Estimation Of Vegetation Net Primary Productivity In Coastal Cities Of Yangtze River Delta Based On Multi-source Data Fusion

Terrestrial ecosystem is not only the basis of human survival and development,but also an important factor of global climate change.As the main body of terrestrial ecosystem,vegetation plays an important role in maintaining global material and energy cycle and carbon balance.Net primary productivity(NPP)of vegetation refers to the residual part of the total organic matter produced by photosynthesis per unit time and per unit area after deducting autotrophic respiration.The research on NPP of vegetation can help to understand the interaction mechanism between climate change and ecosystem,and provide scientific basis for regional ecological protection and resource development.In this paper,coastal cities in Yangtze River Delta are taken as research areas,and the space-time resolution of NPP estimation results is improved as the starting point.Firstly,based on estarfm model,Landsat 8 high spatial resolution data and MODIS 09a1 high-time resolution data are fused to construct monthly NDVI vegetation index data with resolution of 30m.Secondly,combined with meteorological data and land use data,the net primary productivity of vegetation in 2017 is estimated based on CASA model.The main conclusions are as follows:(1)By comparing the fusion accuracy of starfm model,estarfm model and stnlffm model,it is found that the correlation coefficient between the fusion data of estarfm model and the real Landsat data is 0.8715.At the same time,the fusion results of the model are more obvious in hierarchy and better in describing the spatial details.Based on this model,IB and Bi fusion schemes are verified,and the results show that IB scheme is better than Bi scheme in both model running time and fusion quality.The results show that the higher the vegetation index is,the better the surface vegetation coverage is.In August,the average NDVI of coastal cities in Zhejiang Province was the highest,followed by Jiangsu Province,and Shanghai was the smallest,with the average NDVI of 0.415,0.320 and 0.168respectively.(2)The CASA model was compared with the field measured data,MODIS NPP data and previous research results.The correlation coefficient between the estimated NPP value and the measured data was 0.8876,which was consistent with the previous research results,indicating that the accuracy of the model was good.By analyzing the NPP value of vegetation,the results show that the vegetation grows vigorously and the vegetation coverage is high in summer,and the average NPP value is the highest.The average NPP values of coastal cities in Zhejiang Province,Jiangsu Province and Shanghai were231.24g C/m~2,109.48g C/m~2and 79.89g C/m~2,respectively.(3)Affected by the physiological characteristics of vegetation and the external environment,the NPP values of medium,medium and high coverage areas in different seasons are different,while the NPP values of low,medium and low coverage areas change little.The coastal cities in Zhejiang Province,Jiangsu Province and Shanghai accounted for the largest proportion of high coverage areas in summer,with the average NPP of289.44g C/m~2,140.62g C/m~2and 109.47g C/m~2,respectively.In different land use types,the annual mean NPP of broad-leaved forest was higher than that of other woodlands;Cultivated land and construction land are disturbed by human activities,and the vegetation coverage is unstable;The lower NPP value of shrubs may be due to the small distribution area and the slow accumulation of NPP due to the influence of natural conditions.