Coded aperture
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Coded apertures or coded-aperture masks are grids, gratings, or other patterns of materials opaque to various wavelengths of electromagnetic radiation. The wavelengths are usually high-energy radiation such as
Rationale
Imaging is usually done at optical wavelengths using lenses and mirrors. However, the energy of hard
In a coded aperture more complicated than a pinhole camera, images from multiple apertures will overlap at the 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
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.
- FZP = Fresnel Zone Plate
- ORA = Optimized RAndom pattern
- URA = Uniformly Redundant Array
- HURA = Hexagonal Uniformly Redundant Array[4]
- MURA = Modified Uniformly Redundant Array
- Levin[5]
Coded-aperture space telescopes
- Spacelab-2 X-ray Telescope XRT (1985)
- Rossi X-ray Timing Explorer (RXTE) – ASM (1995–2012)
- BeppoSAX – Wide Field Camera (1996–2002)
- INTEGRAL – IBIS and SPI (2002–present)
- Swift– BAT (2004–present)
- Ultra-Fast Flash Observatory Pathfinder mission (launched 2016) and UFFO-100 (its next generation) [6]
- Astrosat– CZTI (Launched in 2015)
- SVOM – ECLAIRs (Projected launch in 2022)
- In addition, the rotational modulation
See also
- Computational imaging § Coded aperture imaging
- Computational photography
- Deconvolution
- Pinhole camera
- Range imaging § Coded aperture
- Rotational modulation collimator
- Tomographic reconstruction
- X-ray computed tomography
References
- S2CID 117093492.
- doi:10.1086/180230.
- PMID 20174412.
- ^ Jean in 't Zand and Heiko Groeneveld. "coded aperture instruments designed for astronomical observations".
- doi:10.1145/1276377.1276464.)
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: CS1 maint: multiple names: authors list (link - ^ A next generation Ultra-Fast Flash Observatory (UFFO-100) for IR/optical observations of the rise phase of gamma-ray bursts