Hampton, VA, United States
Hampton, VA, United States

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Grant
Agency: Department of Defense | Branch: Navy | Program: STTR | Phase: Phase II | Award Amount: 490.55K | Year: 2012

Non-invasive, stealthy nature of passive remote sensing combined with its low cost make passive techniques a promising supplement or replacement of traditional active remote sensing techniques. Coherent processing of diffuse wave fields has a proven potential for remote sensing of stationary environments. The proposed research extends noise interferometry to characterization of dynamic environments. We will develop"acoustic daylight"and"radio wave daylight"techniques for retrieval of information about targets and their surroundings from the ambient acoustic noise and the background radio waves; and determine which environmental parameters and types of targets can be effectively monitored through ambient noise interferometry. The interferometric approach will be extended to ambient acoustic noise in the ocean, infrasonic noise in the atmosphere, and to electromagnetic ambient noise in the atmosphere. Through optimization of the data acquisition geometry, frequency band, and data processing algorithms, we will improve accuracy of passive travel time measurements and sensitivity to weak, transient environmental perturbations. In case of positive results of Phase II efforts, specialized passive acoustic and/or HF or microwave electromagnetic sensors and systems will be designed during Phase III for passive remote sensing as well as detection and localization of silent targets in the ocean and atmosphere.


Grant
Agency: Department of Defense | Branch: Navy | Program: STTR | Phase: Phase I | Award Amount: 100.00K | Year: 2010

Non-invasive, stealthy nature of passive remote sensing combined with its low cost make passive techniques a promising supplement or replacement of traditional active remote sensing techniques. Coherent processing of diffuse wave fields has a proven potential for remote sensing of stationary environments. The proposed research extends noise interferometry to characterization of dynamic environments. We will develop “acoustic daylight” and “radio wave daylight” techniques for retrieval of information about targets and their surroundings from the ambient acoustic noise and the background radio waves; and determine which environmental parameters and types of targets can be effectively monitored through ambient noise interferometry. During Phase I we propose to demonstrate experimentally the feasibility of passive acoustic measurements of sound speed and flow velocity in a moving fluid and to evaluate necessary noise averaging times and receiver network geometry for detection of targets and achieving desired accuracy of passive acoustic measurements of environmental parameters. In case of positive results of Phase I, the efforts of Phase I optional part and Phase II will be directed toward extension of the interferometric approach to ambient acoustic noise in the ocean and to electromagnetic ambient noise in the microwave band in the atmosphere as well as to optimization of the data acquisition geometry, frequency band, and data processing algorithms to improve accuracy of passive travel time measurements and sensitivity to weak, transient environmental perturbations.


Charnotskii M.,Zel Technologies, LLC
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2013

Monte Carlo (MC) simulation of phase front perturbations by atmospheric turbulence finds numerous applications for design and modeling of the adaptive optics systems, laser beam propagation simulations, and evaluating the performance of the various optical systems operating in the open air environment. Accurate generation of two-dimensional random fields of turbulent phase is complicated by the enormous diversity of scales that can reach five orders of magnitude in each coordinate. In addition there is a need for generation of the long "ribbons" of turbulent phase that are used to represent the time evolution of the wave front. This makes it unfeasible to use the standard discrete Fourier transform-based technique as a basis for the MC simulation algorithm. We propose a new model for turbulent phase: the sparse spectrum (SS) random field. The principal assumption of the SS model is that each realization of the random field has a discrete random spectral support. Statistics of the random amplitudes and wave vectors of the SS model are arranged to provide the required spectral and correlation properties of the random field. The SS-based MC model offers substantial reduction of computer costs for simulation of the wide-band random fields and processes, and is capable of generating long aperiodic phase "ribbons." We report the results of model trials that determine the number of sparse components, and the range of wavenumbers that is necessary to accurately reproduce the random field with a power-law spectrum. © 2013 Optical Society of America.


Charnotskii M.,Zel Technologies, LLC
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2013

A recently published sparse spectrum (SS) model of the phase front perturbations by atmospheric turbulence [J. Opt. Soc. Am. A 30, 479 (2013)] is based on the trigonometric series with discrete random support. The SS model enables fewer computational efforts, while preserving the wide range of scales typically associated with turbulence perturbations. We present an improved version of the SS model that accurately reproduces the powerlaw spectral density of the phase fluctuations in the arbitrary wide spectral band. We examine the higher-order statistics of the SS phase samples for four versions of the SS model. We also present the calculations of the long-exposure Strehl numbers and scintillation index for the different versions of the SS model. A nonoverlapping SS model with a log-uniform partition emerges as the most appropriate for the atmospheric turbulence representation. © 2013 Optical Society of America.


Charnotskii M.,Zel Technologies, LLC
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2012

We propose a novel Sparse Spectrum (SS) model of the sea surface, where each surface realization contains a finite, possibly random, number of sinusoidal components with random frequency, phase and amplitude. Unlike the FFT-based model, the number of spectral components forming the surface is determined by the sea state, but not the desired spatial resolution and domain size. A single constraint on the probability distribution of the wave vectors, and the amplitude variances of the components allows the SS surface to conform to any prescribed spectral density. The SS model is capable of providing a well-defined statistics of the individual waves that are important for the marine engineering and remote sensing applications. Copyright © 2012 by the International Society of Offshore and Polar Engineers (ISOPE).


Charnotskii M.,Zel Technologies, LLC
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2012

Gerçekcioǧlu and Baykal presented an investigation of the dependence of the scintillation index of flat-topped Gaussian beams on the exponent ? of the power-law-type spectra of non- Kolmogorov turbulence. In particular, they found that the scintillation index reaches a maximum at α ? 3.2. We show that this conclusion is an artifact of their specific calculation, and depends on the choice of the length unit. Gerç ekcioǧlu and Baykal's calculations are made for the 3 < alpha; < 5 range of the spectral exponent. We show that for the homogeneous and isotropic turbulence the correct range is 3 < alpha; & 4, when Markov pproximation is used. © 2012 Optical Society of America.


Charnotskii M.,Zel Technologies, LLC
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2012

This review paper addresses typical mistakes and omissions that involve theoretical research and modeling of optical propagation through atmospheric turbulence. We discuss the disregard of some general properties of narrow- angle propagation in refractive random media, the careless use of simplified models of turbulence, and omissions in the calculations of the second moment of the propagating wave. We also review some misconceptions regarding short-exposure imaging, propagation of polarized waves, and calculations of the scintillation index of the beam waves. © 2012 Optical Society of America.


Charnotskii M.,Zel Technologies, LLC
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2010

We extend our theory of on-axis beam scintillations [Waves Random Media 4, 243 (1994)] for the case of propagation on slant turbulent paths, where turbulence is concentrated in a relatively thin layer near the transmitter. Our technique is based on the parabolic equation for optical wave propagation and the Markov approximation for the calculation of statistical moments of beam intensity. This first of two companion papers presents the details of the path integral formulation of the solution for the fourth-order coherence function. We also discuss in detail two analytic techniques that can be used for the treatment of the path integrals. © 2010 Optical Society of America.


Charnotskii M.,Zel Technologies, LLC
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2015

Extended Huygens-Fresnel principle (EHF) currently is the most common technique used in theoretical studies of the optical propagation in turbulence. A recent review paper [J. Opt. Soc. Am. A 31, 2038 (2014)] cites several dozens of papers that are exclusively based on the EHF principle. We revisit the foundations of the EHF, and show that it is burdened by very restrictive assumptions that make it valid only under weak scintillation conditions. We compare the EHF to the less-restrictive Markov approximation and show that both theories deliver identical results for the second moment of the field, rendering the EHF essentially worthless. For the fourth moment of the field, the EHF principle is accurate under weak scintillation conditions, but is known to provide erroneous results for strong scintillation conditions. In addition, since the EHF does not obey the energy conservation principle, its results cannot be accurate for scintillations of partially coherent beam waves. © 2015 Optical Society of America.


Charnotskii M.,Zel Technologies, LLC
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

Monte-Carlo simulation of phase front perturbations by atmospheric turbulence finds numerous applications for design and modeling of the adaptive optics systems, laser beams propagation simulations, and evaluating the performance of the various optical systems operating in the open air environment. Accurate generation of two-dimensional random fields of turbulent phase is complicated by the enormous diversity of scales that can reach five orders in magnitude in each coordinate. In addition there is a need for generation of the long 'ribbons' of turbulent phase that are used to represent the time evolution of the wave front. This makes it unfeasible to use the standard discrete Fourier transform-based technique as a basis for the Monte-Carlo simulation algorithm. We propose a novel concept for turbulent phase ' the Sparse Spectrum (SS) random field. The principle assumption of the SS model is that each realization of the random field has a discrete random spectral support. Statistics of the random amplitudes and wave vectors of the SS model are arranged to provide the required spectral and correlation properties of the random field. The SS-based Monte-Carlo model offers substantial reduction of computer costs for simulation of the wide-band random fields and processes, and is capable of generating long aperiodic phase 'ribbons'. We report the results of model trials that determine the number of sparse components, and the range of wavenumbers that is necessary to accurately reproduce the random field with a power-law spectrum. © 2013 SPIE.

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