speckle

n.
A speck or small spot, as a natural dot of color on skin, plumage, or foliage.

[Middle English spakle.]

speckle speck'le v.

The generation of a random intensity distribution, called a speckle pattern, when light from a highly coherent source, such as a laser, is scattered by a rough surface or inhomogeneous medium. See also Laser.

The surfaces of most materials are extremely rough on the scale of an optical wavelength (approximately 5 × 10⁻⁷ m). When nearly monochromatic light is reflected from such a surface, the optical wave resulting at any moderately distant point consists of many coherent wavelets, each arising from a different microscopic element of the surface. Since the distances traveled by these various wavelets may differ by several wavelengths if the surface is truly rough, the interference of the wavelets of various phases results in the granular pattern of intensity called speckle. If a surface is imaged with a perfectly corrected optical system, diffraction causes a spread of the light at an image point, so that the intensity at a given image point results from the coherent addition of contributions from many independent surface areas. As long as the diffraction-limited point-spread function of the imaging system is broad by comparison with the microscopic surface variations, many dephased coherent contributions add at each image point to give a speckle pattern.

The basic random interference phenomenon underlying laser speckle exists for sources other than lasers. For example, it explains radar “clutter,” results for scattering of x-rays by liquids, and electron scattering by amorphous carbon films. Speckle theory also explains why twinkling may be observed for stars, but not for planets. See also Coherence; Diffraction; Interference of waves; Twinkling stars.

In metrology, the most obvious application of speckle is to the measurement of surface roughness. If a speckle pattern is produced by coherent light incident on a rough surface, then surely the speckle pattern, or at least the statistics of the speckle pattern, must depend upon the detailed surface properties. An application of growing importance in engineering is the use of speckle patterns in the study of object displacements, vibration, and distortion that arise in nondestructive testing of mechanical components.

Astronomical speckle interferometry is a technique for obtaining spatial information on astronomical objects at the diffraction-limited resolution of a telescope, despite the presence of atmospheric turbulence. Speckle interferometry techniques have proven to be an invaluable tool for astronomical research, allowing studies of a wide range of scientifically interesting problems. They have been widely used to determine the separation and position angle of binary stars, and for accurate diameter measurements of a large number of stars, planets, and asteroids. Speckle imaging techniques have successfully uncovered details in the morphology of a range of astronomical objects, including the Sun, planets, asteroids, cool giants and supergiants, young stellar objects, the supernova SN1987A in the Large Magellanic Cloud, Seyfert galaxies, and quasars. See also Binary star; Interferometry.

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verb

To mark with many small spots: bespeckle, besprinkle, dapple, dot, fleck, freckle, mottle, pepper, speck, sprinkle, stipple. See marks.

or Specklin, Daniel
(1536–89)

Alsatian architect, engineer, and cartographer. He designed fortifications in numerous places, and wrote an important treatise, Architectura von Vestungen (Architecture of Fortresses) (1584), which contains a design for an ideal town, the plan of which is like a wheel, with houses laid out along the ‘spokes’: his ideas about town plans and town fortifications remained influential until well into C18. He also wrote Collectanea (1587), an architectural history of Strasbourg, with autobiographical information.

Bibliography

• Kruft (1994)
• Oud-Holland, xix (1911), 111–17
• Rosenau (1975)
• Jane Turner (1996)

The full bibliography for this book is available to download as a pdf file.
Download the bibliography for A Dictionary of Architecture and Landscape Architecture (PDF: 1.2MB)

Dansk (Danish)
n. - stænk, plet
v. tr. - plette

Nederlands (Dutch)
spikkel, spikkelen

Français (French)
n. - petite tache, moucheture
v. tr. - tacheter, moucheter, marquer

Deutsch (German)
n. - Tupfen, Sprenkel
v. - sprenkeln

Ελληνική (Greek)
n. - στίγμα, πιτσίλα, μικροκηλίδα
v. - (δια)στίζω, πιτσιλίζω

Italiano (Italian)
macchiolina, punteggiare

Português (Portuguese)
n. - mancha pequena (f), ponto (m)
v. - pintar, salpicar

Русский (Russian)
пятнышко, веснушка, мушка, метка

Español (Spanish)
n. - manchita, puntito, peca
v. tr. - manchar, motear, salpicar

Svenska (Swedish)
n. - fläck, stänk
v. - fläcka ned, sätta en fläck på

中文（简体）(Chinese (Simplified))
小的斑点, 斑点, 褐斑, 弄上斑点, 沾上斑点, 弄成斑纹

中文（繁體）(Chinese (Traditional))
n. - 小的斑點, 斑點, 褐斑
v. tr. - 弄上斑點, 沾上斑點, 弄成斑紋

한국어 (Korean)
n. - 작은 반점, 얼룩, 반문
v. tr. - ~에 반점을 짓다, 얼룩덜룩하게 하다, 얼룩지게 하다

日本語 (Japanese)
n. - 小斑点, スペックル, 斑点
v. - 小斑点を付ける, 斑入りにする

العربيه (Arabic)
‏(الاسم) بقعه, نقطه, رقطه (فعل) رقط, نقط‏

עברית (Hebrew)
n. - ‮נקודה, כתם זעיר‬
v. tr. - ‮נימר בכתמים או בטלאים‬

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