Measuring sky temperature?

[acey]

Does anyone use an infrared thermometer to measure sky temperature? I'm thinking of getting an all-in-one unit (i.e. not something to hook up to a PC) and would be interested to hear from anyone who has used one or can make any recommendation.

My aim is to use the ground/sky difference as a way of measuring transparency on nights that are clear but hazy (I'm not looking for a cloud detector as such).

Lots of low-cost IR thermometers are available, my question is whether these would be any good for my intended use.

I previously posted a similar query in Weather Discussion but got no response, hence I'm asking again here.

[Shibby]

I know some members have made their own cloud cover monitors using IR thermometers - check the DIY Astronomer forum.

[Shibby]

http://stargazerslounge.com/showthread.php?t=152842

http://stargazerslounge.com/showthread.php?t=122093

http://stargazerslounge.com/showthread.php?t=106144

[iwatkins]

Acey,

Yes they would work. Point up and measure, then point at something on the ground that is at the ambient air temp (be careful what you choose) and then subtract one from the other. This should be give you a fair indication of the amount of "clag" in the air.

If you do decide to go PC controlled, Phidget are now doing a combined IR sensor (10degree field of view) plus ambient temp sensor for around £80. Plug into a PC via USB cable and you are away. Phidgets have excellent software support. This widget is here: http://www.active-robots.com/sensors/temperature-humidity/phidgettemperaturesensor-ir.html

For example, I've got hooked up to my "shed" PC and it collects and runs all day/night. There is a web server package that comes in the software and I can interrogate it from my phone as both the PC and my phone are on the same Wifi network. I'm just writing a Flash app to run on my run to graph the temps in an app. Easy to setup and if you are happy writing software, you can do some very good stuff with them.

Cheers

Ian

[rfdesigner]

I have a hand held remote IR thermometer.

It does detect that the sky is cold, but always reads 'out of range' when the sky is clear.

I think it copes with down to -30C, and the sky can be quite a bit colder than that.

Derek

[acey]

Thanks for all these replies. I'm looking to get one of the self-contained gun-type IR thermometers, so it's a case of finding one with sufficient low-temperature range and accuracy to be worthwhile - if anyone has one or can suggest a brand then I'd be interested to know. The cheapest models start at around a fiver and there are loads around £20-30. But it sounds like it would need to go below -30C.

[iwatkins]

The gun ones tend to have different ranges for temperature. Choose wisely

In the UK, clear sky temp at the zenith tends to be in the range of around 15-25 degrees C cooler than ambient if that helps.

Cheers

Ian

[George]

The one we built in the previously mentioned thread was built for less than £25, it gives both ambient and sky temperature and is quite accurate & it has ascom compliant software.

Not used it for a while because of siting issues but from memory a clear sky can get down to -60C+

[JamesF]

the amount of "clag" in the air.

Blinding us with your meteorological terminology now

James

[iwatkins]

Blinding us with your meteorological terminology now

James

It's a technical term, trust me.

Easier than saying "water vapour, dust, pollen, pollutants, smoke, insects and ash"

George,

Yes, if you can get below -30, you will be in a good position to detect very clear skies. Do note, that you are not actually detecting sky temperature though, you are simply detecting IR radiation being reflected/emitted by stuff in the atmosphere, mainly water vapour.

Cheers

Ian

[acey]

Thanks for all these. I've seen some that claim to go down to -50C at around £15 so may go for one of those, unless I come across something that goes further.

From what I can gather, more expensive models offer features such as close focusing or variable emissivity settings, which wouldn't be relevant to sky readings, so it looks like cheap might be good enough in this case.