## 3 Campaign Description  
The flight campaign was carried out in May 2018 over an arid region located in southeastern Morocco, around the city of Erfoud at the northern edge of the Sahara Desert. Several tracks, covering different test sites, have been flown by exploiting all the three available radar acquisition modes. As observed above (see again Figure 1), the radar system was installed onboard an Eurocopter AS-350 series helicopter, and it was possible to embark onboard simultaneously the Sounder antenna and only one SAR antenna. Exploitation of the two different SAR modes has thus required during the mission the swap of the two different SAR antennas.  
In order to minimize the effects of structural vibration noise, during the campaign the INS has been placed inside the helicopter cabin (as close as possible to the SAR antenna) on the floor, by using vibration absorbers.  
Figure 2 shows all the tracks flown during the campaign, superimposed to an optical image of the overall test area. In particular, the red, green and blue tracks are relevant to the acquisitions carried out with the Sounder, SAR-Low and SAR-High modes, respectively. As can be seen, the flight tracks were flown basically over four different test sites that in the following are named TS1, TS2, TS3 and TS4, respectively. More specifically, the test site TS1, which is located in proximity of the cities of Errachidia and Erfoud, covers an aquifer located in Cretaceous rocks at a depth ranging approximatively between 100 m and 200 m. The test sites TS2 and TS3 are both located in proximity of the city of Rissani. In particular, TS2, which belongs to the great Basin Ziz-Rheris, is an almost flat region characterized by alluvial sediments with the presence of aquifers at depth varying approximatively between 20 m and 40 m, whereas TS3 includes the archeological area of Sijillasa. The test site TS4 is located in proximity of the Erg Chebbi and is characterized by the presence of several dunes and covers an aquifer located at a depth ranging approximatively between 150 m and 200 m.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameters** & **Sounder** & **SAR-Low** & **SAR-High** \\ \hline Carrier frequency & 165 MHz & 450 MHz & 860 MHz \\ Bandwidth & 40 MHz & 40 MHz & 80 MHz \\ Frequency steps & 1 & 1 & 2–3 \\ PRF & 500 Hz & 1000 Hz & 2000–3000 Hz \\ Pulse width & 2 μs & 2 μs & 2 μs \\ Mode & Pulsed & Pulsed & Pulsed \\ Antenna type & Log Periodic & array of microstrip & array of microstrip \\ Antenna gain & 7 dBi \({}^{\ast}\) & antennas & antennas \\ Antenna dimension & \(8\times 58\times 107\) cm & \(10\times 45\times 165\) cm & \(10\times 45\times 165\) cm \\ Antenna weight & 2 Kg & 15 Kg & 15 Kg \\ Nominal elevation pointing & Nadir & 45\({}^{\circ}\) & 45\({}^{\circ}\) \\ Nominal azimuth pointing & Nadir & 0\({}^{\circ}\) & 0\({}^{\circ}\) \\ Range aperture & 68\({}^{\circ}\) & 75\({}^{\circ}\) & 37\({}^{\circ}\) \\ Azimuth aperture & 50\({}^{\circ}\) & 20\({}^{\circ}\) & 10\({}^{\circ}\) \\ Range resolution & 3.8 m (free sp.) & 3.8 m & 1.9 m \\ Azimuth resolution & 1 m & 1 m & 1 m \\ \hline ADC Sampling frequency & & 200 MHz & \\ Peak power & & 200 W & \\ Power consumption & & 500 W & \\ Rack Weight & & 30 Kg & \\ Rack Dimension & & \(50\times 50\times 65\) cm & \\ \hline \hline \end{tabular} \({}^{\ast}\) dBi measures the gain of an antenna with respect to an isotropic radiator.  
\end{table}
Table 1: System parameters.