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 <[email protected]>wrote:
> 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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