*2.4. MODIS LAI*

The MODIS LAI can be derived from two satellites, TERRA and AQUA. Here we use TERRA MODIS Collection 5 product MOD15A2, available from https://ladsweb.nascom.nasa.gov/. The product was designed at 1 km spatial resolution and eight-day temporal resolution. The main algorithm was based on look-up-tables (LUTs) that estimated from a 3D radiation transfer model [27]. It compared MODIS directional spectral reflectance with model-based entries stored in LUTs and derived the distribution of all possible solutions [12]. In addition, the algorithm output is the mean LAI computed over the set of acceptable LUT elements for which simulated and measured MODIS surface reflectance differ within specified levels of model and surface reflectance uncertainties [22]. If the main algorithm failed, a back-up algorithm was employed that was based on the relationship between NDVI and LAI. A quality control (QC) layer was also provided to assess the retrieval quality.

Table 1 provides a summary of the four LAI products used in our study. According to Table 1, the overlapping period of four products is 2000–2011. Consequently, the comparison and evaluation work is focused on this period in this study.


**Table 1.** Main information on the LAI products under study.
