## 4 Discussion  
We now analyze the capabilities of the IREA-CNR infrastructure to support the monitoring activities required in a possible emergency scenario. To this end, we consider the case study presented in Section 3, which, as remarked above, was conducted within the framework of the agreement with the Department of Civil Protection of the Italian Presidency of the Council of Ministers, aimed at creating an infrastructure for the periodic monitoring of volcanic areas, and capable of being rapidly operative during crisis events. In this context, the response time of the infrastructure represents a key parameter that needs to be analyzed. For the IREA-CNR airborne SAR infrastructure described above, this response time basically depends on the following three main terms: the activation time of the airborne SAR sensor; the time required for data download and transfer; and the processing time needed to generate the final product that, in the test case of Section 3, is represented by the final InSAR-derived DEM. To evaluate the activation time of the MIPS system, we recall that the system is not permanently installed on one specific airplane. Therefore, as described in Section 2.2.3, the execution of each acquisition campaign involves the installation of the instrumentation on an aircraft and the measurement of the radar antenna lever arms. The activation time of the MIPS system, thus, depends on the time required by these procedures, along with the  
Figure 15: Relevant to the Stromboli campaign: final InSAR DEM of the observed area. Processing parameters are summarized in the right column of Table 2.  
time needed for the aircraft to reach the area of interest and the operational flight altitude once it has departed. The assembly of the MIPS sensor on board an aircraft generally requires the intervention of two operators for a time of approximately 3 h.  
Since the antenna positions may slightly change for each installation, it is mandatory to measure the antenna lever arms after the installation of the system on the aircraft. This activity generally requires the intervention of a surveyor and his staff collaborators (at least one person) for a time of approximately 5 h, including the time required for the proper processing of the measurement data. To save time, this operation is typically performed after the radar data acquisition, during the data download and transfer. In this regard, it is observed that if the antennas and the navigation system were jointly bound to the same physical structure, the lever arms would not change for each installation of the system on board an aircraft; therefore, they could be measured only once. Reaching the operational flight altitude of the aircraft strongly depends on the air traffic and weather conditions. Under ideal conditions, this phase requires approximately a bit more than twenty minutes. This duration is generally shorter than that required for the airplane to reach the area of interest and to come back after the radar acquisition. In the case at hand, the time required to reach the Stromboli area from the airport was on the order of 1 h and half. Moreover, considering the flight autonomy of the used airplane, the radar acquisitions along the two circuits shown in Figure 10 were split into two missions in the same day, for a total of about 10 h.  
Turning to the time required for data download and transfer, for the Stromboli campaign the download of data onto hard disks took place at the departure/landing airport, which is about 200 km far from the IREA-CNR laboratory. The hard disks were then physically transferred using a car. The overall procedure took about 5 h.  
Regarding the time required to process the SAR data, we, first of all highlight that, overall, 130 GByte of data were recorded during the eight considered single-pass InSAR acquisitions. For each acquisition, the range dimension of the SAR raw data was about 4 k samples, whereas the azimuth dimension changed from 110 to 180 k samples, depending on the used circuit trace.