Infrared Training Center

Wednesday, June 24, 2015

Frogs are Cool! (well, actually they are ambient!)

By Ron Lucier, ASNT NDT Level III, FLIR Infrared Training Center

There is a nice koi pond not 50 feet away from my pool, filled with fish, plants and plenty of flying protein. Yet this American Bullfrog (Lithobates catesbeianus), also known in certain parts of the US South as (tastiest frieduppes legges) has taken residence in my pool and has become quite tame. The silly frog will even swim up to me!

Anyway, according to wikipedia ( frogs are “cold blooded” as are all amphibians. Let’s examine that term!

The following image was taken with my FLIR T650sc – I inverted the Grey scale for clarity.


Yes, time to vacuum the pool but we have had thunderstorms the past two days!

The warmest temperature on the frog is 80.2 ˚F. Air temperature was 81.1 ˚F and water temperature was 78.8 ˚F according to my Extech 401014 Big Digit Indoor/Outdoor Thermometer ( I placed the outdoor sensor in the water next to the frog.

The warmest part of the frog was in the Sun so let’s ignore that reading. I have to assume an emissivity of 0.98 as he/she wouldn’t cooperate with the Scotch 88 electrical tape and I doubt it would stick nor would heating the skin with a heat shrink gun be humane. Also, since the frog is moist and the emissivity of water is near 0.96 at perpendicular angles and variation in temperatures here is pretty small regardless of what emissivity I choose. Spot 3, at 79.3 ˚F is a good enough value.

I looked up the National Weather Service data for my home at found that at the time that I took the data humidity was 91%. Yes, it was oppressive! Who was the smart one by the way? The frog in the pool or the fool with the IR camera looking at him, sweating in the heat? With such high humidity I would expect a small drop in temperature on my skin due to evaporation so the 1.8 ˚F difference between air temperature isn’t surprising. Plus the frog continuously produces mucous to keep moist skin so the evaporation (latent heat) will keep the frog a bit cool anyway.

The summary of this adventure: are all the science books written about amphibians correct when referring to them as “cold blooded?” I would argue that the term would be more accurate labeled “ambient blooded” as they appear to be very close to ambient temperature.

I challenge my friends in the FLIR community! Go out into your backyard, neighborhood, local park or zoo and look with your IR camera. It gets boring looking at pumps, pipes, valves and breakers all day long so looking at nature can be fun and interesting!