## 2 Experiment Design  
Two test sites in Switzerland were selected for the placement of the trihedral CRs that served as geometric reference targets. They are indicated at the top of Figure 1. The CR sizes ranged from 90 cm to 120 cm, large enough to be visible as bright \"point targets\" in the SM mode images. The first site was in the west of Switzerland near the village of _Torny-Le-Grand_, which had been used successfully in the past for a similar long-term experiment [7] devoted to the analysis of TerraSAR-X data. Four trihedral \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Acq. Mode**} & \multirow{2}{*}{**Product Type**} & \multirow{2}{*}{**Resolution Class**} & **Resolution \({}^{1,2}\)** & **Pixel Spacing \({}^{2}\)** & **No. Looks** & \multirow{2}{*}{**ENL \({}^{4}\)**} \\  & & & \(\left[\mathbf{Rg}\times\mathbf{A}\mathbf{z}\right]\) & \(\left[\mathbf{Rg}\times\mathbf{A}\mathbf{z}\right]\) & \(\left[\mathbf{Rg}\times\mathbf{A}\mathbf{z}\right]\) & \(\left[\mathbf{Rg}\times\mathbf{A}\mathbf{z}\right]\) & \\ \hline \multirow{4}{*}{SM} & \multirow{4}{*}{SLC} & \multirow{4}{*}{FR} & \(1.7\times 4.3\) to & \(1.5\times 3.6\) to & \multirow{4}{*}{\(1\times 1\)} & \multirow{4}{*}{\(1\)} \\  & & & \(3.6\times 4.9\) & \(3.1\times 4.1\) & & \\ \cline{2-6}  & & & FR & \(9\times 9\) & \(3.5\times 3.5\) & \(2\times 2\) & 3.7 \\ \cline{2-6}  & \multirow{2}{*}{GRD} & HR & \(23\times 23\) & \(10\times 10\) & \(6\times 6\) & 29.7 \\ \cline{2-6}  & & MR & \(84\times 84\) & \(40\times 40\) & \(22\times 22\) & 398.4 \\ \hline \multirow{4}{*}{IW} & \multirow{4}{*}{SLC} & \multirow{4}{*}{HR} & \(2.7\times 22\) to & \multirow{4}{*}{\(2.3\times 14.1\)} & \multirow{4}{*}{\(1\)} & \multirow{4}{*}{\(1\)} \\  & & & \(3.5\times 22\) & & & \\ \cline{2-6}  & \multirow{2}{*}{GRD} & HR & \(20\times 22\) & \(10\times 10\) & \(5\times 1\) & 4.4 \\ \cline{2-6}  & & MR & \(88\times 87\) & \(40\times 40\) & \(22\times 5\) & 81.8 \\ \hline \multirow{4}{*}{EW} & \multirow{4}{*}{SLC} & \multirow{4}{*}{FRD} & \(7.9\times 43\) to & \multirow{4}{*}{\(5.9\times 19.9\)} & \multirow{4}{*}{\(1\times 1\)} & \multirow{4}{*}{\(1\)} \\  & & & \(15\times 43\) & & & \\ \cline{1-1} \cline{2-6}  & & & HR & \(50\times 50\) & \(25\times 25\) & \(3\times 1\) & 2.7 \\ \cline{1-1} \cline{2-6}  & & MR & \(93\times 87\) & \(40\times 40\) & \(6\times 2\) & 10.7 \\ \hline \hline \end{tabular} \({}^{1}\) For GRD Products, the resolution corresponds to the mid-range value at mid-orbit altitude, averaged over all swaths; \({}^{2}\) For SLC SM/IW/EW products, the resolution and pixel spacing are provided from lowest to highest incidence angle; \({}^{3}\) For SLC products, the range coordinate is slant range. For GRD products, it is ground range; \({}^{4}\) For GRD IW/EW products, the equivalent number of looks corresponds to an average over all swaths.  
\end{table} 
Table 1: Level 1 Product Family Summary; adapted from Table 5-1 in [2]. CRs were placed at the site, with two facing the S1A sensor in its ascending orbit and two facing its descending orbit (bottom left of Figure 1). A permanent GPS reference station of the Automated Global Navigation Satellite System Network of Switzerland (AGNES), located \(<5\) km from the site near the town of _Payerne_, was used for the differential positioning. Trimble R7 GPS receivers were used to measure their locations with accuracies better than 1 cm (confirmed by Chapter 8 in [10]). The pair-wise arrangement of the CRs not only created redundancy (in case of problems with one reflector) but also served to help validate the accuracy of their positions, as identical geolocation results should in principle be obtained for both CRs of a given pair. For each reflector, a fixed reference point on the concrete surface was surveyed; the reflector was mounted above it with the correct orientation and elevation, and the offset to its phase center (corner) was measured.