## 4 Discussion of the Outcomes
The different latitude bands covered in WSM, ISM4 and ISM2 are clearly visible. \begin{table}
\begin{tabular}{|c|c|c|c|c|c|} \hline
**Mode** & **ISM1** & **ISM2** & **ISM3** & **ISM4** & **WSM** \\ \hline
**Duty Cycle [\%]** & 13.0 & 12.9 & 11.9 & 21.5 & 40.1 \\
**Lat. Min. 1[deg]** & \(-\)71.7 & \(-\)66.2 & \(-\)53.2 & \(-\)43.5 & \(-\)71.7 \\
**Lat. Max. 1[deg]** & \(-\)48.5 & \(-\)39.6 & \(-\)24.2 & 42.9 & 71.6 \\
**Lat. Min. 2[deg]** & 48.9 & 40.5 & 25.6 & & \\
**Lat. Max. 2[deg]** & 71.7 & 66.2 & 51.3 & & \\
**Swath [km]** & 39.9 & 37.2 & 29.2 & 24.1 & 39.1 \\ \hline \end{tabular}
\end{table} 
Table 3: Coverage statistics and duty cycle, assuming Envisat in different Swath Modes as illuminator. Minimum and maximum acquisition latitudes, and mean width of the bistatic swath (minimum is 10 km) are reported. Note that for ISM1, ISM2 and ISM3, two latitude belts are identified. To quantify the spatial coverage of the bistatic measurements, we have evaluated the ratio between the sum of the areas of bistatic targets and the area of the Earth surface within the covered latitude range. Such a computation sums up all the areas imaged during a complete Envisat cycle of 35 days, including also zones already observed in previous orbits. This result is therefore an estimate of the fractional coverage that does not ensure that every point within a specific latitude range is actually  
Figure 5: Data acquisition (red dots) for a one week scenario considering a passive system acquiring ASAR signal in WSM (upper panel), ISM4 (central panel) and ISM2 (lower panel). Green/blue lines are the Envisat/passive satellite ground tracks. covered by a bistatic acquisition, but that can indicate whether full coverage could be potentially obtained in such a range. The ratio is minimum for ISM4 and is in the order of 65% for WSM, while for ISM1 and ISM2 our evaluation indicates that full coverage might be achieved within 35 days. Finally, Figure 6 shows the trends of the baseline absolute value \(|B|\) (distance between the satellites) and of its components (\(B_{x}\),\(B_{y}\),\(B_{z}\)) throughout one orbit, that we obtained as a consequence of our design. The baseline is evaluated on the orbital reference frame centered in the centre of mass of the active satellite, with \(x\)-axis towards its instantaneous velocity vector, \(y\)-axis normal to the orbital plane and \(z\)-axis in direction of the Earth center. The distance between the satellites achieves its maximum value at the equator and the minimum one near the poles. \(B_{y}\) represents the main component of \(B\) and changes its sign at the orbit interceptions near the poles, when the satellites change their relative orientation, while it achieves the maximum value at the equator. Also \(B_{z}\) goes to zero at the orbits interceptions and the minimum baseline at the orbit crossing, _i.e._, the safety distance between the satellites, has turned out to be equal to 35.5 km, a result similar to that found in [18] in which Envisat was used as the active satellite. Observing Figure 6, it can be noted that the maximum value of the baseline (at the equator), is slightly larger than 500 km.