Hi Philippe,

I found this: I think it detects at a greater distance:

Professional long-range infrared thermometer QT4242L, range -76/1600 degrees F, ratio 30: 1; alternatively you can try with these cameras:

KKmoon professional infrared camera

FLIR TG167 Spot Thermal camera with extended range

good luck

Max

Hi Massimo,

Thanks for taking the time to answer my question. I have been investigating the matter over the last days and I think that IR cameras are probably the best option, as you suggest. They offer many more possibilities that actually would be very useful for my study. However the spot size is still an issue as only the expensive models are precise enough for my purpose. Not going too much into details here, but the minimum spot size of these cameras is the instantaneous field of view (IFOV = size of one detector element) multiplied by 3. "Entry level" IR cameras usually have an IFOV of 5mm, which means a minimum spot size of 15mm, which is too large for my purpose. Other issue is that the accuracy is 2°C even in expensive models.

I have the feeling that many studies overlooked the issue of the minimum spot size.

I am considering buying the FLIR E8, but I am quite over my budget!

Cheers,

Philippe

Hi Philippe,

as these devices use (infread) light through special optics, the problem is mainly a physical one. Think of you request as the analogue to a telephoto-lens which should give you maximum magnification (small spot size) over maximum distance (minimal disturbance). With photo cameras, such lenses get huge and very expensive pretty quick, and such is the case with IR thermometers. Now FLIR cameras do nothing but replacing the single temperature sensor with a 2-dimensional image chip that can detect IR, analogous to the chip in a photo camera. Then detection area theoretically is limited by the pixel size, however, as each pixel is considerably smaller as the sensor of a IR meter, also accuracy will be reduced, as less photons will be received per sensor site/pixel, and you will end up with noise the smaller the pixels (sensor).

What is the exact purpose of your measurements? As you emphasize minimal disturbance I assume you want to measure body temperature of frogs that are resting or calling on a substrate for a while already (not moving, and you don't want to scare them away). As poikolotherms, the frogs will, by and large, have the same temperature as their substrate unless two things are the case - 1. either they are capable to produce some heat internally, or 2. they have (considerably large) different heat absorbance characteristics than the substrate they are sitting on, causing them to heat up either more or less then then substrate.

To detect this latter case of frogs having a body temperature which deviates considerably from their substrate temperature, you still can make differential measurements, (mostly) regardless of the spot size of your IR meter - so male one measurement with the frog covering as much as possible of the spot, and one of the substrate directly beside the frog. However, as I said the effect you want to measure has to be quite strong, as also the accuracy of IR thermometers in the price range you specified is mostly within 0.5-1 °C (although they give readings at0.1 °C).

So long story short, unless the purpose of your study is to measure (tiny) temperature difference across (within) the surface of a frog, and with the money you state you have available, you will be fine with IR thermometers with a spot size within 1-3 times the SUL of the frogs you want to measure.These devices mostly have optics with a distance to spot ratio of 20:1 - so at 20 cm distance your spot size is 1 cm in diameter, at 40 cm its 2, ... at 1 m its 5 cm and so on. Also they often are available at different calibration qualities (accuracies) which problaby should be of equal, if not even more concern as the spot size.

Hope these ideas help a little

Max

Hi Max,

Thanks for the extensive answer. I have been through all these thoughts since my initial question, and I expanded my expectations a bit since some more questions arose in the meantime. I am actually also quite interested to detect differences in temperature between the individual and the substrate, depending on activity and time of the day/night. I ordered the FLIR E8 (don’t have it yet) as I believe it will do the job. It also allows to take IR photos and analyze them afterwards as they retain all the information. It can detect differences as low as 0.06°C and has a spot size that should make possible to evaluate the temperature of very small species (spot size is less than 5mm at a distance of 50cm; see my previous answer). Anyway, there is apparently no perfect device as most have some flaws, especially when you try to stay in a reasonable price range. I will also take the Fluke IR thermometer for some comparisons and test. I kind of exploded my budget, so I hope it will give nice results ;-)

Cheers,

Philippe

With Amphibians and IR measurements/imagery one thing you also need to consider is that moist skin, like with photo cameras will give you all sorts of reflections, also in the IR part of the spectrum, and especially under varying, natural illumination conditions. So to make meaningful measurements of (small) frog surfaces, unless it is a mostly dry skinned species, you will have to somehow overshadow the frog to make sure it is actual IR emission,and not IR reflections from the sun that you are measuring. Of course this then comes with severe constraints in terms of not disturbing frogs and is also the reason why we mostly switched to measure substrate surface temperatures of perches immediately after the frog moved away. But of course I understand there are circumstances where the actual surface temperature of the frog can be of interest!

Best

Max

I Had great advise a few years back using IR pyrometers measuring polished copper, I have pasted this below from Barry. I have also used Flir with Fluke black body sources 4180/4181 and standing a meter away the cross hairs were able to detect the edge within 5mm, although this was generally some 40-400°C away from ambient.

All the best

All materials have variations in emissivity in relation to the material, in this case copper, and the surface condition. I do not have a definitive figure for polished copper but oxidized copper is between 0.4 and 0.6 so I would guess at possibly as low as 0.1 in the polished state.

The Fluke 561 I believe to have only 3 emissivity settings High, Medium and Low, Low being 0.3 which you may be able to manage with but bear in mind that any error in the emissivity setting will increase with temperature.

We would have to calibrate the devise at a setting of 0.95(high) to comply with our procedures and for best accuracy but this should not cause you a problem.

Unfortunately the majority of this type of low temperature infrared device using 8-14 microns wavelength suffer from “size of source” effect which means you will get different measurements at different distances depending on the size of target.

This has probably now caused you to ask whether it is worth using infrared at all but it is still a very good tool if you want speed of measurement and good repeatability provided the material and surface condition is the same each time and the distance used is constant. Measurements taken with these conditions will be useful for quality purposes but the temperature value may not be absolutely correct, I tend to advise clients to find the “magic number” that may not be the temperature expected but which will give consistency for product quality.

Obtaining the magic number involves trials with the material under test to get a close as possible to the correct figures such as attaching black tape to the material and taking a measurement at 0.95 emissivity and then comparing it with the measurement taken at 0.3 0n the raw material. The black tape will assume the temperature of the copper and give a better indication of the true temperature.

One final warning, any device with a low distance to spot ratio will in reality be influenced by a much larger area than indicated, the 12:1 ratio claiming 1” @ 12” would be influenced by additional radiant heat from outside the target so if you try the black tape method give yourself as bigger area as possible but align with the centre of the “blacked”area. Best practice is to buy Pyrometers with as large as possible D:S ratio’s such as 50:1.

I use a cheap Chinese IR- LED pointer thermometer to get on surface temperature ( frog calling for example). At night no problems with IR measuring of substrate and frogs. Frogs usually follow closely the ambient temperature while herps can differ if they bask. Micro- thermistors can give you a frogs cloakal temperature if tested with caution. If frogs can carry a backpack transmitter, they can transmit coded temperature as frecuency from a micro thermistor in pulses. A calibration curve of the thermistor before use will give the frecuency- temperature relationship.

Thanks all for your valuable input! I got the FLIR E8 and will perform several tests while in the field.