Remote thermal detection

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

On Sunday, October 2, 2016 at 8:04:39 AM UTC-7, Jonathan St. Cloud wrote:
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

A helicopter pilot flying in the first Iraq war reported on seeing thermals clearly visible in daylight using his night vision FLIR. Kind of tough to thermal a chopper, however.

Tom

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 |

Systems which transmit power such lidars need to throw out large amounts
of energy to get even tiny detectable returns. Not good for battery based
power supplies. Batteries are not really that power dense and I'm no where

near as confident that we will see the really big step forward that most
tech
pundits are predicting.

Thermal imaging needs a fair bit of power to get a reasonable temperature
difference to the warm air your trying to detect. Again this is too power
hunger for batteries.

Even if you could realise these they both suffer from the basic flaw, in
that
they tell what's happening 10k down track while you're 10+minutes away
from actually getting to it. By the time you arrive it' frequently
changed.

My vision of the next step in remote thermal detection follows a different
tac.
Computer CPU processing will certainly continue its quite staggering
increase
in capacity. So I reckon we could see a super high fidelity RASP. This
would
be constant refining its numerical predictions based on real time
observations
from both you flight and others via flarm. It would also use historical
"big
data" previously collected from hundreds if not thousands of flights in the

same area to further tune the predictions with likely thermal nucleation
locations. Now we would have a systems which is actively modelling the
atmosphere in a strip say 50k down track and 10 k wide, in real time. The
really intriguing aspect of this is that it's producing predictions both in
terms
of what thermals will be further down the intended track and what strength

they will be when you actually arrive.

An imagination can be a scary thing.

Fraser

I have many times used ridge and thermal lift hime flying a helicopter.

On Sunday, October 2, 2016 at 12:19:12 PM UTC-7, 2G wrote:

A helicopter pilot flying in the first Iraq war reported on seeing thermals clearly visible in daylight using his night vision FLIR. Kind of tough to thermal a chopper, however.

Tom

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)

A HUD would be cool, but don't you think it would be a bit of a problem, or annoyance, keeping track of the towplane on tow, finding oncoming traffic, especially on the ridge, and obstructing part of your view in general? i mean it's a cool idea, but is it practical?

On Friday, September 30, 2016 at 3:17:59 PM UTC-4, Jonathan St. Cloud wrote:
Really, why is that? Not that this applies to you, but I have noticed that when new technology comes along so do the naysayers, GPS, Flarm, stealth Flarm, "entertainment system computers..." "This is the end of our sport".....

Having been an offshore sailor and glider pilot for many years, I can tell you that whatever you invent, it will still take a sharp mind and earned skills to guide an airplane or sailboat using just the energy in the atmosphere.

Personally, I want a Hud projected onto the canopy.


On Friday, September 30, 2016 at 6:33:01 AM UTC-7, wrote:
On Friday, September 30, 2016 at 6:21:27 AM UTC-5, Tony wrote:
Awesome I can't wait!!

Here comes the end of this world as we know i