Astrophysics (index)

Speckle Suppression

(methods of reducing noise in telescope observations)

Speckle Suppression is the reduction of Speckle Noise in an image produced by a telescope. Speckle noise is a general term that includes signal noise inherent in the instrument.

Adaptive Optics (AO) can be classified as speckle suppression, as do attempts to realize better Angular Resolution than indicated by the Rayleigh criterion. For the latter, the following practices are of use:

  • imaging using more than one Aperture size and/or shape. A single telescope may be modified with masks, or different telescopes can be used (Apodization). This results in a different Point-Spread Function (PSF) and Airy Disk.
  • noting and using the Polarization of the light.
  • changing the aim of the telescope (Angular Differential Imaging).
  • observing different parts of the spectra (Spectral Differential Imaging or SDI).
  • PSF Fitting - untangling overlapping Airy disks.

Combining information from such multiple images can be used to reveal detail otherwise hidden.

Speckle suppression has value for many types of observation, and is of particular interest when used in conjunction with Coronagraphs for imaging objects very near stars such as Extra Solar Planets or Protoplanetary Disks. The term also applies to additional techniques for producing a good Signal-To-Noise Ratio (SNR) in Direct Imaging exoplanets. Nulling is using Interferometry, specifically light interference patterns to place a dark band over the star. If multiple such images are taken, varying factors, processing can be devised produce an image taking advantage of the information each individual image captures.


Referenced by:
Angular Resolution
Keck Planet Imager And Characterizer (KPIC)
N-Point Function
Subaru Telescope