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Ideas requested for making distant air visible

  1. Mar 29, 2016 #1
    This is a really tough problem. I have spent years studying and experimenting about this. Outdoor air contains tracers such as dust, pollen, etc. called aerosols. It is possible to use LIDAR to detect these at distances in the scale of kilometers away. But lasers of the power to use at even 1km. are very expensive and and the required light gathering power of the reciever requires telescopes of 8 inch or larger diameter and photon counting.
    I would like to use optics with a diameter of 3 inches maximum. I need a range of 1000 feet or more. A passive system using daylight would be preferable to an active system. I am aware that the polarization of light is changed by aerosols but my experiments in finding this effect (polaization filter and image processing) have not been successful. ANY other ideas about this topic are apreciated!
  2. jcsd
  3. Mar 29, 2016 #2
    Some aerosols are a lot more visible in the near infrared - and efficient IR lasers are less expensive.
    I don't know if that leads to a solution, but it's what came to mind.
  4. Apr 1, 2016 #3

    jim mcnamara

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    Staff: Mentor

    .Scott is probably on to what you you need. If you have IR absorption/reradiation spectra for the chemical species in question you may want. The other issue is 'why?' You want to use reflected light. Transmitted light is also a viable answer. Then set up two stations - transmitter and receiver.

    Would it not be simpler to use existing data sources - unless you want to examine a geographically limited point source? Perhaps if you explained what (NOT how you thought to do it) your goal is, then one of the well informed people on the forum probably already knows the answer. Give it a try.

    Example maybe like this: 'I want to pinpoint emissions of XXX from location YYY with a home built system.'
  5. Apr 11, 2016 #4
    I was thinking of a balloon or drone lifting ether a retro reflector, or maybe a pulsed IR light source
    on the far side of the target. The reflector would give you two passes through the gas,
    but the single point source may cut down on the noise.
  6. Apr 11, 2016 #5


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    Science Advisor

    You know the air is there, why make it visible? Are you interested in CAT or aerosols?

    Whatever technique you use will provide information from the whole path length. You need some way to focus on different distances.

    A frequency swept lidar or radar system, (chirp), where the transmitted signal is used to down convert the received signal, will give you a plot of scatterer density against range for all selected points on the path.

    You could fly a drone down the line, then back, sampling the aerosols on the way.
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