Retrieval Of Vegetation Parameters Of The Saltmarshes In The Yangtze Estuary Using Multi-Spectral Satellite Images

Quantitative remote sensing of biophysical and biochemical properties by physical models is of great significance for vegetation monitoring,ecosystem functions,and global carbon and nitrogen cycles.However,the retrieval of vegetation physiological parameters by remote sensing was mainly applied in terrestrial ecosystems presently,with few studies in coastal wetlands.In this study,leaf area index?LAI?,leaf chloro-phyll content(C_ab),and fraction of absorbed photosynthetically active radiation?f PAR?of salt marsh vegetation was retrieved quantitatively by a coupled model?Soil-Canopy-Observation of Photochemistry and Energy fluxes,SCOPE?,using Landsat-8,Sentinel-2A,and Rapid Eye multispectral satellite imageries.The retrieval authenticity was ver-ified by the measured values at the same time of images acquisition.We analyzed the differences and similarities of retrieval accuracy for multispectral remote sensing im-ages with different spatial resolutions and band settings.The tidal effects on the re-trieval of physiological properties in coastal wetlands were also discussed.The results showed that Rapid Eye outperformed Landsat-8 and Sentinel-2A in the retrieval of LAI and C_ab,with higher coefficients of determination?R²=0.539 and0.488,respectively?and lower normalized root mean square errors?NRMSE=0.32and 0.28,respectively?.For Rapid Eye without the red-edge band,R² values between the modelled and observed LAI and C_ab decreased by 27.83%and 5.33%,respec-tively,while the NRMSE increased by 3.13%and 46.43%,respectively.This high-lighted the importance of the red-edge band in vegetation parameter retrieval.Re-trieval results from Sentinel-2A was poor because of tidal flooding.The accuracy of C_ab retrieval improved significantly by removing the sampling sites near tidal creeks and in low-lying areas.This indicated that tidal inundation exerted a notable effect on the retrieval of saltmarsh vegetation parameters when using multispectral images.In addition,the spatial patterns of the simulated f PAR from Rapid Eye is consistent with that of the gross primary productivity.This also verified the feasibility of this study method.This study would provide reference for the application of similar satellite images to the retrieval of physiological parameters in coastal salt marshes,and serve as a foun-dation for large-scale and fine retrieval.It would also provide technical support for the evaluation of ecological function in coastal salt marshes.