High Resolution Optical Imaging Through the Atmosphere

High Resolution Optical Imaging Through the Atmosphere
Author: Robert W. Noyes
Publisher:
Total Pages: 57
Release: 1989
Genre: Astronomical instruments
ISBN:

This program has concentrated on three major areas: the application of high angular resolution image reconstruction techniques to the reconstruction of solar surface features; speckle imaging of a wide range of astronomical sources; and the implementation of adaptive optics for faint object imaging. In this project, we have made substantial modifications to a technique for reconstruction of high resolution images from single short exposure solar frames, blind iterative deconvolution (IDC). We have been testing these improvements using numerical simulation data. Analysis of speckle data of the supernova SN1987A has detected a new bright source, 0.9 arcseconds south of the SN, as well as substantial structure in the region surrounding the SN. We also have new results on several Young Stellar Objects and supergiants. In the area of adaptive optics, an AOA wavefront sensor has been set up and tested using an image intensifier which increases its sensitivity by three orders of magnitude. Faint object image active tilt correction has also been tested with some important enhancements, including new highly linear and sensitive CCD quad cells developed by Cal Tech and Tektronix, and an off-the-shelf high speed 2-D tilting mirror with greatly improved specifications. The effects of only partially correcting atmospheric turbulence have been theoretically analyzed and numerically simulated.

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.

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.

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.

Investigations of High Resolution Imaging Through the Earth's Atmosphere Using Speckle Interferometry

Investigations of High Resolution Imaging Through the Earth's Atmosphere Using Speckle Interferometry
Author: E. Keith Hege
Publisher:
Total Pages: 360
Release: 1987
Genre:
ISBN:

Speckle Interferometry can now be used to produce images with spatial resolution of order 100x sharper than that normally permitted by the Earth's atmosphere. During this two year program of technique development we achieved high resolution imaging capability (wavelength dependent; 60 nrad at 410 nm) and approached that resolution in imaging a geosynchronous communications satellite utilizing the Multiple Mirror Telescope (MMT) and the Fienup method. We continued the pattern of parallel programs established in our previous AFGL work: E.D. Hege, P.A. Strittmatter and N.J. Woolf, Investigations of High Resolution Imaging Through the Earth's Atmosphere Using Speckle Interferometry, AFGL Report AFGL-TR-84-0116, 1984. Specific to this contract work, in our first year we completed a fully co-phased optical beam-combiner for implementation of the full 6.9m aperture imaging capability of the MMT. During our second year we met our final objective, by producing a 100 nrad resolution image of the geosynchronous Earth satellite FLTSATCOMl. We have proposed designs for systems to accomplish in real-time the data integrations necessary for Fienup and Knox-Thompson image reconstructions. Throughout the interval we continued work on algorithm development and seeing calibration. Our most notable achievement was applications of seeing calibration techniques and refinements of the shift-and-add method applied successfully in our scientific program of studies of red supergiants.