Spectra of short‐term fluctuations of line‐of‐sight signals: Electromagnetic and acoustic

Mandics, P. A.; Lee, R. W.; Waterman, Alan T.

doi:10.1029/rs008i003p00185

Cited by 22 publications

(3 citation statements)

References 21 publications

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“…This general expression is also derived in a more physical fashion by Lee and Harp (1969, eqs. 13, 14), and is discussed at some length by Mandics, Lee, and Waterman (1973).…”

Section: G2 Spatial Covariances Of Log-amplitude and Phasementioning

confidence: 99%

Group Delay Tracking with the Sydney University Stellar Interferometer

Lawson¹

1994

PASP

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In the Sydney University Stellar Interferometer (SUSI), fringes are detected when the optical path-difference between the arriving wavefronts is less than the coherence length for the observation. While observing a star, it is necessary to compensate not only for the changes in pathlength due to the earth's rotation, but also for those due to the effects of atmospheric turbulence. Apertures smaller than r 0 are used and active tilt-compensation is employed so that the wavefronts in the combined beams are made parallel. The remaining path-difference between the wavefronts must then be tracked for an accurate calibration of the fringe visibility. Improved tracking allows larger bandwidths to be used and therefore improves the sensitivity of the instrument. In this thesis a fringe tracking system is developed for SUSI based on group delay tracking with a PAPA detector. The method uses short exposure images of fringes detected in the dispersed spectra of the combined starlight. The number of fringes across a fixed bandwidth is directly proportional to the path-difference between the arriving wavefronts, and a Fast Fourier Transform is used to calculate the spatial power spectrum of the fringes, thereby locating the delay. Several topics are developed in the thesis. The visibility loss due to a non-constant fringe spacing on the detector is investigated, and the improvements obtained from rebinning the photon data are shown. The low light level limitations of group delay tracking are determined, with emphasis on the probability of tracking error, rather than on signalto-noise performance. Experimental results from both laboratory studies and stellar observations are presented. These show the first closed-loop operation of a fringe tracking system based on observations of group delay with a stellar interferometer. A new photon counting PAPA detector is also described, which was developed for use in this work. The design principles of the PAPA camera are outlined, and the potential sources of image artifacts are identified. These artifacts arise from the use of optical encoding with Gray coded masks. The new camera is distinguished by its mask-plate, which was designed to overcome artifacts due to vignetting. New lens mounts are also presented which permit a simplified optical alignment without the need for tilt-plates. The performance of the camera is described and its images are shown to be free of the effects of vignetting. i Declaration of Originality To the best of my knowledge, this thesis contains no copy or paraphrase of work due to any other person, except where duly acknowledged. None of the remaining work has been presented for any degree at the University of Sydney or elsewhere.

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“…This general expression is also derived in a more physical fashion by Lee and Harp (1969, eqs. 13, 14), and is discussed at some length by Mandics, Lee, and Waterman (1973).…”

Section: G2 Spatial Covariances Of Log-amplitude and Phasementioning

confidence: 99%

Group Delay Tracking with the Sydney University Stellar Interferometer

Lawson¹

1994

PASP

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“…For a single spherical wave which originates from a point source the amplitude and phase covariances B a,•,('r ) are enpressed as double integrals over distance s (from source s = 0 to receiver s = L) and wave number K. Normalizing the received signal to unit mean, taking the logarithm and expanding x(t) = 1 + l(t) + jc•(t), these covarianc½s are [Lee and Harp, 1969;Mandics et al, 1973] Ba. (2) Normalizations similar to Mandic, et al [1973] have been used:…”

Section: Summary Of Weak-scattering Theorymentioning

confidence: 99%

Remote atmospheric probing on a line‐of‐sight path, using spatial filter concepts: 1. Theory

Leuenberger¹,

Lee²,

Waterman³

1979

Radio Science

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A rigorous treatment is given to a spatial filtering method for remotely determining the transverse wind velocity and the atmospheric structure constant along a line‐of‐sight path, assuming a Kolmogorov spectrum of refractivity and weak scattering. The results are applicable from the millimeter‐wave range to the optical range for linear array configurations at either one end or both ends of the path. Various methods of signal detection are considered, such as coherent, quasi‐coherent (knowledge of relative phases), and incoherent. In order to determine the two parameters the integral for the time covariance or the spectrum of the wave fluctuations must be inverted. For simple arrangements of single elements or pairs of elements at the transmitting and receiving locations the inversion is ill conditioned and yields only three or four resolution cells along the path. A statement of the problem in spectral form for line apertures representing narrow bandpass‐type spatial filters leads to optimal orthogonality of the inversion problem. In the limiting case of ideally sharp spatial filters, the inversion is shown to degenerate into a simple one‐to‐one relationship between spectral measurements of the spatially filtered wave fluctuations and the values of the parameters at a specified location along the path. A subsequent paper will be devoted to an experimental application of the principle in the mm‐wave region.

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“…Inherent in (5) is the assumption t,hat the effect, of wind velocity fluctuations is small compared to t,he average m-ind velocity u. Using (6) where t,he coordinate p" = e'ut is att,ached to the moving turbulence. Since n 1 in (6) is a function of posit.ion only, t.he usual time-independent spectral representation for n 1 may be used.…”

Section: Introductionmentioning

confidence: 99%

Effects of turbulence in a planetary atmosphere on radio occultation

Woo

Ishimaru²

1974

IEEE Trans. Antennas Propagat.

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There has been considerable interest in the amplitude and phase fluctuations of the radio signal received from a flyby spacecraft during occultation by a planetary atmosphere. For planetary flyby missions, the Fresnel-zone size exceeds the outer scale size of turbulence, and existing formulations for the frequency spectra of the amplitude and phase fluctuations are inadequate because they do not account for the inhomogeneity of the turbulence in the direction transverse to the propagation path. In this paper, the formulation is given for the correlation functions for the logamplitude and phase fluctuations of both spherical and plane waves propagating in a turbulent medium whose correlation function for refractive index fluctuations is described by the product of a function of the average coordinate and a function of the difference coordinate.The results are applied to radio occultation of a flyby space probe by the atmosphere of Venus, assuming that the turbulence in the atmosphere exists as a layer, that it is localized, isotropic, and smoothly varying, and that the localized turbulence is described by the Kolmogorov spectrum. Closed-form solutions for both variances and frequency spectra of the log-amplitude and phase fluctuations are obtained using Rytov's method, and it is seen that the shape of the frequency spectra depends a great deal on the characteristics and extent of the turbulence.

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Spectra of short‐term fluctuations of line‐of‐sight signals: Electromagnetic and acoustic

Cited by 22 publications

References 21 publications

Group Delay Tracking with the Sydney University Stellar Interferometer

Group Delay Tracking with the Sydney University Stellar Interferometer

Remote atmospheric probing on a line‐of‐sight path, using spatial filter concepts: 1. Theory

Effects of turbulence in a planetary atmosphere on radio occultation

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