Ecological Indicators (Mar 2021)
Estimation of remote sensing based ecological index along the Grand Canal based on PCA-AHP-TOPSIS methodology
Abstract
The Beijing-Hangzhou Grand Canal was an important water conservancy project in Chinese history, which is honored as the spiritual symbol of Chinese canal culture. Over the past thousands of years, it has played its role of water transportation and irrigation. However, with the development of social economy and urbanization in cities along the Grand Canal, the ecological environment along it is being adversely affected. In order to find out the changes in the ecological environment along the Grand Canal in the past 20 years, this study proposes a RSEI (Remote Sensing based Ecological Index) comprehensive evaluation method combined with PCA-AHP-TOPSIS, which uses the PCA to extract the contribution rates of the main components. By referring to the contribution rates, this method combines the AHP to calculate the weights of ecological environmental factors such as air temperature, precipitation, atmospheric PM2.5 concentration, tropospheric NO2 columns and NDVI. This study uses the TOPSIS algorithm to estimate the distance between each ecological environmental factor and the optimal solution, and quantify them into the RSEI comprehensive evaluation results of the areas along the Grand Canal. Combining the self-adaptability of the PCA algorithm, the comprehensive evaluation ability of the AHP algorithm and the intelligent ranking of the TOPSIS algorithm, this method successfully avoids the subjectivity, extensiveness and other limitations of conventional multi-factor decision analysis. The study results have shown that the spatial and temporal differences of the ecological environment are significant in the Grand Canal area. For example, the quality of the ecological environment in the central and southern sections is significantly higher than that in the north. The ecological environment in the northern section of the Grand Canal is quite unique. It is significantly different from the overall ecological environment of the Grand Canal area. From 2000 to 2019, the ecological environment of the Grand Canal showed a clear decline and then an upward trend until reaching the top in 2019. The improving ecological environment of the Grand Canal is closely related to the increase of vegetation coverage, the improvement of environmental quality and the implementation of national governance policies. Since the ecological environment along the Grand Canal is becoming increasingly heterogeneous, different areas along the Grand Canal need to be treated differently according to their characteristics during the eco-environment restoration and improvement process.
