Quality Assessment of Global Modis Lai Product for the Regional Scale Applications

MODIS LAI product has been increasingly important for analyzing the process and productivity of terrestrial ecosystems at global scale. This study was aimed to assess the quality of global MODIS LAI product for applications in regional and even in local scales. To examine the quality of MODIS LAI data, we produced a reference LAI map that was derived by relating the ground-measured LAI to Landsat ETM+ reflectance over the forest of the Kyongan watershed in central Korean peninsula. After the reference LAI map was rescaled at 1km spatial resolution, it was compared with the MODIS LAI product that was generated about the same time with the reference data. From the comparison between the MODIS LAI and the reference LAI, it was found that MODIS LAI values were slightly higher at the forestland than the reference map and they were generally lower in grasslands and croplands. Specially, MODIS LAI pixels estimated by the backup algorithm by using NDVI were obviously under-estimated comparing with the reference LAI value. The MODIS LAI pixels that were attenuated by cloud cover also showed large difference from the reference LAI value. The discrepancy between the MODIS LAI and the reference LAI can be also caused by the misclassification of MODIS land cover product that is one of the input variable to create MODIS LAI. The quality of MODIS LAI product was largely dependent on the estimation algorithm, cloud cover, and the accuracy of MODIS land cover product.