Wang; Yu Gao; Senhao Liu; Junmin Zhang. 2019. "The Dynamic Change of Bosten Lake Area in Response to Climate in the Past 30 Years." Water 12, no. 1: 4.