Thermal imaging & vision systems


Butterflies of the family Pieridae in thermal. Image credit: Nanfang Yu and Cheng-Chia Tsai


Thermal imaging helps reveal how butterflies like this hickory hairstreak keep from overheating. The membrane between the wing veins is actually hotter than the rest of the wing, but looks cooler because it’s semi-transparent and against a cool background. Image credit: Nanfang Yu and Cheng-Chia Tsai


membrane, and other structures like scent pads. They found that the areas of butterfly wings that contain live cells (wing veins) have higher thermal emissivity than the “lifeless” regions of the wing (the membrane). “This imaging technique enables us to examine


physical adaptations that decouple the wing’s visible appearance from its thermodynamic properties,” Yu says in an article from Columbia Engineering. “We discovered that diverse scale nanostructures and non-uniform cuticle thicknesses create a heterogeneous distribution of radiative cooling - heat dissipation through


Instrumentation Monthly November 2022


thermal radiation—that selectively reduces the temperature of living structures such as wing veins and scent pads.”


Measuring the temperature of butterfly wings with thermal imaging is not without obstacles. “The challenge here is that, in the case of the butterfly wing, the thermal camera gives you a temperature reading, but you cannot trust the temperature reading,” Yu says. “The butterfly wing is semi-transparent in the infrared, so when you are looking at a butterfly wing in a thermal camera, you’re not just receiving the thermal radiation of the


wing itself, you’re also receiving the thermal radiation generated by the background behind the wing.” A similar phenomenon can be observed with a thin sheet of plastic, like a plastic grocery bag, which just like a butterfly wing is opaque in the visible light spectrum but transparent in the infrared. Very thin materials like a plastic bag or a


butterfly wing may be transparent in the infrared spectrum. To get a true temperature reading of a butterfly wing, Yu’s team had to quantify the emissivity and reflectivity of the wing and remove those sources of background


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