# An Autonomous Thermal Camera System for Monitoring Fumarole Activity
## 2 The Thermal Camera System  
### Hardware  
The design of the cameras has several commonalities with the equipment presented by [PERSON] et al. (2010), who uses an autonomous thermal infrared camera for continuous monitoring of an active lava lake. In Olkaria, these cameras monitor fumarole activity hourly, with a deep sleep of the system in between recordings. This led to different choices for hardware and software solutions, which are presented below. The camera system is an aggregation of a thermal camera unit and a control unit placed in an air-tight stainless steel enclosure (Figure 2a) and a 12 V battery charged by a solar panel in a separate housing. Except for the control unit, all components are off-the-shelf parts that only need connecting. The control unit itself consists of several off-the-shelf parts that need assembling (Figure 2b) and require a custom code to read and process camera data. The camera, control unit and customized code are discussed in detail in the following sections. The camera unit is an FLIR A655 SC, which has an uncooled microbolometer that measures in a 7.5 um to 14 um wavelength range [11]. The factory calibration of the camera is saved as non-uniformity compensation (NUC) coefficients which are applied during operation to maintain image quality. The camera automatically selects the optimum calibration table based on its temperature [12]. We compensate for possible drift of the camera by triggering an NUC before data acquisition. The power for the camera unit comes via a 12 V DC connector which, when enabled via a switched relay in the control unit, directly runs from the 12 V battery. The non-proprietary GenICam interface [13] allows capture parameters to be set and recorded frames to be received via a 1 Gbit Ethernet connection. In our system, we set several capture parameters via the control unit: 640 \(\times\) 480 pixels at a 3 Hz single frame acquisition mode, a 10 mK linear temperature in 16 bit integer format, and focus distance by proxy of a digital number for the focus ring position on the lens. The lens position is, for each location where the camera is installed, found in the field by averaging 3 autofocus repeats with the manufacturer's software [14], and the focus ring position is read out via GenICam interface before running the camera autonomously. During autonomous image capture, the implied focus distance is read back from the camera and written into a log file (together with other environmental parameters, detailed below). Found by experimenting, we decided to capture, for each acquisition, about 30 frames and average these to reduce noise and avoid occasional frame dropouts. Figure 2: (**a**) The opened camera housing in the field and (**b**) the opened control unit. The control unit is based on a single-board computer that is connected to the camera via the Ethernet. We use a \"Raspberry Pi 3 Model B\" with a quad-core 1.2 GHz ARM CPU, 1 Gbit RAM, and a 100-Base Ethernet adapter [15]. Although this board does not have the 1 Gbit Ethernet adapter that is according to the manual recommended for this camera, this setup appears to work as long as certain precautions are taken (discussed in the Deployment section). The onboard Bluetooth and WiFi adapter are disabled by the operating system to save power. The Raspberry Pi only wakes up to take the hourly measurement. Always on is a \"Sleepy-Pi 2\" add-on board, which connects directly to the Raspberry Pi [16]. This board is equipped with an Arduino microcontroller and a real-time clock with a backup battery. It controls the power to the Raspberry Pi with a 5 V 10 A switched relay, which allows the Raspberry Pi to enter a deep sleep mode, wake up at a specific time, or act when an event is triggered (e.g., when a certain amount of time has passed). The Sleepy-Pi also controls a relay that switches power to the camera. The Sleepy-Pi accepts 5 V to 30 V DC power input and can therefore run, together with the Raspberry Pi, from the same 12 V DC power source as the FLIR camera.