Digital temperature determination using a radiometrically calibrated and a non-calibrated digital thermal imager
A method, system, and non-transitory computer readable medium storing a plurality of computer executable instructions for calibrating an uncalibrated thermal imager is provided. The system includes a calibrated pyrometer for determining a first temperature of a Region of Interest under a first condition, and an uncalibrated thermal imager for determining a first average count value over the region of interest under the first condition and for determining a second average count value over the region of interest under a second condition. A temperature sensor for determining a second temperature of the region of interest under a second condition is also provided. Control electronics determine a Planck function that intersects the points (first temperature, first average count value) and (second temperature, second average count value). The uncalibrated thermal imager is calibrated using the Planck function.
1. A method for calibrating an uncalibrated thermal imager, the method comprising:
setting a region of interest in a field of view of the uncalibrated thermal imager;
determining a first temperature of the region of interest using a calibrated pyrometer under a first shutter condition;
determining a first average count value over the region of interest using a digital pixel output of the uncalibrated thermal imager under the first shutter condition;
determining a second temperature of the region of interest under a second shutter condition;
determining a second average count value over the region of interest using a digital pixel output of the uncalibrated thermal imager under the second shutter condition;
determining a Planck function by fitting a Planck curve to the first temperature, the first average count value, the second temperature and the second average count value using a processor; and
calibrating the uncalibrated thermal imager using the determined Planck function.
2. The method of claim 1 , wherein the second temperature is determined by a thermocouple.
3. The method of claim 1 , wherein the second temperature is determined by the calibrated pyrometer.
4. The method of claim 1 , wherein the second shutter condition occurs when a shutter is closed.
5. The method of claim 1 , wherein the second temperature is a shutter temperature.
6. The method of claim 1 , wherein the second temperature is a focal plane array temperature.
7. The method of claim 1 , wherein a spectral response of the calibrated pyrometer and a spectral response of the uncalibrated thermal imager are the same.
8. The method of claim 1 , wherein a size of the region of interest is the same as an interrogation area of the pyrometer.
9. A system comprising:
a calibrated pyrometer for determining a first temperature of a region of interest under a first shutter condition;
an uncalibrated thermal imager for determining a first average count value based on a digital pixel output of the uncalibrated thermal imager over the region of interest under the first shutter condition and for determining a second average count value based on a digital pixel output of the uncalibrated thermal imager over the region of interest under a second shutter condition;
a temperature sensor for determining a second temperature of the region of interest under the second shutter condition;
control electronics for determining a Planck function by fitting a Planck curve to the first temperature, the first average count value, the second temperature and the second average count value using a processor and for calibrating the uncalibrated thermal imager using the determined Planck function.
10. The system of claim 9 , wherein the temperature sensor is a thermocouple.
11. The system of claim 9 , wherein the temperature sensor is the calibrated pyrometer.
12. The system of claim 9 , wherein the second shutter condition occurs when a shutter is closed.
13. The system of claim 9 , wherein the second temperature is a shutter temperature.
14. The system of claim 9 , wherein the second temperature is a focal plane array temperature.
15. The system of claim 9 , wherein a spectral response of the calibrated pyrometer and a spectral response of the uncalibrated thermal imager are the same.
16. The system of claim 9 , wherein a size of the region of interest is the same as an interrogation area of the pyrometer.
17. The system of claim 9 , wherein the calibrated pyrometer and the uncalibrated thermal imager are located in the same enclosure.
18. A non-transitory computer readable medium storing a plurality of computer executable instructions for calibrating an uncalibrated thermal imager, the computer executable instructions comprising functionality to:
set a region of interest in a field of view of the uncalibrated thermal imager;
determine a first temperature of the region of interest using a calibrated pyrometer under a first shutter condition;
determine a first average count value over the region of interest using a digital pixel output of the uncalibrated thermal imager under the first shutter condition;
determine a second temperature of the region of interest under a second shutter condition;
determine a second average count value over the region of interest using a digital pixel output of the uncalibrated thermal imager under the second shutter condition;
determine a Planck function by fitting a Planck curve to the first temperature, the first average count value, the second temperature and the second average count value using a processor; and
calibrate the uncalibrated thermal imager using the determined Planck function.
19. The non-transitory computer readable medium of claim 18 , wherein the temperature sensor is the calibrated pyrometer.
20. The non-transitory computer readable medium of claim 18 , wherein the second shutter condition occurs when the shutter is closed.