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
Flow visualization or flow visualisation in fluid dynamics is used to make the flow patterns visible, in order to get qualitative or quantitative information on them.
Overview
Flow visualization is the art of making flow patterns visible. ...
.
In principle, a difference in temperature, a different gas, or a
shock wave in the transparent air cannot be seen by the human eye or cameras. 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
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
.
Sunlight shadowgraph
Some aquatic predators detect their transparent prey by way of their shadows cast upon the ocean floor. It was
Robert Hooke
Robert Hooke FRS (; 18 July 16353 March 1703) was an English polymath active as a scientist, natural philosopher and architect, who is credited to be one of two scientists to discover microorganisms in 1665 using a compound microscope that ...
who first scientifically demonstrated the sunlight shadowgraph and
Jean-Paul Marat
Jean-Paul Marat (; born Mara; 24 May 1743 – 13 July 1793) was a French political theorist, physician, and scientist. A journalist and politician during the French Revolution, he was a vigorous defender of the ''sans-culottes'', a radical ...
who first used it to study fire. A modern account of shadowgraphy is given by
Gary S. Settles
Gary may refer to:
* Gary (given name), a common masculine given name, including a list of people and fictional characters with the name
* Gary, Indiana, the largest city named Gary
Places
;Iran
*Gary, Iran, Sistan and Baluchestan Province
;Un ...
.
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
combustion research,
ballistics
Ballistics is the field of mechanics concerned with the launching, flight behaviour and impact effects of projectiles, especially ranged weapon munitions such as bullets, unguided bombs, rockets or the like; the science or art of designing and a ...
,
explosions
An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Supersonic explosions created by high explosives are known ...
, and in the testing of
glass. Ideal for identification of flow patterns.
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
In mathematics, the Laplace operator or Laplacian is a differential operator given by the divergence of the gradient of a scalar function on Euclidean space. It is usually denoted by the symbols \nabla\cdot\nabla, \nabla^2 (where \nabla is the ...
) of the
refractive index 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 Studios
The Walt Disney Studios is an American film and entertainment studio, and is the Studios Content segment of the Walt Disney Company. Based mainly at the namesake studio lot in Burbank, California, the studio is best known for its multifaceted ...
on the ''
Three Blind Mouseketeers
''Three Blind Mouseketeers'' is a Silly Symphonies cartoon based on the nursery rhyme ''Three Blind Mice'' and the 1844 novel ''The Three Musketeers'' by Alexandre Dumas. Directed by Dave Hand and Jack Cutting, it stars Billy Bletcher.
Plot
The ...
'' (1936) in the series of animated short films
Silly Symphonies.
[Russel Merritt & JB Kaufman, ''Walt Disney's Silly Symphonies : A Companion to the classic cartoons series'', Italy:La Cinecita del Friuli, 2006, p 46]
Postcards
Additionally the term ''Shadowgraph'' was used by English postcard publishers E.T.W. Dennis & Sons Ltd. of London and Scarborough for a series of 'Hold up to the Light' postcards in the 1950s. In these a saucy image can be seen through what seems an innocent picture when a light is shone through the card.
Gallery
See also
*
Laser schlieren deflectometry
*
Mach–Zehnder interferometer
*
Optical comparator
*
Schlieren
*
Schlieren photography
References
{{Commons category, Shadowgraph
Imaging