187 research outputs found
Multi-frequency image reconstruction for radio-interferometry with self-tuned regularization parameters
As the world's largest radio telescope, the Square Kilometer Array (SKA) will
provide radio interferometric data with unprecedented detail. Image
reconstruction algorithms for radio interferometry are challenged to scale well
with TeraByte image sizes never seen before. In this work, we investigate one
such 3D image reconstruction algorithm known as MUFFIN (MUlti-Frequency image
reconstruction For radio INterferometry). In particular, we focus on the
challenging task of automatically finding the optimal regularization parameter
values. In practice, finding the regularization parameters using classical grid
search is computationally intensive and nontrivial due to the lack of ground-
truth. We adopt a greedy strategy where, at each iteration, the optimal
parameters are found by minimizing the predicted Stein unbiased risk estimate
(PSURE). The proposed self-tuned version of MUFFIN involves parallel and
computationally efficient steps, and scales well with large- scale data.
Finally, numerical results on a 3D image are presented to showcase the
performance of the proposed approach
Distributed Deblurring of Large Images of Wide Field-Of-View
Image deblurring is an economic way to reduce certain degradations (blur and
noise) in acquired images. Thus, it has become essential tool in high
resolution imaging in many applications, e.g., astronomy, microscopy or
computational photography. In applications such as astronomy and satellite
imaging, the size of acquired images can be extremely large (up to gigapixels)
covering wide field-of-view suffering from shift-variant blur. Most of the
existing image deblurring techniques are designed and implemented to work
efficiently on centralized computing system having multiple processors and a
shared memory. Thus, the largest image that can be handle is limited by the
size of the physical memory available on the system. In this paper, we propose
a distributed nonblind image deblurring algorithm in which several connected
processing nodes (with reasonable computational resources) process
simultaneously different portions of a large image while maintaining certain
coherency among them to finally obtain a single crisp image. Unlike the
existing centralized techniques, image deblurring in distributed fashion raises
several issues. To tackle these issues, we consider certain approximations that
trade-offs between the quality of deblurred image and the computational
resources required to achieve it. The experimental results show that our
algorithm produces the similar quality of images as the existing centralized
techniques while allowing distribution, and thus being cost effective for
extremely large images.Comment: 16 pages, 10 figures, submitted to IEEE Trans. on Image Processin
Spatial interferometry in optical astronomy
A bibliographic guide is presented to publications of spatial interferometry techniques applied to optical astronomy. Listings appear in alphabetical order, by first author, as well as in specific subject categories listed in chronological order, including imaging theory and speckle interferometry, experimental techniques, and observational results of astronomical studies of stars, the Sun, and the solar system
Direct Multipixel Imaging and Spectroscopy of an Exoplanet with a Solar Gravity Lens Mission
We examined the solar gravitational lens (SGL) as the means to produce direct high-resolution, multipixel images of exoplanets. The properties of the SGL are remarkable: it offers maximum light amplification of ~1e11 and angular resolution of ~1e-10 arcsec. A probe with a 1-m telescope in the SGL focal region can image an exoplanet at 30 pc with 10-kilometer resolution on its surface, sufficient to observe seasonal changes, oceans, continents, surface topography. We reached and exceeded all objectives set for our study: We developed a new wave-optical approach to study the imaging of exoplanets while treating them as extended, resolved, faint sources at large but finite distances. We properly accounted for the solar corona brightness. We developed deconvolution algorithms and demonstrated the feasibility of high-quality image reconstruction under realistic conditions. We have proven that multipixel imaging and spectroscopy of exoplanets with the SGL are feasible. We have developed a new mission concept that delivers an array of optical telescopes to the SGL focal region relying on three innovations: i) a new way to enable direct exoplanet imaging, ii) use of smallsats solar sails fast transit through the solar system and beyond, iii) an open architecture to take advantage of swarm technology. This approach enables entirely new missions, providing a great leap in capabilities for NASA and the greater aerospace community. Our results are encouraging as they lead to a realistic design for a mission that will be able to make direct resolved images of exoplanets in our stellar neighborhood. It could allow exploration of exoplanets relying on the SGL capabilities decades, if not centuries, earlier than possible with other extant technologies. The architecture and mission concepts for a mission to the strong interference region of the SGL are promising and should be explored further
Solar System Remote Sensing : September 20-21, 2002, Pittsburgh, Pennsylvania
This international meeting presents the current state of research over a wide range of topics including:; Photometric theory; Spectroscopic modeling; Laboratory exploration of scattering phenomena; Space weathering processes throughout the inner solar system; Photometric and spectroscopic studies of the Moon, Mars, Mercury, and asteroids; Photometric and spectroscopic studies of cold, icy places such as comets and outer planet satellites.This international meeting presents the current state of research over a wide range of topics including:; Photometric theory; Spectroscopic modeling; Laboratory exploration of scattering phenomena; Space weathering processes throughout the inner solar system; Photometric and spectroscopic studies of the Moon, Mars, Mercury, and asteroids; Photometric and spectroscopic studies of cold, icy places such as comets and outer planet satellites.sponsors, University of Pittsburgh ... [and others]conveners, William Cassidy, Deborah Domingue, Robert M. Nelson ; scientific organizing committee William Cassidy ... [and others].PARTIAL CONTENTS: Interpreting Photometry of Planetary Regoliths: Progress and Problems as Seen from Kharkov / Yu.G. Shkuratov--Toward an Improved Single-Particle Model for Large, Irregular Grains / W.M. Grundy, B. Schmitt, S. Doute--A New Method for Estimating the Single Scattering Phase Functions of Regolith Grains / P. Helfenstein--The Opposition Effect: A Very Unusual Case / R.M. Nelson--Coherent Backscattering by Random Particulate Media in the Solar System / K. Muinonen--The Diverse Surface Compositions of the Galilean Satellites / R.W. Carlso
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