Solar-induced Chlorophyll Fluorescence Observation And GPP Estimation Of The Tower-based Platform

The spectral data observed by the tower-based platform can be matched with the carbon flux data observed by the eddy covariance technique on the time and space scales,which can solve the time and space matching of the flux-scale observation data of the ecosystem scale and the satellite remote sensing data.The problem,as a"bridge"between the connected flux site and satellite remote sensing data.The gross primary productivity of terrestrial ecosystems is an important component of the carbon cycle.More accurate understanding of the temporal and spatial dynamics of GPP is an important prerequisite for understanding the carbon cycle.The main work of the thesis is as follows:?1?Design a new dual-channel AutoSIF-1 observation system.The observation data is recorded in the order of down-welling irradiance,upwelling radiance and down-welling irradiance.After the indoor absolute radiation calibration,the raw data without physical meaning can be converted into the radiance or irradiance provides the basis for inverting the diurnal variation of solar-induced chlorophyll fluorescence.?2?Due to the effect of atmospheric absorption and scattering between the horizontal surface and the tower base platform,the error of inversion of SIF in the O₂-A absorption band is difficult to ignore.Firstly,the influence of atmospheric radiation transfer on the up-welling radiance and down-welling irradiance of the tower-based platform is analyzed,and the atmospheric correction method of based on upward and downward transmittance is established,that is,the influence of the upwelling radiance and down-welling irradiance is corrected by the direct transmittance and the total transmittance.Secondly,using the simulation data of MODTRAN model,the influence of AOD₅₅₀ and radiative transfer path length on atmospheric transmittance is quantitatively analyzed,and the LUT of AOD₅₅₀ is established based on the ratio of down-welling irradiance of near-infrared and red bands and solar zenith angle,as well as the upward and downward atmospheric transmittance LUT based on the AOD₅₅₀ and the radiative transfer path length.Finally,using the spectral data of corn canopy in different growth stages observed by the tower-based platform,the difference of the apparent reflectance of the O₂-A band absorption line before and after atmospheric correction and the inversion of the SIF of the corn canopy and the tower base platform were analyzed.The results show that the atmospheric correction method based on LUT of AOD₅₅₀ and radiative transfer path length proposed in this paper can better correct the influence of upwelling radiance and down-welling on the O₂-A absorption band of the tower-based platform,and provides important method support for applications such as SIF observation on the tower platform.?3?Using the flux data and tower-based spectral data of the Daman Super Station as the data source,the product of three vegetation indices and photosynthetically active radiation and SIF were used to invert the GPP of the corn canopy scale respectively,and a linear regression model was constructed to model and verification.The results show that:VI×PAR,SIF and GPP have higher consistency in the time series dynamic analysis of the whole period,and the overall change is first increased and then decreased,and reached the maximum during the tassel.In the early stage of tasseling,NDVI×PAR,EVI2×PAR and CIred edge×PAR were selected as the preferred model.The modeling data R²>0.835,RMSE<1.982 gC/m²/d;CIred edge×PAR was selected as the preferred model,modeling data R²=0.830,RMSE=2.200 gC/m²/d;EVI2×PAR and CIred edge×PAR were selected as the preferred model in the whole period,and the modeling data R²>0.793,RMSE<2.288 gC/m²/d.The GPP inversion model based on SIF is relatively stable,and the modeling data R²>0.663,RMSE<2.988 gC/m²/d.