Study The Effects Of Light Use Efficiency And Photo-chemical Reflectance Index

Photosynthesis plays an indispensable role in maintaining various kinds of vital movements and its close connection with solar radiation. Estimating the photosynthesis of terrestrial ecosystem with accuracy and quantity is the fundamental step to further estimate gross primary productivity (GPP) and net primary productivity (NPP), models based on light use efficiency (LUE) are more widely applied than that of GPP and NPP. However, as one of the key elements influence gross primary productivity, LUE is hard to define because it will be affected by temperature, water supply and some other elements. In recently years, researches on photochemical reflectance index (PRI) based on remote sensing give a new sight to estimate accurate LUE value.This thesis makes exploratory and experimental research on the relationship between light use efficiency and photochemical reflectance index, which includes:a. designs field experiment, measurements with different LUE and PRI values of winter wheat under different nitrogen treatment conditions to see how crop’s internal constitutions affect LUE and PRI;b. deals with the observed data from field experiment and studies the sensitivity to find a suitable parameter for PROSAIL, fit tests are performed on simulated data to compare the fit of the model;c. conducts rice field trials to figure out physiological and ecological factors as well as hyperspectral observation of rice canopy with different sun angles under different observation conditions;d. calculates observed values of rice’s LUE and PRI, analyzes the relationship between LUE and PRI values under multi-angles.The main conclusions are as follows:1. The value of LUE and PRI of winter wheat in two growing season both increases significantly with three nitrogen treatment conditions. Winter wheat at early heading stage has a bigger correlation than that of ones at early jointing stage because absorbed more nitrogen.2. Leaf area index has an impact on near-infrared band and short-wave infrared band canopy spectral reflectivity. Thy matter has an effect on near-infrared band and middle-infrared band spectral reflectivity. Equivalent water thickness has a notable impact on short-wave infrared band, chlorophyll content of leaves effects visible band and the change of view zenith angles has a wide effect on all band canopy spectral reflectivity. The result of sensitivity tests is the inversion of the value of chlorophyll, the inversions of equivalent water thickness and thy matter is close to the setting value. On the other hand, N,LAI and Theta_v belong to colony and leaves’structural parameters which don’t have specific absorb bands, so there’s little distinguish between their impacts on canopy spectral reflectivity. As a result, the interaction makes an unstable structure inversion of Theta_v.3. The back-reflection and back-PRI values in four days are all greater than that of forward-reflection and forward-PRI on the principal plane, and the form of expression is similar to the trend which is that PRI decreases gradually when spectrometer moves backward.4. Under good weather conditions, medium-angle of forward-reflection and low-angle of backward-reflection of PROSAIL can simulate well the PRI with low canopy.