Infrared Thermography in Biology

Infrared thermography is the measurement of temperatures through detectors sensitive to infrared radiation. Infrared radiation is part of the electromagnetic spectrum:

This schematic shows various aspects of the spectrum of electromagnetic radiation. In multiple horizontal rows, wavelength, relative size of waves, frequency and temperature are shown, for wavelengths ranging from radio waves (103m) to gamma waves (10-12m). Visible light occupies only a small central part of this spectrum (0.5 x 10-6m) and infrared radiation is adjacent to visible light (10-5m).

The salient features of infrared radiation (IR) relevant to our application are:

  • IR wavelength at around 10-5m is longer than visible light (0.5 x 10-6m).
  • IR is invisible to the human eye and to and most animals.
  • IR is emitted from objects based on their temperature, and is not dependent on external sources – as opposed to visible light, which can be reflected from objects not emitting any visible light on their own.
  • IR is proportional to the temperature of the emitting body.
  • IR is used by: military and search & rescue (night vision), astronomers, veterinarians, and researchers.

We use infrared cameras based on uncooled micro-bolometer type sensors, manufactured by FLIR Systems. These cameras collect digital images that are called ‘false color’ images: temperature is represented through different colors. Using such cameras, highly accurate temperature measurements can be collected remotely.

Here is an example of what we see, versus what a false color image from an IR camera looks like:

These side by side images show the face of a Weddell seal, one as we can see the seal, which has eyebrows and vibrissae (whiskers) covered in ice, the other an infrared false color image that shows cool temperatures as blue and violet, such as the vibrissae, and hot temperatures as yellow and read, such as the top of the head of the seal.

The vibrissae (whiskers) of the seal that are covered in ice are shown in blue-violet in the false color image, indicating low temperatures, and the top of the head is shown in yellow and red, indicating warm temperatures. In the following side view of a sea lion, one can see cold areas on the body (the flippers, chest, shoulders, hips, most of the body trunk) and hot spots (the axillae or armpits, eyes and nose).

Side view of a sitting sea lion. This is a false color infrared image. Most of the body of the animal is blue, violet and green, indicating cold temperatures. The flippers are violet to black, indicating very cold temperatures. The axillae (armpits) are red, and the eyes and nose are red-white, indicating very high temperatures.

We are working on developing models that will allow us to estimate blubber thickness based on thermal patterns. In addition, we are investigating whether thermal patterns can be used to remotely diagnose health and reproductive status of pinnipeds. As an example, the following set of images illustrate a healing surgical incision on a sea lion, in a visible light image and an infrared image. The incision site shows clearly elevated temperatures.

Visible light picture of a healing surgical incision on the belly of a sea lion

Infrared image of a healing surgical incision on the belly of a sea lion. The incision area is red and orange indicating elevated temperatures, in contrast to the surrounding skin which is blue, indicating cold temperatures.

Check out our project on Infrared Thermography in the Research Projects section of our website for more information.