cool pictures

[[email protected]]

I want to make pictures like this!

http://www.businessinsider.com.au/scientists-why-helicopters-are-so-loud-2014-2

They would be useful for glider airflow studies, and you're staring at a thermal detector, shear detector, whatever.

John Cochrane

[SoaringXCellence]

Looks a lot like the old Schlieren photography.

http://en.wikipedia.org/wiki/Schlieren_photography

You have to split the light source into offset phases or in this case photograph it against a known background. Both of those techniques are hard if not impossible to do at altitude in flight.

[[email protected]]

The choice of background was key for their method. The rocky backdrop has enough structure that small optical distortions can be picked out through image differencing. A blue sky would be problematic. Anyhow, if anyone wants to do a low pass in a gravel quarry I'm sure it would make a cool picture.

On Thursday, February 6, 2014 12:37:27 PM UTC-8, SoaringXCellence wrote:
> Looks a lot like the old Schlieren photography.
>
>
>
> http://en.wikipedia.org/wiki/Schlieren_photography
>
>
>
> You have to split the light source into offset phases or in this case photograph it against a known background. Both of those techniques are hard if not impossible to do at altitude in flight.

[Eric Bick (1DB)]

On Thursday, February 6, 2014 10:33:55 AM UTC-8, wrote:
> I want to make pictures like this!
>
>
>
> http://www.businessinsider.com.au/scientists-why-helicopters-are-so-loud-2014-2
>
>
>
> They would be useful for glider airflow studies, and you're staring at a thermal detector, shear detector, whatever.
>
>
>
> John Cochrane

It is schlieren, but updated to modern technology - read on in the Wikipedia article. This is synthetic schlieren - works against any known (meaning stable) background, the image is brought out through digital processing (the rocky background will make this easier, but in principle can be done against blue sky). What is of real interest is the ability to get a 3D image. However, there are limitations related to the 3D-ness of the flow field being studied - multiple cameras are needed to get the 3D part, partly to offset the 3D property of the air mass flow. The thicker and more complex this flow field, then the more difficult it is to bring out a meaningful image (showing specific features, rather than being washed out). For the helicopter image, compare the rotor down wash with the tip vortices. The vortices stand out clearly,while the down wash is without specific feature other than obviously being different from the less disturbed air. To know whether it is moving up or down, a sequence of frames is needed, such as from a video cam. However, the rotor downwash, perhaps similar to a thermal, does stand out. Whether this would work to detect thermals or shear lines, which have a refractive index different from the surrounding or neighboring air mass, is an interesting question. The sky is sort of the right type of background, and we see this when we see heat streamers off a hot surface against the sky. However, a cloudy sky might not work (noise due to changing background) Whether there is sufficient stability of the blue sky background and refractive index change in a thermal (or shear line) is one question. The other is having a camera and computer on board to process and display the images in real time ($XK?). It might work better using a ground background, but the image extraction from background requires an undisturbed background image to subtract from the disturbed - which is what they did with the helicopter photos. There are photos of just the background that are taken prior to the helicopter coming on scene and disturbing the air. Also a ranging question without multiple cameras. Really neat photos.
Eric Bick -

[StaPo]

similar interesting optical visualisation of airflow around your tug propeller you can attain with good camera in winter cold, stable weather, see http://www.marecek.cz/image/201005240011_bb.jpg
Whole article describing details and more photos are at
http://www.marecek.cz/view.php?cisloclanku=2010052401
but the article is in language you are probably not familiar with :-).