**5. Conclusions**

This case study presents a two-step workflow using thresholds to discriminate wet snow and firn for SAR data. In a first step, the workflow distinguishes dry and wet surfaces and subsequently analyzes wet surfaces for wet snow and firn with a second threshold value. Deviations to the extent of snow covered areas derived from visual and shortwave infrared channels are less than 10% (8.5%) in area for C-band data. WSCAF is sensitive to increases in threshold values, which can lead to offsets up to 18.1%. Average offsets of annual minimum in WSCAF from SAR data and field data on annual AAR are at below 10% (8.2%) as well for three observed GYs and three different glacier areas. For analysis, we included 12 individual glaciers covering a wide range of elevation and exposition as well as area extent. All glaciers are located within the Rofental, Austria. For two glaciers within this study, long-term mass balance series are available. We used these time series to establish linear relationships between AAR and B and compared field measurements on B with outcomes for the relationships for SAR derived AAR values. Deviations between field assessments of B and SAR derived values are at 200–300 mm w.e. on average. Such results are not an improvement compared with conventional measurements but enable mass balance estimates for regions not accessible or too dangerous for conventional mass balance observations. Results are very encouraging and demonstrate the feasibility of the proposed workflow to derive AAR from SAR data. In addition, we could show that glacier surface conditions during the melt season can be quasi-continuously be monitored using S1 SAR data, which is essential for glacier runoff modeling. Implementation of this workflow for other regions worldwide has to be analyzed with extended SAR data acquisitions. However, apart from SAR data, solely the availability of DEMs with sufficient accuracy is required to apply the proposed workflow.

**Author Contributions:** A.H. performed the scientific analysis, acquired the optical data, designed the structure and prepared the manuscript. A.W. is responsible for the download of SAR data and geocoding in the Kennaugh processing chain. A.S. provided the Kennaugh processing chain. C.M. contributed with the design and planning of the study and helped to improve the quality of the manuscript. All authors contributed to editing the manuscript.

**Funding:** This research received funding by the German Science Foundation through DFG gran<sup>t</sup> HE7501/1.

**Acknowledgments:** We would like to thank the Copernicus Service for providing the Sentinel-1 and Sentinel-2 data free of charge and sincerely appreciate the support by Rainer Prinz, Irmgard Juen and the Institute of Atmospheric and Cryospheric Sciences at University Innsbruck, Austria for providing data and information about HEF and KWF. Landsat data were obtained through GLOVIS USGS. A.H. was supported by DFG gran<sup>t</sup> HE7501/1.

**Conflicts of Interest:** The authors declare no conflict of interest.
