## 2 Materials and Methods
### Database
#### 2.2.2 Polarimetric SAR Data and Decompositions  
PolSAR data from R-2, TSX, ALOS and ALOS-2 were available for the test site. Table 3a lists the main acquisition parameters and shows that all data was acquired in the summer months, during the growing season of the tundra vegetation. Note that the ALOS-2 data was acquired at a steep incidence angle (28\({}^{\circ}\)) in 2016, while the data of the other sensors were acquired with incidence angles between 34\({}^{\circ}\) and 40\({}^{\circ}\) in 2010/2011; along with the in situ reference data. Changes of the land cover were considered to be of less relevance for the analysis, considering the recent studies on the decadal changes in composition of the tundra vegetation here [37; 38] the spatial resolution of the data, and the rather broadly defined classes. Figure 1b shows a false-color composite of the HV intensities of TerraSAR-X (TSX), R-2 and ALOS. Figure 2: Example in situ imagery of select land cover classes of interest: (**a**) sand (BS); (**b**) mixed sediment (BM); (**c**) driftwood accumulation (BW); (**d**) herb dominated tundra (HT); (**e**) shrub dominated tundra (ST) and (**f**) wetland (WT). Photos were taken in 2012 on the Tuktoyaktuk Peninsula by [PERSON]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & & **(a) PolSAR Database** & \\ \hline
**Sensor** & **Wavelength/Band** & **Date of Acquisition** & **Mode** & **Polarization** & **Incidence Angle** \\ TX & 3.1 cm/\(\chi\) & 3 August 2011 & Stripmap & Dual HH/VV & 38.8\({}^{\circ}\) \\ TSX & 3.1 cm/\(\chi\) & 23 July 2011 & Stripmap & Dual HH/HV & 38.8\({}^{\circ}\) \\ R-2 & 5.5 cm/\(\chi\) & 19 August 2011 & Fine & Quad HH/VV/VH/VV & 40.5\({}^{\circ}\) \\ ALOS & 23.6 cm/\(\rm L\) & 21 July 2010 & Fine Beam Dual (FBD) & Dual HH/HV & 34.3\({}^{\circ}\) \\ ALOS-2 & 24.2 cm/\(\rm L\) & 15 September 2016 & Stripmap (SM) & Quad HH/VV/VH/VV & 28.4\({}^{\circ}\) \\ \hline \multicolumn{4}{c}{**(b) Multispectral Imagery**} \\ \hline
**Sensor** & **Spectrum** & **Date of Acquisition** & **Path/Row** & **Sun Azimuth/Elevation** \\ Landsat TM 5 & 0.07 \(\mu\)m-0.27 \(\mu\)m & 19 August 2011 & 63/11 & 171\({}^{\circ}\)/32\({}^{\circ}\) \\  & & (excluding the thermal band) & & \\ \hline \multicolumn{4}{c}{**(c) Polarimetric Features**} \\ \hline
**Name/Model** & **Polarization** & **Feature Names(s)** & **Feature Symbol(s)** & **Source** \\ \hline \multicolumn{4}{c}{HH} \\ Polarimetric Channels & \multirow{2}{*}{Single/Dual/Quad} & \multirow{2}{*}{n/a} & HV & \multirow{2}{*}{n/a} \\ (sigma nonb intensities) & & VH & & \\ \hline Two Component Decomposition & Dual (HH/VV) & Double Boume & DBI2 & [14] \\ \multicolumn{4}{c}{Surface Scattering} & ODD2 & \\ \hline Two Component Decomposition & Dual (HH/VV) & Volume Scattering & VOL2 & \\ Ground Scattering & GRD2 & & \\ \hline Yamaguchi Decomposition & Quad & Double Boume & DBI3 & \\ \multicolumn{4}{c}{Volume Scattering} & VOL3 & [27] \\ Surface Scattering & OD3 & & \\ \hline Eigen-decomposition/ & \multirow{2}{*}{Dual/Quad} & Entropy & ENT & \\ Entropy/Alpha & & Alpha of T-Matrix & ALPT & [25,26] \\ Alpha of C-Matrix & & ALPC & \\ \hline \multicolumn{4}{c}{Kennaugh Matrix Elements; total intensity} \\ \multicolumn{4}{c}{(K0), absorption elements (K1,K2,K3),} & K0, K1, K2, K3, K4, K5, \\ \multicolumn{4}{c}{flattenuation elements (K4,K5,K6),} & K6, K7, K8, K9 & [31] \\ \multicolumn{4}{c}{retordance elements (S7,K6,K9)} \\ \hline \end{tabular}
\end{table} 
Table 3: **(a) Acquisition parameters of TerraSAR-X (TSX), Radarsat-2 (R-2), ALOS PALSAR (ALOS), and ALOS-2 PALSAR-2 (ALOS-2); (b) acquisition parameters of Landsat TM imagery and (c) overview on the polarimetric features considered in the analysis. **The following processing steps were applied to the PolSAR data: First, synthetic dual-polarized data (HH/VV, VV/VH and HH/HV) were generated from the R-2 and the ALOS-2 quad-polarized data.