57,353 research outputs found
The Ultraviolet Imaging Telescope: Instrument and Data Characteristics
The Ultraviolet Imaging Telescope (UIT) was flown as part of the Astro
observatory on the Space Shuttle Columbia in December 1990 and again on the
Space Shuttle Endeavor in March 1995. Ultraviolet (1200-3300 Angstroms) images
of a variety of astronomical objects, with a 40 arcmin field of view and a
resolution of about 3 arcsec, were recorded on photographic film. The data
recorded during the first flight are available to the astronomical community
through the National Space Science Data Center (NSSDC); the data recorded
during the second flight will soon be available as well. This paper discusses
in detail the design, operation, data reduction, and calibration of UIT,
providing the user of the data with information for understanding and using the
data. It also provides guidelines for analyzing other astronomical imagery made
with image intensifiers and photographic film.Comment: 44 pages, LaTeX, AAS preprint style and EPSF macros, accepted by PAS
Separating true range measurements from multi-path and scattering interference in commercial range cameras
Time-of-flight range cameras acquire a three-dimensional image of a scene simultaneously for all pixels from a single viewing location. Attempts to use range cameras for metrology applications have been hampered by the multi-path problem, which causes range distortions when stray light interferes with the range measurement in a given pixel. Correcting multi-path distortions by post-processing the three-dimensional measurement data has been investigated, but enjoys limited success because the interference is highly scene dependent. An alternative approach based on separating the strongest and weaker sources of light returned to each pixel, prior to range decoding, is more successful, but has only been demonstrated on custom built range cameras, and has not been suitable for general metrology applications. In this paper we demonstrate an algorithm applied to both the Mesa Imaging SR-4000 and Canesta Inc. XZ-422 Demonstrator unmodified off-the-shelf range cameras. Additional raw images are acquired and processed using an optimization approach, rather than relying on the processing provided by the manufacturer, to determine the individual component returns in each pixel. Substantial improvements in accuracy are observed, especially in the darker regions of the scene
Blur aware metric depth estimation with multi-focus plenoptic cameras
While a traditional camera only captures one point of view of a scene, a
plenoptic or light-field camera, is able to capture spatial and angular
information in a single snapshot, enabling depth estimation from a single
acquisition. In this paper, we present a new metric depth estimation algorithm
using only raw images from a multi-focus plenoptic camera. The proposed
approach is especially suited for the multi-focus configuration where several
micro-lenses with different focal lengths are used. The main goal of our blur
aware depth estimation (BLADE) approach is to improve disparity estimation for
defocus stereo images by integrating both correspondence and defocus cues. We
thus leverage blur information where it was previously considered a drawback.
We explicitly derive an inverse projection model including the defocus blur
providing depth estimates up to a scale factor. A method to calibrate the
inverse model is then proposed. We thus take into account depth scaling to
achieve precise and accurate metric depth estimates. Our results show that
introducing defocus cues improves the depth estimation. We demonstrate the
effectiveness of our framework and depth scaling calibration on relative depth
estimation setups and on real-world 3D complex scenes with ground truth
acquired with a 3D lidar scanner.Comment: 21 pages, 12 Figures, 3 Table
CHEC: A Compact High Energy Camera for the Cherenkov Telescope Array
The Cherenkov Telescope Array will provide unprecedented sensitivity and
angular resolution to gamma rays across orders of magnitude in energy. Above 1
TeV up to around 300 TeV an array of Small-Sized Telescopes (SSTs) will cover
several kilometres on the ground. The Compact High-Energy Camera (CHEC) is a
proposed option for the camera of the SSTs. CHEC contains 2048 pixels of
physical size about 6 mm x 6 mm, leading to a field of view of over 8 degrees.
Electronics based on custom ASICs (TARGET) and FPGAs sample incoming signals at
a gigasample per second and provide a flexible triggering scheme. Waveforms for
every pixel in every event are read out without loss at over 600 events per
second. A telescope prototype in Meudon, Paris, saw first Cherenkov light from
air showers in late 2015, using the first CHEC prototype. Research and
development for CHEC is currently focussed on taking advantage of the latest
generation of silicon photomultipliers (SiPMs).Comment: 12 pages, 9 figures, PSD11. arXiv admin note: substantial text
overlap with arXiv:1709.0579
Improving Photometry and Astrophotography by Eliminating Dark Frames and Flat Fields
I report on the efforts to improve the dark frames and flat fielding procedure for the charged-coupled device (CCD) camera for the Celestron C14 telescope at the UNH observatory. Dark frames are images taken while the shutter of the camera is closed so that only electronic and dark noise and other internal inconsistencies are recorded. These are important because they allow astronomers to subtract out interference from dark current. Additionally, flat fields are images of the entire field of the telescope so that the brightness in the pixels of the telescopeâs field of view is uniform. Flat fields are vital since they provide a consistent illumination for all photos taken from the camera. With the combination of these two features, I was able to optimize the clarity of the telescopeâs pictures and show through photometry how the new calibrated images appear in comparison to images prior to the calibration. Overall, these enhanced photographs will assist in achieving better results for future astronomy labs at UNH
High Contrast Imaging and Wavefront Control with a PIAA Coronagraph: Laboratory System Validation
The Phase-Induced Amplitude Apodization (PIAA) coronagraph is a high
performance coronagraph concept able to work at small angular separation with
little loss in throughput. We present results obtained with a laboratory PIAA
system including active wavefront control. The system has a 94.3% throughput
(excluding coating losses) and operates in air with monochromatic light.
Our testbed achieved a 2.27e-7 raw contrast between 1.65 lambda/D (inner
working angle of the coronagraph configuration tested) and 4.4 lambda/D (outer
working angle). Through careful calibration, we were able to separate this
residual light into a dynamic coherent component (turbulence, vibrations) at
4.5e-8 contrast and a static incoherent component (ghosts and/or polarization
missmatch) at 1.6e-7 contrast. Pointing errors are controlled at the 1e-3
lambda/D level using a dedicated low order wavefront sensor.
While not sufficient for direct imaging of Earth-like planets from space, the
2.27e-7 raw contrast achieved already exceeds requirements for a ground-based
Extreme Adaptive Optics system aimed at direct detection of more massive
exoplanets. We show that over a 4hr long period, averaged wavefront errors have
been controlled to the 3.5e-9 contrast level. This result is particularly
encouraging for ground based Extreme-AO systems relying on long term stability
and absence of static wavefront errors to recover planets much fainter than the
fast boiling speckle halo.Comment: 18 pages, 12 figures. Accepted for publication in PASP. The pointing
control scheme for this system is described in a separate paper
(Coronagraphic Low-Order Wave-Front Sensor: Principle and Application to a
Phase-Induced Amplitude Coronagraph, The Astrophysical Journal, Volume 693,
Issue 1, pp. 75-84 (2009)
A Compact High Energy Camera (CHEC) for the Gamma-ray Cherenkov Telescope of the Cherenkov Telescope Array
The Gamma-ray Cherenkov Telescope (GCT) is one of the Small Size Telescopes
(SSTs) proposed for the Cherenkov Telescope Array (CTA) aimed at the 1 TeV to
300 TeV energy range. GCT will be equipped with a Compact High-Energy Camera
(CHEC) containing 2048 pixels of physical size about 66~mm, leading
to a field of view of over 8 degrees. Electronics based on custom TARGET ASICs
and FPGAs sample incoming signals at a gigasample per second and provide a
flexible triggering scheme. Waveforms for every pixel in every event are read
out are on demand without loss at over 600 events per second. A GCT prototype
in Meudon, Paris saw first Cherenkov light from air showers in late 2015, using
the first CHEC prototype, CHEC-M. This contribution presents results from lab
and field tests with CHEC-M and the progress made to a robust camera design for
deployment within CTA.Comment: All CTA contributions at arXiv:1709.0348
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