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Thread: Thermal Seeking Instrument for Sailplane?

  1. #1

    Thermal Seeking Instrument for Sailplane?

    Hello all, sailplane enthusiast here. I have been entranced by the lure of infinite flight by means of thermal soaring, I've been looking to create a little instrument for my sailplane that searches for thermals by means of infrared imaging.

    My current idea is to have an onboard GPS running on a Raspberry Pi which takes an infrared map generated from an IR camera, "crops" out the regions with the largest thermal readings, and overlays them onto the GPS display.

    I know that a German paraglider took a FLIR up with him and claimed he achieved exactly what I described above, however, he was met with skepticism, because this method simply looks at the temperature differences on terrain and cannot see temperature differences in the ambient air (this remains the problem with my theory, as I am aware that thermals are mainly caused by the uneven heating of the Earth, however, other factors such as differences in terrain height creating updrafts which wouldn't be observed by my instrument)

    I am not aware of any other instrument that could be used to detect temperature differences in the ambient air save for something like a Doppler radar, which would require extensive (not to mention expensive!) FCC permission and a bunch of tinkering with radar which is beyond my understanding.

    I'm sure this idea isn't new, but I'm really hellbent on inventing something to give me some extra altitude for hours on end.

    I'd like y'alls thoughts on this idea, surely I'm not the only one who has thought about this? Is there any other way could I go about this besides thermal imaging?

    Thank you in advance, happy New Year from the sunny Rio Grande Valley in Texas.

  2. #2

    Join Date
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    To be distinguishable with an IR camera, two things must emit different intensities or wavelengths. I wonder how much of a temperature difference typically exists between a thermal and the air around it. I doubt clear air emits enough infrared to be detected. After all, the air is mostly empty space. Which explains why it conducts the radiation from the solar-heated ground.

  3. #3
    pylon500's Avatar
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    Not knocking the idea/concept, and as you say, must have been thought of before, but I can see a few problems to resolve before this works;

    •First off, it probably wont work while you're in a thermal, trying to look out through the temperature gradient, hoping to see the next thermol.

    •Yes, thermol lift is generated by the temperature difference 'in the local area', this difference is possibly less than the change in temperature with altitude.
    The problem I see being created here is that the sensor will have to look out horizontally (or slightly upwards) to avoid looking down into warmer air and just thinking there is lift everywhere.
    This could imply the need for a gyro stabilised sensor?

    •This is probably all reliant on there being clear enough air to see the minor temperature changes, as soon as there is haze, smoke, smog, dust, things get a bit harder.
    Actually, speaking dust, back in my Hang Gliding days, many pilots swore by the use of 'rose' coloured sunglasses, which they said let them see dust columns (thermols) better, but this was in outback Australia soaring.

    There are probably even more technical aspects to get around, that I haven't thought of here, but I wish you luck.

  4. #4
    Quote Originally Posted by pylon500 View Post
    Not knocking the idea/concept, and as you say, must have been thought of before, but I can see a few problems to resolve before this works;

    •First off, it probably wont work while you're in a thermal, trying to look out through the temperature gradient, hoping to see the next thermol.

    •Yes, thermol lift is generated by the temperature difference 'in the local area', this difference is possibly less than the change in temperature with altitude.
    The problem I see being created here is that the sensor will have to look out horizontally (or slightly upwards) to avoid looking down into warmer air and just thinking there is lift everywhere.
    This could imply the need for a gyro stabilised sensor?

    •This is probably all reliant on there being clear enough air to see the minor temperature changes, as soon as there is haze, smoke, smog, dust, things get a bit harder.
    Actually, speaking dust, back in my Hang Gliding days, many pilots swore by the use of 'rose' coloured sunglasses, which they said let them see dust columns (thermols) better, but this was in outback Australia soaring.

    There are probably even more technical aspects to get around, that I haven't thought of here, but I wish you luck.
    How about instead of looking at the air, look at the ground with a thermal camera, and just look for greater areas of thermal signatures.


    Sent from my iPhone using Tapatalk

  5. #5
    Remote thermal detection has been a "holy grail" topic for years, and much speculation and even experimental study as been expended on this topic.

    A quick summary is that detection via temperature differences are likely doomed to failure, not only due to the fact that air is transparent (non-emissive) in the bands (8-12 um) where FLIR systems operate, but also due to the very small or negligible temperatures differences in thermals above the very low boundary layer (moist air is lighter than dry air and water vapor content picked up at the surface may be more important than temperature in determining buoyancy).

    A more promising approach is likely to be detection of the backscatter from particulate matter picked up at the surface and carried aloft in the thermal. This is the basis for the laser radar detection exhibited in a number of experimental studies.

    A good review of the current state of the art in thermal structure can be found in the following NOAA paper;

    https://www.esrl.noaa.gov/csd/staff/...rmals_2014.pdf

    Note, this link is temporally unavailable during the Trump shutdown :-(

    Bob

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