What things look like in IR

[JMartJr]

Similar to the "balloon shapes" thread, I wonder if it would be worth compiling a small reference library of IR imagery of known stuff all in one handy place. I recall that @Mick West has already done some balloon imagery, which of course I can't find now! Stuff created by MB members can go here, as can pre-existing stuff found by members. I'll start off with some balloons in IR that my son and I did, playing around with his IR drone used to detect roof leaks and the like.

Here is the video:

Source: https://youtu.be/QkZZ1lOgMrg


Some stills here:

"Mylar" foil balloon and latex balloon, visual and IR white=hot.

Same balloons, visual and IR false color

Same balloons against sky, from below. The clouds in this one are also possibly worth noting.

(We can take suggestions if anything interests folks here. His tendency is to default to the colorful ones, as they make it easier to show clients what he found, but I can request black or white = hot, or the use of other color palettes, if helpful.)

 

[Mick West]

I recall that @Mick West has already done some balloon imagery, which of course I can't find now!

Source: https://youtu.be/snwqUpQ6oSE?t=112


Your footage looks awesome, what camera is it exactly? A DJI 3T? Enterprise Dual? My concern there is that it seems too good. Does it use the MSX blending? That mixes in the visible-light footage to make the edges a lot cleaner.

Although this image would suggest not as the beams behind the balloon seem great.

 

[Mick West]

Some birds flying, filmed from above, would be interesting. As high as possible. I know that's a bit of an ask.

 

[JMartJr]

Your footage looks awesome, what camera is it exactly? A DJI 3T? Enterprise Dual? My concern there is that it seems too good. Does it use the MSX blending? That mixes in the visible-light footage to make the edges a lot cleaner.

Yeah, it is a DJI 3T. I'll ask about MSX blending when I see him next, you've moved beyond my area of knowledge on drone and imaging tech! ^_^

Some birds flying, filmed from above, would be interesting. As high as possible. I know that's a bit of an ask.

Will try, maybe we can lure some in with birdseed or soemthing...

 

[eleggua]

Some birds flying, filmed from above, would be interesting. As high as possible. I know that's a bit of an ask.

Such turn up on Google Satellite View, tho don't have one handy to share.

 

[eleggua]

The two white spots below the island, American White Pelicans. Smaller white spots at the top of the island, shoreline, likely Snowy Egrets.

Size comparison: automobile tire between the islands.

I know, they're not inflight (the pelicans nor the tire), however it gives some idea of how a larger bird (pelican) shows up on Google Satellite View on Google Maps, relative to a smaller bird (egret).

 

[jarlrmai]

The two white spots below the island, American White Pelicans. Smaller white spots at the top of the island, shoreline, likely Snowy Egrets.


View attachment 73609

Size comparison: automobile tire between the islands.
View attachment 73610


I know, they're not inflight (the pelicans nor the tire), however it gives some idea of how a larger bird (pelican) shows up on Google Satellite View on Google Maps, relative to a smaller bird (egret).

We're asking about them in IR though.

 

[jplaza]

Similar to the "balloon shapes" thread, I wonder if it would be worth compiling a small reference library of IR imagery of known stuff all in one handy place. I recall that @Mick West has already done some balloon imagery, which of course I can't find now! Stuff created by MB members can go here, as can pre-existing stuff found by members. I'll start off with some balloons in IR that my son and I did, playing around with his IR drone used to detect roof leaks and the like.

Here is the video:

Source: https://youtu.be/QkZZ1lOgMrg


Some stills here:
View attachment 73555View attachment 73556
"Mylar" foil balloon and latex balloon, visual and IR white=hot.

View attachment 73557View attachment 73558
Same balloons, visual and IR false color

View attachment 73559View attachment 73560
Same balloons against sky, from below. The clouds in this one are also possibly worth noting.

(We can take suggestions if anything interests folks here. His tendency is to default to the colorful ones, as they make it easier to show clients what he found, but I can request black or white = hot, or the use of other color palettes, if helpful.)

What range of IR are those images? While it is a good idea to compile such library of reference images, it is also important to note that not all IR is the same.

IR is usually divided in short wave IR (SWIR, 0.7 to ~1 micron in wavelength), medium wave IR (MWIR, 3 - 5 micron in wavelength, and the band usually used by ATFLIR), and long wave IR (LWIR, 8 to 12 microns in wavelength). Each band has its uses and properties, so the same object could be seen differently depending on the circumstances.

Usually, for SWIR, you will see an object after the IR light from a source (like the sun) is reflected on the object (in the same way we see visible light, we see the light reflected from an object)

For LWIR, you will usually see the black-body thermal emission of room-temperature objects, and so it is usually used to measure temperature of objects. If an IR image shows a temperature reading or colorbar, it is likely a LWIR camera.

For MWIR, is a kind of mix between both. You will see the black-body thermal emission of hot objects (hundreds of ºC), but you can also see the reflection of an IR source (like the sun) on the objects. Also, using the 3-5 micron IR windows includes the emission lines of some hot gases. Thus, when looking at the exhaust from a plane, you have both the black-body emission from the nozzle, but also discrete emission lines from the exhaust plume.

from: https://www.sciencedirect.com/science/article/pii/S2590123021001213

The primary source of IR signature of an aircraft is the exhaust nozzle and hot exhaust plume. The temperature of these sources is up to several hundred degrees, and it is very easy for a missile to lock and track the aircraft from the engine's heat [12]. The radiations of the exhaust tailpipe are greater than the rest of the body, and the exhaust plume radiations from the exhaust plume are prominent in MWIR spectral band, due to which the aircraft is more susceptible to IR guided missile from the rear aspect [13]. In non-afterburning mode, most IR radiations are absorbed in the intervening atmosphere [14]. The ground radiations do not affect the radiations from the plume, and the plume signature is more prominent in the MWIR spectral band [15]. Aircraft flight conditions affect the plume IR signature, which is subsequently reduced at high altitudes [16]. Low exhaust gas density with increasing height deteriorates the pressure drop and further affects the engine performance [17]. The IR signature of an aircraft's exhaust plume can be reduced by changing the exhaust nozzle's geometry from circular to square cross-section [18]. IR radiations from the exhaust plume are mainly due to the emissions by CO2, CO, and H2O. and are limited to few narrow bands, the most prominent of which are focused around 2.7 μm, 4.3 μm, 5.5 μm, 6.5, and 15 μm [19]. Concentration of oxygen affects the combustion parameters and species in the exhaust plume [20]. Increasing the exhaust nozzle's aspect ratio enhances the mixing of hot exhaust plumes with the ambient air and shortens the plume length [21]. Unlike conventional empirical methods, this paper describes the parametric design of an exhaust nozzle for a low flying UAV using the CFD approach to predict exhaust gases' temperatures. The IR signatures are calculated in MWIR spectral band.

To have a proper library, I would add the kind of camera used, and specifically, the range of IR it is sensitive to.

 

[JMartJr]

To have a proper library, I would add the kind of camera used, and specifically, the range of IR it is sensitive to.

I agree, though had not thought of it. I'll get Here's that info. But of course it may not always be available for "found online" imagery.
requested wavelength sensitivity info in RED.

Thermal Imager Uncooled VOx Microbolometer
Pixel Pitch 12 μm
Frame Rate 30 Hz

Lens DFOV: 61°
Format Equivalent: 40 mm
Aperture: f/1.0
Focus: 5 m to ∞

Noise Equivalent Temperature Difference (NETD)
≤50 mK@F1.0

Temperature Measurement Method
Spot Meter, Area Measurement

Temperature Measurement Range
-20° to 150° C (-4° to 302° F, High Gain Mode)
0° to 500° C (32° to 932° F, Low Gain Mode)

Palette White Hot/Black Hot/Tint/Iron Red/Hot Iron/Arctic/Medical/Fulgurite/Rainbow 1/Rainbow 2

Photo Format JPEG (8-bit) R-JPEG (16-bit)

Video Resolution 640×512@30fps
Bitrate 6 Mbps

Video Format MP4 (MPEG-4 AVC/H.264)

Still Photography Modes
Single: 640×512
Timed: 640×512
JPEG: 2/3/5/7/10/15/20/30/60 s

Digital Zoom 28x

Infrared Wavelength 8-14 μm
Infrared Temperature Measurement Accuracy
±2° C or ±2% (using the larger value)

Most of that means nothing to me, so not being sure what might be of interest I dumped it all!
Source (with more info on the drone and the visual light camera): https://enterprise.dji.com/mavic-3-enterprise/specs

 

[jplaza]

I agree, though had not thought of it. I'll get Here's that info. But of course it may not always be available for "found online" imagery.
requested wavelength sensitivity info in RED.

Thermal Imager Uncooled VOx Microbolometer
Pixel Pitch 12 μm
Frame Rate 30 Hz

Lens DFOV: 61°
Format Equivalent: 40 mm
Aperture: f/1.0
Focus: 5 m to ∞

Noise Equivalent Temperature Difference (NETD)
≤50 mK@F1.0

Temperature Measurement Method
Spot Meter, Area Measurement

Temperature Measurement Range
-20° to 150° C (-4° to 302° F, High Gain Mode)
0° to 500° C (32° to 932° F, Low Gain Mode)

Palette White Hot/Black Hot/Tint/Iron Red/Hot Iron/Arctic/Medical/Fulgurite/Rainbow 1/Rainbow 2

Photo Format JPEG (8-bit) R-JPEG (16-bit)
ld
Video Resolution 640×512@30fps
Bitrate 6 Mbps

Video Format MP4 (MPEG-4 AVC/H.264)

Still Photography Modes
Single: 640×512
Timed: 640×512
JPEG: 2/3/5/7/10/15/20/30/60 s

Digital Zoom 28x

Infrared Wavelength 8-14 μm
Infrared Temperature Measurement Accuracy
±2° C or ±2% (using the larger value)

Most of that means nothing to me, so not being sure what might be of interest I dumped it all!
Source (with more info on the drone and the visual light camera): https://enterprise.dji.com/mavic-3-enterprise/specs

Thanks! That's much more information than I was asking for. In terms of comparing images, I just think the IR wavelength is the most basic, but extra information like optics and resolution is always welcome.

In case of images found online, I think at least the IR wavelength should be noted if possible.

 

[Ravi]

In case of images found online, I think at least the IR wavelength should be noted if possible.

Good points!
Unfortunately, it also seems the be the info that is mostly "redacted" from imagery.. Often even "BLK=HOT" info etc is not visible (when viewing supposedly FLIR type imagery).

 

[jplaza]

From https://apps.dtic.mil/sti/tr/pdf/AD1059353.pdf, a couple of images of birds and drones in LWIR. The study combines two types of images: the raw LWIR image, and a polarimetric image. Just ignore the latter.

Imagery and video presented for this study were recorded using an LWIR polarimetric camera that was based on a division-of-time, SAR approach. The polarimetric camera consisted of a Stirling-cooled, 640× 480 array-size, Mercury Cadmium Telluride (MCT) FPA with a spectral response range of 7.5–11.1μm. The camera was fitted with an Ophir SupIRduel field-of-view (FOV) LWIR objective.

 

[Ann K]

It was at first counterintuitive to me to picture a bird-and-sea image as water=hot, bird=cold in IR. But the supposed UFO images on the (in)famous videos were taken off Southern California, where the surface of the water might be expected to be warmer, and a bird (ANY bird) is well-insulated with feathers, which are especially necessary in the cold air of higher altitudes.

 

[jdog]

It was at first counterintuitive to me to picture a bird-and-sea image as water=hot, bird=cold in IR. But the supposed UFO images on the (in)famous videos were taken off Southern California, where the surface of the water might be expected to be warmer, and a bird (ANY bird) is well-insulated with feathers, which are especially necessary in the cold air of higher altitudes.

Would disagree with the water temperature expectation off Southern California. The California Current brings Arctic water down along the coast and our coastal sea-surface temperatures are usually around 55-65 degrees, rising into the 70s in late summer. (Some surfers here wear shorty wetsuits much of the year, depending on their tolerance for the cold.)

So something like a pelican would have a body temperature several tens of degrees warmer than the water; not sure about the feather surface temperature.

 

[Ann K]

Would disagree with the water temperature expectation off Southern California. The California Current brings Arctic water down along the coast and our coastal sea-surface temperatures are usually around 55-65 degrees, rising into the 70s in late summer. (Some surfers here wear shorty wetsuits much of the year, depending on their tolerance for the cold.)

So something like a pelican would have a body temperature several tens of degrees warmer than the water; not sure about the feather surface temperature.

Nevertheless, in images clearly labeled "black-hot", the water is black and the "bird" is conspicuously white. If it's not a bird, it's still something colder than the sea surface.

(And as someone who has been for a swim in the North Sea, I'm amused at your assumption that 55-65° is cold!)

 

[Z.W. Wolf]

Re: Birds versus ocean surface. Which one is hotter?

I suspect the ocean is highly luminous in the birds and ocean photo because it's reflecting the sky.

I'm going talk in terms as they are used in photography, because that's what I know. Not in terms a physicist would use.

Reflective Surfaces: These surfaces reflect light rather than producing it. Reflective surfaces are described in terms of specular reflection (mirror-like) or diffuse reflection (scattered light).

Light-Emitting Surfaces: These surfaces generate light, either naturally (like the Sun or a flame) or artificially (like a light bulb, LED, or screen).
Light-emitting sources may be referred to as luminous or radiant sources.

We have to sort out the difference between two words that sound a lot alike: luminance (noun) and luminous (adjective). To add to the confusion, there's a difference between luminous and a luminous source.

In photography, the technical term for the amount of light an object emits or reflects is luminance.

Luminance refers to the brightness of light perceived from an object in a specific direction, measured in candelas per square meter (cd/m²). (I have no idea how it's measured in IR photography.)

If the object is producing light, it's considered a luminous source, and its output is also described using luminous intensity or radiance.

For reflective surfaces, the amount of reflected light is influenced by their albedo or reflectivity and described by luminance as well. This measurement accounts for both emitted and reflected light.

A bright object in a photo is described as more luminous. It doesn't matter if the brightness comes from reflected light or produced light. I'm not sure if this is properly technical or just a colloquial usage.


In this visible light photo...

The wall is a reflective surface. It's reflecting light diffusely. It has a high albedo. (It's white.)

The mirror is a reflective surface. It's reflecting light specularly.

The light bulbs are luminous sources. (The glass of the bulb is transparent and reflective.)

The phone screen is both a luminous source and reflective.

The mirror is reflecting the sky, objects in the room, and the light bulbs in a specular manner. I could say it's reflecting the diffused light in the sky, light diffusely reflected by objects in the room, and the produced light from the light bulbs.

The wall is reflecting light in a diffuse manner. Even though the wall has a high albedo, it doesn't appear as bright as the mirror.


Going back to the birds versus sky. The luminance of both is not determined solely by how much IR light they producing. They are also reflecting light.

Even in visible light, water is tricky. It reflects light both diffusely and in a specular manner. Is that also true in IR? I would guess that's true.

The question is, how reflective is water in IR, and how reflective in a certain wavelength of IR. Does water have a high albedo in IR?

I suspect the ocean is highly luminous in the birds and ocean photo because it is reflecting the sky and has a high albedo. Not because it is producing IR light as a luminous object. It could be reflecting the sky diffusely or specularly. Specular reflections are brighter.

I suspect feathers have a lower albedo, in IR. I don't know. They would be diffuse reflectors. While water could reflect both diffusely and specularly.



After considering reflectivity we have to to go on to consider how well these surfaces produce IR light as luminous objects. How well do feathers produce IR light?

I'm talking as a photographer. Those more knowledgeable in the physics of light might want to chime in.

 

[JMartJr]

I suspect the ocean is highly luminous in the birds and ocean photo because it is reflecting the sky and has a high albedo. Not because it is producing IR light as a luminous object. It could be reflecting the sky diffusely or specularly. Specular reflections are brighter.

Trying to follow along -- isn't the sky notoriously cold (or cold looking) in IR? Just looking at some images, though, it does look like clouds might be warmer, and so reflect "warmer" than just "sky" would. (Lower right image is a good one of reflection in water across a range of temperature/IR.)

https://www.tester.co.uk/blog/news/...is-with-teledyne-flir-one-pro-thermal-camera/

 

[Z.W. Wolf]

Good point. Maybe we should say the water and feathers are reflecting direct sunlight, rather than the sky. And maybe I'm over emphasizing the role of reflectivity.

I was thinking in terms of visible light photography. My own false assumption getting in the way.

Come to think of it, I've already pointed out, in times past, that so-called mylar balloons reflect the colder sky.

How bright is sunlight in IR? How much IR light has been absorbed by the atmosphere? How is the luminance of objects influenced by the IR sunlight? By the visible light in sunlight?

I think we need to straighten out the role of luminous sources versus reflective surfaces. Is IR photography all about luminous sources? What is the role of reflected light?

 

[Zang]

User JFDee covered thermal imaging of pelicans back in 2018, with some nice shots of feathers being insulators.
Also notes that water can reflect sky conditions on a gradient depending on angle.

https://www.metabunk.org/threads/go...e-stars-academy-bird-balloon.9569/post-220039

 

[Z.W. Wolf]

I had to go to the widely distrusted GPT as a guide.

The IR light in sunlight plays a critical role, as it provides the illumination needed for IR photography. Sunlight contains a significant amount of infrared radiation, and surfaces reflect or absorb it differently, creating the unique tonal contrasts characteristic of IR images, such as bright foliage and dark skies.

In daylight IR photography, the dominant role is typically played by reflected IR from sunlight, as most objects reflect significant infrared wavelengths from the Sun. This is why foliage appears bright due to high IR reflectivity, while water and sky absorb more IR and appear dark.

The contribution from IR emitted by objects is usually negligible during the day because thermal IR emissions depend on an object's temperature and are faint compared to the abundance of reflected solar IR. Thermal IR photography generally requires specialized sensors and low-light conditions.

If this is true...

It looks to me as if the relative albedo of the feathers and the water is the important factor in a daylight IR photo and the temperature of either is a negligible factor. The water has a low albedo in IR... but the feathers have an even lower albedo. Making the water more luminous than the birds.

It looks as if some of us have been over-emphasizing the role of luminous sources of IR in daylight IR photography.

We should recognize that nighttime thermal IR photography and daylight IR photography are different animals.

 

[Z.W. Wolf]

In both the visible light mode and IR mode:
-The candle is a luminous source

But note that the candle flame is dim in the visible light mode and is also dim in the IR mode. Proving that the heat of the object is not as important a factor in daylight IR photography as many of us have been assuming.



There is a difference in how the latex balloon appears. The latex balloon looks white in visible light. It's reflecting all the wavelengths of visible light. (I think that latex is naturally white. It appears in different colors when dyes or other things are added.)

The balloon appears transparent in IR light. Which means the IR light is passing through it.

But we can also sometimes see specular reflections in the surface of the balloon, even in IR light. This means that even a latex balloon can take on the brightness of objects in the environment around it. Reflections of the sky will make the balloon look dim and reflections of trees will make it look bright. (The opposite of the way it would look in visible light.)


That sunlight is rich in IR should be obvious when thinking about a common life experience. Standing in sunlight makes you feel warm.

 

[Z.W. Wolf]

Trying to follow along -- isn't the sky notoriously cold (or cold looking) in IR? Just looking at some images, though, it does look like clouds might be warmer, and so reflect "warmer" than just "sky" would. (Lower right image is a good one of reflection in water across a range of temperature/IR.)

View attachment 73648
https://www.tester.co.uk/blog/news/...is-with-teledyne-flir-one-pro-thermal-camera/

This is a thermal IR camera.

 

[Z.W. Wolf]

The source is GPT. So if you're a GPT Hata, feel free to reject.

• Near-Infrared (NIR) or Reflected IR Cameras: These cameras capture infrared light reflected off objects, primarily using wavelengths just beyond visible light (about 700–1100 nm). They're used in daylight conditions, often for vegetation analysis or night-vision purposes.
• Thermal Infrared Cameras: These detect emitted infrared radiation from objects based on their temperature, typically using wavelengths in the mid to far-infrared range (3–14 μm). They are used for thermal imaging, heat loss analysis, or detecting living beings in darkness.

Thermal infrared cameras can be used in daylight. They detect heat emitted by objects, which is independent of visible light. Daylight conditions generally do not affect their performance because thermal cameras work in the mid-to-far infrared range (3–14 μm), far beyond the wavelengths of visible or near-infrared light.

However, very high ambient temperatures or sunlight heating objects unevenly can create thermal noise or reduce contrast. Despite this, thermal cameras remain effective for many applications, including detecting temperature differences, even during the day.

When presenting images we must distinguish between the two. What kind of camera was used?

(Now we have color IR cameras that mix IR and low levels of visible light.)

 

[jplaza]

Luminance refers to the brightness of light perceived from an object in a specific direction, measured in candelas per square meter (cd/m²). (I have no idea how it's measured in IR photography.)

In IR radiometry, the usual units are [watts / cm^2] or [watts / cm^2 · stereoradian]. And there are also some analogies, like having confusing terms like radiance and irradiance.

Apart from that, you can find the same phenomena of reflection, transmission and absorption of IR light, which depends on the wavelength.

In both the visible light mode and IR mode:
-The candle is a luminous source

In IR it is a radiant source.

There is a difference in how the latex balloon appears. The latex balloon looks white in visible light. It's reflecting all the wavelengths of visible light. (I think that latex is naturally white. It appears in different colors when dyes or other things are added.)

The balloon appears transparent in IR light. Which means the IR light is passing through it.

The rule of thumb is that light (or electromagnetic radiation in general) interacts with objects of a size at least similar to the wavelength. Visible light wavelength is about 0.4 to 0.7 microns. IR light (for that camera) is 8 to 14 microns, that's about 10 times longer. How thick is a latex balloon? How many wavelengths fit into the thickness of the latex balloon?

It may be thin enough in IR to allow radiation pass through, but thick enough to be opaque in visible. Depends on the transmittance, and its dependence on the wavelength.

This thing about the wavelength also applies to the roughness of a surface: it is easier for a longer wavelength (like IR) to "ignore" imperfections/defects of a surface, and thus have better transmittance or reflectance properties than a shorter wavelength (like visible)

The source is GPT. So if you're a GPT Hata, feel free to reject.

• Near-Infrared (NIR) or Reflected IR Cameras: These cameras capture infrared light reflected off objects, primarily using wavelengths just beyond visible light (about 700–1100 nm). They're used in daylight conditions, often for vegetation analysis or night-vision purposes.
• Thermal Infrared Cameras: These detect emitted infrared radiation from objects based on their temperature, typically using wavelengths in the mid to far-infrared range (3–14 μm). They are used for thermal imaging, heat loss analysis, or detecting living beings in darkness.

When presenting images we must distinguish between the two. What kind of camera was used?

(Now we have color IR cameras that mix IR and low levels of visible light.)

There is another subdivision in the "thermal" IR: MWIR (3-5 μm) and LWIR (8-12 μm). This is because the atmosphere shows those two windows of transmission.

From wikipedia: https://en.wikipedia.org/wiki/Infrared_window#/media/File:Atmosfaerisk_spredning.png :

Also, objects at room-temperature (~300 K) have a black body emission that peaks in the range 8-14 μm. That means that those objects seen in a 3-5 μm camera would not be bright, and it is more likely to see the reflection of the sun on them (which can be treated like a black body with a temperature of ~5700 K, peaking at 0.5 μm, in the visible light range).

 

[FatPhil]

Trying to follow along -- isn't the sky notoriously cold (or cold looking) in IR?

The sky is transparent to some IR, therefore you're looking at the almost infinite heat sink of 3K deep space. This is what permits passive radiative cooling. e.g. (emphasis mine):

Radiative cooling is a thermal radiation process that carries heat energy. When a hot object and a cold object undergo radiative exchange, there is a net heat flow from the hot to the cold object10,11. Such a heat flow by thermal radiation leads to radiative cooling. Radiative cooling happens in our everyday life. For example, clear nights lead to cooler weather during autumn and winter. The Earth at ~300 K is hotter than the universe at 3 K12. Hence, the Earth emits the heat of thermal radiation to the universe through the atmosphere. Moreover, the Earth has a largely transparent atmospheric area in the mid-infrared wavelength range of 8–13 µm. This area, referred to as the atmospheric window, overlaps with the spectral peak of the thermal radiation due to the Earth's temperature, and the heat escaping from the Earth's surface to the universe via the atmospheric window causes a temperature drop. Consequently, the Earth's heat radiations in the mid-infrared range through the atmospheric window to the cold space cause a rapid temperature drop at night. This nighttime radiative cooling in nature has been recognized and investigated systematically for many decades13,14,15,16.

-- https://www.nature.com/articles/s41377-023-01119-0