## 3 Results and Discussion
### Evergreen Needleleaf Forest  
The comparisons between GlobAlbedo-derived (GA) and MODIS (MO) values at the evergreen needleleaf forest sites are shown in Figure 5. There is a much greater disagreement between the GA and MODIS fAPAR values than in previous cases. This difference is apparent across all sites, with peak MO values being approximately double the GA values in all cases. Timing is also somewhat different between the two estimates, particularly for the US-NR2 site, where both greenup and senescence are delayed in the MODIS fAPAR compared to the GlobAlbedo-derived values, by up to 2-3 weeks in some cases. The uncertainty in both datasets is also large, but particularly for the MODIS at the DE-SfN and FI-Ves sites. This is almost certainly due to clouds, snow and low sun angles, particularly in the Finnish site. For fAPAR, r\({}^{2}\) values range from 0.52 to 0.77, _i.e._, markedly lower than for the cover types above, with positive slope ranging from 1.4 up to 2.23 for the FI-Ves site, and intercept between \(-0.16\) and 0.1. The LAI values agree in timing, but not in magnitude at all. This is illustrated by r\({}^{2}\) values of 0.6-0.84, but with very large slopees in all cases, from 3.1 to >8 in the case of the FI-Ves site, and intercept values of \(-1.74\)-0.04. These values would suggest that there is a significant difference in the way the respective parameter retrievals operate over evergreen needleleaf forests. The MODIS algorithm requires tree cover to exceed 70% to be classified as forest, which may be marginal in some of these areas; it is also possible that including understory in the MODIS RT retrieval scheme introduces further differences. Notably, uncertainty is large in the MODIS LAI retrievals, particularly in the DE-SfN and FI-Ves sites. The latter is a very northerly site, with a short growing season, persistent snow cover and observations that will contain low sun angles through large parts of even mid-summer. These factors will all introduce greater uncertainty to RT parameter retrievals. Figure 4: Top row: GlobAlbedo-derived and MODIS fAPAR values for 2002–2011; second row: scatter plot of fAPAR values; third row: GlobAlbedo-derived and MODIS LAI values for 2002–2011; fourth row: scatter plot of LAI values. Error bars for GlobAlbedo values represent the uncertainty of parameter retrieval, and for the MODIS data, the variance of the \(3\times 3\) pixel window centered on the comparison site. The comparisons between GlobAlbedo-derived (GA) and MODIS (MO) values at the mixed forest sites are shown in Figure 6. The ST-StM and CH-Dsc sites show similar behavior in fAPAR to the evergreen needleleaf forest sites above _i.e._, with peak MO values being \(\sim\)1.5\(\times\) higher than GA. Lower values agree well, and the timing of greenup/senescence is generally within 2 weeks in the two datasets. The exception to this is the US-Ha2 site, where peak values are closer, but timing is more variable. The r\({}^{2}\) values lie between 0.77 and 0.88 with slope lying between 1.1 and 1.74, and with intercept \(-\)0.1-0.08. The closer agreement in timing is illustrated by the LAI values, albeit with large differences in peak values for the AT-StM, CH-Dsc and US-Ha2 cases particularly. The r\({}^{2}\) values lie between 0.75 and 0.83, with slope between 1.5 and 3.5 and intercept between \(-\)0.72 and 0.2  
Figure 5: Top row: GlobAlbedo-derived and MODIS fAPAR values for 2002–2011; second row: scatter plot of fAPAR values; third row: GlobAlbedo-derived and MODIS LAI values for 2002–2011; fourth row: scatter plot of LAI values. Error bars for GlobAlbedo values represent the uncertainty of parameter retrieval, and for the MODIS data, the variance of the 3 \(\times\) 3 pixel window centered on the comparison site. Figure 6: _Cont_. Crop/Natural  
The comparisons between GlobAlbedo-derived (GA) and MODIS (MO) values at the mixed forest sites are shown in Figure 7. In these cases, the fAPAR values agree closely in both timing and peak values for all sites.