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.