## 3 Results and Analysis of Radiometric Thermal Data
### Basic Calibration When Using Several Different Cameras
In Figure 20 a comparison can be seen of the size of the thermogram when the cameras were 1 m away from the object to be imaged. In the middle, the field of view of the unit sensor of the IFOV sensor can be seen and compared. From this, we can conclude that in order to achieve nominal accuracy, it is important that the IFOV completely cover the area where the analyzed object is located. Furthermore, we can see that for certain applications where it is important to see a large area in a small space, the resolution itself is not as important as the optics of the camera, i.e., the angle that the camera captures. In addition to the infrared thermal imagers listed in Table 3, two pyrometers were also used in the calibration. The reason for this was to investigate the possibility of using a pyrometer as an additional support for a targeted temperature measurement at any point exposed to a temperature outside the temperature range of thermal imagers due to fire. Compared to thermal-imaging cameras, pyrometers are inexpensive, widely available, and easy to integrate into a system. The first was the Raytek RAYMX2D with a temperature range of \(-\)30 \({}^{\circ}\)C to 900 \({}^{\circ}\)C and a measurement error of \(\pm\)1 \({}^{\circ}\)C or \(\pm\)1% of the reading; the other was the Parkside PTIA 1 with a temperature range of \(-\)50 \({}^{\circ}\)C to 380 \({}^{\circ}\)C and a \begin{table}
\begin{tabular}{c c c} \hline \hline
**Blackbody** & **Volcraft IRS-350** & **Fir Systems BB150-P** \\ \hline Temperature range & 50 \({}^{\circ}\)C to 350 \({}^{\circ}\)C & 45 \({}^{\circ}\)C to 150 \({}^{\circ}\)C \\  & \(\pm\)0.5 \({}^{\circ}\)C at 100 \({}^{\circ}\)C & \(\pm\)0.7 \({}^{\circ}\)C to 10 \({}^{\circ}\)C \\ Accuracy & \(\pm\)1.2 \({}^{\circ}\)C at 350 \({}^{\circ}\)C & \(\pm\)0.5 \({}^{\circ}\)C to 40 \({}^{\circ}\)C \\  & \(\pm\)0.1 \({}^{\circ}\)C at 100 \({}^{\circ}\)C & \\ Stability & \(\pm\)0.2 \({}^{\circ}\)C at 350 \({}^{\circ}\)C & \(\pm\)0.2 \({}^{\circ}\)C \\ Emissivity of measuring area & 0.95 & 0.98 \\ Operating temperature & 5 \({}^{\circ}\)C to 35 \({}^{\circ}\)C & 0 \({}^{\circ}\)C to 40 \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of blackbodies used for imaging and analysis. Figure 20: Visual comparison of FOI and IFOV of individual cameras set 1 m from object. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Specifications**} & \multicolumn{6}{c}{**Camera**} \\ \cline{2-9}  & **Fir E6** & **Fir One Pro** & **Fir E60 bx** & **HTI HT-301** & **Fir A500 24\({}^{\circ}\)** & **Fir A70 29\({}^{\circ}\)** & **Fir A70 95\({}^{\circ}\)** \\ \hline IR resolution & 160 \(\times\) 120 & 160 \(\times\) 120 & 320 \(\times\) 240 & 384 \(\times\) 288 & 464 \(\times\) 348 & 640 \(\times\) 480 & 640 \(\times\) 480 \\ \hline NETD & 60 mK & 70 mK & 45 mK & 60 mK & 40 mK & 45 mK & 60 mK \\ \hline FOV & 45\({}^{\circ}\)\(\times\) 34\({}^{\circ}\) & 55\({}^{\circ}\)\(\times\) 43\({}^{\circ}\) & 25\({}^{\circ}\)\(\times\) 19\({}^{\circ}\) & 28.2\({}^{\circ}\)\(\times\) 21.3\({}^{\circ}\) & 24\({}^{\circ}\)\(\times\) 18\({}^{\circ}\) & 29\({}^{\circ}\)\(\times\) 22\({}^{\circ}\) & 95\({}^{\circ}\)\(\times\) 74\({}^{\circ}\) \\ \hline IFOV & 5.2 mrad & 6 mrad & 1.36 mrad & 1.28 mrad & 0.90 mrad & 0.79 mrad & 2.59 mrad \\ \hline Spectral range & 7.5–13 \(\mu\)m & 8–14 \(\mu\)m & 7.5–13 \(\mu\)m & 8–14 \(\mu\)m & 7.5–14 \(\mu\)m & 7.5–14 \(\mu\)m & 7.5–14 \(\mu\)m \\ \hline Temp. range (\({}^{\circ}\)C) & \(-\)20 to +250 & \(-\)20 to +120 & \(-\)20 to +120 & \(-\)20 to +120 & \(-\)20 to +120 & \(-\)20 to +175 & \(-\)20 to +175 \\ \hline Accuracy (\({}^{\circ}\  
measurement error of \(\pm\)1.5 \({}^{\circ}\)C. Two different blackbodies were used during the calibration process, and their specifications are listed in Table 4.  
The reason for this is thermal inertia and the time required to reach a steady state. Five hours of effective labor and two people were required to calibrate nine devices.