# Volume Loss Assessment with MT-InSAR during Tunnel Construction in the City of Naples (Italy)
## 2 Area of Interest and Dataset  
The city of Naples lies on the west coast of the Italian peninsula, about 200 km south-east of Rome. With a population of almost a million, it is the third largest city in Italy after Rome and Milan. Its prominent position on the coast of the Mediterranean Sea, flanked by natural and historical beauties and a warm climate, make it one of the most attractive destinations for tourists during the summer season, with peaks reaching 3.7 million tourists [24]. Many arriving by air transportation must connect through the only airport in the city, known as Capodicino Airport. The latter is located in the north-east area of the city (Figure 1), about 4 km away from the city center, and currently it is connected only by road transport to the urban center (unless specifically stated, all subsequent figures are oriented such that the vertical upward direction indicates north and, consequently, the horizontal rightward direction indicates east). Commuters are limited to road transport and are subjected to daily heavy traffic. Therefore, to increase mobility between the airport and the city center, the City Council of Naples decided to contract out the extension of the existing Line 1 (Figure 2a) of the metro system, thus connecting the main train station to Capodichino Airport. Two tunnels, one for each direction, were designed along the stretch between the two upcoming metro stations of Capodichino and Poggioreale (Figure 2b). The excavation of the first tunnel started from the shaft at Capodichino in July 2020 [25] and ended on 30 March  
Figure 1: City of Naples, Italy. Highlighted in blue is the city center and in orange is the airport of Capodichino. The red solid line represents the city bounds. (image modified after Google Earth, Google). 2021 [26]. The length of the excavation is roughly 1000 m per tunnel and it was performed using a tunnel boring machine (TBM) with a cutterhead of 7 m in diameter, mainly in a soft rock layer ('ignimbrite campana') covered by sandy and silty sand deposits [27]. The excavation of the first tunnel started 40 m below ground level from the shaft made for Capodichino station and arrived at Poggiaceae station at 10 m below ground level [25; 26]. The TBM was then disassembled and moved back to the Capodichino shaft, and used for the excavation of the second tunnel. In this study, synthetic aperture radar (SAR) images were obtained from the Italian Space Agency (ASI) dataset. SAR images were acquired by the first generation of the COSMO-SkyMed satellites. The constellation consists of four low Earth orbit (\(\approx\)600 km) satellites, each of them carrying an X-band SAR antenna with a repeat cycle of 16 days over the major cities of the world. The images can be acquired primarily in three modes: Spotlight mode, which acquires single polarized SAR images at a very high spatial resolution (1 m or lower), covering an area up to 100 km\({}^{2}\) (10 \(\times\) 10 km); Stripmap mode, which acquires single or double polarized SAR images at a medium-high spatial resolution (3-15 m), covering an area up to 1600 km\({}^{2}\) (40 \(\times\) 40 km); and ScanSAR mode, which acquires single polarized SAR images at a low spatial resolution (30-100 m), covering an area up to 40,000 km\({}^{2}\) (200 \(\times\) 200 km). Our dataset is formed by a stack of 237 CSK Stripmap-Himage collected in an ascending path direction from 7 March 2018 to 29 January 2022, and covers an area of 40 \(\times\) 40 km at 3 m resolution in both the azimuth and range directions (i.e., along track and cross track directions, respectively). The reflectivity map (RM), i.e., the average amplitude of the microwave signal in the area, is shown in Figure 2(a), while in Figure 2(b), a subset of RM representing the analyzed area is shown. The timeline of image acquisition is presented in Figure 4, where the more frequent acquisition period is 16 days. Figure 2: (**a**) Metro Line 1 of the city of Naples.