Shadowgraph
Encyclopedia
Shadowgraph is an optical method that reveals non-uniformities in transparent
media like air, water, or glass. It is related to, but simpler than, the schlieren
and schlieren photography
methods that perform a similar function. Shadowgraph is a type of flow visualisation.
In principle, we cannot directly see a difference in temperature, a different gas, or a shock wave
in the transparent air. However, all these disturbances refract light rays, so they can cast shadows. The plume of hot air rising from a fire
, for example, can be seen by way of its shadow cast upon a nearby surface by the uniform sunlight
.
who first scientifically demonstrated the sunlight shadowgraph and Jean-Paul Marat
who first used it to study fire. A modern account of shadowgraphy is given by G.S. Settles.
research, ballistics
, explosions, and in the testing of glass
.
field in the transparent medium under study. Once the distance from the transparent disturbance to the cast shadow becomes too large, then the shadow no longer constitutes a useful representation of the disturbance that caused it.
on the Three Blind Mouseketeers (1936) Silly Symphonies
.
Transparency and translucency
In the field of optics, transparency is the physical property of allowing light to pass through a material; translucency only allows light to pass through diffusely. The opposite property is opacity...
media like air, water, or glass. It is related to, but simpler than, the schlieren
Schlieren
Schlieren are optical inhomogeneities in transparent material not visible to the human eye. Schlieren physics developed out of the need to produce high-quality lenses devoid of these inhomogeneities. These inhomogeneities are localized differences in optical path length that cause light deviation...
and schlieren photography
Schlieren photography
Schlieren photography is a visual process that is used to photograph the flow of fluids of varying density. Invented by the German physicist August Toepler in 1864 to study supersonic motion, it is widely used in aeronautical engineering to photograph the flow of air around objects...
methods that perform a similar function. Shadowgraph is a type of flow visualisation.
In principle, we cannot directly see a difference in temperature, a different gas, or a shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
in the transparent air. However, all these disturbances refract light rays, so they can cast shadows. The plume of hot air rising from a fire
Fire
Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....
, for example, can be seen by way of its shadow cast upon a nearby surface by the uniform sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
.
Sunlight shadowgraph
This technique is as old as nature itself. For example, some aquatic predators detect their transparent prey by way of their shadows cast upon the ocean floor. Nevertheless it was Robert HookeRobert Hooke
Robert Hooke FRS was an English natural philosopher, architect and polymath.His adult life comprised three distinct periods: as a scientific inquirer lacking money; achieving great wealth and standing through his reputation for hard work and scrupulous honesty following the great fire of 1666, but...
who first scientifically demonstrated the sunlight shadowgraph and Jean-Paul Marat
Jean-Paul Marat
Jean-Paul Marat , born in the Principality of Neuchâtel, was a physician, political theorist, and scientist best known for his career in France as a radical journalist and politician during the French Revolution...
who first used it to study fire. A modern account of shadowgraphy is given by G.S. Settles.
Applications
Applications of shadowgraphy in science and technology are very broad. It is used in aeronautical engineering to see the flow about high-speed aircraft and missiles, as well as in combustionCombustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
research, ballistics
Ballistics
Ballistics is the science of mechanics that deals with the flight, behavior, and effects of projectiles, especially bullets, gravity bombs, rockets, or the like; the science or art of designing and accelerating projectiles so as to achieve a desired performance.A ballistic body is a body which is...
, explosions, and in the testing of glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
.
Shadowgram
According to F. J. Weinberg, the result of applying the shadowgraph technique should be known as a shadowgram. A shadowgram is not a focused image, rather it is a mere shadow. In the shadowgram, the differences in light intensity are proportional to the second spatial derivative (Laplacian) of the refractive indexRefractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
field in the transparent medium under study. Once the distance from the transparent disturbance to the cast shadow becomes too large, then the shadow no longer constitutes a useful representation of the disturbance that caused it.
Cartoons
The Shadowgraph, and shadowgram have been used in animation, where they reinforce the cartoon's realism. One first use was made by Disney StudiosWalt Disney Pictures
Walt Disney Pictures is an American film studio owned by The Walt Disney Company. Walt Disney Pictures and Television, a subsidiary of the Walt Disney Studios and the main production company for live-action feature films within the Walt Disney Motion Pictures Group, based at the Walt Disney...
on the Three Blind Mouseketeers (1936) Silly Symphonies
Silly Symphonies
Silly Symphonies is a series of animated short subjects, 75 in total, produced by Walt Disney Productions from 1929 to 1939, while the studio was still located at Hyperion Avenue in the Silver Lake district of Los Angeles...
.