# Pre-Flight SAOCOM-1A SAR Performance Assessment by Outdoor Campaign
## 4 SAOCOM Outdoor Experiment Results  
The raw data, provided by a dedicated implementation of the CONAE User Segment Service (CUSS), called mini-CUSS, were non-Block-Adaptive-Quantizer (BAQ) compressed and modulated (at 30 MHz) data. The processing software had then to perform the following steps:  
* digital down conversion
* range compression
* azimuth compression  
The digital down conversion step performs the demodulation of the signal to baseband. In the employed software, it also allowed the sub-sampling of the input dataset in order to speed up the processing for a fast analysis of the input data. In fact, the PRF of the SAOCOM is quite high compared to the Doppler content of the illuminated scene. The real input samples are also converted into complex samples during this step. The range compression performs the matched filter either with an ideal chirp (synthetically generated by the routine itself, or with the chirp replica coming from internal calibration. It is noted that the chirp replica is close to the ideal chirp, except for an amplitude tapering in the upper part of the chirp (Figure 4a). The effect of the imperfect flatness in frequency is seen in the impulse-response-function (IRF) side-lobes level, which are lower than the ideal level of the perfectly rectangular spectrum of the ideal chirp (Figure 4b). The effect on resolution is of about 4% \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value (Linear)** & **Value (Log-Scale)** \\ \hline Peak power & 750.0 W & 28.75 dBW \\ Antenna area transmit (TX) & 4.87 m\({}^{2}\) & 6.88 dBm \\ Instrument and antenna TX losses & 1.17 & 0.70 dB \\ TX path loss (R = 3755 m) & 5.64 \(\times\) 10\({}^{-9}\) & \(-\)82.48 dB \\ RCS corner (1-m corner case) & 75.66 m\({}^{2}\) & 18.79 dBm \\ Receive (RX) path loss & 5.64 \(\times\) 10\({}^{-9}\) & \(-\)82.48 dB \\ Instrument and antenna RX losses & 1.17 & 0.70 dB \\ Received power & 6.4 \(\times\) 10\({}^{-12}\) W & \(-\)111.94 dBW \\ Noise figure & 2.14 & 3.3 dB \\ Noise power at receiver & 4.28 \(\times\) 10\({}^{-13}\) W & \(-\)123.69 dBW \\ SNR raw & 14.96 & 11.75 dB \\ Number of focused steps & 1000 & 30 dB \\ SNR focused & 14,962 & 41.75 dB \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Link budget computation and Signal to Noise Ratio (SNR) computation (ideal propagation media). \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Acquisition mode & Stripmap/TOPSAR \\ Center frequency & 1,274,140,000 Hz \\ Bandwidth & 50 MHz \\ Sampling window start time & 23 μs \\ Chirp duration & 11 μs \\ Sampling window length & 20 μs \\ Acquisition duration & variable 1 min–10 min \\ Polarization & Quad Pol \\ Pulse Repetition Frequency (PRF) & 4545 Hz \\ Chirp & Down \\ \hline \hline \end{tabular}
\end{table} 
Table 3: SAOCOM 1A acquisition parameters for outdoor test. resolution loss (see Table 4), which is almost completely recovered when the replica is focused with the ideal chirp. The range power profile of one acquisition is shown in the following figure, for the VV polarization. The high backscatter from the small hill and three main peaks can be recognized, corresponding to the fixed corner reflector (closest), a small heap of dirt (mid), and the moving target inside the radome (at 3755 m). The signal to clutter ratio of the latter is approximately 13 dB. Considering the 100-cm corner RCS as in Table 1, we can estimate a clutter RCS in the resolution cell in the order of 5 dBm. This value is 12 dB lower than the assumption made during the design phase (clutter RCS of 17 dBm) and reported in Section 2. We can then refine the clutter signal level to \(-27\) dB. The analysis in the Doppler domain (Figure 5b) of the clutter shows a very low impact of the wind, with an estimated stable to time-variant components ratio (also called DC/AC ratio) of 40 dB.