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52 a p p e N D I x h accuracy The vehicle-mounted thermal camera system used in this study is described in Appendix J, which discusses the test- ing done in Finland. A commercially available FLIR A325 camera was used. According to FLIR, the accuracy of the temperature readings is ±3.6°F (±2°C) or ±2% of the reading. Images from this system do not indicate depths of defects. However, the images can indicate possible tile debonding, delaminations up to 1 in. deep with a minimum surface area of 1 sq ft, and voids up to 3 in. deep with a minimum surface area of 1 sq ft, based on specimen testing. The system can locate defects within 1 ft of their actual location. precision According to FLIR, the precision of the system is less than 0.09°F (0.05°C). The areas of possible defects can be located within 1 foot of the actual defects with any system as long as the thermal contrast of the area of interest has not changed and the systems are properly calibrated. Calibration procedures Each thermal camera manufacturer has published its own calibration procedures (if needed). With the FLIR cameras used in the Finnish tests, the manufacturer recommends the equipment be calibrated every year. The user cannot make this calibration; the camera has to be sent to the manufac- turer or authorized reseller. Calibration is also needed for the distance measurement indicator (DMI). This usually involves driving the vehicle over a known distance (usually 1,000 ft) and checking the DMI reading against that known distance. testing procedures The operator needs to ensure that the camera is properly focused before beginning data collection. No other special testing procedures are needed. Cost The thermal camera itselfâincluding a 90° wide-angle lensâcosts approximately $15,000. The price for a complete package with racks, software, and positioning system is approximately $30,000. Limitations According to the FLIR A325 camera default calibration, the equipment is not accurate at temperatures below -4°F (-20°C) or above 248°F (120°C). The normal operating tem- peratures are between 5°F (-15°C) and 122°F (50°C). Data Management Data management consists of thermal camera data and posi- tioning data collection and storage. The research team used the Road Doctor CamLink software with the Road Doctor TD Module for data management. Data analysis and Interpretation Data analysis requires specialized software that allows the viewing of thermal camera image data as a video image. The software also needs to be able to create a thermal color map from the tunnel wall or roof that can be used for monitoring real changes in temperature and detecting anomalies. In addi- tion, the software should be able to filter unwanted external noise from the thermal data. Vehicle-Mounted Thermal Camera Testing Criteria
