Validation And Analysis Of Global Leaf Area Index Products

Leaf Area Index(LAI)characterizes the structure and function of vegetation canopy and is one of the key parameters to describe the vegetation.LAI is closely related to the photosynthesis,evapotranspiration,and energy balance processes of vegetation,and is of great significance to research the exchange of material,energy and momentum in earth and atmosphere system.Single sensor approach sometimes cannot provide sufficient valid observations due to bad weather or geometry conditions,which would limit the accuracy of LAI products and cause temporal and spatial discontinuities.Therefore,the LAI algorithms based on multi-sensor observations have been gradually developing.This paper analyzes and evaluates the global and regional MuSyQ LAI products qualitatively and quantitatively in terms of spatiotemporal continuity,spatio-temporal consistency,and accuracy.The methods we used are intercomparison between Multi-source data Synergized Quantitative remote sensing production system(MuSyQ)LAI product(which is produced by multi-sensor reflectance data from Terra/MODIS,Auqa/MODIS,FY3A/MERSI and FY3B/MERSI)and other LAI products and direct validation of MuSyQ LAI product based on Ground-measured LAI data.The validation results show that the temporal and spatial continuity of MuSyQ LAI products has been greatly improved than other global LAI products(MODIS c5,GLASS LAI)both at the global and regional scales.It shows good consistency compared with other LAI products(MODISc5,GLASS LAI)on the global scale and regional scale(RMSE = 0.75,RMSE = 0.83),and the MuSyQ LAI product exhibits reliable dynamic range and reasonable spatial distribution and overcomes the unreasonable high value and low value phenomena of MODIS products at extreme conditions.For evergreen broad-leaved forest,the reliability of the input reflectance used for algorithm is reduced due to factors such as cloud or snow,and thus resulted in the highest contrast(systematic and total)and lowest correlation between MuSyQ and MODIS and GLASS LAI.Qualitative analysis of the time series shows that MuSyQ has a more reasonable LAI range and has consistent seasonal changes with the other two LAI products.A comparison with LAI ground measurements shows that the precision of the global-scale MuSyQ product is slightly lower(RMSE=1.15)at the regional scale,the accuracy of the MuSyQ product(RMAS=0.96)is a little higher.On tie whole,MuSyQ LAI based on multi-source remote sensing data not only improves the time resolution of products to five days,but also greatly improves the temporal and spatial continuity of LAI products.The global spatial distribution of MuSyQ LAI is reasonable,with the best temporal and spatial continuity;the time series curve well reflects the seasonal characteristics of the vegetation;the product is consistent with ground measured data in general.