###### Abstract
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Country** & **Reservoir Type** & **No. of Projects** \\ \hline Austria & Depleted fields & 11 \\ Croatia & Depleted field & 1 \\ Czech Republic & Depleted fields, Aquifers, Salt caverns & 14 \\ Denmark & Aquifer, Salt caverns & 3 \\ France & Depleted fields, Aquifers, salt caverns & 21 \\ Germany & Depleted fields, Aquifers, Salt caverns & 56 \\ Hungary & Depleted fields & 6 \\ Italy & Depleted fields & 15 \\ Latvia & Aquifer & 1 \\ Netherlands & Depleted fields, Salt caverns & 6 \\ Poland & Depleted fields, Salt caverns & 11 \\ Portugal & Salt cavern & 1 \\ Romania & Depleted fields & 6 \\ Slovakia & Depleted fields & 2 \\ Spain & Depleted fields, Aquifers & 5 \\ Sweden & Salt cavern & 1 \\
**TOTAL** & & **160** \\ \hline \hline \end{tabular}
\end{table} 
Table 1: European underground gas storage inventory at the end of 2021 [6]. Figure 1: Typical cycles of injection (red) and withdrawal (blue) of underground gas storage activity. Data from Uelsen, Germany [4]). is concentrated in five states: Germany, Italy, France, Netherlands, and Austria. The increase in the pressure of the gas stored in existing facilities is one of the most economical ways of improving the working gas capacity (the amount of gas that can be stored and extracted) in a UGS reservoir [8]. Typically, the limitation in pressure is set dynamically following the response to the gas pressure during the filling process; however, these values do not always represent the maximum short-term pressure capacity of the reservoir. Therefore, there is a growing demand for reliable procedures that can assess the maximum operating pressure without compromising safety conditions and negatively impacting the surrounding environment. The constant increase in the number and capacity of UGS facilities has increased the importance of monitoring them. Indeed, UGS activities can induce vertical ground deformations, leading to subsidence (associated with natural gas extraction) or uplift (linked to natural gas injection) [9]. Continuous monitoring is paramount to ensure caprock integrity and the efficiency and longevity of injection/withdrawal wells. The high costs of in situ monitoring systems, especially when considering the limited spatial density of the instruments, have paved the way for remote sensing technologies. The latter issue is the main reason why remote sensing technologies such as Interferometric Synthetic Aperture Radar (InSAR) are becoming increasingly attractive to companies for monitoring their activities. Notably, the efficacy of InSAR in monitoring UGS activity is evident in its ability to detect vertical ground deformation due to UGS operations through time series analysis [5]. As a result, InSAR is fast becoming a standard technology adopted in many UGS projects across Europe, offering wide-area monitoring at a fraction of the cost of traditional methods e.g., [5; 9; 10; 11]. Additionally, ground deformation data can be linked to reservoir parameters through geomechanical models [12]. It is essential to carefully monitor and manage the impact of UGS activities on the subsurface--and indirectly on the surface--in order to maintain local environmental safety. Such vigilance stems from the inherent risks of UGS activities, including potential gas leaks from pipelines that could lead to fires or create flammable methane clouds [13]. Several incidents involving gas leakage and subsequent fires or explosions have been documented globally [14; 15]. Monitoring three-dimensional land surface deformation, which reflects seasonal stress variations due to injection and withdrawal activities, is instrumental in managing these risks [10]. Notably, well failures can result in a catastrophic Loss of Containment (LoC) of natural gas, as evidenced by the large-scale surface blowout at the Aliso Canyon UGS facility in California in October 2016 [16; 17]. This study shows the potential of using the InSAR approach for monitoring ground displacement in areas close to UGS facilities.