Management of thermal drift of bolometric infrared cameras: limits and recommendations

ABSTRACT

In this article, the authors propose a general framework for checking the calibration of the A325sc camera and then minimizing the temperature measurement errors due to thermal drift. Thermal drift and non-uniformity affect the measurement accuracy of infrared bolometric cameras and remain a major problem for the reproducibility and repeatability of radiance quantification. Any thermal camera is pre-calibrated at the factory to correct for thermal drift. This pre-calibration was done for specific case temperatures, and variations in these temperatures are a major source of uncertainty. To improve the accuracy of the camera measurements, it’s important to control the housing temperatures. To this end, a cold box was build up. The effectiveness of the thermal drift compensation was examined over the two ranges of the camera. In the [-20°C; 120°C] range, the thermal drift compensation is efficient up to 110°C. The range [0°C; 350°C] highlights two behaviors: for an emitting temperature within [65-225] °C, the thermal drift compensation is made difficult by the self-heating of the measurement chain due to the intensity of the source. Above 225°C, the self-heating of the optics is significant, as it becomes more absorbent. A correction of the thermosignal is suggested.

KEYWORDS:

• Thermal drift management
• non-uniformity correction
• black body
• cold box
• LWIR bolometric camera

Acknowledgements

The authors would like to thank the Sénart-Fontainebleau Institute of Technology and the University Paris-Est-Créteil for their financial support of the PhD thesis of Samy BRAZANE.

Disclosure statement

No potential conflict of interest was reported by the authors.

Nomenclature

$\mathrm{\Delta }\lambda$	=	Spectral range of the camera (µm)
${\mathrm{L}}_{\mathrm{\Delta }\lambda }$	=	Thermosignal (OS)
${\mathrm{L}}_{\mathrm{\Delta }\lambda }^0$	=	Thermosignal of black body (OS)
εΔλ(t)	=	Apparent emissivity
$\mathrm{s}\left(\mathrm{t}\right)$	=	Thermal sensitivity (OS/°C)
$\mathrm{V}\mathrm{O}\mathrm{x}$	=	Vanadium oxide FPA detecting technology
$\mathrm{P}\mathrm{e}\mathrm{l}$	=	Elementary measurement point (bolometric sensor and its associated read-out circuit)
$\mathrm{t}{ }_{\mathrm{a}\mathrm{p}\mathrm{p}}^{\circ }$	=	Apparent temperature (°C)
$\mathrm{t}{ }_{\mathrm{r}\mathrm{e}\mathrm{f}\mathrm{l}}^{\circ }$	=	Reflected temperature (°C)
$\mathrm{t}{ }_{\mathrm{B}\mathrm{B}}^{\circ }$	=	Blackbody temperature (°C)
$\mathrm{t}{ }_{\mathrm{c}\mathrm{a}\mathrm{m}}^{\circ }$	=	Temperature of camera housing (°C)
$\mathrm{t}{ }_{\mathrm{a}\mathrm{m}\mathrm{b}}^{\circ }$	=	Ambient temperature (°C)
$\mathrm{O}\mathrm{S}$	=	Object signal
$\mathrm{P}\mathrm{i}\mathrm{x}\mathrm{e}\mathrm{l}$	=	Elementary imagery point