Imaging Techniques Through the Atmosphere

Imaging Techniques Through the Atmosphere
Author: Murat Tahtali
Publisher:
Total Pages:
Release: 2008
Genre: Algorithms
ISBN:

Whilst the underlying mechanisms of atmospheric turbulence are complex, the observed effects on imaging can be described in simpler terms. In this thesis, I address the effects seen as geometric distortions in anisoplanatic imaging and propose new digital restorations techniques that are real-time capable and predictive. The anisoplanatic problem arises in wide-field telescopic imaging and in new ventures of astronomy such as giant telescopes that process wide-field imagery. The methods proposed here, both digital and digital-optical hybrid, remove the position dependent distortions as a precursor to image analysis. Previous existing digital restoration techniques have used a prototype formed by averaging an image time sequence for image registration where valuable high frequencies information is lost due to the low-pass filtering effect of averaging. The proposed techniques are capable of using any arbitrary frame in the sequence as prototype, thus circumventing the low pass filtering effect and also allowing real-time implementation. Furthermore, these techniques are made predictive by the use of Kalman filtering. The predictive capabilities of these techniques open a new path to the combination of digital processing and adaptive optics that can result in hybrid systems. The key to adoption of hybrid systems is to reduce the complexity and expense of the optics and couple this with digital processing prediction. To this end I also propose a new type of inexpensive and fast piezoelectric deformable mirror based on the vibration modes of circular PVDF membranes that exhibit striking similarities to Zernike polynomials. It requires only two electrodes for actuation and a very simple driving signal generator, therefore constituting an inexpensive and viable alternative to existing deformable mirrors. With the emergence of multi-conjugate adaptive optics (MCAO) and multiobject adaptive optics (MOAO) in astronomy, and the more demanding correction required for long range surveillance imaging, this inexpensive deformable mirror and the real-time capable digital algorithms are promising building blocks for a hybrid solution to the anisoplanatic imaging problem.

General Theory of Light Propagation and Imaging Through the Atmosphere

General Theory of Light Propagation and Imaging Through the Atmosphere
Author: T. Stewart McKechnie
Publisher: Springer Nature
Total Pages: 694
Release: 2022-10-06
Genre: Science
ISBN: 3030988287

This 2nd edition lays out an updated version of the general theory of light propagation and imaging through Earth’s turbulent atmosphere initially developed in the late ‘70s and ‘80s, with additional applications in the areas of laser communications and high-energy laser beam propagation. New material includes a chapter providing a comprehensive mathematical tool set for precisely characterizing image formation with the anticipated Extremely Large Telescopes (ELTS), enabling a staggering range of star image shapes and sizes; existing chapters rewritten or modified so as to supplement the mathematics with clearer physical insight through written and graphical means; a history of the development of present-day understanding of light propagation and imaging through the atmosphere as represented by the general theory described. Beginning with the rudimentary, geometrical-optics based understanding of a century ago, it describes advances made in the 1960s, including the development of the ‘Kolmogorov theory,’ the deficiencies of which undermined its credibility, but not before it had done enormous damage, such as construction of a generation of underperforming ‘light bucket’ telescopes. The general theory requires no a priori turbulence assumptions. Instead, it provides means for calculating the turbulence properties directly from readily-measurable properties of star images.

Analysis of Techniques for Imaging Through the Atmosphere

Analysis of Techniques for Imaging Through the Atmosphere
Author: David L. Fried
Publisher:
Total Pages: 78
Release: 1978
Genre:
ISBN:

This report is concerned with the application of speckle imagery to space object identification for deep space objects. A novel type of variable Michelson Stellar Interferometer setup for forming speckle image data is described. Also, the theory of noise in speckle imagery is developed on a rigorous basis. This report is the final technical report on this contract. (Author).

Carbon Dioxide Angiography

Carbon Dioxide Angiography
Author: Kyung Cho
Publisher: CRC Press
Total Pages: 310
Release: 2007-07-17
Genre: Medical
ISBN: 1420016261

With an abundance of illustrations and tables to highlight critical information, this source provides a practical approach to the use of CO2 as a contrast agent for diagnostic angiography, vascular intervention, and other interventional procedures in both adults and pediatrics. Clearly laying-out key points in the science, technique, and clinical a

Spectral Imaging of the Atmosphere

Spectral Imaging of the Atmosphere
Author: Gordon G. Shepherd
Publisher: Elsevier
Total Pages: 340
Release: 2002-07-15
Genre: Science
ISBN: 008051751X

Optical instruments are routinely employed to obtain a wealth of information about the atmosphere, including its composition, temperature, and winds. A bewildering variety of optical instruments have been proposed over the years, making it difficult to decide which instrument should be chosen to make a specific measurement. Spectral Imaging of the Atmosphere traces the historical development of both spectral and imaging methods and places them in a unified framework relevant to observations of the troposphere, stratosphere, mesosphere and thermosphere. The underlying concepts of various measurement methodologies are presented and paired with appropriate applications. A selection of specific spectral imaging instruments, appropriate to illustrate each conceptual type, is described in detail.Shepherd's work provides both scientists and engineers with an in-depth understanding of the fundamental concepts they need to know in order to plan a program of atmospheric measurements. Expected future methods and developments are also presented. Problems designed to test and enhance the reader's understanding of the material are included in each chapter. Provides a unique and unifed approach to the methodology of optical atmospheric observations from the troposphere through the thermosphere, which allows the practitioner to choose the best instrument for a given measurement.Describes state-of-the-art atmospheric observing instruments with an eye to future developments.Includes problems designed to test and enhance students' unerstanding of the material presented in each chapter.Contains concise descriptions of selected current and planned spectral imagers, including the Fabry-Perot spectrometer, the Michelson interferometer and the diffraction grating spectrometer.Written from a scientific perspective in an engineering framework, this work is accessible to atmospheric scientists and instrumentation engineers alike.

Imaging Through Turbulence

Imaging Through Turbulence
Author: Michael C. Roggemann
Publisher: CRC Press
Total Pages: 389
Release: 2018-02-06
Genre: Technology & Engineering
ISBN: 1351439308

Learn how to overcome resolution limitations caused by atmospheric turbulence in Imaging Through Turbulence. This hands-on book thoroughly discusses the nature of turbulence effects on optical imaging systems, techniques used to overcome these effects, performance analysis methods, and representative examples of performance. Neatly pulling together widely scattered material, it covers Fourier and statistical optics, turbulence effects on imaging systems, simulation of turbulence effects and correction techniques, speckle imaging, adaptive optics, and hybrid imaging. Imaging Through Turbulence is written in tutorial style, logically guiding you through these essential topics. It helps you bring down to earth the complexities of coping with turbulence.

Lucky Exposures

Lucky Exposures
Author: Robert Tubbs
Publisher: VDM Publishing
Total Pages: 152
Release: 2008-05-01
Genre: Science
ISBN: 9783836497695

This monograph describes the "Lucky" imaging method developed at the University of Cambridge between 1999 and 2003. This technique allows the distorting effects of the Earth's atmosphere to be reduced, so that high resolution images of astronomical sources can be captured. The Lucky Exposures method is passive, relying on a high frame-rate camera in the image plane of a telescope to record the atmospheric speckle patterns. In the past the poor signal-to-noise performance of high frame-rate cameras has often limited passive high-resolution observations to relatively bright targets. Through a combination of novel processing techniques and new L3Vision camera technology, the Lucky Exposures method can now image much fainter targets. Details of these processing techniques and an assessment of the L3Vision performance are presented in this monograph. From good astronomical observatories, up to one quarter of the night sky is within range of a suitable reference star for this technique. The processing techniques described are applicable to data taken with a wide range of astronomical instruments, including observations using webcams on small- to medium-sized telescopes.

Improving Imaging Through Turbulence Via Aperture Partitioning

Improving Imaging Through Turbulence Via Aperture Partitioning
Author:
Publisher:
Total Pages: 14
Release: 2010
Genre:
ISBN:

Speckle imaging techniques make it possible to do high-resolution imaging through the turbulent atmosphere by collecting and processing a large number of short-exposure frames, each of which effectively freezes the atmosphere. In severe seeing condition, when the characteristic scale of atmospheric fluctuations is much smaller than the diameter of the telescope, the reconstructed image is dominated by?turbulence noise? caused by redundant baselines in the pupil. I describe a generalization of aperture masking interferometery that dramatically improves imaging performance in this regime. The approach is to partition the aperture into annuli, form the bispectra of the focal plane images formed from each annulus, and recombine them into a synthesized bispectrum form which the object may be retrieved. This may be implemented using multiple cameras and special mirrors, or with a single camera and a suitable pupil phase mask. I report results from simulations as well as experimental results using telescopes at the Air Force Research Lab's Maui Space Surveillance Site.