Download or read book Understanding the Effect of Atmospheric Turbulence on Optical and Infrared Propagation Using Hilbert Phase Analysis written by and published by . This book was released on 2007 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: The refractive index structure parameter C(2/n) is a figure of merit used to describe the magnitude of the effect of turbulence in the atmosphere. Understanding the influence of different local climate parameters upon C(2/n) is an important step toward developing a prediction model for in-field laser interrogators. The layered structure of the atmosphere and its random behavior present unique challenges to theoretical and experimental studies in propagation research. This article presents a novel technique termed Hilbert Phase Analysis (HPA) to provide insights into the physical interactions. We explore the technique's use in analyzing the dependence of C(2/n) on local climate variables using data recently obtained from campaigns conducted in Puerto Rico.

Download or read book A Simulation of Optical Propagation Through Atmospheric Turbulence Using Two dimensional Fourier Transform Techniques written by Jeffrey L. Turner and published by . This book was released on 1989 with total page 71 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Humidity s Influence on Visible Region Refractive Index Structure Parameter Cn2 written by and published by . This book was released on 2007 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the near-infrared and visible bandpasses optical propagation theory conventionally assumes that humidity does not contribute to the effects of atmospheric turbulence on optical beams. While this assumption may be reasonable for dry locations, we demonstrate that there is an unequivocal effect owing to the presence of humidity upon the strength of turbulence parameter, Cn 2, from data collected in the Chesapeake Bay area over 100 m length horizontal propagation paths. We describe and apply a novel technique, Hilbert phase analysis, to the relative humidity, temperature, and Cn 2 data to show the contribution of the relevant climate variable to Cn 2 as a function of time.

Download or read book Experimental Investigations of Optical Propagation in Atmospheric Turbulence written by Michael W. Fitzmaurice and published by . This book was released on 1971 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: The pertinent theoretical background and the results of a group of experiments conducted over 0.4- and 1.17-km near-ground horizontal ranges are presented. (1) The log-amplitude variances for HeNe (0.633 μm) and CO2 (10.6 μm) laser beams were found to have a ratio of 26.8, which is in close agreement with the predictions of Rytov-based spherical-wave theory. (2) Published measurements of the saturation level of the log-amplitude variance are reviewed and several inconsistencies noted. (3) The spatial correlation function of irradiance field was measured and found to agree with theory. The degree of correlation between different frequency beams which had traversed the same optical path was also measured and compared to theory. The data exhibited an unacceptably large scatter and did not show the wavelength dependence. (4) The log-normal, Rayleigh, and Rice probability distributions are discussed in terms of their applicability to irradiance statistics. Relatively weak 10.6 μm irradiance fluctuations were found to be equally well described by the log-normal and Rice distributions; strong fluctuations obtained at 0.488 μm were clearly best described by the log-normal distribution.

Download or read book Atmospheric Effects on Electro optical Infrared and Millimeter Wave Systems Performance written by Richard B. Gomez and published by . This book was released on 1981 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Adaptive Beaming and Imaging in the Turbulent Atmosphere written by Vladimir Petrovich Lukin and published by SPIE-International Society for Optical Engineering. This book was released on 2002 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to the wide application of adaptive optical systems, an understanding of optical wave propagation in randomly inhomogeneous media has become essential, and several numerical models of individual AOS components and of efficient correction algorithms have been developed. This monograph contains detailed descriptions of the mathematical experiments that were designed and carried out during more than a decade's worth of research.

Download or read book Effects of Atmospheric Turbulence on Optical Propagation written by R. S. Lawrence and published by . This book was released on 1984 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: The optical refractive index of the atmosphere depends on temperature, pressure, and humidity. Naturally occurring variations of these quantities, with scales of a few centimeters and associated with atmospheric turbulence, cause optical scintillation, image distortion, and laser beam broadening. I review the meteorological conditions that influence the occurrence of this optical turbulence, discuss the optical significance of turbulence at various heights in the atmosphere, and point out the differences between these optical effects and the corresponding phenomena at radio wavelengths. While beam broadening increases indefinitely with the strength of optical turbulence, scintillation saturates and eventually decreases with increasing turbulence.

Download or read book The Effect of Real Atmospheric Turbulence on Passive Phase Calibration in Optical Aperture Synthesis written by Wilson McKellar and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Investigation of Anisoplanatic Chaos based Signal and Image Transmission and Retrieval Through Atmospheric Thase Turbulence written by Ali Mohamed and published by . This book was released on 2020 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt: This research began as a continuation of work on the propagation of planar electromagnetic (EM) waves through a turbulent atmosphere, specifically a form of refractive index based phase turbulence modeled by the Modified von Karman Spectrum (MVKS). In the previous work within our group, EM propagation through a turbulent atmosphere under the MVKS model was investigated for essentially isoplanatic propagation, whereby the propagation from the source to the receiver progressed along a horizontal path, such that the effective structure parameter associated with the turbulence remained unchanged along the propagation. The problem was numerically set up by using the split-step propagation model, whereby the EM wave from the source (sometimes interpreted as a planar aperture) propagates alternately through non-turbulent regions (governed by standard Fresnel-Kirchhoff diffraction), and thereafter through MVKS regions where the phase turbulence occurs. A narrowly turbulent layer is described by a random 2D phase screen in the transverse plane; extended turbulence is modeled by a series of planar phase screens placed along the propagation path. In the above analyses, propagation of both uniform as well as profiled plane waves was considered. The present research commenced with investigating uniform, Gaussian and Bessel beam propagation along a turbulent path, and detailed numerical simulations were carried out relative to infinite as well as finite apertures in the source plane (including single and double slits, and single and double circular apertures), considering both non-turbulent and turbulent paths for comparison. Results were obtained in the near, far and deep far fields. The problem was further developed to include the case of anisoplanatic plane EM wave propagation over a slanted path. The turbulence structure function (Cn2) in this environment was considered to be altitude dependent, and for this purpose the Hufnagel-Valley (HV) model for the structure function. A standard prototype tested for this system consisted of propagation along a slanted path with a fixed horizontal distance, and made up along the propagation path of a diffractive (LD) and a turbulent (LT) section. The effect of turbulence was examined for test 2D images/transparencies under two environments: (a) the 2D image, under digital encoding converted to time signals, being used to modulate a carrier (typically optical) wave, which is thereafter propagated across the LD+LT path, and recovered in the "image" plane using heterodyne-type communications strategies. Of special note here is the fact that since MVKS and most other turbulence models are intrinsically spatial in nature, a method has been developed within the group whereby the time-statistics of the turbulence is derived from received intensities (typically on-axis) as the phase screen(s) is/are varied at a specific rate corresponding to the average turbulence frequency (in the range 20 Hz-200 Hz). Using this statistical information, the modulated wave propagation across the turbulence is examined; and (b) the source image/transparency is treated as a spatial amplitude distribution through which an unmodulated carrier wave (in the phasor domain) is propagated, and later the object transparency is recovered via a positive thin lens in its back focal plane (assuming thereby that the object transparency is essentially located at infinity relative to the lens). Of the two strategies, it was found that the carrier modulation method yielded better image cross-correlation (CC) products than the method using the thin lens, in the presence of turbulence. Overall, it is seen that recovered EM signals (2D object transparencies, modulated plane waves, and also dynamic/video scenes) are adversely affected by MVKS turbulence (which incidentally is limited in its applicability to only cases where in the Rytov criterion is satisfied, and therefore in many cases works for only weak to moderate levels of turbulence; some cases involving strong turbulence have been investigated nevertheless), and the degree of drop in the CC product goes up as the strength of the turbulence increases. In view of this, a strategy was adopted later whereby the goal was to ascertain if by "packaging" the incident signal/digitized image inside a chaotic carrier, and thereafter propagating the encrypted chaos wave across the turbulent path might help mitigate the loss of CC product (leading to image distortion) during propagation through (MVKS) turbulence. This concept has thereafter been tested for several 2D image scenarios, using an acousto-optically generated chaotic carrier for the encryption prior to turbulent propagation. The corresponding recovered signals (obtained via two levels of demodulation) consistently indicate improvements in the CC products of the recovered images relative to the source. Additionally, the MVKS turbulent system used along the slanted path is also examined under an interchanging of the source and receiver positions. Following extended examinations of the altitude-dependent propagation along an MVKS turbulent path, this work next focused on an alternative turbulence model, viz., the gamma-gamma turbulence (also refractive index) model, which it turns out actually is valid for all atmospheric turbulence (weak through strong) conditions. The use of the HV model for Cn2 assumes, however, that much of the turbulence considered is within a relatively low-altitude limit. For the gamma-gamma problem as well, applications similar to those used for the MVKS cases (i.e., propagation of modulated EM carriers with message signals transmitted along a turbulent (LT) path) using the gamma-gamma time statistics. This problem was analyzed via numerical simulation for both non-chaotic and chaotic carriers. Once again, use of a chaotic carrier is consistently found to improve the bit error rates (BERs) of the recovered image relative to the source image.

Download or read book Effects of Atmospheric Turbulence on Optical Instrumentation written by Randolph A. Becker and published by . This book was released on 1961 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: The results of research on optical turbulence at White Sands Missile Range are presented. It has been shown that elevating camera stations 33 feet above ground level can yield nearly a threefold increase in optical resolution during periods of atmospheric turbulence. Early research postulated the existence of thermal-induced air-lenses as the cause of optical turbulence effects. Recent research has shown that air-lenses can account for most of the observed effects. The 'prism' concept of turbulence appears to be unnecessary for explaining trubulence -induced image motion. The dependence of the optical effects of turbulence upon exposure time and aperture size is discussed qualitatively. The source of optical turbulence in the atmosphere and a method of measuring the trubulence-generating potential of various terrain surfaces are described on the basis of micrometerology. This research has been limited to an investigation of optical turbulence during the period from sunrise to sunset. However, many of the results apply to the nighttime turbulence encountered by astronomers. (Author).

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 702 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Interferometry and Synthesis in Radio Astronomy written by A. Richard Thompson and published by Wiley-Interscience. This book was released on 1986-04-28 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt: A unified description of the theory and practice of radio interferometry and synthesis mapping techniques as they apply to astronomy and geology. Beginning with an historical review, it goes on to provide a detailed description of all aspects of radio inferometry, from basic principles through instrumental design to data reduction. Over 450 original papers and monographs are cited.

Download or read book Journal of the Optical Society of America written by and published by . This book was released on 1999 with total page 732 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 682 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Physics Briefs written by and published by . This book was released on 1994 with total page 1146 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book OAR Cumulative Index of Research Results written by United States. Air Force. Office of Aerospace Research and published by . This book was released on 1963 with total page 550 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book OAR Quarterly Index of Current Research Results written by United States. Air Force. Office of Aerospace Research and published by . This book was released on 1964 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: