## 3 Results
### Remotely Sensed Phenological Metrics  
Figure 3 shows the BBRK30 and LCOLOR20 for 1991-2010 along with the remotely sensed onset and offset derived using satellite methods for 2000-2010. At Harvard Forest, BBRK30 varies in the range of DOY112 to DOY135 with an average date of DOY125. In each year, BBRK30 also varies across species and individual trees. The standard deviation fell in the range of 1.1-9.0 days. When NDVI was used to retrieve the leaf onset, LOGISTIC1 and CAMELBACK produced earlier dates than BBRK30 (Figure 3a) with an RMSD of 36.1 and 16.5 days (Table 3), respectively. The onset dates retrieved using LOGISTIC2 and MOVING varied around BBRK30 showing the smallest RMSD (less than a week) and relatively high \(\rho\) (Figure 3a, Table 3). MIDPOINT and DERIVATIVE generally produced onset dates that are later than BBRK30. MOVING had the best performance capturing the inter-annual variability with the highest \(\rho\) of 0.54 (Table 3), whereas the \(\rho\) of LOGISTIC1, CAMELBACK and DERIVATIVE were relatively low (Table 3). When EVI was used to retrieve the leaf onset, LOGISTIC1 and CAMELBACK still produced earlier dates although they were closer to BBRK30, whereas LOGISTIC2, MIDPOINT and DERIVATIVE produced later dates (Figure 3b). The RMSD of LOGISTIC2, MIDPOINT and MOVING were larger than those when NDVI was used (Table 3). For all the methods, the onset dates derived from EVI have better correlation with BBRK30 than those derived from NDVI (Table 3), suggesting that the inter-annual variability was better captured with EVI. The average date of LCOLOR20 at Harvard Forest is DOY273 over the period of 1991-2010 with relatively small inter-annual variability (Figure 3c). However, in a certain year, the difference between individual trees is larger than that for BBRK30 (the standard deviation ranges from 5.8-12.7 days). When NDVI was used to retrieve the offset, all the methods produced later dates than LCOLOR20 except for LOGISTIC1 (Figure 3c). The discrepancy was large with the RMSD ranging from 20.6-59.1 days (Table 4). The correlations between remotely sensed offsets and LCOLOR20 were weak (Table 4). A similar pattern was found for the offsets retrieved using EVI (Figure 3d) except that the later dates were closer to LCOLOR20 (_i.e._, smaller RMSD) whereas the earlier dates (_i.e._, offset derived using LOGISTIC1) were farther. LOGISTIC2 had relatively good performance as the offsets fell within one standard deviation of the ground observation for most years. LOGISTIC1, DERIVATIVE and CAMELBACK were negatively correlated with LCOLOR20, whereas MOVING showed relatively high \(\rho\) (Table 4). Moreover, the phenology from the MCD12Q2 product showed similar biases as LOGISTIC1 with EVI calculated using MOD09A1 (Figure 3b,d, Tables 3 and 4). **Figure 3.** Ground observed phenology with remotely sensed onset from NDVI **(a)**; onset from EVI **(b)**; offset from NDVI **(c)**; and offset from EVI **(d)**. Error bars indicate the standard deviation of observation. \begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Leaf Onset**} & \multicolumn{2}{c}{**NDVI**} & \multicolumn{2}{c}{**EVI**} \\ \cline{2-5}  & **RMSD** & \(\boldsymbol{\rho}\) & **RMSD** & \(\boldsymbol{\rho}\) \\ \hline LOGISTIC1 & 36.1 & 0.06 & 13.8 & 0.44 \\ LOGISTIC2 & 6.3 & 0.31 & 13.3 & 0.80 \\ MIDPOINT & 9.2 & 0.42 & 13.1 & 0.54 \\ MOVING & 5.3 & 0.54 & 6.5 & 0.68 \\ DERIVATIVE & 14.5 & 0.28 & 14.7 & 0.51 \\ CAMELBACK & 16.5 & 0.30 & 12.2 & 0.48 \\ \hline \hline \end{tabular}   
The RMSD and \(\boldsymbol{\rho}\) between the onset from MCD12Q2 product and observations are 11.2 days and 0.79, respectively.