Analyses of the correlation between rice LAI and simulated MODIS vegetation indices, red edge position

In the present study, analyses of the correlation between rice Leaf Area Index (LAI), hyperspectal data, Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and the Red-Edge Position (REP) were studied. Hyperspectral data of hybrid rice and common rice in whole growing stage during 2002 was measured using the ASD FieldSpec UV/VNIR Spectroradiometer with resolution of 3 nm and at the same time the rice LAI was measured. The REP may be defined using the first derivative spectrum. The three bands of the Moderate Resolution Imaging Spectroradimeter (MODIS), band 1(620～670 nm, red), band 2(841～876 nm, NIR) and band 3(459～479 nm, blue) were simulated and MODIS-NDVI and EVI were calculated by averaging the continuous reflectance factor (350～1000 nm) over the spectral range of each band. A strong non-linear correlation was found between LAI of two rice varieties and the REP. The REP, MODIS-EVI and MODIS-NDVI were well related with LAI for the common rice, but the REP and MODIS-EVI were more sensitive than MODIS-NDVI to rice LAI for the hybrid rice. The reasons were that LAI of hybrid rice became greater with growth, and MODIS-NDVI was more affected by saturation, but MODIS-EVI and REP were less affected. This showed that the REP and MODIS-EVI will be more effective in monitoring the rice LAI.