## 4 Discussion  
The CyCLOPS network is the first strategic infrastructure, deployed at a national scale, dealing with the collocation of two CRs (one for each pass direction), with a permanent GNSS station. The Multi-Criteria Decision Analysis for the collocated infrastructure must be carried out so that the instruments' installation and performance follow the literature guidelines and requirements set by global authorities. The GNSS should be installed on bedrock, at a location with high visibility, to ensure both high stability and satellite availability. Furthermore, the two CRs should be installed in such a way as to achieve the maximum RCS, while at the same time, the GNSS signal is not affected by unwanted multipath.  
The main criteria for selecting the most suitable location for installing a CR are sigma 0, slope, aspect, and land cover. Sigma 0 was acquired from SAR images, whilst the rest of the criteria were created using the final products from the UAV missions. Furthermore, the geology formation and the boundaries of the AOI were used as constraints in the site suitability analysis process. The criteria and their values were categorized based on their relative importance and influence on achieving the goal (i.e., the most suitable locations).  
The sigma 0 was selected as the criterion of the strongest importance, whilst the remaining criteria, which influence the performance of sigma 0, were categorized as criteria with lower importance. For instance, if an area includes dense vegetation, exposed rocks, and flat terrain, the clutter will be higher than if it comprises a proper slope (\(<\)10\({}^{\circ}\)) without vegetation or soil (large slope causes high backscattering due to the foreshortening effect). Therefore, the land cover criterion is the second priority in the intensity scale, and the slope is the third. The criterion with the weakest importance is the terrain aspect, which determines where the slope is facing. Nevertheless, this information is helpful because areas with a low sigma 0 are usually obscured from satellite LOS and, thus, have a low backscattering coefficient. As a result, if such a location is chosen for CR installation, the latter is unlikely to have LOS with the satellite.  
The AHP and WO methods, along with 3D visibility analysis, were used for the suitability analysis. In more detail, AHP was performed to derive priority scales for use in WO, while the latter was used for the image production and extraction of the candidate locations. Finally, the 3D visibility analysis was performed to finalize the most suitable locations.  
The installation of the CRs at the sites resulted in RCS values greater than 34 dBm\({}^{2}\) on average. Similarly to the CR results, the evaluation of GNSS sites demonstrated sufficient daily horizontal stability (coordinate changes \(\leq\) 10 mm in 24 h) and satellite availability (\(>\)10 satellites above the elevation angle of 0\({}^{\circ}\)).  
The results are fully aligned with all the requirements derived from the current scientific literature. This fact indicates that the installation of collocated GNSS and dual CR permanent infrastructures, via the proposed methodology, is successful at first glance. It is worth highlighting that some of the criteria used for this research are not mandatory, since the factors differ from area to area. For instance, if an AOI is plain, the slope and aspect criteria can be ignored.