# An Autonomous Thermal Camera System for Monitoring Fumarole Activity
## 2 The Thermal Camera System
### Hardware
The Raspberry Pi reportedly needs a current of approx. 0.5 A during normal operation, making the total power consumption approx. 2.5 W [17]. With the Raspberry Pi powered down, the Sleepy-Pi alone uses approx. 180 mA, dropping the total power consumption to approx. 0.9 W.  
Although accurate time stamping is not essential for our measurements, hardware clocks could drift over time. Consequently, the control unit is equipped with a \"GlobalSat G-Star IV USB GPS\" receiver [18] to keep the clock synchronized. The Raspberry Pi obtains its system time from the Sleepy-Pi when it boots. Directly after booting, the \"network time protocol daemon\" [19] is started to obtain GPS time. Depending on the satellite constellation of that moment, it may take several minutes for the GPS to obtain a lock and for the system time to become synchronized. Only when the system time is synchronized with the GPS, the system time is written to the real-time clock on the Sleepy-Pi. This means that time synchronization is in effect after a measurement has been taken and comes into effect at the next event. Several sensors on the camera, the Raspberry Pi, and the Sleepy-Pi are being logged. The camera can report its settings and several environmental parameters via the GenICam interface; this information is written to a text file with every image that is saved to disk. Specifically, the focus distance of the camera and two of the six internal temperatures are monitored: The temperatures reported on the front, lens, and shutter appear to have similar readings all of the time, and the same holds for temperatures reported for the atmosphere, external optics, and reflected temperature. In addition, the Raspberry Pi reports the temperature of the CPU and the time reported by the hardware clock, the operating system, and the GPS. The Sleepy-Pi reports on the input voltage coming from the battery. As the control unit is not equipped with telemetry, the camera measurements and sensor readings are primarily stored on the flash memory card in the Raspberry Pi, which also hosts the operating system. To reduce the chances of data loss and simplify regular data readout, the data on the flash memory card are also synchronized to a USB stick which is accessible outside of the camera enclosure. As synchronizing the image collection to an empty USB stick takes time, this task is carried out immediately in the 5 min after boot when the system is waiting for the camera to warm up and stabilize. After taking a measurement, the newest results are also added to the USB stick before the Raspberry Pi goes back to sleep. The camera and the control unit are placed in a weather-proof and air-tight enclosure made of stainless steel, which should be resistant to acidic gases coming out of fumaroles. The enclosure is a customized \"Tecnovideo 204 SHIR70\" with a 7 cm diameter Germanium window, an added sun shield on top, and no heater nor window wiper. The enclosure is mounted on a steel pole. The 12 V 65 A h battery and solar charger are placed in a separate custom-made metal enclosure on the ground, which is covered by a 100 W solar panel (Figure 3). The power cables running from the battery to the control unit are uninterrupted, and \"Terostat-IX\" putty is used to seal the cable openings in the enclosure. Silica gel packages keep the airtight enclosure dry; these need replacing when the enclosure is opened for a longer time during maintenance.