speckleefekt

The speckle effect is a granular interference pattern that appears when coherent light interacts with a rough surface or a scattering medium and is detected by an imaging system with spatial coherence. The pattern results from many micro‑scattered waves that interfere constructively and destructively, producing bright and dark spots that are random yet deterministic for a given geometry and wavelength.

The characteristic speckle size depends on the wavelength and the imaging aperture; roughly, it scales with lambda divided by the effective aperture. In fully developed speckle, the intensity distribution follows an exponential (negative exponential) law, and the pattern changes when the viewing angle, wavelength, or the surface moves. Because speckle is tied to the coherent nature of the illumination and the surface roughness, it is common across many imaging modalities, including laser projection, holography, ultrasound, and synthetic aperture radar (SAR).

In imaging, speckle often degrades contrast and resolution, acting as noise that obscures fine details. However, it can also be exploited for measurement and visualization: speckle tracking and correlation methods estimate motion or velocity; speckle statistics reveal surface roughness; SAR uses multi-look processing to reduce speckle and extract information about terrain. Despeckling techniques, spatial or temporal averaging, and diversity in illumination or polarization are common strategies to manage speckle.

See also: laser speckle, coherent imaging, speckle variance, speckle tracking.