# Estimating the Fractional Vegetation Cover from GLASS Leaf Area Index Product
## 4 Result Analysis  
### Comparison with GEOV1 FCover Product  
#### 4.1.1 Spatial Consistency  
Figure 2 show the global maps of the mean values for the TRAGL and GEOV1 FCover products for January and July 2001\(-\)2005. Areas masked in dark gray correspond to pixels where the FCover values are zero, and areas masked in light gray correspond to pixels where the FCover values are missing. GEOV1 FCover product has many missing pixels in rainforest regions and in mid- and high-latitude zones of the northern hemisphere, especially in January. [PERSON] _et al._[19] reported that the GEOV1 products presented the higher percentage of missing values at high latitudes in the northern hemisphere, with a wide variability as a function of the period of the year (it maximize in winter time), mainly due to snow coverage changes along the year as well as increase in observations under dark conditions particularly above the polar circle in winter, and also presented a large fraction of gaps (up to 50%) over the equatorial region as a consequence of the higher cloudiness. However, there are no missing data for the TRAGL FCover product, because the retrieval algorithm uses the spatially and temporally complete GLASS LAI product. The TRAGL and GEOV1 FCover products are generally consistent in their spatial patterns. Higher FCover values are produced over equatorial forest regions and around 50\({}^{\circ}\)N\(-\)60\({}^{\circ}\)N, whereas they are intermediate at mid- and high-latitude zones, and very low over sparsely vegetated areas. However, discrepancies are evident in the relative magnitude of the FCover products. In January, TRAGL FCover values are between 0.05 and 0.15 lower than those of GEOV1 for tropical rainforests in Amazon River Basin and Southeast Asia. At these regions, the GEOV1 FCover values can reach 0.99. However, the GEOV1 FCover values are significantly lower than the TRAGL FCover values over the Congo Basin and the Gulf of Guinea. The largest difference between the TRAGL and GEOV1 FCover values at these regions goes up to 0.4. In July, GEOV1 FCover values are slightly lower than those of TRAGL in Amazon rainforest region, but clearly higher than those of TRAGL over broadleaf crops in East-central United States and needleleaf forests in Europe and Siberia. The GEOV1 FCover algorithm proposed to correct for the systematic underestimation of CYCLOPES FCover product by applying a scaling factor. These discrepancies between the TRAGL and GEOV1 FCover products should be partly explained by a slightly too large scaling factor, resulting in more dynamic FCover values. These discrepancies should probably also be explained by a lack of representativeness of the training data base used to calibrate the algorithm [19]. Compared with the GEOV1 FCover product, the TRAGL FCover product reports a more uniform signal. The TRAGL FCover values for tropical rainforests present almost no seasonality, as expected for these evergreen forests, which is consistent with the findings of [PERSON] _et al._[19]. Statistical distributions of the FCover values for 2001-2005 for each biome type according to the MODIS land cover type are shown in Figure 3 to illustrate the similarities and differences between the TRAGL and GEOV1 FCover products. For grasses and cereal crops, shrubs, evergreen needle forests, and deciduous needle forests, the histogram distributions of the TRAGL FCover values are generally consistent with those of the GEOV1 FCover values. For the savannah biome type, the frequencies of TRAGL FCover values between 0.1 and 0.6 are significantly larger than those of GEOV1 FCover values, while the frequencies of TRAGL FCover values greater than 0.6 are significantly less than those of GEOV1 FCover values and reduce to 0 when FCover values are greater than 0.85. Similar distributions of FCover values are also observed for evergreen broadleaf forests and deciduous broadleaf forests.