## 2 Experiment Design
S1A acquisitions were obtained over _Torny-le-Grand_ from 4 May to 30 October 2014, although the few very early products (until the beginning of June 2014) were deemed too unreliable for geolocation  
Figure 1: University of Zurich (Switzerland) corner reflector test sites _Torny-le-Grand_ and _Dubendorf_. Four reflectors (two per orbital direction) were located at _Torny-le-Grand_ from April to October 2014, then two (one per orbital direction) at _Dubendorf_ from October 2014 to January 2015.  
estimation, possibly because of orbital uncertainties. The site was no longer available to UZH after October 2014, so a new site (_Dubendorf_) was used for the remainder of the calibration phase. On 4 November 2014, two CRs (with 1 m and 1.2 m side lengths) were placed at the _Dubendorf_ test site (indicated at the top of Figure 1) and their positions surveyed using DGPS, this time using an AGNES reference station in nearby Zurich (station code _ETH2_). Table 2 lists the approximate test site positions in WGS84 geographic coordinates. Extracts from three SM products are shown in Figure 2, with yellow crosshairs indicating the automatically predicted CR image locations, and two zoomed imagettes centered on those CR positions. In Figure 2a, two extracts from SM Single Look Complex (SLC) products are centered on the ascending-orbit reflectors at _Torny-le-Grand_. Figure 2b is from a similar SM SLC product, but centered on a product acquired over the _Dubendorf_ site. In Figure 2c one of the _Dubendorf_ reflectors is visible in an extract from an SM ground range fine-resolution (GRDF) product. The GRDF products have a coarser sample spacing (4 m azimuth and ground range) than SLC products generated from the same acquisition. A total of 44 SM acquisitions were obtained over both test sites during the observation period, from 4 May 2014 to 7 January 2015. The first three of these acquisitions (before early June 2014) had to be \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Site** & **Longitude [°]** & **Latitude [°]** & **Height above Ellipsoid [m]** \\ \hline _Torny-le-Grand_ & 6.956008 & 46.770323 & 779.0 \\ _Dubendorf_ & 8.647244 & 47.397544 & 487.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Approximate test site positions in WGS84 geographic coordinates. Figure 2: Corner reflectors as seen in S1A StripMap products, with predicted positions indicated by the yellow crosshairs in each case and a higher zoom level at the bottom; **(a)** SLC over _Torny-le-Grand_, north-west reflector (**left**) and south-west reflector (**right**), product S1A_S6_SLC_1 SDV_20140627T172926_20140627T172949_001239_001318_53C9.SAFE; **(b)** SLC over _Dubendorf_, product S1A_S3_SLC_1 SDV_20150107T054240_20150107T054303_004061_004E73_ACA0.SAFE; **(c)** GRDF over _Dubendorf_, product S1A_S2_GRDF_1 SDV_20141118T170652_20141118T170721_003339_003 DF1_99A0.SAFE. (Copernicus Sentinel data 2014-2015). eliminated due to problems possibly caused by the early orbital maneuvers required for the satellite to reach its reference orbit. For all of these acquisitions, both the SLC and GRDF products were obtained. Only the SLC products, which maintain the full sensor resolution, were used for estimation of the processor-inherent range and azimuth biases. GRDF products were tested for validation purposes (as opposed to sensor calibration), in particular the quality of the slant to ground range projection. The acquisition timeline is shown in Figure 3.