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

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

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

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

This has been one of my favorite subject since the early 1980's.
Everyone's comments have been great and useful!
Let's review some of the possiblites.
Because thermals are equated with heat the first thing most people jump to is infrared. Mike the Strike has pointed out that thermals only have a fraction of a degree difference from surrounding air. TW and David Hurst have also pointed out that air is a very poor radiator of infrared and is invisible to commercial thermal cameras. This is all true.
However I would ask Tom (2G) to please tell us where he heard or read of the military night vision system user seeing thermals over Iraq. That might be a case of intense desert thermals near the ground. Scientific aircraft monitoring has shown that thermals often are cooler than the local air above halfway to cloudbase.
I would also like to ask Jonathan St.Cloud to dig up the reference he had about an Apache trainee. A search for "Apache" in the Soaring mag database does not find anything useful.
Next subject is LIDAR. Lidar is laser radar. It has been shown to be able to detect thermals since the early 1970's. It does this by sensing backscatter from dust and pollen in the air. Very clean air is harder to see. See articles by Eloranta (University of Wisconsin) and many others. Problems are many: the required laser power is large, 100K Watts+ in the pulse, the light-gathering optics are physically large (think 8 inch diameter telescope)as pointed out by someone here, and the cost is huge. You can get a nice little laser that has the required power and is small enough but it costs $75K. Then add the complex electronics that generate and detect picosecond pulses and you see the real-world problems that make this a difficult instrument to cram into a sailplane. It can be done if you have lots of money to spend.
Next possibilty is RADAR. Most of the radar schemes detect bugs.(Raptors most likely see bugs in the air with their superior vision.) No bugs today and your expensive, bulky radar won't work today. A better choice is something called FM-CW radar. This has been shown to work at less power by detection of the moisture differences between the thermal edge and the surrounding air. This scheme may not work in very dry environnments. The amount of power required is in the hundreds of Watts. The antenna is likely to present a very draggy problem.
I won't bore you with other possiblites but there are some that have not been adequetly explored. I'm working on a few. Technology gets us closer every year. It will happen eventually. This will not make soaring boring at all. It's just another useful tool to help you. Probably the first thing to come out will be a short range solution. Many times you can see a cloud, get to it and find nothing. Then you explore all areas under the cloud and on one corner there is lift. A 1000 foot range detector would help greatly in this situation.

Soaring June 1993, article named "Chasing Ghosts". The author said he could see thermals during the day while, training in "The Bag", so he was using the monocle with PNVS. Not sure what PNVS is but it sounds like a combo of night vision and IR?

On Wednesday, October 5, 2016 at 11:27:30 AM UTC-7, Soartech wrote:

I would also like to ask Jonathan St.Cloud to dig up the reference he had about an Apache trainee.

Did a bit of research http://www.lockheedmartin.com/us/pro...Arrowhead.html very disappointing to find that this system is optimized for target detection, not thermal detection, although according to the June, 1993, article in Soaring it can detect thermals, but it did not say at what distance. Maybe an Apache pilot is on RAS?

I'm also a fan.

No, it won't turn the sport into a video game, any more than vario and GPS did. Flying -- and racing -- airplanes without engines will always be a challenge.

It will be the single greatest increase in performance since fiberglass (also loudly predicted to kill the sport).

Thermal detectors will end start gate roulette, gaggling and leeching and team flying. There is no need to wait for other gliders if you can detect thermals on your own.

Thermal detectors will also enhance safety. Finding that last thermal might help an outlining. More importantly, if you really know there are NO thermals out there, you get busy with the business of landing!

Even 200 feet will be of immense use. Really, all the great team flyers are getting for their efforts is sampling air 200 feet away. Imagine if you had two guys 200 feet ahead one on each side 45 degrees -- any of us could win the worlds. Think of how many great contests have been won or lost by missing one thermal by a few hundred feet.

Contrary to earlier posts, so what if it doesn't work all the time! Give me a thermal detector that works 200 feet out 1/4 of the time and I can win any contest!

More physical principles:

Doppler Lidar, of course. Somewhere I saw the military is working on a portable lidar based system that detects crosswinds to make shooting more accurate. That's just what we need.

Non-doppler lidar. Thermals have more dust in them than surrounding air. See the concentration of dust, bugs, etc. and you know where the thermal is.

Radar, as mentioned. Tuned to bugs, birds, moisture gradients, etc.

Passive radar. Radar needs power. But why shine your own light when the FAA does it for you? Monitoring the primary and return echoes you should be able to see what's out ahead with no primary source.

Shimmer. As reported here, Boeing was working on a system to process visual images for shimmer to see clear air turbulence. Set up video camera to take pictures every second or two, software to compare the images, and enhance shimmer induced turbulence, thus seeing thermal structure.

More optical. Process optical images to see birds! (and other gliders) Again, take two optical images a few seconds apart, signal process to correct for glider motion, then show anything that's moving. (The last two, since they only involve taking pictures, would be arguably legal under US rules too. SHHH. )

Humidity. Infra-red cameras tuned to moisture frequencies, like the satellite moisture channel. Thermals are more moist than the surrounding environment.

You don't need to see motion, you only need to see structure of the air and you can deduce motion.

Bring it on!

John Cochrane (Flame suit on)

On Wednesday, October 5, 2016 at 2:04:16 PM UTC-7, John Cochrane wrote:
I'm also a fan.

No, it won't turn the sport into a video game, any more than vario and GPS did. Flying -- and racing -- airplanes without engines will always be a challenge.

It will be the single greatest increase in performance since fiberglass (also loudly predicted to kill the sport).

Thermal detectors will end start gate roulette, gaggling and leeching and team flying. There is no need to wait for other gliders if you can detect thermals on your own.

Thermal detectors will also enhance safety. Finding that last thermal might help an outlining. More importantly, if you really know there are NO thermals out there, you get busy with the business of landing!

Even 200 feet will be of immense use. Really, all the great team flyers are getting for their efforts is sampling air 200 feet away. Imagine if you had two guys 200 feet ahead one on each side 45 degrees -- any of us could win the worlds. Think of how many great contests have been won or lost by missing one thermal by a few hundred feet.

Contrary to earlier posts, so what if it doesn't work all the time! Give me a thermal detector that works 200 feet out 1/4 of the time and I can win any contest!

More physical principles:

Doppler Lidar, of course. Somewhere I saw the military is working on a portable lidar based system that detects crosswinds to make shooting more accurate. That's just what we need.

Non-doppler lidar. Thermals have more dust in them than surrounding air. See the concentration of dust, bugs, etc. and you know where the thermal is..

Radar, as mentioned. Tuned to bugs, birds, moisture gradients, etc.

Passive radar. Radar needs power. But why shine your own light when the FAA does it for you? Monitoring the primary and return echoes you should be able to see what's out ahead with no primary source.

Shimmer. As reported here, Boeing was working on a system to process visual images for shimmer to see clear air turbulence. Set up video camera to take pictures every second or two, software to compare the images, and enhance shimmer induced turbulence, thus seeing thermal structure.

More optical. Process optical images to see birds! (and other gliders) Again, take two optical images a few seconds apart, signal process to correct for glider motion, then show anything that's moving. (The last two, since they only involve taking pictures, would be arguably legal under US rules too. SHHH. )

Humidity. Infra-red cameras tuned to moisture frequencies, like the satellite moisture channel. Thermals are more moist than the surrounding environment.

You don't need to see motion, you only need to see structure of the air and you can deduce motion.

Bring it on!

John Cochrane (Flame suit on)

John, I completely agree. Many of our most important scientific advances are based on improving our ability to "see" the world around us. Telescopes, microscopes, radar, the list goes on and on. I'm eagerly awaiting improvements in thermal detection for sailplanes. I don't see it taking away the fun or the magic. There's still lots to explore.

Craig