4. Umbroscopy, diascopy

Readers may also wish to consult the article Visualization and optical measurements in aerodynamics. , § 1.2 in this treatise.

To carry out ombroscopic measurements, the part to be measured is illuminated from behind with a parallel or diffuse light beam, and the image of the part or its shadow, magnified or not, is measured on a detector (diascopy).

Three main methods are used for ombroscopic measurements:

• use of a static parallel web or bundle ;

• use of diffused lighting ;

• laser beam scanning.