Coded aperture

Coded aperture

Coded Apertures or Coded-Aperture Masks are grids, gratings, or other patterns of materials opaque to various wavelengths of light. The wavelengths are usually high-energy radiation such as X-rays and gamma rays. By blocking and unblocking light in a known pattern, a coded "shadow" is cast upon a plane of detectors. Using computer algorithms, properties of the original light source can be deduced from the shadow on the detectors. Coded apertures are used in X- and gamma rays because their high energies pass through normal lenses and mirrors.

Contents

Rationale

Image formation, normally done at optical wavelengths by lenses and mirrors, must be done for non-focusable wavelengths via image modulation. The pinhole camera is the most basic form of such a modulation imager, but a single aperture mask can contain many holes, in one of several particular patterns, to improve the throughput for hard X-rays and γ-rays, for example. Multiple masks, at varying distances from a detector, add flexibility to this tool. Specifically the modulation collimator, invented by Minoru Oda, was used to identify the first cosmic X-ray source and thereby to launch the new field of X-ray astronomy in 1965. Many other applications in other fields, such as tomography, have since appeared.

In a coded aperture more complicated than a pinhole camera, images from multiple apertures will overlap at the plate or detector array. It is thus necessary to use a computational algorithm (which depends on the precise configuration of the aperture arrays) to reconstruct the original image. In this way a sharp image can be achieved without a lens. The image is formed from the whole array of sensors and is therefore tolerant to faults in individual sensors; on the other hand it accepts more background radiation than a focusing-optics imager (e.g., a refracting or reflecting telescope, and therefore is normally not favored at wavelengths where these techniques can be applied.

The coded aperture imaging technique is one of the earliest forms of computational photography and has a strong affinity to astronomical interferometry

Well known types of masks

Different mask patterns exhibit different image resolutions, sensitivities and background-noise rejection, and computational simplicities and ambiguities, aside from their relative ease of construction.

  • URA
  • MURA
  • Levin
  • Veeraraghavan

Coded-Aperture Space Telescopes


See Also

External links

  • Coded Aperture Imaging in High-Energy Astronomy [1]
  • In the news: [2]

Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • Computational photography — Computational imaging refers to any image formation method that involves a digital computer. Computational photography refers broadly to computational imaging techniques that enhance or extend the capabilities of digital photography. The output… …   Wikipedia

  • Light field — The light field is a function that describes the amount of light traveling in every direction through every point in space. Michael Faraday was the first to propose (in an 1846 lecture entitled Thoughts on Ray Vibrations ) that light should be… …   Wikipedia

  • Telescope — A telescope is an instrument designed for the observation of remote objects and the collection of electromagnetic radiation. The first known practically functioning telescopes were invented in the Netherlands at the beginning of the 17th century …   Wikipedia

  • Hadamard matrix — In mathematics, a Hadamard matrix is a square matrix whose entries are either +1 or −1 and whose rows are mutually orthogonal. This means that every two different rows in a Hadamard matrix represent two perpendicular vectors. Such matrices can… …   Wikipedia

  • Swift Gamma-Ray Burst Mission — Infobox Space telescope name = Swift Gamma Ray Burst Mission ( Swift ) caption = (credit: NASA) organization = NASA major contractors = alt names = nssdc id = location = orbit type = height = 600 km period = 90 min velocity = accel gravity =… …   Wikipedia

  • Great Observatories program — Four Great Observatories satellites NASA s series of Great Observatories satellites are four large, powerful space based telescopes. Each of the Great Observatories has had a similar size and cost at program outset, and each has made a… …   Wikipedia

  • Lichtfeld — Das Lichtfeld ist eine Funktion, welche die Lichtmenge beschreibt, die an jedem Punkt des dreidimensionalen Raums in alle Richtungen fällt. Inhaltsverzeichnis 1 Geschichte 2 Die Plenoptische Funktion 3 Das 4 D Lichtfeld …   Deutsch Wikipedia

  • BeppoSAX — Infobox Space telescope name = BeppoSAX caption = Artist s conception of BeppoSax in space (credit: the Agenzia Spaziale Italiana (ASI) and BeppoSAX Science Data Center (SDC)) organization = ASI / NIVR alt names = Satellite per Astronomia X… …   Wikipedia

  • Imaging spectrometer — An imaging spectrometer is an instrument used in the field of imaging spectroscopy to acquire a spectrally resolved image of an object or scene, often referred to as a datacube due to the three dimensional representation of the data. Namely, two… …   Wikipedia

  • AFP-675 — (Air Force Program 675) was a Space Shuttle experiment package that was carried into orbit on Discovery as part of STS 39.AFP 675 consisted of six experiment packages mounted on a pallet in the Discovery s cargo bay. The total weight of the… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”