Remote thermal detection

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.

On Monday, October 3, 2016 at 8:12:38 AM UTC-5, ND wrote:
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?

It's really not a HUD that you want, it's a HMD (Helmet Mounted Display) - now being used in most fighters (look up JHMCS). A HUD only covers a small piece of sky in front of you - it's really just a fancy gunsight. A HMD is more like a super Google Glass - puts the appropriate data in front of your eyes wherever you are looking. So for example, in a hypothetical glider-optimized BHMD (Bucket Hat Mounted Display), you would see airspeed, altitude, vario, heading, a pointer to the next turnpoint, reachable airfields, FLARM and ADS-B aircraft, etc; essentially you never have to look down into the cockpit.

With the head tracking tech used for VR, it's not really too far fetched - but we may need bigger canopies to fit over our helmets!

Kirk
66

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

Corn Devils. Very common in the spring and fall in the Midwest

While seeing thermals with IR camera is close to impossible, you can at least see hot spots on the ground:

http://www.paragliding.de/en/thermik...rmebildkamera/

Apparently works only close range.

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)

Sorta like A-10 pilots didn't have night vision, but, they looked at the FLIR display from missles as an alternate. Crude, but it worked.

Hey, use what ya got........