# Scanning Inside Volcanoes with Synthetic Aperture Radar Echography Tomographic Doppler Imaging
## 4 Validation of the Sonic Tomographic SAR Results
### Tomographic Validation  
In this section, the comparison of data estimated through magnetotelluric tomography with those estimated through SAR tomography is evaluated. Successively, the visual comparison relates the magnitude of the earthquakes that occurred during the month, within which the SAR observation is made. The estimated tomographic planes found the perfect overlap of the estimated results with the radar. In Figure 24a-d, we report the radar-estimated tomographic maps superimposed on the magnetotelluric tomography results. More precisely, Figure 24a is the in-range SAR tomography; Figure 24c is the superposition of Figure 24a radar tomography with magnetotelluric tomography. On the other hand, Figure 24b shows the range-azimuth oblique SAR tomography, while  
Figure 21: IV-VCRE seismograph station versus SAR synchronized time-domain vibrational streaming. (**a**) Native (**b**) low-pass filtered. (**c**) errors. Figure 22: IV-VCRE seismograph station versus SAR synchronized signals spectrum. (**a**) unfiltered. (**b**) low-pass filtered. (**c**) 1 kHz filtered particular. Figure 24c is the superposition of the oblique radar tomography in Figure 24b with the magnetotelluric tomography. In Figure 25a,i, some details are depicted to better show the existing tomographic overlay. The images in Figure 25a-c refer to the topographic detail of Figure 24a, where a reference area is indicated by arrow number 1. Figure 25a is the radar data alone, Figure 25b is the 50% overlay of the radar data on the magnetotelluric tomography, and finally Figure 25c is the magnetotelluric tomography map shown alone. The images of Figure 25d-f refer to the tomographic detail of Figure 24b, indicated by arrow 2. Figure 25d is the radar data alone, Figure 25e is the 50% overlay of the radar data with the magnetotelluric tomography, and finally Figure 25f is the magnetotelluric tomography, again shown alone. Finally, the images of Figure 25g-i refer to the tomographic detail of Figure 24b, indicated by arrow 3. Figure 25g is the radar data alone, Figure 25h is the 50% overlay of the radar data with the magnetotelluric tomography, and finally Figure 25i is the magnetotelluric tomography without any overlay. The comparative assessment formed by the  
Figure 23: IV-VCRE seismograph station versus SAR synchronized time-domain vibrational streaming. Figure 24: Overlay of SAR Doppler tomography with magnetotelluric tomography. (**a,b**) tomographic results. (**c,d**) Tomographic versus resistivity tomography results. The resistivity scale refers to captures (**c,d**). The symbol represents the scalar multiplication. visual validation between the results estimated through the seismic sensors network installed in the proximity of Vesuvius and measured satellite results are secondly performed. The data were extrapolated from the public and institutional websites of the INGV. In this context, the seismic values map is shown in Figure 26, and is correlated to the SAR tomographic results of Figure 14b. In the Figure, blue and colored circles represent some seismic events. The center of each point is placed in the 3D space on which the source of the seismic event was measured, while the radius of each circle measures its magnitude. The Figure also contains the magnitude legend and four scales can be distinguished, the number 0 value represents all seismic events between 0 and 1 Richter scale magnitude. Number 1 represents all events of magnitude between 1 and 2, circle 2 between 2 and 3, and finally, the largest circle is the number 3, which represents all seismic events greater than 3 degrees of magnitude on the Richter scale. The blue circles represent seismic events that occurred throughout January 2022, while the red color represents only those seismic events that occurred in February 2022, which is the month in which the SAR data was acquired. From a visual comparison, we keep a good correspondence of the data if compared to the one estimated through SAR tomography.