# The Combined ASTER MODIS Emissivity over Land (CAMEL) Part 2: Uncertainty and Validation
## 4 Validation with Laboratory Spectra
### RTTOV IASI Brightness Temperature Calculations
#### 4.3.2 Results
Figure 7: (**a**) Calculated constant 0.98 (black) and CAMEL (red) emissivity brightness temperature (BT) minus observed IASI BT bias (top panel) and mean emissivities (bottom panel) for a 29 September 2008 nighttime granule over Egypt. Number of samples, N, shown in legend. Debiased variances listed for three spectral regions; (**b**) Map of 8.5 \(\upmu\)m calculated CAMEL minus observed IASI BTs differences in Kelvin. Figure 9 shows nighttime statistics of the calculated minus observed IASI BTs for various IGBP land classification categories for the 29 September 2008 case day. While these examples are not comprehensive of all days and seasons, some general characteristics can be seen. For all categories shown, the CAMEL calculated BT is seen to generally be closer to the observed IASI BT than the 0.98 emissivity calculated BT. Land classification categories with emissivity spectra close to 0.98, such as the evergreen broad-leaf forests and croplands show the smallest bias difference between the CAMEL and 0.98 emissivity BT calculations. Largest differences are seen in the barren/desert land category around 8-9.5 \(\upmu\)m, where the emissivity spectra have prominent quartz spectral features and reach values less than 0.7, as expected. The CAMEL calculations also show better agreement with the observations than the 0.98 emissivity calculations within the 3.6-4.2 \(\upmu\)m region. Improved agreement around these wavelengths is seen for all other land categories shown as well. Comparison of the de-biased variance statistics for the CAMEL and 0.98 emissivity also confirms that for all land categories shown the CAMEL HSR emissivity is a spectral improvement upon the constant 0.98 emissivity within the 3.6-5 and 8-9 \(\upmu\)m region. The 10-13 \(\upmu\)m region de-biased variance statistics show neutral improvement using the CAMEL emissivity for all categories shown except for the open shrub and barren/desert land category where reductions in variance are significant. To summarize the global RTTOV calculated minus observed statistics over the 4 case days, the CAMEL and 0.98 emissivity de-biased variances are listed for the 8-9 \(\upmu\)m spectral region in Table 4. While variances for the 10-13 and 3.6-4.2 \(\upmu\)m regions were calculated in a similar fashion, the results are not listed here and are only discussed qualitatively. The 8-9 \(\upmu\)m region was selected to be shown since this spectral region is the region of largest expected improvement in comparison to the previous UWIREMIS. The numbers shown in Table 4 are averages of de-biased variances for the focus days and IGBP land classification categories shown. The corresponding number of samples are illustrated in Figure 9.  
Table 4 results show in general that CAMEL is an improvement upon the 0.98 constant emissivity for this spectral region. For all categories with over 2000 samples, the CAMEL de-biased variance is lower than the 0.98 emissivity de-biased variance. The open shrub and barren/desert land categories again show the largest percent decreases in de-biased variance from the 0.98 emissivity to CAMEL. The CAMEL de-biased variance is decreased on average for the four days to \(\sim\)41% and \(\sim\)21% of the 0.98 emissivity value respectively for the open shrub and barren/desert land categories. Figure 8: Same as Figure 7a except for daytime granule located over the coast of Antarctica. In addition to the 8-9 \(\upmu\)m region, the 3.6-5 \(\upmu\)m region of CAMEL also better matches the IASI observations than does the 0.98 constant emissivity. De-biased variances for CAMEL are overall lower than those for the 0.98 constant emissivity in the 3.6-5 \(\upmu\)m region, with the exceptions being for cases with a low (e.g., less than 100) number of samples. The open shrub and barren/desert categories showed the most CAMEL improvement--the de-biased variances for CAMEL are decreased respectively to be \(\sim\)79% and \(\sim\)56% of the 0.98 emissivity de-biased variance.