Comparison of the performance of LWIR and MWIR thermal imagers for varying ambient temperature and humidity conditions

Abstract

Hodgkin (SPIE 6207(2006)) extended NVThermIP to be applicable to cold weather conditions. We also (IRPhys&Technol.51 (2008)520) later published an analysis of the effect of varying ambient temperature (T amb ) by modifying the inputs to NVTherm2002, and by using spectrally-weighted atmospheric transmission calculated from MODTRAN at different ambient temperatures and relative humidities (RH). We took into account the effects on the integration time and NETD, and we now account for the variation of ΔT with varying T amb , as Hodgkin has done. The overall trends are similar, but we have NVTherm, not NVThermIP. We vary the parameters associated with Johnson's criteria to obtain similar results. Note that diurnal, seasonal, climatic and microclimatic variations of relative humidity (RH) significantly impact the performance of thermal imagers, especially LWIR ones. We compare the performance of thermal imagers a horizontal mean-sea-level path in clear weather conditions for terrestrial imagers and ground targets/scenes in both LWIR and MWIR bands, as a function of the ambient temperature from -40°C to +40°C and also as a function of RH (30%, 50% and 70%). To understand the differences in the results reported by Hodgkin and our paper, we do a sensitivity analysis as a function of system and environmental parameters (f/#, RH, detection probability, spectral width etc). For one set of parameters, we observe that the range curves R LW and R MW intersect at more than one value of T amb and suggest an analogy to a 're-entrant phase'. We also analyze how motion blur affects the two bands, at different T amb .

Thermal Imager Range: Predictions, Expectations, and Reality

“…Visible imaging through the atmosphere is reviewed in [19,20,21], and IR imaging is analyzed in [88,89,90]. Adverse weather influences in marine conditions are analyzed in [90,91,92,93] for maritime conditions, desert conditions [94], and heavy fog [91]. Atmospheric transmission influence on IR temperature measurements is presented in [26,28], and thermal imager application in civil aviation [95].…”

In-situ monitoring of selective laser melting process

“…Between the selection of mid-wavelength and long-wavelength infrared cameras, the former is more suitable for inspection of high-temperature objects while the latter is best suited for assessment of objects at room or low temperatures [72]. The solidified metal could reach a temperature of approximately 2000 K or higher immediately after the laser scans the powder bed, necessitating the use of a mid-wavelength infrared camera [73].…”