D51 High resolution infrared thermography

Topic

Infrared thermography records the temperature distribution across an insect's surface without direct contact, exploiting the fact that any body above absolute zero emits infrared radiation in accordance with Planck's law.

Modern infrared cameras—whether utilizing an uncooled microbolometer or a specialized cooled detector—detect this infrared radiation within the specific atmospheric window that coincides with the peak emission of a warm-blooded animal; this mirrors the operation of infrared drones, achieving both fine temperature resolution and a high capture rate.

The emissivity of the insect's cuticle—specifically in a mechanosensory zone—represents the most critical correction factor in this thermographic process: a dark cuticle emits a fraction of infrared radiation very close to that of a perfect blackbody at the same temperature. The darker the cuticle, the closer its emissivity approaches that of a perfect blackbody.

The temperature difference equivalent to the system's noise constitutes the key figure of merit for the entire setup: the minimum temperature difference capable of generating a signal variation equal to the system's background noise. The fact that this thermography system further reduces the noise-equivalent temperature difference means that the thermography can distinguish even more subtle temperature differences on the insect's surface.

The final heat flux on the insect's surface is determined by combining the temperature revealed by the thermography with a convective coefficient—either measured via anemometry or calculated using an appropriate Nusselt correlation—representing the very heat flux that another model in this set identifies as the physical quantity actually detected by a cutaneous thermoreceptor. A higher convective coefficient on the insect's surface results in a higher final heat flux on that surface for any given temperature difference.

Consequently, given the non-contact surface temperature distribution established at the outset, the final spatial resolution of the thermography—defined as the system's instantaneous field of view multiplied by its working distance, a resolution parameter also established by another model in this set—must be considerably smaller than the insect's actual size; this is essential to map the thermal gradient within the body of the specific fly addressed by yet another model in this set. Further reducing the thermography system's instantaneous field of view results in an even finer final spatial resolution on the fly's surface.

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