# Pre-Flight SAOCOM-1A SAR Performance Assessment by Outdoor Campaign
## 3 SAOCOM Outdoor Experiment Setup  
The SAOCOM-1A outdoor test (ODT) took place in the Investigacion Aplicada (INVAP) facility close to the Bariloche Airport, Patagonia, Argentina. The facility consisted of a radome hosting one tile of the SAOCOM antenna and the SAOCOM electronics, connected to a control and data-processing room. The moving target was hosted in a radome placed at a distance of 3755 m in the plane in front of the facility. Figure 2 shows the setup on Google Earth (a) and an aerial view of the area (b). The picture was taken standing on a small hill of approximately 50 m altitude above the large plane. In the foreground, there is the area hosting the shelter with the guard and the power generator, connected to the small radome hosting the moving target. The fixed target was placed on the right, approximately 20 m away from the radome. Far beyond, the facility hosting the SAOCOM with the large radome can be seen. Three trihedral corner reflectors were available during the ODT campaign:  
* 75 cm
* 100 cm (visible in Figure 3b)
* 150 cm  
The first two corner reflectors could be mounted on the moving actuator, while the large one was placed to be kept immobile at approximately 20 m from the moving target radome. The Advanced Remote Sensing Systems (ARESYS) corners are trihedral-shaped aluminum reflectors with modular faces that were assembled on-site. Table 1 below reports the RCS in dB square meters (dBsm) of the corner reflectors at the SAOCOM center wavelength (0.2353 m). \begin{table}
\begin{tabular}{c c c} \hline
**75 cm Corner RCS** & **100 cm Corner RCS** & **150 cm Corner RCS** \\ \hline
13.79 dBsm & 18.79 dBsm & 25.83 dBsm \\ \hline \end{tabular}
\end{table} 
Table 1: Radar Cross Section (RCS) of the corner reflectors. Figure 2: SAOCOM-1A outdoor test setup. (**a**) View on map; (**b**) aerial photo. The accurate pointing of the corner reflectors mounted on the moving rail was ensured by the alignment of the rail itself with the line of sight, which was carried out by Comision Nacional de Actividades Espaciales (CONAE) with the use of a differential Global Positioning System (GPS). The pointing of the large corner reflector was instead performed with the use of a compass and an inclinometer (resulting thus in a coarser pointing). This method was employed because the large corner reflector was thought to have sufficient RCS so as to be left movable around the scene, in order to ease the execution of preliminary visibility tests. The SAOCOM antenna was one single tile of the total antenna. One tile is composed of 20 elements in the elevation direction and one element in the azimuth direction, with a total size of 3.48 m in elevation and 1.424 m in azimuth. Each TRM was transmitting 50 W with an efficiency of 75%. The excitation coefficients were set according to a Taylor (amplitude only) tapering, in order to shape the side-lobes. The pointing in elevation and azimuth was possible thanks to the mechanical support equipment which could be steered with steps of approximately 1 degree and the knowledge of the pointing was of approximately 0.1 degree. The link budget, accounting for all the gains and losses from the transmitter, through the medium, and to the receiver, and the corresponding signal-to-noise-ratio (SNR) computation, are reported in Table 2 below. The noise figure N\({}_{\mathrm{F}}\) term is used to define the equivalent noise temperature of the receiver and to then compute the thermal noise power with the classical equation:  
\[P_{Noise,Thermal}=K_{B}T_{eq}B=K_{B}N_{F}T_{a}B \tag{11}\]  
where \(K_{B}\) is the Boltzmann constant, \(B\) is the signal bandwidth, and \(T_{a}\) is the ambient temperature (290 K). The acquisition parameters were set in order to ease the execution of the outdoor test by putting:  
* a short chirp to allow close range
* the maximum bandwidth to reduce the resolution
* a reduced sampling window length to avoid unnecessarily large datasets  
The main SAOCOM settings are described in Table 3 below.