# Generation of High Resolution Vegetation Productivity from a Downscaling Method
## 3 Results
### Comparison of GPP and NPP Time Series  
Among the twenty field measurement sites, we chose seventeen sites that were mainly covered by vegetation to analyze the temporal dynamic patterns of GPP and NPP during the growing season of 2012. These 17 sites included 14 sites in croplands, one in orchard, one in vegetable field and one in wetland. The time series of the ground-based GPP, MODIS GPP, estimated GLASS GPP, D_GPP_MODIS and D_GPP_GLASS were shown in Figure 15. In cropland, we could find that D_GPP_MODIS and D_GPP_GLASS agreed better with the ground-based GPP in most times. While the MODIS GPP and estimated GLASS GPP underestimated the ground measurement GPP significantly, and could not reflect the temporal patterns of GPP. The MODIS GPP and estimated GLASS GPP were less than 6 g C\(\cdot\)m\({}^{-2}\).d\({}^{-1}\) during the whole growing season, but the GPP D_GPP_GLASS and D_GPP_MODIS were higher than 8 g C\(\cdot\)m\({}^{-2}\).d\({}^{-1}\) in most times, and could be as high as 16 g C\(\cdot\)m\({}^{-2}\).d\({}^{-1}\) at the peak of growing season. In orchard, estimated GLASS GPP and MODIS GPP were about 3\(\sim\)4 g C\(\cdot\)m\({}^{-2}\).d\({}^{-1}\) lower than ground-based GPP, GPP D_GPP_GLASS and D_GPP_MODIS. But estimated GLASS GPP and MODIS GPP achieved good agreements. In vegetable field, the time series of the ground-based GPP, MODIS GPP, estimated GLASS GPP, D_GPP_GLASS and D_GPP_MODIS matched well in most times. In wetland, MODIS GPP underestimated the ground based GPP obviously, while estimated GLASS GPP matched well with ground-based GPP, D_GPP_GLASS and D_GPP_MODIS.  
Temporal patterns of the estimated GLASS NPP, D_DPP_MODIS and D_DPP_GLASS were demonstrated in Figure 16. In cropland, the temporal variation trend of D_DPP_MODIS and D_DPP_GLASS matched well. But estimated GLASS NPP was lower than 4 g C\(\cdot\)m\({}^{-2}\).d\({}^{-1}\) in the growing season, which was much lower than D_DPP_MODIS and D_DPP_GLASS. In orchard, vegetable field and wetland, estimated GLASS NPP, D_DPP_MODIS and D_DPP_GLASS generally achieved good agreements generally. In vegetable field and wetland, estimated GLASS NPP is a little higher than D_DPP_MODIS and D_DPP_GLASS.  
Figure 13: Cross validation of estimated GPP against high resolution GPP: (**a**) Comparison of D_GPP_GLASS and modelled GPP; (**b**) Comparison of D_GPP_MODIS and modelled GPP. D_GPP_MODIS means the GPP from downscaled FPAR/LAI based on MODIS data by using MusyQ GPP/NPP algorithm. D_GPP_GLASS means the GPP from downscaled FPAR/LAI based on GLASS data by using MusyQ GPP/NPP algorithm. Modelled GPP is the GPP from retrieved FPAR/LAI by using MusyQ GPP/NPP algorithm.  
Figure 14: Cross validation of estimated NPP against high resolution NPP: (**a**) Comparison of D_NPP_GLASS and modelled GPP; (**b**) Comparison of D_NPP_MODIS and modelled GPP. D_NPP_MODIS means the NPP from downscaled FPAR/LAI based on MODIS data by using MusyQ GPP/NPP algorithm. D_NPP_GLASS means the GPP from downscaled FPAR/LAI based on GLASS data by using MusyQ GPP/NPP algorithm. Modelled NPP is the NPP from retrieved FPAR/LAI by using MusyQ GPP/NPP algorithm.  
Figure 15: Comparison of ground-based GPP, MODIS GPP, estimated GLASS GPP, D_GPP_MODIS and D_GPP_GLASS: (**a**) Cropland; (**b**) orchard; (**c**) vegetable field; (**d**) wetland. Note that the GPP in cropland are the mean values of all sites in cropland.