## 5 Conclusions
In this context, the combination of PolSAR information via a multi-sensor approach seems very promising, since it will combine dielectric, and geometrical properties of the targets. An interesting future question will be to also address the use of hybrid-polarimetric/compact-polarimetric data that can be synthetically generated from quad-polarimetric data, also using the Kennaugh Matrix approach [31]. The question will be how such data perform compared to quad-, or dual-polarized data. As well, the potential for land cover classification should be addressed, e.g., via the Random-Forest approach that was shown to provide an interesting classification framework also for PolSAR data [16; 51]. In this context, upcoming studies should further acknowledge if the Random-Forest approach is appropriate and essential for a successful PolSAR classification. The inclusion of Sentinel-1 C-Band PolSAR data is another option, as the Interferometric Wide-Swath mode provides large spatial coverage at high spatial resolutions, and the planned continuity of the Sentinel SAR systems will offer the capacity to support long term monitoring and consistent remote observations of Arctic land covers. However, as shown in this study the VV/VH polarization mode, employed by Sentinel-1 over most parts of the Canadian Arctic, seems less suited for characterizing of the tundra land cover classes; thus the use of a multi-frequency or multi-sensor approach is advisable. In summary, the SAR data of all wavelengths--also of the L-Band--were shown to provide important information about the tundra environment and utilization of such remotely sensed information is strongly recommended. PolSAR data provide unique information on dielectric, and geometrical properties that can help to increase the information space. Whenever possible dual- or quad-polarized data should be used, as polarimetry was shown to be of high value and importance. The authors like to thank [PERSON] (DLR) and [PERSON] (University of Wuerzburg) for the helpful discussions and support. Further, we like to thank [PERSON] and [PERSON] (NWRC & Carleton University Ottawa) for the organization of the field trip and the support during the field work. TerraSAR-X imagery is shown under permission of German Remote Sensing Data Center (DFD): Related Proposals COAI736 and COA1144. RADARSAT-2 imagery is shown under permission of MacDonald Dettwiler and Associates (MDA)--Related Multi-User Request Form MDA GSI-Ref.-Number: CG0061(2)-12-2011. ALOS and ALOS-2 imagery was obtained via the JAXA Proposal \"Derivation of Environmental Parameters of Arctic Tundra Landscapes from Radar Remote Sensing\"--PI No. 1186: Dr. [PERSON] (Alfred Wegener Institute for Polar and Marin Research). This publication was funded by the German Research Foundation (DFG) in the funding program \"Open Access Publishing\" and by the University of Wuerzburg. The authors would like to thank the anonymous reviewers for their helpful and constructive comments. [PERSON], [PERSON] and [PERSON] conceived and designed the experiments; [PERSON] and [PERSON] performed the experiments; all authors analyzed the data and wrote the paper. The authors declare no conflict of interest.