Vegetation chlorophyll content estimation based on model simulation and OLI image

Leaf optical model PROSPECT and canopy reflectance model SAIL are used to simulate vegetation canopy reflectance. The relationships between vegetation chlorophyll content and vegetation indices, view zenith angle and LAI are analyzed, in order to provide scientific basis for the estimation of chlorophyll content. We make field measurement of winter wheat in Luancheng County in Hebei Province, China, and the location, altitude, LAI, height, mean leaf angle of winter wheat at sampling points are obtained. In model simulation, LAI 4 is used, and view zenith angles 0°, 36°and 55°are selected according to five imaging angles of CHRIS (Compact High Resolution Imaging Spectrometer) sensor onboard PROBE satellite. Other view zenith angles include 40°, 60° and 90°. Many vegetation indices are selected to make this study. Results show that when LAI is 4, MCARI₇₀₅ and CI_{red edge} are the most effective indices to estimate chlorophyll content. Under different view zenith angles, MCARI₇₀₅ and CI_{red edge} are related linearly to chlorophyll content, and the correlation coefficients are all close to 1. The correlation coefficients of chlorophyll content with GRVI and MCARI₆₇₀ are greater than 0.91. At a certain view zenith angle, with the increase of chlorophyll content, RVI, PRI, GRVI, CI_{red edge} and MCARI₇₀₅ tend to increase, while EVI and MCARI₆₇₀ tend to decrease. DVI values are close to saturation when chlorophyll content is greater than 40μg/cm². When view zenith angles are less than 90°, the influence of view zenith angle on PRI is very small. Using GRVI and RVI calculated from Landsat-8 OLI image, chlorophyll content mapping of winter wheat is made.