Importance of NETD for birds in flight (1 Viewer)

[Gladiator96]

Hi everyone. I am looking into getting my first thermal device and I am considering the new Pulsar Axion XG30 Compact. The only thing worrying me is the NETD which is 40mK, i.e. on the higher side.

I am a newbie in this field but my understanding is that the NETD is mostly important for picking out thermal signals when there is a lot of noise in the air, such as due to mist. One of the things I would like to use the thermal device for is for seeing birds migrating at night, such as flocks of herons or ducks. In these cases the camera would be pointed against the sky. How much would such a high NETD hinder this? A friend of mine had good results with the Telos XP50 which had a much lower NETD of 18mK.

Thanks.

 

[Mono]

NETD is effectively contrast. The minimum temperature difference that the unit can discern. A flying bird is going to be more than 30⁰C, unless you are in the serious tropics it is going to be many, many degrees warmer than mist. Much more than the 0.04⁰ a 40mK device can discern.

Some other things to bear in mind. The thermal imager will show 256 levels of temperature regardless of its NETD. In a worst case you might be on a frosty night somewhere urban. A metal fence post might be at ‐10⁰C, a car exhaust pipe might be at 250⁰C. Each shade of grey, the effective contrast, is going to be 1⁰C regardless of the NETD. Thermal imagers aimed at the engineering market will allow you to set the black point and white point of the display so as to ignore those extremes of temperature you are not interested in. Most wildlife and security thermals don't allow you do this. That is what the calibration is doing, assessing the hottest thing and coldest thing and setting the display range. On most devices you can lock the calibration once you have pointed it at your typical scene. It will take practice to get the most out of a particular device, they are not the same.

As with all specs it is important to take them with a pinch of salt. The manufacturer will be testing them in ideal conditions. As with many things, computers, phones, hi-fi, people will buy things because of the spec sheet to use in situations where they won't be able to tell the difference. Buying a top of the range phone to do WhatsApp and order pizza.

 

[wllmspd]

In thick mist/fog thermal will be as equally useless as your eyes are as the water vapour absorbs the infrared. A clear night sky is very cold (lower clouds are progressively warmer till they reach ambient when at ground level), so I wouldn’t think NETD would be an issue.

Peter

 

[Gladiator96]

As with all specs it is important to take them with a pinch of salt. The manufacturer will be testing them in ideal conditions. As with many things, computers, phones, hi-fi, people will buy things because of the spec sheet to use in situations where they won't be able to tell the difference. Buying a top of the range phone to do WhatsApp and order pizza.

Thanks and fully agreed. I have only tried my friend's Telos XP50 so that is my point of reference and the NETD seems to be the largest difference between the two hence my query.

 

[Gladiator96]

In thick mist/fog thermal will be as equally useless as your eyes are as the water vapour absorbs the infrared. A clear night sky is very cold (lower clouds are progressively warmer till they reach ambient when at ground level), so I wouldn’t think NETD would be an issue.

Peter

Thanks. I'm in the Mediterranean so air temperatures would be considerably higher than the UK. Nevertheless I think I should be fine with the Axion XG30 Compact.