## 4 Results and Discussion
### MT-InSAR Data Precision, Calibration and Validation  
The present study is based on ascending SAR dataset only (see Section 3.1). Therefore, all results and values reported hereinafter are LOS values if not explicitly stated otherwise. The uncertainty observed in the estimated \(V_{\text{LOS}}\) (i.e., standard deviation of the time series) is 2.8 mm/year on average for the PS dataset and 2.6 mm/year for the DS dataset. These values provide an indication of the precision of the MT-InSAR results and suggest that the \(\pm\)3.0 mm/year \(V_{\text{LOS}}\) interval can be considered the velocity range, indicating stability. On the other hand, in order to estimate the accuracy of the MT-InSAR results, these were validated using the local velocity values of the GPS benchmark stations MESO and MENO in Methana Peninsula with respect to LYGO cGNSS station (Table 2). A frame of reference transformation was applied to the velocity vectors in order to calculate the estimated LOS velocity of the two GPS benchmark stations and to allow for comparison with the MT-InSAR data. Figure 7: (**a**) Aerial view of the Mavri Petra andesitic dome and (**b**) details from the south-east, including Kameni Chora village (photographs © [PERSON]SS]). Knowledge of the Euler angles (i.e., \(\omega_{x}\), \(\omega_{y}\) and \(\omega_{z}\); Table 3) of the Sentinel-1 LOS along the ascending relative orbit 102 allowed us to generate the rotation table for each axis: \(R_{1}\), \(R_{2}\) and \(R_{3}\) via Equations (1)-(3), respectively:  
\[R_{1}=\left[ \begin{array}{ccc}1&0&0\\ 0&\cos\omega_{x}&\sin\omega_{x}\\ 0&-\sin\omega_{x}&\cos\omega_{x}\\ \end{array} \right] \tag{1}\]  
\[R_{2}=\left[ \begin{array}{ccc}\cos\omega_{y}&0&-\sin\omega_{y}\\ 0&1&0\\ \sin\omega_{y}&0&\cos\omega_{y}\\ \end{array} \right] \tag{2}\]  
\[R_{3}=\left[ \begin{array}{ccc}\cos\omega_{z}&\sin\omega_{z}&0\\ -\sin\omega_{z}&\cos\omega_{z}&0\\ 0&0&1\\ \end{array} \right] \tag{3}\]  
The right-hand rule was used to calculate the Euler angles because the reference frames are right-handed. The incidence angle for the area where the two GPS benchmark stations are found (namely, \(\omega_{y}\)) was estimated using the European Space Agency (ESA)'s SeNtinel Application Platform (SNAP) software -- Sentinel-1 toolbox S1 TBX (v.7.0, SkyWatch, Waterloo, Canada),while the azimuth angle of the ascending relative orbit 102 in the area (namely, \(\omega_{z}\)) was estimated using QGIS software (v.3.14, QGIS.ORG, Switzerland). Then, using Equation (4), the rotation matrix (5) was composed and finally exploited to transform the reference frame into the LOS geometry:  
\[R=R_{1}(\omega_{x})\cdot R_{2}(\omega_{y})\cdot R_{3}(\omega_{z}) \tag{4}\]  
\[R=\left[ \begin{array}{ccc}0.78293&0.15219&0.60321\\ -0.19081&0.98163&0\\ -0.59213&-0.11510&0.79758\\ \end{array} \right] \tag{5}\]  
The velocity vectors of GPS benchmark stations MENO, i.e., (6), and MESO, i.e., (7), were transformed to the new reference of frame using Equation (8):  
\[V_{\rm MENO}=\left[ \begin{array}{c}-0.49\\ 0.08\\ 0.55\\ \end{array} \right]{\rm mm/year} \tag{6}\]  
\[V_{\rm MESO}=\left[ \begin{array}{c}0.03\\ 0.20\\ -4.48\\ \end{array} \right]{\rm mm/year} \tag{7}\]  
\[V^{\prime}=R\cdot V \tag{8}\]  
The LOS velocity of the two benchmark stations was finally estimated: \(V_{\rm LOS}=-0.16\) mm/year for MENO and \(V_{\rm LOS}=-3.61\) mm/year for MESO. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Euler Angle** & **Degrees** & **Physical Interpretation** \\ \hline \(\omega_{x}\) & 0 & – \\ \(\omega_{y}\) & \(-37.1\) & Incidence angle \\ \(\omega_{z}\) & \(11\) & Declination from the north (azimuth) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Euler angles of the Sentinel-1 LOS along ascending mode relative orbit 102. We calibrated the PS and DS datasets by tying the estimated \(V_{\text{LOS}}\) at the closest scatterer to the MESO station (i.e., 40 m away) to the value measured at the GPS station (i.e., \(-3.61\) mm/year).