# Estimating the Fractional Vegetation Cover from GLASS Leaf Area Index Product
## 3 Methodology
### Comparison and Analysis  
For clarification, the FCover product derived in this study is denoted by TRAGL. Just like the GLASS LAI product, the TRAGL FCover product has 8-day temporal and 1 km spatial resolution and is provided in a sinusoidal projection from 2000 to 2014. The spatial and temporal consistencies of the TRAGL FCover product are assessed by comparison with the GEOV1 FCover product, and the accuracy of the TRAGL FCover values was evaluated against ground-based FCover estimates.  
For comparisons of spatial consistency, the TRAGL and GEOV1 FCover products were re-projected onto the geographic latitude/longitude projection using nearest-neighbor resampling and were aggregated to 0.05\({}^{\circ}\) resolution using spatial averaging for the sake of computation efficiency. The average value over a 0.05\({}^{\circ}\) pixel was computed if more than 70% of the pixels projected into the 0.05\({}^{\circ}\) pixel had FCover values. The FCover products were then aggregated into a monthly time step by computing the monthly average from the FCover values. The global maps of mean FCover for the TRAGL and GEOV1 FCover products from 2001 to 2005 in January and July were computed to investigate spatial patterns specific to a given product as well to check the fraction and distribution in space of the missing data. Histograms of the TRAGL and GEOV1 FCover products from 2001 to 2005 were generated for each biome type according to the MODIS land-cover type product (MCD12Q1) to analyze the similarities and differences between these FCover products. To further evaluate the consistency between the TRAGL and GEOV1 FCover products, the differences between these FCover products from 2001 to 2005 were computed as a function of latitude and as a function of the biome type to qualitatively assess the main discrepancies between these FCover products.  
Temporal consistency between TRAGL and GEOV1 FCover products was evaluated over a sample of VALERI sites with different biome classes. Detailed information about the sites and mean values and standard deviations of the high resolution FCover maps over the 3 km \(\times\) 3 km regions centered on the location of the sites are given in Table 1. For comparison of temporal consistency, the original temporal resolution for each FCover product was considered. Average FCover profiles for the TRAGL and GEOV1 FCover products over 3 \(\times\) 3 pixels centered on the selected sites were calculated to reduce effects from co-registration errors between them. The average FCover value over the 3 \(\times\) 3 pixels was computed if there were more than five FCover values among the nine pixels [19]. The average FCover profiles over one year were compared for each site to provide a qualitative assessment of seasonal variations between the products. The specific years used for comparison were not the same for all sites, but varied according to the availability of the high resolution FCover maps derived from ground measurements.  
Figure 1: First-order and total-order indices of sensitivity analysis for Equation (3).  
The TRAGL and GEOV1 FCover products were compared with high-resolution FCover maps to evaluate differences in FCover magnitude between the products. The high-resolution FCover maps and the TRAGL and GEOV1 FCover products were aggregated over 3 km \(\times\) 3 km regions centered on the location of the validation sites using spatial averaging. TRAGL and GEOV1 FCover values were linearly interpolated to the acquisition date of FCover ground measurements if the two closest FCover values were within \(\pm\)10 days from that date. A total of 28 sites, providing 47 high resolution FCover maps were retained for which TRAGL or GEOV1 FCover products provided FCover values.