Evaluation of MODIS VI Products Using the AERONET-based Surface Reflectance Validation Network Dataset

MODIS vegetation index (VI) products (MOD13) are widely used in many science applications that aim to monitor and characterize spatial and temporal vegetation dynamics from space. The quality and reliability of the MODIS VI products are vital to these studies, and thus there is a need to assess their quality. In this study, the AERONET-based Surface Reflectance Validation Network (ASRVN) dataset is used to evaluate the quality of the MODIS 1 km, 16-day composite NDVI and EVI products. Our results show a positive bias of red reflectances, which is responsible for bias in the MODIS NDVI and two-band EVI (EVI2). The negative bias of the MODIS blue reflectance nullifies this effect on the standard EVI, resulting in insignificant bias in EVI. EVI and NDVI temporal profiles match ASRVN VI profiles even during higher aerosol optical thickness (AOT) periods, indicating that the VI products are not significantly affected by aerosols.