## 3 Results  
Figure 2 shows the scenes of images using NIR-red-green as red-green-blue composites for three study areas. The sub-images at the upper and lower rows are Landsat and MODIS images, respectively. The synthetic image at Landsat spatial resolution was simulated by two pairs of Landsat and MODIS imagery data and one MODIS imagery dataset at the simulated date. For example, Landsat-like imagery data (11 July 2001) can be simulated by two pairs of Landsat and MODIS imagery data acquired on 24 May and 12 August 2001, and one MODIS imagery dataset acquired on 11 July 2001. The performance can be assessed by comparing the simulated image and the observed Landsat TM/ETM+.  
Figure 3 shows the original Landsat ETM+ and simulated images by ESTARFM and mESTARFM, respectively. For each study area, two simulated images based on two approaches were overall close to the observed image.  
The fusion model performance was assessed by regression-based methods. For monthly changes over a forested area, Figure 4 shows the per-pixel comparison between the simulated and observed reflectance values on 11 July 2001 for the green, red and NIR bands of Landsat ETM+. Simulated  
Figure 2: Near-infrared (NIR)-red-green composite of Landsat Enhanced Thematic Mapper Plus (ETM+) (upper row) and MODIS (lower row) surface reflectance images. The labels (**a**–**c**) represent the monthly changes over a forested area (study area 1, Canada), the annual changes of a heterogeneous region (study area 2, China) and the changes of a heterogeneous region (study area 3, Canada) over several years, respectively.  
pixel values were close to the observed ones, as indicated by the 1:1 line, demonstrating that both ESTARFM and mESTARFM can capture the reflectance changes. Table 2 (monthly changes over a forested area) shows the statistical characteristics of linear regression analysis between the simulated and observed reflectance values on a pixel basis. The simulated images for 11 July 2001 using both approaches are closer to the observed image than those for 24 May and 12 August, suggesting that the incorporated changes can be captured on the basis of MODIS images to estimate the Landsat-like image.  
Figure 4: Scatter plot of observed and simulated reflectance by mESTARFM and ESTARFM for the NIR, red and green band (**a–f**, monthly changes over a forested area).  
Figure 3: Comparison of the observed image, the simulated image ((**a**) monthly changes over a forest area (study area 1, Canada); (**b**) annual changes of heterogeneous region (study area 2, China); (**c**) changes of heterogeneous region (study area 3, Canada) over several years) by ESTARFM and the modified enhanced spatial and temporal adaptive reflectance fusion model (mESTARFM) at three study areas.  
For annual changes of the heterogeneous region around the Qianyanzhou flux site, Figure 5 shows the scatter-plots of simulated and observed reflectance values on April 13, 2002 for the NIR, red and green bands of Landsat ETM+. The rows represent the reflectance of the NIR, red and green band of Landsat ETM+, respectively (Figure 5). The linear regression parameters (R\({}^{2}\), slope, intercept) are shown in Figure 5.  
shown in Figure 5. Table 2 (annual changes of the heterogeneous region) shows the detailed statistical parameters of linear regression between simulated and observed reflectance for the QYZ study area.  
For changes of the heterogeneous region over several years around the EOBS flux site, Figure 6 shows the original Landsat TM and simulated Landsat-like images using ESTARFM and mESTARFM. The rows represent the reflectance of the NIR, red and green band of Landsat TM, respectively. Table 2 shows the detailed statistical parameters of the linear regression between the simulated and observed reflectance for the EOBS study area.