| Summary: | Accurate visualization of air temperature distribution can be useful for various thermal analyses in fields such as human health and heat transfer of local area. This paper presents a novel approach to measuring air temperature from midwave hyperspectral Fourier transform infrared (FTIR) imaging in the carbon dioxide absorption band (between 4.25–4.35 <inline-formula> <math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi></semantics></math></inline-formula>m). In this study, the proposed visual air temperature (VisualAT) measurement is based on the observation that the carbon dioxide band shows zero transmissivity at short distances. Based on analysis of the radiative transfer equation in this band, only the path radiance by air temperature survives. Brightness temperature of the received radiance can provide the raw air temperature and spectral average, followed by a spatial median-mean filter that can produce final air temperature images. Experiment results tested on a database obtained by a midwave extended FTIR system (Telops, Quebec City, QC, Canada) from February to July 2018 show a mean absolute error of 1.25 <inline-formula> <math display="inline"> <semantics> <msup> <mrow></mrow> <mo>∘</mo></msup></semantics></math></inline-formula>K for temperature range of 2.6−26.4 <inline-formula> <math display="inline"> <semantics> <msup> <mrow></mrow> <mo>∘</mo></msup></semantics></math></inline-formula>C.
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