## 2 Study Subjects and Monitoring System Configuration
### VLBI Antenna Monitoring System Configuration  
As shown in Figure 2, a static displacement monitoring system was configured for this study, using close-range photogrammetry. Two fixed cameras were deployed to measure static displacement in the antenna with close-range photogrammetry, and another camera was deployed to observe the state of the antenna surface. The study used IP cameras controlled via an internet connection. We used Arecont Vision model AV10005 DN cameras (Los Angeles, CA, USA), which can measure 10-megapixel images at six frames per second. The cameras were connected to the VLBI observation room through a Local Area Network (LAN) communication, which allowed the analysis system to control them.  
Figure 1: Facility configuration at the Space Geodetic Observation Center (SGOC).  
The general IP camera model selected for this study can be used during the day and at night. The user can select between Day mode, Night mode, and Lighting mode in our analysis software. The frame rate is unimportant because the camera is installed on a fixed pillar, the VLBI antenna is fixed during image acquisition, and analysis is carried out on a single frame.  
The cameras were mounted in weatherproof housings (Samsung Technwin MHG-200 HA, Changwon, South Korea) that were waterproof, dustproof, snowproof, had an integrated sun shield, and had internal heaters, which activate below 0 \({}^{\circ}\)C \(\pm\) 5 \({}^{\circ}\)C. They were also equipped with internal ventilation, which activated above 45 \({}^{\circ}\)C \(\pm\) 5 \({}^{\circ}\)C. Sejong City in South Korea, where this monitoring system was installed, had an average high temperature of 31.9 \({}^{\circ}\)C and average low temperature of \(-\)11.7 \({}^{\circ}\)C over the last five years. Therefore, the camera housing used in this study should sufficiently protect the camera from the external environment.  
The cameras must be installed with a separation of about 16 m so that the 3D coordinates of the remote observation points can be accurately measured. They must be installed solidly so that their positions and pointing will not change because they are used as references for the displacement measurement.  
As shown in Figure 3, the static displacement monitoring system was constructed using close-range photogrammetry. In this study, the VLBI antenna was pointed to azimuth and elevation angles chosen such that the front would face the camera installation direction at fixed intervals. The images and control point coordinates of feature points on the fixed VLBI antenna surface were also collected, and the camera interior and exterior orientation parameters were calculated. Then, the 3D position coordinates of the target were calculated using close-range photogrammetry. Using this process, the condition of the VLBI antenna was monitored constantly, and the monitoring  
Figure 2: Static displacement measurement system for the main reflector of the Very Long Baseline Interferometry (VLBI) antenna.  
results were used in the repair and improvement of the antenna to maintain its performance and measurement accuracy.  
The fixed focal lengths of CCD Camera 1 and CCD Camera 2 in Figure 3 were 12.466 mm and 10.367 mm, respectively. The distances from these two cameras to the VLBI antenna were approximately 37 m and 41 m, respectively. The image size of the cameras was 2560 (H) \(\times\) 1920 (V) pixels, the sensor size was 1/2.3\", and the pixel pitch was 1.67 \(\upmu\)m.