Remote thermal detection

I've seen enough soaring birds make a beeline for a thermal 1/4 mile away from them that I have to believe there is something visible, at least in some cases. Perhaps a creative optical solution might work if we find the right wavelength and polarization?

I also spent many happy years playing with the electric fields around clouds and sadly think they will be too chaotic around turbulent thermals to be any use.

Mike

A FLIR unit might offer a visual indication from much larger distance?

On Sunday, October 2, 2016 at 7:46:12 AM UTC-7, Mike the Strike wrote:
I've seen enough soaring birds make a beeline for a thermal 1/4 mile away from them that I have to believe there is something visible, at least in some cases. Perhaps a creative optical solution might work if we find the right wavelength and polarization?

I also spent many happy years playing with the electric fields around clouds and sadly think they will be too chaotic around turbulent thermals to be any use.

Mike

On Monday, October 3, 2016 at 4:04:39 AM UTC+13, Jonathan St. Cloud wrote:
A FLIR unit might offer a visual indication from much larger distance?

A few moons ago, I got chatting to a guy selling FLIR imaging systems at a trade show. I asked him about the problem of trying to see thermals, so we set an imager up to look at the hot air rising from a nearby vent and saw nothing (as he expected).
There's no problem seeing warm solid objects, since they consist of a lot of closely-packed warm emitters - high spatial density - but warm gas is so much more diffuse that any infrared 'brightness' just fades into the background, like a small amount of dye in a large volume of liquid. To do effective background subtraction, you need to know what the background is to begin with and on a typical thermal day this is the average temperature of the air which has high spatial variability.
I think birds can see all those rising insects, which makes the birds the best thermal indicators, if they can be bothered to fly where we want them to.

DH
TX

In the eighty's or nineties there was an article in "Soaring" by an U.S. Army Apache trainee, who noticed he could see raising thermal through his monocle. Not sure which sensor array was picking that up, but I thought it was the FLIR.

On Sunday, October 2, 2016 at 11:04:32 AM UTC-7, David Hirst wrote:
On Monday, October 3, 2016 at 4:04:39 AM UTC+13, Jonathan St. Cloud wrote:
A FLIR unit might offer a visual indication from much larger distance?

A few moons ago, I got chatting to a guy selling FLIR imaging systems at a trade show. I asked him about the problem of trying to see thermals, so we set an imager up to look at the hot air rising from a nearby vent and saw nothing (as he expected).
There's no problem seeing warm solid objects, since they consist of a lot of closely-packed warm emitters - high spatial density - but warm gas is so much more diffuse that any infrared 'brightness' just fades into the background, like a small amount of dye in a large volume of liquid. To do effective background subtraction, you need to know what the background is to begin with and on a typical thermal day this is the average temperature of the air which has high spatial variability.
I think birds can see all those rising insects, which makes the birds the best thermal indicators, if they can be bothered to fly where we want them to.

DH
TX

Weather radar can see insects in thermals, if adjusted for weak echos. No need to carry radar on board, just form a composite image from ground based radars and link image data to cockpit. Technology exists already.

On Sun, 02 Oct 2016 12:20:59 -0700, krasw wrote:

Weather radar can see insects in thermals, if adjusted for weak echos.
No need to carry radar on board, just form a composite image from ground
based radars and link image data to cockpit. Technology exists already.

When Maynard Hill[*] was working for NACA/NASA (at Langley I think) a new
radar they'd developed showed mysterious woolly blobs over a nearby
field. He had an idea what they were, refused to say more and went home,
grabbed an RC sailplane and took it plus an RT set out to the field,
launched and had the crew talk his model into the blob. It went up,
proving the radar was spotting thermals. IIRC this story appeared on the
Academy of Model Aeronautics's magazine, Model Aviation. The AMA is the
governing body for American model aviation.

Do any of you know more about this? Esp the frequency the radar used and
how/why it detected thermals.
[*] Maynard Hill was a well-known American RC pilot and record breaker.
He set out to break records because he found that more fun than competing
in any type of organised competition.
https://www.modelaircraft.org/mag/mhill/hillindex.htm

Among other feats he was the first to fly a model aircraft across the
Atlantic. That was done with his self designed and built autonomous
model. To qualify as a model its all-up weight (including fuel) at launch
had to be 5kg or less.

There's an article about his Trans Atlantic Model he
https://en.wikipedia.org/wiki/The_Sp..._Butts%27_Farm



--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

sunnuntai 2. lokakuuta 2016 22.49.17 UTC+3 Martin Gregorie kirjoitti:

Do any of you know more about this? Esp the frequency the radar used and
how/why it detected thermals.

Insects are sucked to thermals from close to ground. These are roughly same size as rain or snow coming down from clouds, so they are visible in weather radar images accordingly, as are birds and larger objects. I believe weather radars operate in centimeter scale wavelength.

Le dimanche 2 octobre 2016 20:57:45 UTC+2, Jonathan St. Cloud a écritÂ*:
In the eighty's or nineties there was an article in "Soaring" by an U.S. Army Apache trainee, who noticed he could see raising thermal through his monocle. Not sure which sensor array was picking that up, but I thought it was the FLIR.

On Sunday, October 2, 2016 at 11:04:32 AM UTC-7, David Hirst wrote:
On Monday, October 3, 2016 at 4:04:39 AM UTC+13, Jonathan St. Cloud wrote:
A FLIR unit might offer a visual indication from much larger distance?

A few moons ago, I got chatting to a guy selling FLIR imaging systems at a trade show. I asked him about the problem of trying to see thermals, so we set an imager up to look at the hot air rising from a nearby vent and saw nothing (as he expected).
There's no problem seeing warm solid objects, since they consist of a lot of closely-packed warm emitters - high spatial density - but warm gas is so much more diffuse that any infrared 'brightness' just fades into the background, like a small amount of dye in a large volume of liquid. To do effective background subtraction, you need to know what the background is to begin with and on a typical thermal day this is the average temperature of the air which has high spatial variability.
I think birds can see all those rising insects, which makes the birds the best thermal indicators, if they can be bothered to fly where we want them to.

DH
TX

You cannot detect hot air from a distance by any infrared detector (and FLIR is infrared imaging). Obviously, your sales guy wasn't up to speed with physics.

Hot air emits infrard radiation. However, as emission and absorption coefficients are the same thing, the air inbetween the thermal and your FLIR will absorb all of this radiation, and you won't see anything on your imager. That's how physics works. The stories about people having seen infrared images of thermals are just urband legends.

Bert (who has been developing infrared sensors and systems for more than 15 years)

At 13:03 03 October 2016, Tango Whisky wrote:
Le dimanche 2 octobre 2016 20:57:45 UTC+2, Jonathan St. Cloud
a =C3=A9crit=
=C2=A0:
In the eighty's or nineties there was an article in "Soaring" by
an U.S.
=
Army Apache trainee, who noticed he could see raising thermal
through his
m=
onocle. Not sure which sensor array was picking that up, but I
thought it
=
was the FLIR.
=20
On Sunday, October 2, 2016 at 11:04:32 AM UTC-7, David
Hirst wrote:
On Monday, October 3, 2016 at 4:04:39 AM UTC+13,
Jonathan St. Cloud
wro=
te:
A FLIR unit might offer a visual indication from much larger
distance=
? =20

A few moons ago, I got chatting to a guy selling FLIR imaging
systems
a=
t a trade show. I asked him about the problem of trying to see
thermals,
s=
o we set an imager up to look at the hot air rising from a nearby
vent and
=
saw nothing (as he expected). =20
There's no problem seeing warm solid objects, since they
consist of a
l=
ot of closely-packed warm emitters - high spatial density - but
warm gas
is=
so much more diffuse that any infrared 'brightness' just fades
into the
ba=
ckground, like a small amount of dye in a large volume of liquid.
To do
ef=
fective background subtraction, you need to know what the
background is to
=
begin with and on a typical thermal day this is the average
temperature of
=
the air which has high spatial variability.
I think birds can see all those rising insects, which makes the
birds
t=
he best thermal indicators, if they can be bothered to fly where we
want
th=
em to.
=20
DH
TX

You cannot detect hot air from a distance by any infrared detector
(and
FLI=
R is infrared imaging). Obviously, your sales guy wasn't up to
speed with
p=
hysics.

Hot air emits infrard radiation. However, as emission and
absorption
coeffi=
cients are the same thing, the air inbetween the thermal and your
FLIR
will=
absorb all of this radiation, and you won't see anything on your
imager.
T=
hat's how physics works. The stories about people having seen
infrared
imag=
es of thermals are just urband legends.

Bert (who has been developing infrared sensors and systems for
more than
15=
years)
In the early 70's Wally Scott was flying a OD Green 1-34 ? for MIT
and they were trying to see dust particles in thermals in west texas.
with todays tech. it may be possible.any body else remember this.

Bert (who has been developing infrared sensors and systems for more than 15 years)

Yes, and the air in thermals isn't even very hot compared to the surrounding air - perhaps just fractions of a degree. The only significant difference the thermal has that you might be able to detect is its upward motion. Entrained dust or insects might work sometimes. I had a thermal full of corn stalks one time - very easy to see!

Mike