XCSoar

> Can infrared cameras be used to spot thermals?

Sorry, I couldn't restrain myself. There is a joke in my club that goes 
like this:

Russians said in 60s that they are just about to invent a remote thermal 
detector. After the dissolution of the Soviet Union, they are still 
working on it ;)

-- 
Michal

On Thu, 2010-08-26 at 09:34 +0200, Michal Jezierski wrote:
> > Can infrared cameras be used to spot thermals?
>
> Sorry, I couldn't restrain myself. There is a joke in my club that goes 
> like this:
> 
> Russians said in 60s that they are just about to invent a remote thermal 
> detector. After the dissolution of the Soviet Union, they are still 
> working on it ;)
> 
The only believable story I've heard about this involved Maynard Hill, a
well-known RC flyer and record breaker - he flew a 5.0 kG model aircraft
across the Atlantic (Newfoundland -> Ireland - the Alcock & Brown route)
in 2003. He was working at Johns Hopkins Applied Physics Laboratory on
either UHF radar or Lidar when they saw some odd diffuse blobs. Maynard
guessed what they were but wouldn't say. Instead, he went home, grabbed
an RC glider and back at the lab went out with a two-radio, launched the
model and had the guys talk him into a blob: it was a thermal, of
course. The radar was picking up dust, insects, etc. carried up by the
thermal.


Martin

Have a look at http://www.paraglidingforum.com/viewtopic.php?p=8030#8030

As for LIDAR, see this for actual LIDAR videos:

http://lidar.ssec.wisc.edu/movies/index.htm

Luke


On 26 August 2010 19:56, Martin Gregorie <martin@...> wrote:

> On Thu, 2010-08-26 at 09:34 +0200, Michal Jezierski wrote:
> > > Can infrared cameras be used to spot thermals?
> >
> > Sorry, I couldn't restrain myself. There is a joke in my club that goes
> > like this:
> >
> > Russians said in 60s that they are just about to invent a remote thermal
> > detector. After the dissolution of the Soviet Union, they are still
> > working on it ;)
> >
> The only believable story I've heard about this involved Maynard Hill, a
> well-known RC flyer and record breaker - he flew a 5.0 kG model aircraft
> across the Atlantic (Newfoundland -> Ireland - the Alcock & Brown route)
> in 2003. He was working at Johns Hopkins Applied Physics Laboratory on
> either UHF radar or Lidar when they saw some odd diffuse blobs. Maynard
> guessed what they were but wouldn't say. Instead, he went home, grabbed
> an RC glider and back at the lab went out with a two-radio, launched the
> model and had the guys talk him into a blob: it was a thermal, of
> course. The radar was picking up dust, insects, etc. carried up by the
> thermal.
>
>
> Martin
>
>
>
>
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I have seen experiments including gliders equipped with said to be dual polarised IR cameras and also with infrasound microphones attached to each wing tip, because thermals also have an acoustic signature in a very low frequency range. The problem with all this appears to be eliminating the background noise. So far no experiment I know of has been successful.  
   

Viele Grüße, 
Martin Kopplow

---

Am 24.08.2010 um 12:53 schrieb "Schoen, Andre (Siemens TS)" <andre.schoen@...>:

> Can infrared cameras be used to spot thermals?

On Fri, 2010-08-27 at 14:32 +1000, Luke O'Donnell wrote:

Many thanks for posting those links.
>
> Have a look at
> http://www.paraglidingforum.com/viewtopic.php?p=8030#8030
> 
The girl on the hill with a sensitive thermometer is *not* a spoof. 

Competitive free flight model fliers have used ground rigs to find
thermals for decades. I built my first such system around 1971 and have
used them when flying small power models ever since - 1/2A and F1J for
those who understand FF. If you want to know more about these devices,
look here: 

http://www.gregorie.org/freeflight/thermal_detector/thermal_detector.html


These days you can buy suitable thermometers over the counter. Digital
thermometers with external sensors work just fine provided the sensor is
small and has no thermal inertia work well. The temperature change as a
thermal goes through can vary from 0.2C on a cool, overcast early
morning to 2.0C just after midday on a calm, hot, thermally summer day.

If you know what you're looking for you can feel thermals using only
bare skin. As a thermal approaches the wind speed drops and the air
feels warmer. A sudden temperature drop and increase in wind speed shows
the core has just passed. This is the moment you launch the model to put
it in the thermal. Almost all the wind speed and direction changes you
notice on the glider field are thermal related: next time you're out on
a strong day and waiting to fly try it for yourself. The combination of
wind speed and temperature changes aren't hard to feel. There's usually
a strong periodicity to them: if you have a stopwatch, use it to time
the gap between thermals. The gap varies from day to day but is fairly
constant on any particular day unless conditions change.

I also flew F1A towline gliders but never with a thermal detector.
Simply towing the model, watching it and feeling what its doing through
the towline works much better.
  
> As for LIDAR, see this for actual LIDAR videos:
> 
> http://lidar.ssec.wisc.edu/movies/index.htm
> 
Fascinating. Thats' the first time I've seen what Lidar images of
thermals look like.


Martin

I wonder if a more feasible approach to thermal detection is using IR
cameras pointed at the ground. From what i can gather, air is a poor medium
for producing IR radiation, whereas presumably any solid object (anything on
the ground) would be much, much easier to detect. A real life example is the
police helicopters following suspects at night with ease, they light up like
a Christmas tree.

I can see that perhaps it's somewhat plausible (in theory) to be perhaps a
few KM from a thermal source, see the signature heat pattern on the ground
and head toward it. The idea being you will be in the general area by the
time the newly triggered thermal reaches your altitude. Of course there are
issues such as wind drift, however in theory i can see how it could improve
general decision making when there is not many other visual cue's to use...
such as cu's.

Having said that, i have no idea as to the technical requirements of such a
camera, weather it would need to be super cooled etc.

Luke

On 27 August 2010 19:34, Martin Gregorie <martin@...> wrote:

> On Fri, 2010-08-27 at 14:32 +1000, Luke O'Donnell wrote:
>
> Many thanks for posting those links.
> >
> > Have a look at
> > http://www.paraglidingforum.com/viewtopic.php?p=8030#8030
> >
> The girl on the hill with a sensitive thermometer is *not* a spoof.
>
> Competitive free flight model fliers have used ground rigs to find
> thermals for decades. I built my first such system around 1971 and have
> used them when flying small power models ever since - 1/2A and F1J for
> those who understand FF. If you want to know more about these devices,
> look here:
>
> http://www.gregorie.org/freeflight/thermal_detector/thermal_detector.html
>
>
> These days you can buy suitable thermometers over the counter. Digital
> thermometers with external sensors work just fine provided the sensor is
> small and has no thermal inertia work well. The temperature change as a
> thermal goes through can vary from 0.2C on a cool, overcast early
> morning to 2.0C just after midday on a calm, hot, thermally summer day.
>
> If you know what you're looking for you can feel thermals using only
> bare skin. As a thermal approaches the wind speed drops and the air
> feels warmer. A sudden temperature drop and increase in wind speed shows
> the core has just passed. This is the moment you launch the model to put
> it in the thermal. Almost all the wind speed and direction changes you
> notice on the glider field are thermal related: next time you're out on
> a strong day and waiting to fly try it for yourself. The combination of
> wind speed and temperature changes aren't hard to feel. There's usually
> a strong periodicity to them: if you have a stopwatch, use it to time
> the gap between thermals. The gap varies from day to day but is fairly
> constant on any particular day unless conditions change.
>
> I also flew F1A towline gliders but never with a thermal detector.
> Simply towing the model, watching it and feeling what its doing through
> the towline works much better.
>
> > As for LIDAR, see this for actual LIDAR videos:
> >
> > http://lidar.ssec.wisc.edu/movies/index.htm
> >
> Fascinating. Thats' the first time I've seen what Lidar images of
> thermals look like.
>
>
> Martin
>
>
>
>
>
> ------------------------------------------------------------------------------
> Sell apps to millions through the Intel(R) Atom(Tm) Developer Program
> Be part of this innovative community and reach millions of netbook users
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>

On Fri, 2010-08-27 at 20:52 +1000, Luke O'Donnell wrote:
> I wonder if a more feasible approach to thermal detection is using IR
> cameras pointed at the ground. From what i can gather, air is a poor
> medium for producing IR radiation, whereas presumably any solid object
> (anything on the ground) would be much, much easier to detect.
>
I think the problem is not to find hot spots that might act as thermal
generators, but to know where the thermal is. For example, a flat black
concrete roof or car park is going be be bright in IR on a sunny day,
but there is unlikely to be a continuous standing thermal above it.
Similarly, a thermal travelling across a hayfield will certainly be fed
by hot air pooling among or just above the grass stems, but it probably
will have little effect on the temperature of the dry grass it crosses,
so how can your camera see where the thermal is in a large field or even
if there is one?

>  A real life example is the police helicopters following suspects at
> night with ease, they light up like a Christmas tree. 
> 
They also have quite a large temperature difference to work with. The
back of my hand is currently 28.5C in a room at 21.3C, a 6.2C
difference. Here its a cold, damp overcast day for summer and my heating
is off. Outdoors at night the ground temp is going to be around 10-15C,
and a moving perp is unlikely to be colder than my hand, so we're
looking at a 13-18C temp difference for the camera to spot. The air temp
of a thermal is somewhere between 0.2-2.0C above the surrounding air, so
I suspect its impossible to pick out against the natural variations in
daytime ground temperature: it would be hard enough to spot against the
background air temperature looking horizontally.

I'd well believe that an IR camera can see the hot air column above a
candle flame with the ambient room temperature as background, but again
that's a big temperature difference. You don't leave your hand above a
candle flame for long!

 
Martin

>
> Valid points. I suspect that you wouldn't be necessarily looking for just
> hot spots, but perhaps looking at rapid decreases in temperature. Depending
> on the level of achievable contrast as well as how muchj temp trace there is
> when a thermal moves though, it might be possible to visually 'see' the
> thermal tracking over the ground, cooling it as it goes. Still, i would be
> suprised if it would be nearly as easy to use IR to detect changes in
> temperature of air, as opposed to changes in temperature of the ground.
>
> I'm not an expert in this topic by any stretch of the imagination, so i
> could be completely off the mark. However, a read of:
> http://en.wikipedia.org/wiki/Thermal_conductivity
> Indicates that there is a close relationship between thermal conductivity
> (absorption of heat) and transmittance (losing heat, such as through IR
> radiation). Some figures are (lower = less conductivity/transmittance):
>
> Air     0.025
> Wood     0.04 - 0.4
> Water (liquid)     0.6
> Soil     1.5
> Concrete, stone 1.7
>
> So soil has a conductivity around 60 times that of air. I suppose it
> follows reason that as such, it would (per unit) output substantially more
> amount of IR radiation than air. As such, detecting it with a camera should
> be much easier than detecting changes in air. The other problem with
> attempting to directly measure the temperature of air at a distance with IR,
> is that because of the relatively high amount of IR being produced 'behind'
> the thermal, it would likely totally whitewash any radiation you might
> pickup from the thermal. I suppose there is an argument along the lines that
> if you have the camera pointed above the horizon, you would not be viewing
> this radiation. However i'd be surprised if this turned out to be practical
> - any form of cloud and perhaps even just high humidity would probably drown
> it out at the sorts of distances that would be useful ( a few km).
> Unfortunately radiation has a nasty habit of decreasing at square the
> distance.
>
> It's interesting stuff anyway.
>
> Luke
>
>
>
> On 27 August 2010 22:00, Martin Gregorie <martin@...> wrote:
>
>> On Fri, 2010-08-27 at 20:52 +1000, Luke O'Donnell wrote:
>> > I wonder if a more feasible approach to thermal detection is using IR
>> > cameras pointed at the ground. From what i can gather, air is a poor
>> > medium for producing IR radiation, whereas presumably any solid object
>> > (anything on the ground) would be much, much easier to detect.
>> >
>> I think the problem is not to find hot spots that might act as thermal
>> generators, but to know where the thermal is. For example, a flat black
>> concrete roof or car park is going be be bright in IR on a sunny day,
>> but there is unlikely to be a continuous standing thermal above it.
>> Similarly, a thermal travelling across a hayfield will certainly be fed
>> by hot air pooling among or just above the grass stems, but it probably
>> will have little effect on the temperature of the dry grass it crosses,
>> so how can your camera see where the thermal is in a large field or even
>> if there is one?
>>
>> >  A real life example is the police helicopters following suspects at
>> > night with ease, they light up like a Christmas tree.
>> >
>> They also have quite a large temperature difference to work with. The
>> back of my hand is currently 28.5C in a room at 21.3C, a 6.2C
>> difference. Here its a cold, damp overcast day for summer and my heating
>> is off. Outdoors at night the ground temp is going to be around 10-15C,
>> and a moving perp is unlikely to be colder than my hand, so we're
>> looking at a 13-18C temp difference for the camera to spot. The air temp
>> of a thermal is somewhere between 0.2-2.0C above the surrounding air, so
>> I suspect its impossible to pick out against the natural variations in
>> daytime ground temperature: it would be hard enough to spot against the
>> background air temperature looking horizontally.
>>
>> I'd well believe that an IR camera can see the hot air column above a
>> candle flame with the ambient room temperature as background, but again
>> that's a big temperature difference. You don't leave your hand above a
>> candle flame for long!
>>
>>
>> Martin
>>
>>
>>
>>
>> ------------------------------------------------------------------------------
>> Sell apps to millions through the Intel(R) Atom(Tm) Developer Program
>> Be part of this innovative community and reach millions of netbook users
>> worldwide. Take advantage of special opportunities to increase revenue and
>> speed time-to-market. Join now, and jumpstart your future.
>> http://p.sf.net/sfu/intel-atom-d2d
>> _______________________________________________
>> Xcsoar-user mailing list
>> Xcsoar-user@...
>> https://lists.sourceforge.net/lists/listinfo/xcsoar-user
>>
>
>

IR cameras are used to detect 'hot spots' on electricty grid insulators. This is normally carried out in the air from a helicopter and the pictures I have seen show plenty of contrast against the beckground. The problem with a thermal is that there is a large quantity or air not many degrees above ambient and with its edges mixing with the ambient air. Most other subjects, such as insulators or human beings are at at much higher temperature than ambient and have a sharp edge !
 
I suspect the technology is still too large and power hungry for applications in gliders just yet.
 
Andy 

--- On Fri, 27/8/10, Luke O'Donnell <l.odonnell11@...> wrote:


From: Luke O'Donnell <l.odonnell11@...>
Subject: Re: [Xcsoar-user] Fwd: Infrared and thermals
To: xcsoar-user@...
Date: Friday, 27 August, 2010, 12:45




Valid points. I suspect that you wouldn't be necessarily looking for just hot spots, but perhaps looking at rapid decreases in temperature. Depending on the level of achievable contrast as well as how muchj temp trace there is when a thermal moves though, it might be possible to visually 'see' the thermal tracking over the ground, cooling it as it goes. Still, i would be suprised if it would be nearly as easy to use IR to detect changes in temperature of air, as opposed to changes in temperature of the ground. 

I'm not an expert in this topic by any stretch of the imagination, so i could be completely off the mark. However, a read of: http://en.wikipedia.org/wiki/Thermal_conductivity
Indicates that there is a close relationship between thermal conductivity (absorption of heat) and transmittance (losing heat, such as through IR radiation). Some figures are (lower = less conductivity/transmittance):

Air     0.025
Wood     0.04 - 0.4
Water (liquid)     0.6
Soil     1.5
Concrete, stone 1.7

So soil has a conductivity around 60 times that of air. I suppose it follows reason that as such, it would (per unit) output substantially more amount of IR radiation than air. As such, detecting it with a camera should be much easier than detecting changes in air. The other problem with attempting to directly measure the temperature of air at a distance with IR, is that because of the relatively high amount of IR being produced 'behind' the thermal, it would likely totally whitewash any radiation you might pickup from the thermal. I suppose there is an argument along the lines that if you have the camera pointed above the horizon, you would not be viewing this radiation. However i'd be surprised if this turned out to be practical - any form of cloud and perhaps even just high humidity would probably drown it out at the sorts of distances that would be useful ( a few km). Unfortunately radiation has a nasty habit of decreasing at square the distance.

It's interesting stuff anyway.

Luke






On 27 August 2010 22:00, Martin Gregorie <martin@...> wrote:


On Fri, 2010-08-27 at 20:52 +1000, Luke O'Donnell wrote:
> I wonder if a more feasible approach to thermal detection is using IR
> cameras pointed at the ground. From what i can gather, air is a poor
> medium for producing IR radiation, whereas presumably any solid object
> (anything on the ground) would be much, much easier to detect.
>
I think the problem is not to find hot spots that might act as thermal
generators, but to know where the thermal is. For example, a flat black
concrete roof or car park is going be be bright in IR on a sunny day,
but there is unlikely to be a continuous standing thermal above it.
Similarly, a thermal travelling across a hayfield will certainly be fed
by hot air pooling among or just above the grass stems, but it probably
will have little effect on the temperature of the dry grass it crosses,
so how can your camera see where the thermal is in a large field or even
if there is one?


>  A real life example is the police helicopters following suspects at
> night with ease, they light up like a Christmas tree.
>
They also have quite a large temperature difference to work with. The
back of my hand is currently 28.5C in a room at 21.3C, a 6.2C
difference. Here its a cold, damp overcast day for summer and my heating
is off. Outdoors at night the ground temp is going to be around 10-15C,
and a moving perp is unlikely to be colder than my hand, so we're
looking at a 13-18C temp difference for the camera to spot. The air temp
of a thermal is somewhere between 0.2-2.0C above the surrounding air, so
I suspect its impossible to pick out against the natural variations in
daytime ground temperature: it would be hard enough to spot against the
background air temperature looking horizontally.

I'd well believe that an IR camera can see the hot air column above a
candle flame with the ambient room temperature as background, but again
that's a big temperature difference. You don't leave your hand above a
candle flame for long!





Martin



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Thats an interesting application, makes sense though.

To add to that, an important difference apart from the pure temp, is that
because the insulators are obviously a hell of a lot more dense than air,
for a given temperature they will produce significantly more radiation to be
picked up by a camera. Unfortunately, it's the worst case scenario detecting
thermals in the air - a substance with low density, and low heat
differential at moderate to long distances.

Luke

On 27 August 2010 23:22, ANDREW BARDGETT <a_g_bardgett@...:

> IR cameras are used to detect 'hot spots' on electricty grid insulators.
> This is normally carried out in the air from a helicopter and the pictures I
> have seen show plenty of contrast against the beckground. The problem with a
> thermal is that there is a large quantity or air not many degrees above
> ambient and with its edges mixing with the ambient air. Most other subjects,
> such as insulators or human beings are at at much higher temperature than
> ambient and have a sharp edge !
>
> I suspect the technology is still too large and power hungry for
> applications in gliders just yet.
>
> Andy
>
> --- On *Fri, 27/8/10, Luke O'Donnell <l.odonnell11@...>* wrote:
>
>
> From: Luke O'Donnell <l.odonnell11@...>
> Subject: Re: [Xcsoar-user] Fwd: Infrared and thermals
> To: xcsoar-user@...
> Date: Friday, 27 August, 2010, 12:45
>
>
>  Valid points. I suspect that you wouldn't be necessarily looking for just
> hot spots, but perhaps looking at rapid decreases in temperature. Depending
> on the level of achievable contrast as well as how muchj temp trace there is
> when a thermal moves though, it might be possible to visually 'see' the
> thermal tracking over the ground, cooling it as it goes. Still, i would be
> suprised if it would be nearly as easy to use IR to detect changes in
> temperature of air, as opposed to changes in temperature of the ground.
>
> I'm not an expert in this topic by any stretch of the imagination, so i
> could be completely off the mark. However, a read of:
> http://en.wikipedia.org/wiki/Thermal_conductivity
> Indicates that there is a close relationship between thermal conductivity
> (absorption of heat) and transmittance (losing heat, such as through IR
> radiation). Some figures are (lower = less conductivity/transmittance):
>
> Air     0.025
> Wood     0.04 - 0.4
> Water (liquid)     0.6
> Soil     1.5
> Concrete, stone 1.7
>
> So soil has a conductivity around 60 times that of air. I suppose it
> follows reason that as such, it would (per unit) output substantially more
> amount of IR radiation than air. As such, detecting it with a camera should
> be much easier than detecting changes in air. The other problem with
> attempting to directly measure the temperature of air at a distance with IR,
> is that because of the relatively high amount of IR being produced 'behind'
> the thermal, it would likely totally whitewash any radiation you might
> pickup from the thermal. I suppose there is an argument along the lines that
> if you have the camera pointed above the horizon, you would not be viewing
> this radiation. However i'd be surprised if this turned out to be practical
> - any form of cloud and perhaps even just high humidity would probably drown
> it out at the sorts of distances that would be useful ( a few km).
> Unfortunately radiation has a nasty habit of decreasing at square the
> distance.
>
> It's interesting stuff anyway.
>
> Luke
>
>
>
> On 27 August 2010 22:00, Martin Gregorie <martin@... href="http://uk.mc865.mail.yahoo.com/mc/compose?to=martin@..." target="_new">http://uk.mc865.mail.yahoo.com/mc/compose?to=martin@...>>
> > wrote:
>
> On Fri, 2010-08-27 at 20:52 +1000, Luke O'Donnell wrote:
> > I wonder if a more feasible approach to thermal detection is using IR
> > cameras pointed at the ground. From what i can gather, air is a poor
> > medium for producing IR radiation, whereas presumably any solid object
> > (anything on the ground) would be much, much easier to detect.
> >
> I think the problem is not to find hot spots that might act as thermal
> generators, but to know where the thermal is. For example, a flat black
> concrete roof or car park is going be be bright in IR on a sunny day,
> but there is unlikely to be a continuous standing thermal above it.
> Similarly, a thermal travelling across a hayfield will certainly be fed
> by hot air pooling among or just above the grass stems, but it probably
> will have little effect on the temperature of the dry grass it crosses,
> so how can your camera see where the thermal is in a large field or even
> if there is one?
>
> >  A real life example is the police helicopters following suspects at
> > night with ease, they light up like a Christmas tree.
> >
> They also have quite a large temperature difference to work with. The
> back of my hand is currently 28.5C in a room at 21.3C, a 6.2C
> difference. Here its a cold, damp overcast day for summer and my heating
> is off. Outdoors at night the ground temp is going to be around 10-15C,
> and a moving perp is unlikely to be colder than my hand, so we're
> looking at a 13-18C temp difference for the camera to spot. The air temp
> of a thermal is somewhere between 0.2-2.0C above the surrounding air, so
> I suspect its impossible to pick out against the natural variations in
> daytime ground temperature: it would be hard enough to spot against the
> background air temperature looking horizontally.
>
> I'd well believe that an IR camera can see the hot air column above a
> candle flame with the ambient room temperature as background, but again
> that's a big temperature difference. You don't leave your hand above a
> candle flame for long!
>
>
> Martin
>
>
>
>
> ------------------------------------------------------------------------------
> Sell apps to millions through the Intel(R) Atom(Tm) Developer Program
> Be part of this innovative community and reach millions of netbook users
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>
>
>
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>
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> https://lists.sourceforge.net/lists/listinfo/xcsoar-user
>
>

On Fri, 2010-08-27 at 22:44 +1000, Luke O'Donnell wrote:
> Valid points. I suspect that you wouldn't be necessarily looking for
> just hot spots, but perhaps looking at rapid decreases in temperature.
>
I don't think you'd see them. For starters, ground temp differences are
a lot bigger than air temp differences. This is both because different
surfaces have quite different reflectance and heat capacity (low
reflectance and low heat capacity give a real hot spot (asphalt parking
lot) while high reflectance and low heat capacity give the opposite) and
there's mixing in the air mass, but none in the ground.

As I said, if you're looking down on that sort of patchwork, the
difference in emitted IR from air with its small temp difference between
lift and sink combine with its low emitted energy mean it simply can't
be resolved.

I'm doubtful that a camera could resolve the low contrast between
thermal and non-thermal even looking horizontally so the thermal is seen
against air rather than ground. Don't forget that the air's thermal
background is also uneven and shows similar contrast differences from
distant thermals to what we're trying to use to locate a nearby one.

>  Depending on the level of achievable contrast as well as how muchj
> temp trace there is when a thermal moves though, it might be possible
> to visually 'see' the thermal tracking over the ground, cooling it as
> it goes.
>
Again I'm doubtful, simply because the heat capacity of air is very low
compared with any solid. This means that the temp change in a bit of
ground that warms a parcel of air will be proportionately lower than the
tempo change in the air parcel. For a given heat exchange we can write:

dT1 * C1 = dT2 * C2  - (1)

Rearranging (1) gives 

dT1 = dT2*C2/C1      - (2)

where dT is the temp change and C is the volumetric heat capacity. I
think this is best used rather than heat capacity per gram for rough
calculations comparing a gas with a solid. Air's volumetric capacity is
0.001297 vs 2.17 for granite (figures from Wikipedia's article on heat
capacity). 

Plugging these into equation (2) and we see that a 2C increase in air
temp (0.7%, not 8% since we use degrees K, not degrees C for this type
of calculation) corresponds to a change of 0.007*0.001297/2.17 which is
0.0004184% or 0.0012 degrees C. You'd need a really good lab set-up to
measure that sort of temperature change. It not anything you'd attempt
outdoors with handheld or portable equipment.

Now, how does a 2C temp change affect the radiance of a parcel of air?
This is relevant because its brightness is directly proportional to an
object's radiance. The  Stefan–Boltzmann law applies, which says that
the emitted radiation power varies as the 4th power of its absolute
temperature, so if we warm air by 2C at 25C the difference is 300**4 -
298**4 or an increase in brightness of 2.7% - again not a lot of
difference.

By comparison my hand at 28.5C is 23% brighter than ground at night
(15C).

>  Still, i would be suprised if it would be nearly as easy to use IR to
> detect changes in temperature of air, as opposed to changes in
> temperature of the ground. 
> 
Exactly so, and that is even without considering differences in the
amount of radiation the ground emits in comparison with air.


Martin

Interesting, i didn't know that there would be such a small heat
differential. So i suppose the upshot is that however you look at it, using
IR for (blue) thermal detection at any sort of range that would be useful
does not appear to be plausible.

I do however find the idea of using IR with clouds to be interesting. Andre
mentioned that he found it possible to detect hotspots in clouds. Assuming
that this is the case, i could see how it could be useful in the real world.
You could be approaching a large cloud (or a group of clouds) and have a
better indication of which ones are highly active, and furthermore where the
best part of them are. Of course you can usually determine this by looking
at shape and active development, but it's an interesting concept anyway.

Luke

On 28 August 2010 00:29, Martin Gregorie <martin@...> wrote:

> On Fri, 2010-08-27 at 22:44 +1000, Luke O'Donnell wrote:
> > Valid points. I suspect that you wouldn't be necessarily looking for
> > just hot spots, but perhaps looking at rapid decreases in temperature.
> >
> I don't think you'd see them. For starters, ground temp differences are
> a lot bigger than air temp differences. This is both because different
> surfaces have quite different reflectance and heat capacity (low
> reflectance and low heat capacity give a real hot spot (asphalt parking
> lot) while high reflectance and low heat capacity give the opposite) and
> there's mixing in the air mass, but none in the ground.
>
> As I said, if you're looking down on that sort of patchwork, the
> difference in emitted IR from air with its small temp difference between
> lift and sink combine with its low emitted energy mean it simply can't
> be resolved.
>
> I'm doubtful that a camera could resolve the low contrast between
> thermal and non-thermal even looking horizontally so the thermal is seen
> against air rather than ground. Don't forget that the air's thermal
> background is also uneven and shows similar contrast differences from
> distant thermals to what we're trying to use to locate a nearby one.
>
> >  Depending on the level of achievable contrast as well as how muchj
> > temp trace there is when a thermal moves though, it might be possible
> > to visually 'see' the thermal tracking over the ground, cooling it as
> > it goes.
> >
> Again I'm doubtful, simply because the heat capacity of air is very low
> compared with any solid. This means that the temp change in a bit of
> ground that warms a parcel of air will be proportionately lower than the
> tempo change in the air parcel. For a given heat exchange we can write:
>
> dT1 * C1 = dT2 * C2  - (1)
>
> Rearranging (1) gives
>
> dT1 = dT2*C2/C1      - (2)
>
> where dT is the temp change and C is the volumetric heat capacity. I
> think this is best used rather than heat capacity per gram for rough
> calculations comparing a gas with a solid. Air's volumetric capacity is
> 0.001297 vs 2.17 for granite (figures from Wikipedia's article on heat
> capacity).
>
> Plugging these into equation (2) and we see that a 2C increase in air
> temp (0.7%, not 8% since we use degrees K, not degrees C for this type
> of calculation) corresponds to a change of 0.007*0.001297/2.17 which is
> 0.0004184% or 0.0012 degrees C. You'd need a really good lab set-up to
> measure that sort of temperature change. It not anything you'd attempt
> outdoors with handheld or portable equipment.
>
> Now, how does a 2C temp change affect the radiance of a parcel of air?
> This is relevant because its brightness is directly proportional to an
> object's radiance. The  Stefan–Boltzmann law applies, which says that
> the emitted radiation power varies as the 4th power of its absolute
> temperature, so if we warm air by 2C at 25C the difference is 300**4 -
> 298**4 or an increase in brightness of 2.7% - again not a lot of
> difference.
>
> By comparison my hand at 28.5C is 23% brighter than ground at night
> (15C).
>
> >  Still, i would be suprised if it would be nearly as easy to use IR to
> > detect changes in temperature of air, as opposed to changes in
> > temperature of the ground.
> >
> Exactly so, and that is even without considering differences in the
> amount of radiation the ground emits in comparison with air.
>
>
> Martin
>
>
>
>
> ------------------------------------------------------------------------------
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Would it make sense to just try it ?

Any volunteers?


What we know:
Air does not / or virtually not transmit IR, so it is not likely that we can see blue thermals (unless bugs, particles, etc. emit sufficient IR).
In clouds, we can see temperature differentials of 0.5 to 2 degrees on the active part of a cumulus (presumably the water vapour emitting sufficient IR) - so we might see which clouds have roughly how strong a thermal (not always easy to spot with the naked eye, depending on your angle or when old and new clouds are mixed).
It might only work when looking from the cockpit/ground upwards or forward, but not down (background noise of warmer surface).

What we need:
A camera capable of detecting temperature differentials of 0.1 to 1.0 degrees Centigrade with sufficient resolution at say 1 to 20 km ahead.
May or may not need a different software to colour code temperature differentials, rather than precisely reproduce shapes.
Could be a stripped down digital camera with the IR block coating removed and an IR only filter added, or a thermal imaging FLIR camera (on loan from work? New ones cost around 2000 Euros); possibly also a night vision CCR binocular with an IR only filter. Lenses used must be transparent to IR (otherwise you measure the temperature of the lens).

Done so far:
I used an infrared remote thermometer (with an 8x lens, costs around 25 Euros) in flight (through open window) and from the ground to measure the temperature of clouds between 1-5km away. On the day, the clouds had around 12 degrees C with a backdrop temperature of around -8 and a ground temperature of 27 degrees. The active part of the clouds were between 0.5 and 2 degrees warmer than the rest of the cloud. This method only allows spot measurements and you can of course only guess the spot size - a camera would give a far more precise understanding.



regards,


Andre

________________________________
From: Luke O'Donnell [mailto:l.odonnell11@...]
Sent: 28 August 2010 00:47
To: XCSoar
Subject: Re: [Xcsoar-user] Fwd: Infrared and thermals

Interesting, i didn't know that there would be such a small heat differential. So i suppose the upshot is that however you look at it, using IR for (blue) thermal detection at any sort of range that would be useful does not appear to be plausible.

I do however find the idea of using IR with clouds to be interesting. Andre mentioned that he found it possible to detect hotspots in clouds. Assuming that this is the case, i could see how it could be useful in the real world. You could be approaching a large cloud (or a group of clouds) and have a better indication of which ones are highly active, and furthermore where the best part of them are. Of course you can usually determine this by looking at shape and active development, but it's an interesting concept anyway.

Luke
On 28 August 2010 00:29, Martin Gregorie <martin@...>> wrote:
On Fri, 2010-08-27 at 22:44 +1000, Luke O'Donnell wrote:
> Valid points. I suspect that you wouldn't be necessarily looking for
> just hot spots, but perhaps looking at rapid decreases in temperature.
>
I don't think you'd see them. For starters, ground temp differences are
a lot bigger than air temp differences. This is both because different
surfaces have quite different reflectance and heat capacity (low
reflectance and low heat capacity give a real hot spot (asphalt parking
lot) while high reflectance and low heat capacity give the opposite) and
there's mixing in the air mass, but none in the ground.

As I said, if you're looking down on that sort of patchwork, the
difference in emitted IR from air with its small temp difference between
lift and sink combine with its low emitted energy mean it simply can't
be resolved.

I'm doubtful that a camera could resolve the low contrast between
thermal and non-thermal even looking horizontally so the thermal is seen
against air rather than ground. Don't forget that the air's thermal
background is also uneven and shows similar contrast differences from
distant thermals to what we're trying to use to locate a nearby one.

>  Depending on the level of achievable contrast as well as how muchj
> temp trace there is when a thermal moves though, it might be possible
> to visually 'see' the thermal tracking over the ground, cooling it as
> it goes.
>
Again I'm doubtful, simply because the heat capacity of air is very low
compared with any solid. This means that the temp change in a bit of
ground that warms a parcel of air will be proportionately lower than the
tempo change in the air parcel. For a given heat exchange we can write:

dT1 * C1 = dT2 * C2  - (1)

Rearranging (1) gives

dT1 = dT2*C2/C1      - (2)

where dT is the temp change and C is the volumetric heat capacity. I
think this is best used rather than heat capacity per gram for rough
calculations comparing a gas with a solid. Air's volumetric capacity is
0.001297 vs 2.17 for granite (figures from Wikipedia's article on heat
capacity).

Plugging these into equation (2) and we see that a 2C increase in air
temp (0.7%, not 8% since we use degrees K, not degrees C for this type
of calculation) corresponds to a change of 0.007*0.001297/2.17 which is
0.0004184% or 0.0012 degrees C. You'd need a really good lab set-up to
measure that sort of temperature change. It not anything you'd attempt
outdoors with handheld or portable equipment.

Now, how does a 2C temp change affect the radiance of a parcel of air?
This is relevant because its brightness is directly proportional to an
object's radiance. The  Stefan-Boltzmann law applies, which says that
the emitted radiation power varies as the 4th power of its absolute
temperature, so if we warm air by 2C at 25C the difference is 300**4 -
298**4 or an increase in brightness of 2.7% - again not a lot of
difference.

By comparison my hand at 28.5C is 23% brighter than ground at night
(15C).

>  Still, i would be suprised if it would be nearly as easy to use IR to
> detect changes in temperature of air, as opposed to changes in
> temperature of the ground.
>
Exactly so, and that is even without considering differences in the
amount of radiation the ground emits in comparison with air.


Martin



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On Sat, 2010-08-28 at 21:16 +1000, Luke O'Donnell wrote:
> I'm not sure exactly the phenomenon you are referring to. Do you mean
> that at cloud base (or within 100ft) that you find the strongest lift
> significantly upwind of the cloud? As i'm sure most have, i've
> experienced thermals being upwind of the cloud within a 1000 feet or
> so - due to wind shear
>
The latter. I've never explored top of an offset thermal, mainly because
the lift falls off - probably to do with horizontal flow at the top
since, as you say, it must join up with the cloud somehow. 

> > Shear wave (perhaps also known as thermal wave) where small scale
> (sometimes strong) wave can form within about a km on the windward
> side of a thermal, going as much as a few thousand feet over the top
> of convection
>
Don't recall noticing that at the time.

> > Another thermal forming as part of a street (or not) just upwind of
> the cloud in questions, in which case a new cloud should form shortly
> after
> 
Its always been in mild streeting conditions with fairly widely spaced
component clouds but the offset thermal has always been the the only one
associated with the cloud, which AFAICR was fairly small. I don't think
they've been new blue thermals or associated with an upwind cloud
either.
  
> I also recall hearing of the use of thermistors. In theory it should
> work, there should be significant temperature differences between the
> tips of wings (especially on larger gliders) while thermalling.
>
I was talking with an older club member today. He was quite definite
that it was tried back in the wooden era and didn't work.

> > Airspeed, as the inboard wing while circling has lower velocity, a
> thermistor in the airstream would likley heat up as a result of less
> wind-chill, giving false readings
>
If they do that its a sign that the wrong thermistors are being used. 

I learnt early on that you never use less than a 100K thermistor on a 9v
system and that 500K or 2M thermistors are much better because high
resistance thermistors don't heat up nearly as much as low resistance
ones. You're right about thermal inertia too - for ground based thermal
detectors anything with a thermal constant bigger than 3 seconds is
totally useless, though hanging it out in a glider's slipstream may make
that less important. I found the best thermistors for my system were all
around 0.5-0.6mm in diameter and naked, i.e. no glass coating.

> > Out of line of sight of the sun, could lead to uneven heating when
> turning etc.
> 
An effective solar shield is essential. It must be both reflective and
insulated - kitchen foil over 6mm thick white foam works really well
provided there's no way that direct or reflected sunlight can reach the
thermistor bead. I used a foam/foil box with an open bottom with the
thermistor just under its top surface and placed a piece of thin ply
with chrome tape on its underside under the bead to prevent reflections
from illuminating the bead.

BTW, I heard back from WeatherJack. See my next post.

Martin

On Sat, 2010-08-28 at 16:53 +0200, Schoen, Andre (Siemens TS) wrote:
> Air does not / or virtually not transmit IR, so it is not likely that
> we can see blue thermals (unless bugs, particles, etc. emit sufficient
> IR).
> 
Yes.

> In clouds, we can see temperature differentials of 0.5 to 2 degrees on
> the active part of a cumulus (presumably the water vapour emitting
> sufficient IR) – so we might see which clouds have roughly how strong
> a thermal (not always easy to spot with the naked eye, depending on
> your angle or when old and new clouds are mixed).
> 
I mentioned this to Weatherjack (Jack Harrison, a former RAF met man and
glider pilot). Here is his reply:

"There is some evidence that cloudy thermals (ie, not blue) are
actually COLDER than surrounding air.  I have to a small extent
confirmed this from my own observations using digital thermometer
measurements thermic conditions.  The reason is probably related to
the fact that air descending outside a cumulus is warmed at the dry
adiabatic but the air going up inside the cumulus is cooling at the
saturated adiabatic."

"Also, the strongest thermals often form a concave dome at the cloud
base.  Because the top of the dome will be higher than the general
base, it will be at a lower temperature."

"So what is needed is not a simple pyrometer but an infra red mapping
camera that can plot temperatures and correlate these with the
measured vertical profile of the air in and outside the thermals.  It
would certainly make a good research project.  This could eventually
lead to a cockpit display showing where the strongest thermals are to
be expected (but you will need to reach them before things change too
much)."

> It might only work when looking from the cockpit/ground upwards or
> forward, but not down (background noise of warmer surface).
> 
That sounds very likely.

> What we need:
> 
> A camera capable of detecting temperature differentials of 0.1 to 1.0
> degrees Centigrade with sufficient resolution at say 1 to 20 km ahead.
> 
Agreed. It looks like suitably sensitive devices are available but there
seems to be a trade-off between sensitivity and speed of response. In
addition the really good ones appear to need some form of cryogenic
cooling. http://en.wikipedia.org/wiki/Bolometer

> I used an infrared remote thermometer (with an 8x lens, costs around
> 25 Euros) in flight (through open window) and from the ground to
> measure the temperature of clouds between 1-5km away. On the day, the
> clouds had around 12 degrees C with a backdrop temperature of around
> -8 and a ground temperature of 27 degrees. The active part of the
> clouds were between 0.5 and 2 degrees warmer than the rest of the
> cloud.
>
Judging by Jack's comments you'd certainly see temperature changes
across the cloud base, but are you sure the warmer spots were thermal
tops or some other cloud base feature? I'm not being critical - just
curious.

>  This method only allows spot measurements and you can of course only
> guess the spot size – a camera would give a far more precise
> understanding.
> 
Yep. The micro-bolometer grids sound like the answer, but as you say
there's always the small matter of getting hold of IR-transparent
optics.


Martin

It seems as though all soaring pilots dream of thermal goggles, but at some
point doesn't it take the fun or challenge out of soaring?  We don't see a
lot of cloud days in our area, but we do have dust devils and that helps
visually, but for many of us it is the puzzle of where the lift may be found
and how to link those sources together to make a cross country flight that
is what makes soaring so appealing.  If I could actually see all of the
working lift, I may as well just rent a Cessna and motor around.  I guess it
could make XC in the commuting sense possible, but I rather enjoy flying
purely for fun.

Great insight and data being tossed around though.



On Sat, Aug 28, 2010 at 11:25 AM, Martin Gregorie <martin@...:

> On Sat, 2010-08-28 at 16:53 +0200, Schoen, Andre (Siemens TS) wrote:
> > Air does not / or virtually not transmit IR, so it is not likely that
> > we can see blue thermals (unless bugs, particles, etc. emit sufficient
> > IR).
> >
> Yes.
>
> > In clouds, we can see temperature differentials of 0.5 to 2 degrees on
> > the active part of a cumulus (presumably the water vapour emitting
> > sufficient IR) – so we might see which clouds have roughly how strong
> > a thermal (not always easy to spot with the naked eye, depending on
> > your angle or when old and new clouds are mixed).
> >
> I mentioned this to Weatherjack (Jack Harrison, a former RAF met man and
> glider pilot). Here is his reply:
>
> "There is some evidence that cloudy thermals (ie, not blue) are
> actually COLDER than surrounding air.  I have to a small extent
> confirmed this from my own observations using digital thermometer
> measurements thermic conditions.  The reason is probably related to
> the fact that air descending outside a cumulus is warmed at the dry
> adiabatic but the air going up inside the cumulus is cooling at the
> saturated adiabatic."
>
> "Also, the strongest thermals often form a concave dome at the cloud
> base.  Because the top of the dome will be higher than the general
> base, it will be at a lower temperature."
>
> "So what is needed is not a simple pyrometer but an infra red mapping
> camera that can plot temperatures and correlate these with the
> measured vertical profile of the air in and outside the thermals.  It
> would certainly make a good research project.  This could eventually
> lead to a cockpit display showing where the strongest thermals are to
> be expected (but you will need to reach them before things change too
> much)."
>
> > It might only work when looking from the cockpit/ground upwards or
> > forward, but not down (background noise of warmer surface).
> >
> That sounds very likely.
>
> > What we need:
> >
> > A camera capable of detecting temperature differentials of 0.1 to 1.0
> > degrees Centigrade with sufficient resolution at say 1 to 20 km ahead.
> >
> Agreed. It looks like suitably sensitive devices are available but there
> seems to be a trade-off between sensitivity and speed of response. In
> addition the really good ones appear to need some form of cryogenic
> cooling. http://en.wikipedia.org/wiki/Bolometer
>
> > I used an infrared remote thermometer (with an 8x lens, costs around
> > 25 Euros) in flight (through open window) and from the ground to
> > measure the temperature of clouds between 1-5km away. On the day, the
> > clouds had around 12 degrees C with a backdrop temperature of around
> > -8 and a ground temperature of 27 degrees. The active part of the
> > clouds were between 0.5 and 2 degrees warmer than the rest of the
> > cloud.
> >
> Judging by Jack's comments you'd certainly see temperature changes
> across the cloud base, but are you sure the warmer spots were thermal
> tops or some other cloud base feature? I'm not being critical - just
> curious.
>
> >  This method only allows spot measurements and you can of course only
> > guess the spot size – a camera would give a far more precise
> > understanding.
> >
> Yep. The micro-bolometer grids sound like the answer, but as you say
> there's always the small matter of getting hold of IR-transparent
> optics.
>
>
> Martin
>
>
>
>
>
> ------------------------------------------------------------------------------
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> worldwide. Take advantage of special opportunities to increase revenue and
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On 2010/08/26 22:13, Tibor Arpas <tibor@...> wrote:
> What are the software pieces missing? Can XCSoar use some airspeed
> data? In what format?

Currently, XCSoar gets all data over a serial port in the NMEA format.
If you want support for other interfaces, and Windows CE provides an
API to access the hardware, we can work it out.  Open a TRAC ticket,
and offer one of these devices to a volunteer developer.

Max

Hi Tibor,

If you don't mind spending the time to set up a development
environment on your computer it should be fairly straightforward to
add support for a new custom protocol for your own personal build of
XCSoar, alternatively it may be possible to avoid code modifications
by mimicking the NMEA strings sent by an already-supported device.
This is probably a conversation better suited for the xcsoar-devel
list, would you mind reposting the question there?

On a more general note, the DIY-UAV guys are coming up with some very
exciting open-source hardware, it's an area worth watching!

Thanks,

Simon

On 26 August 2010 21:13, Tibor Arpas <tibor@...> wrote:
> Hi Guys,
>
> I hope there is cheaper way to get zig-zag wind calculation and
> headwind final glide correction then buying a gliding computer for big
> bucks.
>
> >From the hardware perspective some Arduino board + BT board +
> differential pressure sensor
> http://store.diydrones.com/product_p/br-dev-00666.htm
> http://store.diydrones.com/product_p/br-0004-02.htm
> should do.
>
> What are the software pieces missing? Can XCSoar use some airspeed
> data? In what format?
>
> Thanks,
> Tibor
>
> ------------------------------------------------------------------------------
> Sell apps to millions through the Intel(R) Atom(Tm) Developer Program
> Be part of this innovative community and reach millions of netbook users
> worldwide. Take advantage of special opportunities to increase revenue and
> speed time-to-market. Join now, and jumpstart your future.
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Max, Simon thanks for your remarks.

I definitely think the best way is to mimick already supported NMEA
device. I don't even use XCSoar yet and my primary machine is MAC OS
so I have some homework to do. But I'll followup once I get further.

> On a more general note, the DIY-UAV guys are coming up with some very
> exciting open-source hardware, it's an area worth watching!

Very exciting indeed :-).

Tibor




On Fri, Aug 27, 2010 at 09:47, Simon Taylor <simon.taylor.uk@...> wrote:
> Hi Tibor,
>
> If you don't mind spending the time to set up a development
> environment on your computer it should be fairly straightforward to
> add support for a new custom protocol for your own personal build of
> XCSoar, alternatively it may be possible to avoid code modifications
> by mimicking the NMEA strings sent by an already-supported device.
> This is probably a conversation better suited for the xcsoar-devel
> list, would you mind reposting the question there?
>
> On a more general note, the DIY-UAV guys are coming up with some very
> exciting open-source hardware, it's an area worth watching!
>
> Thanks,
>
> Simon
>
> On 26 August 2010 21:13, Tibor Arpas <tibor@...> wrote:
>> Hi Guys,
>>
>> I hope there is cheaper way to get zig-zag wind calculation and
>> headwind final glide correction then buying a gliding computer for big
>> bucks.
>>
>> >From the hardware perspective some Arduino board + BT board +
>> differential pressure sensor
>> http://store.diydrones.com/product_p/br-dev-00666.htm
>> http://store.diydrones.com/product_p/br-0004-02.htm
>> should do.
>>
>> What are the software pieces missing? Can XCSoar use some airspeed
>> data? In what format?
>>
>> Thanks,
>> Tibor
>>
>> ------------------------------------------------------------------------------
>> Sell apps to millions through the Intel(R) Atom(Tm) Developer Program
>> Be part of this innovative community and reach millions of netbook users
>> worldwide. Take advantage of special opportunities to increase revenue and
>> speed time-to-market. Join now, and jumpstart your future.
>> http://p.sf.net/sfu/intel-atom-d2d
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On 2010/08/22 22:31, "Schoen, Andre (Siemens TS)" <andre.schoen@...> wrote:
> I do have a problem though with this and previous builds.
> When the start-up screen offers the choice "fly" or "simulator", my screen does not respond to tapping, or at least nothing happens (can not select "fly").

Please use the bug tracker for bug reports, not this mailing list:

 http://www.xcsoar.org/trac/

In your bug report, specify which was the last "good" version, and
which was the first "bad" version.

Max