Abstract
The measurement of a wide temperature range in a scene requires hardware capable of high dynamic range imaging. We describe a novel near-infrared thermal imaging system operating at a wavelength of 940 nm based on a commercial photovoltaic mode high dynamic range camera and analyse its measurement uncertainty. The system is capable of measuring over an unprecedently wide temperature range; however, this comes at the cost of a reduced temperature resolution and increased uncertainty compared to a conventional CMOS camera operating in photodetective mode. Despite this, the photovoltaic mode thermal camera has an acceptable level of uncertainty for most thermal imaging applications with an NETD of 4–12 °C and a combined measurement uncertainty of approximately 1% K if a low pixel clock is used. We discuss the various sources of uncertainty and how they might be minimised to further improve the performance of the thermal camera. The thermal camera is a good choice for imaging low frame rate applications that have a wide inter-scene temperature range.
Highlights
The measurement of a wide temperature range in a scene requires hardware capable of high dynamic range imaging
There is a trade-off between these two parameters in a conventional linear response PD camera since the thermal radiation intensity is quantified in discrete steps that are unevenly distributed in temperature by the analog to digital converter (ADC) of the camera sensor
The large dynamic range of the camera is ideal for imaging applications that have a large intra-scene temperature range
Summary
The measurement of a wide temperature range in a scene requires hardware capable of high dynamic range imaging. The system is capable of measuring over an unprecedently wide temperature range; this comes at the cost of a reduced temperature resolution and increased uncertainty compared to a conventional CMOS camera operating in photodetective mode. Photovoltaic (PV) mode cameras have a logarithmic relationship between the incident light intensity and the output camera signal which results in an extremely large dynamic range compared to conventional photodetective (PD) cameras. The logarithmic response of a PV camera should, in theory, partially cancel out the exponential increase in radiance emitted from a hot target as a function of temperature. This means the relationship between the camera output signal and target temperature becomes
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