# The Combined ASTER MODIS Emissivity over Land (CAMEL) Part 2: Uncertainty and Validation
## 3 CAMEL Uncertainty Estimates
### Results  
Figure 1 shows a global map of the CAMEL 8.6 \(\upmu\)m emissivity for January 2007. Located within the quartz doublet region, this channel's emissivity highlights the location of surface types dominated by quartz, for example the Sahara Desert, Namib Desert, and inland Arabian Peninsula. The associated CAMEL quality flag (qf), defined in Table 3, is also shown in Figure 1 and shows where no CAMEL emissivity values are reported over sea/inland water (qf = 0), where the input UW BF and ASTER data are good quality (qf = 1), the input UW BF is good quality and ASTER is filled (qf = 2), the input UW BF is filled but ASTER is good quality (qf = 3), and both the UW BF and ASTER values are filled (qf = 4). The distinct line over which the quality flag changes at \(\sim\)55\({}^{\circ}\)N latitude is an artifact of the day/night emissivity method of the NASA MOD11C product which is used as input to the UW BF product [16]. A lack of MODIS data is also seen over land in the \(\sim\)0-20\({}^{\circ}\)S tropical belt in regions dominated by persistent cloudiness. The north-to-south stripes over Siberia are caused by the cloudiness over the whole month in the ASTER dataset. For these cases, both datasets use filling techniques from the average of the neighboring months or annual data. \begin{table}
\begin{tabular}{c c} \hline
**Value** & **Description** \\ \hline
0 & Ocean or no CAMEL data available \\
1 & Good quality \\
2 & Unphysical uncertainty \\ \hline \end{tabular}
\end{table} 
Table 2: Definition of CAMEL emissivity uncertainty quality flag. \begin{table}
\begin{tabular}{c c} \hline
**Value** & **Description** \\ \hline
0 & Ocean or inland water \\
1 & input UW BF and ASTER data are good quality \\
2 & input UW BF is good quality and ASTER is filled \\
3 & the input UW BF is filled but ASTER is good quality \\
4 & both the UW and ASTER values are filled \\ \hline \end{tabular}
\end{table} 
Table 3: Definition of CAMEL quality flag. The CAMEL uncertainty product for the 8.6 \(\upmu\)m channel during January 2007 is shown in Figure 2. The total uncertainty is shown with its quality flag and three separate uncertainty components. Qualitatively it is apparent how the total uncertainty is a combination of the three components, with the largest contributions coming from the algorithm component. The amount each component contributes to the total value varies with season. For example, the month of July in general has lower algorithm uncertainty and the spatial and temporal uncertainty has increased values north of \(\sim\)60\({}^{\circ}\) latitude which are more readily identified as contributing to the total uncertainty. A line of larger uncertainty values is seen along the -55\({}^{\circ}\)N latitude region in Asia, which is a pattern present in all 3 uncertainty components, and is attributable to the change of CAMEL input data (no UW BF input) as shown in Figure 1's quality flag. A comparison of the 8.6 \(\upmu\)m spatial uncertainty to the monthly mean emissivity in Figure 1 shows areas of spatially uniform emissivity have low spatial uncertainties, for example densely vegetated regions of the Congo Forest, and persistent snow/ice covered regions of Antarctica and areas over Northern Hemisphere winter snow covered areas (northern Arctic Circle). Due to the large difference in the 8.6 \(\upmu\)m emissivity between quartz and non-quartz surfaces, even a small mixing of surface types  
Figure 1: Combined ASTER and MODIS Emissivity over Land (CAMEL) (**a**) 8.6 \(\upmu\)m emissivity and; (**b**) quality flag for January 2007. Quality flag is defined as in Table 3. The University of Wisconsin Baseline-Fit (UW BF) has fill values north of -55\({}^{\circ}\)N congruent with the prevailing winter nighttime of January at those latitudes. This is because the MOD11C3 product used as input to UW BF is dependent on a day–night algorithm that requires a day and night observation close in time, and there is not enough daytime data in the Northern Hemisphere winter. can yield larger spatial uncertainty values.