# Pre-Flight SAOCOM-1A SAR Performance Assessment by Outdoor Campaign
## 4 SAOCOM Outdoor Experiment Results
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**IRF Parameter** & **Replica-Replica Case** & **Ideal-Ideal Case** & **Replica-Ideal Case** \\ \hline Resolution & 2.77 m & 2.66 m & 2.68 m \\ Peak-to-Side-Lobe ratio & \(-16.2\) dB & \(-13.3\) dB & \(-14.98\) dB \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Range IRF analysis results. Figure 4: (a) Comparison between the ideal chirp and the chirp extracted from internal calibration; (b) Range-compressed Impulse Response Function (IRF) comparison. Figure 5: (a) Range-compressed data intensity profile and interpretation; (b) Doppler analysis of the clutter. The effect of the target motion is clearly seen in the range-Doppler map, showing the Doppler spectrum for each range. The two \"targets\" are the focused responses of the moving target. The bright stripe at the higher range is the backscatter of moving people inside the control shelter. The azimuth impulse response function of the system can be extracted as a horizontal cut of the range-Doppler map and is shown in Figure 6. The importance of the result below is to have the possibility to analyze in advance the impulse response of the Synthetic Aperture Radar, normally obtained only once the instrument is flying and the data are properly processed on ground. Concentrating now on the moving target range bin, we can assess the end-to-end overall amplitude and phase stability, which will be a combination of the instrument and of the propagation medium stability. Figure 7 shows, on the left, the reconstructed phase of the signal corresponding to the moving target bin. The expected sawtooth trend can be seen, corresponding to the movement of the corner reflector back and forth during the acquisition. The image in the center shows the corresponding time-variant concentration of the signal energy in the azimuth frequency domain, moving from positive to negative frequencies depending on the direction of motion. The location of the peaks in frequency allows one to estimate with high precision the actual motion velocity and to synthesize an ideal linear motion and the corresponding phase trend. The rightmost plot shows instead the residual phase after linear motion compensation. By collecting the phase of all the peaks from the acquired 10 min of long data, the amplitude and phase stability results reported in Table 5 were obtained. The correctness of the antenna excitation setting and the validation against the theoretical antenna pattern calculation was carried out by repeating the data acquisition with different antenna pointing in elevation thanks to the mechanical steering of the antenna. Figure 8 below shows an example of the obtained results, where each dot on the plot represents the average power at the moving target range, estimated on one data acquisition, either VV or HH. The dots are superimposed over the theoretical antenna pattern shape, corresponding to the applied tapering on the antenna (Taylor tapering). The good agreement of the measures with the expected  
Figure 6: (**a**) Range-Doppler map with the focused moving target clearly visible; (**b**) Azimuth IRF. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value (VV)** & **Value (HH)** \\ \hline Amplitude stability & better than 0.1 dB & better than 0.1 dB \\ Phase stability & 3.9 deg & 3.4 deg \\ Amplitude drift & \textless{}0.1 dB/min & \textless{}0.1 dB/min \\ Phase drift & 0.19 deg/min & 0.35 deg/min \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Amplitude and phase stability results over 10 min. pattern can be seen up to the second side-lobe. The agreement is better for positive angles than for negative angles. This can be explained considering the known interaction of the antenna with the ground, introducing a ripple on the whole pattern. Figure 7: Analysis of the moving target signal. (**a**) Phase versus time; (**b**) Doppler frequency versus time (colorscale in dB, normalized to the maximum); (**c**) Residual phase after linear motion compensation.