# Elevation and Mass Changes of the Southern Patagonia Icefield Derived from TanDEM-X and SRTM Data
## 2 Materials and Methods
### Dataprocessing for DEM Production  
#### 2.2.1 Interferometric Processing  
We used a differential SAR interferometric approach to generate DEMs out of bi-static TDX image pairs [21; 22]. In a first step all scenes along one track and of one date were concatenated. A simulated topographic phase was created from the reference DEM (SRTM) using the geometric parameters of the TDX satellite acquisition and subtracted from the TanDEM-X interferogram. The resulting differential phase was filtered to reduce the noise using a Goldstein filter [23]. Subsequently, the differential phase  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**ID** & **Mosaic** & **Date** & **Start Time** & **Scenes** & **Pass** & **Beff** & **HoA** & **Inc Angle** & **PU** \\  & & & & & **Dir.** & **(m)** & **(m)** & **(degree)** & **Mode** \\ \hline
1 & Summer & 31 January 2012 & 09:54:19-09:54:26 & 2 & D & 69.03 & \(-\)94.04 & 37.17 & mcf \\
2 & 2011/12 & 15 March 2012 & 09:54:19-09:54:26 & 2 & D & 68.97 & \(-\)98.42 & 40.61 & mcf \\ \hline
3 & Autumn & 16 May 2014 & 09:54:32-09:54:39 & 2 & D & 159.71 & 40.20 & 38.41 & mcf \\
4 & 2014 & 27 May 2014 & 09:54:33-09:54:40 & 2 & D & 162.34 & 42.39 & 41.95 & mcf \\ \hline
5 & & & 3 December 2015 & 10:02:40-10:02:51 & 3 & D & 114.68 & 49.91 & 35.35 & mcf \\
6 & & & 3 December 2015 & 10:03:12-10:03:26 & 3 & D & 106.48 & 38.28 & 24.81 & mcf \\
7 & Summer & 9 December 2015 & 09:54:10-09:54:28 & 4 & D & 119.71 & \(-\)65.39 & 44.54 & mcf \\
8 & 2015/16 & 9 December 2015 & 09:54:42-09:54:56 & 3 & D & 115.25 & \(-\)53.47 & 36.03 & mcf \\
9 & & & 20 December 2016 & 09:54:19-09:54:35 & 5 & D & 117.79 & \(-\)62.93 & 42.92 & bc \\
10 & & & 31 December 2015 & 09:54:25-09:54:48 & 5 & D & 117.64 & \(-\)59.31 & 41.09 & mcf \\ \hline
11 & Winter & 20 September 2016 & 09:54:50-09:55:04 & 3 & D & 105.43 & \(-\)61.22 & 38.52 & mcf \\
12 & 2016 & 1 October 2016 & 09:54:45-09:54:57 & 2 & D & 105.63 & \(-\)65.10 & 40.65 & mcf \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of the TanDEM-X data takes used for DEM generation. Beff: effective baseline; HoA: height of ambiguity; Inc. angle: incident angle; PU: phase unwrapping method used for the specific data set.  
was unwrapped. We chose to execute this step in parallel with two algorithms: the branch cut (BC) [24] and the minimum cost flow (MCF) [25] method. Phase unwrapping was guided by a coherence mask using a threshold of 0.2 to discard areas of low signal-to-noise ratios. The product was finally recombined with the reference phase after a phase-to-height conversion to get the absolute terrain heights. In a final step we geocoded the resulting DEMs. Since the unwrapping methods are sensitive to errors in the interpretation we visually checked each scene and chose the results of the algorithm with less apparent faulty areas. We additionally excluded any unreliable parts of images that contained artifacts of obvious phase jumps by masking those out manually digitizing a polygon-shapefile mask. The output is considered a raw DEM product with need for refined horizontal and vertical adjustments on the reference SRTM DEM.