# The Combined ASTER MODIS Emissivity over Land (CAMEL) Part 2: Uncertainty and Validation
## 4 Validation with Laboratory Spectra
### Field Sites
Though the lab data does not lie within the bounds of the CAMEL HSR uncertainty within the \(\sim\)6-7 and 11-11.5 \(\upmu\)m regions, it is important to note that the lab spectra are a pure carbonate (dolomite) and CAMEL is representative of a 5 km pixel which likely contains a mixture of material, not purely carbonate. Additionally, the HSR uncertainty does appropriately reflect the increased difference between the CAMEL HSR emissivity and the lab validation data. Like the Namib Desert site, the Yemen desert site also has a higher CAMEL uncertainty in the shortwave region due to an increased temporal variability but otherwise is dominantly influenced by the algorithm uncertainty component. Figure 3: Emissivity at (**a**) January 2007 Namib Desert (\(-\)24.25N, 15.25E); (**b**) May 2007 Tucson, AZ (32.01N, \(-\)110.77E); (**c**) January 2007 Greenland (72.57N, \(-\)38.45E); and (**d**) January 2007 Yemen (19.15N, 55.57E) case sites. HSR emissivity from UW BF (blue dashed), lab measurements (black), and CAMEL (red solid with dotted uncertainty) are shown in top row panels. UW BF (blue squares, dashed), ASTER (green x’s, solid), and CAMEL (red circles, solid) emissivity are shown in middle row panels. CAMEL total (black solid), spatial (black dash), temporal (red), and algorithm (blue) uncertainty components are shown in bottom panels. Legend in middle and bottom panel include quality flags (QF) for the different products as well as ASTER normalized difference vegetation index (NDVI). The version number (Vs) of the laboratory dataset and the number of principal components (#PCs) used in the CAMEL HSR Algorithm are included in the legend of the top panels. Each of the four case sites represents a different surface type and uses a different number of PCs in the CAMEL HSR emissivity construction. The Namib Desert and Tucson, AZ cases represent surfaces characterized by quartz. Within the quartz signature region located at \(\sim\)8-10.5 \(\upmu\)m, CAMEL and the lab measurements agree within 0.05 for the Namib case and within 0.025 for the partially vegetated Tucson, AZ case. At wavelengths greater than 10.5 \(\upmu\)m, CAMEL and the lab data agree within 0.01 for both sites, while for the Namib SW region from 3.6-6 \(\upmu\)m, CAMEL has departures of \(\sim\)0.1 magnitude away from the lab measurements. This could be explained by surface roughness and terrain elevation changes present in the satellite observation but not in the lab measurement. The Greenland case site illustrates the CAMEL snow/ice emissivity performance: for wavelengths greater than or less than 8 \(\upmu\)m, CAMEL and the lab data agree within 0.005 and 0.01 respectively. The Yemen site characterizes the carbonate surfaces and shows the 6.5 \(\upmu\)m spectral feature is included in the CAMEL dataset but the lab data differs by up to 0.15, with the lab measurement lying outside of the CAMEL HSR uncertainty bounds. The reduced spectral contrast in the CAMEL estimate could be explained by surface roughness or sparse vegetation not accounted for in the lab measurement.