## 3 Results  
### Correlation  
Correlations among the decomposition features of dual- and quad-polarized data were investigated prior to the assessment of the backscatter characteristics of the land cover classes and the separability of classes. The squared Pearson Correlation Coefficient (\(R^{2}\)) was derived using the 50,000 randomly distributed samples on land, and which represented 10% of all land pixels inside the common coverage of the TSX, ALOS, ALOS-2 and R-2 imagery. Results were drawn as correlation matrices for the features of C-Band data of R-2 in Figure 3, for features of L-Band data of ALOS-2 in Figure 4.  
For C-Band data (Figure 3), it was observed that Kennaugh Matrix elements K4, K5, K6, K7, K8 and K9 of the quad-polarized data showed the lowest correlations among all other investigated decomposition features. An explanation for this is that the Kennaugh elements usually are uncorrelated, and that the elements K5 to K8 are phase-based elements, which are more or less stochastically fluctuating over natural targets [31]. The \(R^{2}\) values were less than 0.4 with the exception of K4 and K7. These features were highly correlated with K4 and K7 of HH/VV-polarized data (\(R^{2}\) values of about 0.9). This high degree of correlation is because K4 holds the relation of HH to VV, which is not kept in other decompositions, and the same applies for K7. As well, the correlations between K5 and K5 of HH/HV and VV/VH were moderately high (\(R^{2}\) values of about 0.6). Similarly, the \(R^{2}\) values of K8 and K6 of HH/HV and VV/VH were around 0.5. The reason for these observations are most likely the similar polarimetric behavior (diagonal diattenuation [31]) only with different input channels (HH/HV and VV/VH, respectively). The same observations were made for the L-Band data of ALOS-2 (Figure 4); however, correlations between the Kennaugh Matrix elements K4, K5, K6, K7, K8 and K9 of quad-, HH/VV-, HH/HV- and VV/VH-polarized data were generally higher. For example, correlation between K7 of quad-polarized Kennaugh Matrix and K3 of HH/VV-polarized Kennaugh Matrix showed \(R^{2}\) values of about 0.5. Among the Kennaugh Matrix elements K0, K1, K2 and K3 of quad-, HH/VV-, HH/HV- and VV/VH-polarized data, the following distinct linear correlations were observed: K0 of quad- and HH/VV-polarized Kennaugh Matrix showed \(R^{2}\) values greater than 0.9 in the C- and L-Band; K3 of quad- and HH/VV-polarized Kennaugh Matrix showed \(R^{2}\) values greater than 0.8 in the C- and L-Band; K0 of quad-, HH/HV- and VV/VH-polarized Kennaugh Matrix showed \(R^{2}\) values greater than 0.8 in the C- and L-Band. Again the correlations between the Kennaugh Matrix elements of quad-, HH/VV-, HH/HV- and VV/VH-polarized data were generally higher in the L- than in the C-Band. Thus, most likely the L-Band data is more \"stable\" in a polarimetric sense due to a longer wavelength. Further, the high correlation of K0 of quad- and HH/VV-polarized Kennaugh Matrix is present since HH and VV record the vast majority of backscatter, while the HV contribution is negligible. Among the model-based (power) decomposition features of quad- and HH/VV-polarized data, good correspondence between the DBL3 and DBL2 (\(R^{2}\) values of about 0.8), the ODD3 and ODD2 (\(R^{2}\) values of about 0.7), the VOL3 and VOL2 (\(R^{2}\) values of about 0.7 (L-Band) and 0.4 (C-Band)) and the ODD3 and GRD2 (\(R^{2}\) values of about 0.8 (L-Band) and 0.6 (C-Band)) was observed for both C- and L-Band data. The \(R^{2}\) values between any of the model-based (power) decomposition features and any other polarimetric feature were lower than these observations, with the exception of VOL3 and HV showing \(R^{2}\) values of about 0.95 (C- and L-Band). The reason for this observation can be seen in the low proportion of volume scattering for the tundra environment, making the influence of the cross-polarization component negligible, and decomposition features of quad- and HH/VV-polarized data highly correlated.