## 4 Results  
### Land Surface Heterogeneity at FluxNet Sites  
Figure 4a shows an 18 km subset TM albedo for IT-Col and a magnified image of the measurement point and spatial boundaries of 1.0 km\({}^{2}\) and 1.5 km\({}^{2}\), which provides a detailed visual representation of the landscape heterogeneity at the site. Figure 4b shows the variogram estimator (point values) for the TM albedo subsets. The spatial variability is more obvious over the larger squared regions (1.5 km\({}^{2}\) and 2.0 km\({}^{2}\)), and different land cover types are more likely to be found at larger separation distances. This variogram estimator reaches an asymptote or constant variance between spatial uncorrelated samples near the sample variance. We calculated the range and R\({}_{\rm cv}\) for each Flux site to determine the heterogeneity of MODIS pixels as summarized in Table 2.  
When the TM footprint increased from 1.0 km to 1.5 km, R\({}_{\rm cv}\) increased 0%-10% over CA-Oas, IT-Col, IT-Ro2, FR-Pue, AU-Wac, CH-Dav, NL-Loo, DE-Kli, IT-BCi, FR-Gri, US-ARM, AU-DaP, and US-IB2. These sites differ less from the surrounding landscape; when the TM footprint changes, R\({}_{\rm cv}\) only changes slightly relative to the smaller landscapes in the surrounding regions. The size of R\({}_{\rm cv}\) depends on the degree of landscape similarity within the given range. When surface heterogeneity around the site is weak, the overall degree of stationarity between regions is similar, the overall variability is small, and the value of R\({}_{\rm cv}\) is relatively low. R\({}_{\rm cv}\) increased 32.46% over HI-Fyy and 86.38% over IT-Sro as the TM footprint increased from 1.0 km to 1.5 km. Based on the range of FI-Hyy beyond the 1 km\({}^{2}\) limit, the landscapes around the two sites are obviously different; the small lakes near FI-Hyy are not within the 1 km\({}^{2}\) boundary, IT-Sro is near the sea, and internal (CV\({}_{\rm 1\ km}\)) regions do not include the sea. At the US-Bar, MY-Pso, and AU-Stp stations, the results for R\({}_{\rm CV}\) were moderate (10%-20%). There are two types of vegetation around the three sites which include mixtures of grass and trees. There are some grasslands located approximately 1.0 km north of the US-Bar tower and southeast of the MY-Pso tower. A broadleaf forest is located southwest of the AU-Stp station, but the internal (CV\({}_{\rm 1\ km}\)) does not include the forest. The overall fluctuation between regions was not high--the three sites were moderately heterogeneous.  
Figure 4: _Cont._  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Site** & **TM Overpass Time** & **1 km Range** & **1.5 km Range** & **Rcv** \\ \hline CA-Oas & 10-Aug-09 & 71.00 m & 55.00 m & 5.26\% \\ IT-Col & 25-Jul-09 & 295.00 m & 342.00 m & 7.44\% \\ IT-Ro2 & 03-Jul-09 & 260.00 m & 129.00 m & 5.38\% \\ US-Bar & 17-May-10 & 168.00 m & 353.00 m & 16.87\% \\ FR-Pue & 26-Jul-09 & 624.00 m & 332.00 m & 7.8\% \\ MY-PSO & 11-Sep-09 & 45.00 m & 644.00 m & 14.38\% \\ AU-Wac & 16-Apr-07 & 109.00 m & 112.00 m & 3.40\% \\ CH-Dav & 06-Aug-09 & 1453.00 m & 396.00 m & 9.11\% \\ FI-Hyy & 31-May-09 & 877.00 m & 155.00 m & 32.46\% \\ NL-Loo & 06-Sep-10 & 70.00 m & 34.00 m & 5.33\% \\ IT-SRo & 23-Jul-09 & 304.00 m & 641.00 m & 86.38\% \\ DE-Kli & 24-Aug-09 & 304.00 m & 193.00 m & 7.25\% \\ IT-BCi & 09-Oct-10 & 234.00 m & 182.00 m & 8.94\% \\ FR-Gri & 24-May-10 & 114.00 m & 87.00 m & 7.44\% \\ US-ARM & 16-Jul-11 & 584.00 m & 393.00 m & 5.53\% \\ AU-DaP & 23-Aug-09 & 257.00 m & 422.00 m & 6.74\% \\ US-IB2 & 12-Sep-10 & 216.00 m & 243.00 m & 4.30\% \\ AU-Stp & 25-Aug-09 & 470.00 m & 341.00 m & 16.77\% \\ \hline \hline \end{tabular}
\end{table}
Table 2: Rcv for selected ground sites.  
Figure 4: (**a**) Subset of 18.0 km TM albedo at IT-Col (measurement point) and spatial boundaries of 1.0 km\({}^{2}\) and 1.5 km\({}^{2}\). (**b**) Variogram plot, spherical model (dotted curves), and sample variance obtained via TM albedo on 25 July, 2009 for 1.0 km\({}^{2}\) (asterisks), 1.5 km\({}^{2}\) (diamonds), and 2.0 km\({}^{2}\) (squares) regions.