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Thread: Single leading light.

  1. #1
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    Default Single leading light.

    This acts as a pair of leading marks - but can be bolted to a wall!!


    The better part of thirty years ago I met one of these as the entry to Shotley Point Marina. I'd guessed at how this might work - and now I know.....

    I'd much rather lay in my bunk all freakin day lookin at Youtube videos .

  2. #2
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    Default Re: Single leading light.

    Cool! Thanks for posting.
    "If it ain't broke, you're not trying." - Red Green

  3. #3
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    Default Re: Single leading light.

    sure to play havoc with anti aliasing filters
    Simpler is better, except when complicated looks really cool.

  4. #4
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    Default Re: Single leading light.

    I'd never heard of them. Good video though. Ta.
    ​In a world full of wonders, man invented boredom.

  5. #5
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    Default Re: Single leading light.

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    This acts as a pair of leading marks - but can be bolted to a wall!!


    The better part of thirty years ago I met one of these as the entry to Shotley Point Marina. I'd guessed at how this might work - and now I know.....

    That's the principal of LASER Phase Doppler Anemometers, we called them interference fringes. They can be "injected with" a signal from a Bragg cell to determine flow velocity and vector of minute seed particles for precise hydraulic measurements.

    Using blue -green LASER light 514/488 NM at wave height. works great.
    PaulF

  6. #6
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    Default

    That's brilliant!

    The idea of how to creat a moiré pattern that forms arrows, though, makes my head hurt.
    You would not enjoy Nietzsche, sir. He is fundamentally unsound. — P.G. Wodehouse (Carry On, Jeeves)

  7. #7
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    Default Re: Single leading light.

    The nitty gritty, if your so inclined.

    https://en.wikipedia.org/wiki/Wave_interference
    PaulF

  8. #8
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    Default Re: Single leading light.

    some tests:
    Phase‐Doppler anemometer measurement of bubble concentrations in laboratory‐simulated breaking waves

    William E. Asher
    Paul J. Farley



    First published: 15 April 1995
    https://doi.org/10.1029/95JC00068
    Citations: 27

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    Abstract

    Breaking waves and the bubble plumes they generate are thought to be an important air‐sea gas transfer mechanism. In order to compare bubble populations generated by laboratory‐simulated breaking waves and model bubble‐mediated airwater gas transfer in a whitecap simulation tank (WST), it was necessary to measure bubble sizes and water velocities. The phase‐Doppler anemometer (PDA) is well suited for this research because it provides simultaneous measurement of the size and velocity of a bubble. Bubble concentrations can be estimated from PDA data records with an accuracy of 15% (±1σ) for bubbles with radii in the range of 50 to 160 μm and 40% (±1σ) for larger bubbles. However, estimation of bubble concentrations requires knowledge of the instrument‐scattering cross section as a function of bubble radius. A procedure for calibrating the scattering cross section of the PDA was developed and tested. The PDA was then used to measured size‐segregated bubble concentrations in the WST as a function of depth, water temperature, total concentration of dissolved gas, and surfactant concentration. These measurements show that increases in dissolved gas concentration or decreases in water temperature increase bubble concentrations. Surfactants increased the concentration of small bubbles. Comparison of the WST bubble populations to measurements of oceanic bubbles showed that the two agree within the experimental uncertainty of the PDA.
    PaulF

  9. #9
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    Default Re: Single leading light.

    I love obscure stuff like this. Thanks!

  10. #10
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    Default Re: Single leading light.

    It looks simple - no moving parts, no computers. Why isn't it used more often?
    Will

  11. #11
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    Default Re: Single leading light.

    Quote Originally Posted by willmarsh3 View Post
    It looks simple - no moving parts, no computers. Why isn't it used more often?
    Maybe because 2 towers (what we in the US call a range) works well - with no power needs? This is still cool.
    "If it ain't broke, you're not trying." - Red Green

  12. #12
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    Default

    Quote Originally Posted by Garret View Post
    Maybe because 2 towers (what we in the US call a range) works well - with no power needs? This is still cool.

    As long as one has enough fore-and-aft space betwixt the two range lights.
    You would not enjoy Nietzsche, sir. He is fundamentally unsound. — P.G. Wodehouse (Carry On, Jeeves)

  13. #13
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    Default Re: Single leading light.

    Quote Originally Posted by Nicholas Carey View Post
    As long as one has enough fore-and-aft space betwixt the two range lights.
    Kind of like the difference between "iron sights" on a firearm, where sight radius (distance between front and rear sights) makes a great difference in accuracy, and an "optical" sight (telescope (any magnification), or what are known as "reflex" sights).
    When you can take the pebble from my hand, it will be time for you to leave.

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