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Re: [Phys-L] Infrared

Hi

Ok from the discussion so far the picture on this link (https://www.pbs.org/newshour/science/los-angeles-methane-leak-is-officially-the-worst-in-u-s-history) with a dark cloud makes sense to me, the methane is absorbing IR, blocking it from the background. But some of the pictures here (https://www.nytimes.com/2019/12/13/reader-center/methane-infrared-camera.html) and here (https://www.nytimes.com/interactive/2019/12/12/climate/texas-methane-super-emitters.html) show bright clouds which would be emission spectra. (Look at the second set of comparison pictures on the last link.)

My question is, how is the IR emission from methane different than the IR emission from steam or hot air? Does it only occur at 3.2 to 3.4 micrometers? When I first saw the pictures on the second two links I thought, oh that’s hot gas but it doesn’t tell us what the gas is. The buildings are hot and also emitting (bright) but they aren’t made of methane.

A couple of the comments on the third link seem to be from industry experts who also question what the pictures show.

Kyle

On Dec 19, 2019, at 12:00 PM, phys-l-request@mail.phys-l.org wrote:


Today's Topics:

1. Infrared (Forinash III, Kyle)
2. Re: Infrared (bernard cleyet)
3. Re: Infrared (John Denker)
4. Re: Infrared (bernard cleyet)
5. Re: Infrared (brian whatcott)


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Message: 1
Date: Wed, 18 Dec 2019 21:16:01 +0000
From: "Forinash III, Kyle" <kforinas@iu.edu>
To: "phys-l@mail.phys-l.org" <phys-l@mail.phys-l.org>
Subject: [Phys-L] Infrared
Message-ID: <D958FDA1-2FB4-4F00-A181-63E7CF41C9C9@iu.edu>
Content-Type: text/plain; charset="utf-8"

I?m a bit confused by the following New York Times article. They claim to be detecting methane leaks using IR cameras in the 3.2 to 3.4 Micrometer range. Wouldn?t such an image be overwhelmed by thermal IR? In other words the pictures are of heat, not methane specifically?

https://www.nytimes.com/2019/12/13/reader-center/methane-infrared-camera.html<https://www.nytimes.com/2019/12/13/reader-center/methane-infrared-camera.html?te=1&nl=climate-fwd:&emc=edit_clim_20191218?campaign_id=54&instance_id=14640&segment_id=19701&user_id=f3315a4f40ddaa91b46edcfed5881d14&regi_id=8509815120191218>
--------------
"Travel is fatal to prejudice, bigotry, and narrow mindedness, and many of our people need it sorely on these accounts."
--- Mark Twain

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Message: 2
Date: Wed, 18 Dec 2019 13:37:22 -0800
From: bernard cleyet <bernardcleyet@redshift.com>
To: "phys-l@phys-l.org" <Phys-L@Phys-L.org>
Subject: Re: [Phys-L] Infrared
Message-ID: <0374DBAF-F527-4FFE-A59C-D3338D2C5ED3@redshift.com>
Content-Type: text/plain; charset=utf-8

Broken link, so I?ll just guess that ? this is an absorption band, so the background is the source and the methane blocks it, so it?s an area that looks black instead of bright. It?s just like dental x-rays and metal restoration, or an impland screw w/ a metal crown.


bc who first X-rayed his mechanical pencil 1954.

On 2019/Dec/18, at 13:16, Forinash III, Kyle via Phys-l <phys-l@mail.phys-l.org> wrote:

I?m a bit confused by the following New York Times article. They claim to be detecting methane leaks using IR cameras in the 3.2 to 3.4 Micrometer range. Wouldn?t such an image be overwhelmed by thermal IR? In other words the pictures are of heat, not methane specifically?

https://www.nytimes.com/2019/12/13/reader-center/methane-infrared-camera.html<https://www.nytimes.com/2019/12/13/reader-center/methane-infrared-camera.html?te=1&nl=climate-fwd:&emc=edit_clim_20191218?campaign_id=54&instance_id=14640&segment_id=19701&user_id=f3315a4f40ddaa91b46edcfed5881d14&regi_id=8509815120191218>
--------------
"Travel is fatal to prejudice, bigotry, and narrow mindedness, and many of our people need it sorely on these accounts."
--- Mark Twain
_______________________________________________
Forum for Physics Educators
Phys-l@mail.phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l



------------------------------

Message: 3
Date: Wed, 18 Dec 2019 15:19:08 -0700
From: John Denker <jsd@av8n.com>
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] Infrared
Message-ID: <0b93a19b-a7df-cfba-01c1-a1c7a9f54922@av8n.com>
Content-Type: text/plain; charset=utf-8

On 12/18/19 2:16 PM, Forinash III, Kyle via Phys-l wrote:

I?m a bit confused by the following New York Times article. They
claim to be detecting methane leaks using IR cameras in the 3.2 to
3.4 Micrometer range. Wouldn?t such an image be overwhelmed by
thermal IR? In other words the pictures are of heat, not methane
specifically?

Rather than framing the question in terms of "overwhelmed"
perhaps it would be better to ask whether the foreground
(methane) stands out from the background (whatever that
may be).

Thermodynamics says that IF (big IF) everything were in
thermal equilibrium, then no photography of any kind
would be possible. Everything would look the same in
all directions.

Instead, of course, typically we illuminate ordinary
scenery (300 K) with sunlight (6000 K color temperature)
so the situation is very far from equilibrium.

As for IR photography, the situation is a bit trickier.
I'm not an expert, but based on what I see in the Times
article, here's what I think is happening:

-- The methane plume is optically thick. It has a
temperature on the order of 300 K, and glows accordingly.

-- The camera angle is such that the background is
the sky. The night sky is black, and the daytime
sky is blue, which is the same as black at 3.3 ?m.
To say the same thing another way, the atmosphere
is optically thin at 3.3 ?m, so you are looking out
at outer space, i.e. 4 K background, so the methane
in the foreground definitely stands out.

The Rayleigh scattering that makes the sky blue on
a dry day scales like ?? so it's really small at
3.3 ?m. Even if the air is humid (but not cloudy)
it is optically thin for a different reason, namely
the absorption spectrum of water vapor:
https://en.wikipedia.org/wiki/File:Water_infrared_absorption_coefficient_large.gif

The worst case scenario is where you have a cloud in
the background. That's gonna be optically thick, but
if it is a /high/ cloud it will be cold, so once again
the warmish methane in the foreground will stand out.

If the site is fogged in, then yes, sure, the method
will fail -- but nobody should be surprised by that.
Photography of all kinds fails under such conditions.

Aerial reconnaissance, where you are looking down on
the plume with little if any control of the background,
might be quite a bit more difficult, perhaps impossible.

Here's the article. The link works fine for me:
https://www.nytimes.com/2019/12/13/reader-center/methane-infrared-camera.html


------------------------------

Message: 4
Date: Wed, 18 Dec 2019 14:55:11 -0800
From: bernard cleyet <bernardcleyet@redshift.com>
To: "phys-l@phys-l.org" <Phys-L@Phys-L.org>
Subject: Re: [Phys-L] Infrared
Message-ID: <4536A40D-BBC4-4EF2-956B-8802A13F4595@redshift.com>
Content-Type: text/plain; charset=utf-8



On 2019/Dec/18, at 14:19, John Denker via Phys-l <phys-l@mail.phys-l.org> wrote:


Here's the article. The link works fine for me:
https://www.nytimes.com/2019/12/13/reader-center/methane-infrared-camera.html <https://www.nytimes.com/2019/12/13/reader-center/methane-infrared-camera.html>
_______________________________________________


That is a different link than Kyle?s

bc found works; not read yet.

p.s. not incidentally, during the massive leak in SoCal, this pic. was taken, which, I pray (to Lucifer), illustrates my hypothesis. (Much simpler than JD?s explication.)

https://www.pbs.org/newshour/science/los-angeles-methane-leak-is-officially-the-worst-in-u-s-history

------------------------------

Message: 5
Date: Wed, 18 Dec 2019 18:25:18 -0600
From: brian whatcott <betwys1@sbcglobal.net>
To: phys-l@mail.phys-l.org
Subject: Re: [Phys-L] Infrared
Message-ID: <cc4cb3e0-4bcb-fa02-4ec2-cad7d0b91a17@sbcglobal.net>
Content-Type: text/plain; charset=utf-8; format=flowed

On 12/18/2019 3:16 PM, Forinash III, Kyle via Phys-l wrote:
I???m a bit confused by the following New York Times article. They claim to be detecting methane leaks using IR cameras in the 3.2 to 3.4 Micrometer range. Wouldn???t such an image be overwhelmed by thermal IR? In other words the pictures are of heat, not methane specifically?

https://www.nytimes.com/2019/12/13/reader-center/methane-infrared-camera.html<https://www.nytimes.com/2019/12/13/reader-center/methane-infrared-camera.html?te=1&nl=climate-fwd:&emc=edit_clim_20191218?campaign_id=54&instance_id=14640&segment_id=19701&user_id=f3315a4f40ddaa91b46edcfed5881d14&regi_id=8509815120191218>
/snip/
??Glass provides a green-house effect?? - to green-houses, of course. But
how do I know that??????? The heating provided by a range of visible
wavelengths in sunlight warms the interior that is illuminated, but the
re-radiation is down in the infra red and the glass rebuffs it.?? In
consequence, the greenhouse stays warmer during the night.
OK
If I fly by night, I expect the look-down greenhouse plan view will look
cooler in my 3 to 3.5 um camera than its surroundings, hence darker - at
least early on, until near dawn, the surrounds are so chill that the
green house may no longer be a dark blob, I suspect.
How about if I look up? In the dark clear night sky, the temperatures
seem rather low - a small number Kelvin. - at least, until I duck into
the greenhouse and look up from there, where the glass is impeding
radiation, but is warm along with the air below. My camera will see the
up view warmer than it would outside.
Methane is a quite effective absorber at 3 - 3.5 um so I expect to see
similar effects from methane plumes and clouds as from glass. That is,
thermal IR does not overwhelm methane detectors - it enables them. Or
does it?

Brian W


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End of Phys-l Digest, Vol 180, Issue 6
**************************************


-------------------------------
No one ever reached death's door and said:
"Darn! I should have gone to more meetings."

kyle forinash
kforinas@ius.edu
http://pages.iu.edu/~kforinas/