## 2 Description of the Observation Setup
### Precise Inclination Sensors
**(b)** The sensor on the support surface (steel console platform) with its plastic hood. **(c)** Cover of plastic hood [27]. Because the main objective of this research is to investigate the performance of inclination sensors in monitoring structural deformations, the sensors were deployed at the top (17 th) floor of a 54-meter high building in Istanbul (see the location of the building _vs_. NAF in the Istanbul map in Figure 3), as the top floor is where the maximum displacements were expected. In the setup, each sensor was mounted on the piers of two orthogonal walls, and the orientation of the sensors on the steel mounting platforms (see Figure 4) was arranged so that the tilt components can be calculated in the employed reference system and can be compared to the other sensor. Precise adjustment of the sensors was done electronically before starting the measurements. For visualization and storage of the data, a laptop computer and an uninterruptable power supply (UPS) were placed next to the sensors, and software accompanying the inclinometers was used to manage the data (see user interface of the software in Figure 4(d)). The software interface allows the user to see incoming \begin{table}
\begin{tabular}{l l} \hline
**Specification** & **Value** \\ \hline measuring range & \(\pm\)1.5 mrad (or mm/m) \\ accuracy & \(\pm\)0.001 mrad \\ resolution & 0.001 mrad \\ zero-point stability & \(<\)0.005 mrad/\({}^{\circ}\)C \\ operating temperature range & \(-\)20 to \(+\)50 \({}^{\circ}\)C \\ storage temperature range & \(-\)30 to \(+\)60 \({}^{\circ}\)C \\ relative humidity & 10 to 95\% \\ dimensions of the instrument (L \(\times\) W \(\times\) H) & 90 \(\times\) 90 \(\times\) 63 mm \\ weight of the instrument & 850 g \\ supply voltage & 12 V DC \(\pm\)25\% \\ \hline \end{tabular}
\end{table} 
Table 1: Specifications of the inclinometer [27]. Figure 3: Locations of the tall building (HLKL) and the geodetic network stations (ISTA and KANT) in Istanbul. The red line indicates the approximate location of the North Anatolian Fault (NAF) (refer to [25] and [26] for active tectonic maps of Turkey). data either graphically or numerically during or after the observation period. Apart from a failure in the storage process at the beginning of the measurements, both instruments measured the inclination and temperature values during the whole campaign for 36 days at a sampling interval of about 5 minutes (irregularly occurred sudden changes in the data out of given sampling time is recorded automatically). The analytical results of the inclination and the results from the GPS processing were both used for deformation analysis of the building. While the first experiment evaluates the indoor performance of inclinometers, the second test of the study clarifies their outdoor performance in deformation monitoring. In the second experiment, the structural deformation of the ISTA GPS reference station pillar was monitored. Since the pillar is on a building instead of a geologically safe location on hard terrain, and thus the self-movements of the building might affect its position, concerns about the stability of the pillar required its deformations to be investigated in the second phase of this study. The monitoring setup included the pair of inclination sensors, one of which was mounted on the pillar and the other on the building pier on which the pillar had been constructed (see Figure 5). The observations were performed in two individual campaigns between February and April in 2000 and 2002, with approximately 30 days of observation in each campaign. During the observation period, the sensors were protected against atmospheric effects like direct sunlight, rain, and snow. The sensors' axes were oriented properly with the help of a compass to provide parallel reference systems. Thus, in both campaigns, the sensors' X-axes were set approximately to the North-South direction and the Y-axes were in the East-West direction.