Estimation of Green Leaf Area Index of Winter Wheat and Barley Using Spectral Vegetation Indices Derived from MODIS data

Vegetation Indices (VI) show different results in green leaf area index (gLAI) estimation. The objective of this study is to estimate the gLAI of winter wheat and barley using spectral vegetation indices and presenting equations that are able to properly estimate gLAI on its entire range without any reduction in VIs’ sensitivity to gLAI. Taking field data into account for developing gLAI estimation equations using different VIs derived from MODIS imagery, accuracy assessment of these functions using statistical indices, sensitivity analysis, and presenting the best-fit function for gLAI estimation are the main steps of this study. gLAI was destructively sampled in the fields of Hezarjolfa agro-industry located in Qazvin irrigation network in 2015.Results showed that gLAI changes from 0.07 to 5.81 for wheat and from 0.01 to 3.76 for barley. VIs used in this study derived from band 1 and 2 of MODIS imagery were Normalized different vegetation index (NDVI), simple ratio (SR), wide dynamic range vegetation index (WDRVI), weighted difference vegetation index (WDVI), and soil adjusted vegetation index (SAVI). The best-fit function was concluded from WDRVI with R2 of 0.78 and RMSE of 0.73. Even though the sensitivity analysis showed that WDRVI can properly estimate gLAI in its entire range, NDVI and SAVI had better results in estimating gLAI