Estimation Of Light Use Efficiency Of Rice Based On Multi-angle Solar-induced Chlorophyll Fluorescence

Light use efficiency?LUE?is an important parameter for calculating vegetation productivity,and the existing model has a large deviation in estimating light use efficiency.The solar-induced chlorophyll fluorescence?SIF?based on remote sensing brings new hope to solve this problem.At present,the research on the relationship between sun-induced chlorophyll fluorescence SIF and LUE is emerging.It is proved that SIF has great potential in direct estimation of real LUE.However,the SIF is affected by light conditions and observation angles.There are great temporal and spatial variations between SIF and LUE,which are easily affected by many factors such as observation zenith angle,observation azimuth angle,weather conditions,canopy structure,etc.For this reason,a large number of conventional meteorological observation data were obtained through experimental observation.The ground automatic remote sensing observation platform was designed to obtain solar radiation data and multi angle hyperspectral reflection data of rice canopy.Based on the vorticity correlation system,the CO₂ flux and other data of rice field were obtained.At the same time,the biomass and leaf area index of rice field were obtained through field experiment.Based on the measured data,the Fraunhofer Line Discrimination is verified and analyzed.The SIF calculated from FLD and 3FLD are compared and analyzed.The flux data of typical sunny and cloudy days in the study period are calculated and analyzed,and the variation characteristics of GPP and LUE in rice canopy on the daily and seasonal scales are obtained,and the model of inversion of LUE by SIF in rice canopy under different weather conditions is constructed based on different observation angles.The measured spectral data are obtained,the multi angle SIF of rice canopy is calculated,and the inversion model of LUE by SIF under different angles is constructed;finally,the LUE of rice canopy is calculated based on the two-leaf light use efficiency model.The influence of scattering radiation inside the canopy on LUE is eliminated,the estimation accuracy of LUE is improved,and the indication effect of SIF on LUE is improved.The main conclusions are as follows:?1?Through the spectral observation of the solar incident radiance data and the canopy reflected radiance data under the natural light irradiation of the experimental rice,it can be found that the spectral curve of the rice is near the 688nm band and 760nm band,and there is an obvious phenomenon of solar-induced chlorophyll fluorescence,which conforms to the characteristics of Fraunhofer Line Discrimination.The FLD based on Fraunhofer Line Discrimination and the improved index 3FLD can get the SIF data of rice canopy and the3FLD is more scientific,reasonable and accurate than FLD.?2?The changes of Re,NEE,GPP and APAR in different weather conditions were different in the daily scale,and the absolute value in cloudy days was significantly smaller than that in sunny days.From the whole study period,GPP and APAR showed a decreasing trend.The missing leaf area index?LAI?in the whole study period can be simulated by NDVI-LAI empirical model,which can be used to calculate the seasonal change of LUE in the whole study period,and find that it shows a decreasing trend.It s different for the correlation between SIF-LUE on sunny days and cloudy days.On sunny days,SIF-LUE had obvious linear correlation,but on cloudy days,the correlation was poor.?3?There was a good negative correlation between the SIF and LUE on the daily and seasonal scales on sunny days.But with the change of observation angle,the size of SIF in rice canopy changes,and the correlation of SIF-LUE also changes with the change of observation angle.In a certain range,the larger the observation zenith angle is,the stronger the correlation degree of SIF-LUE is.When the observation zenith angle is 60°,the correlation between SIF and LUE is the most significant,R² is 0.7.?4?The correlation between the sun-induced chlorophyll fluorescence of rice canopy and the improved LUEc is significantly enhanced,and the inversion ability of SIF-LUE is improved.The simulated value of LUE is higher than the measured value of LUE.