Optical Resolution Through a Randomly Inhomogeneous Medium for Very Long and Very Short Exposures

Fried, David L.

doi:10.1364/josa.56.001372

Cited by 1,386 publications

(624 citation statements)

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“…Concerning visual measurements, the CCD results have a great advantage since they should be free from personal bias. On the other hand, they allow a measure of the image quality expressed by the seeing parameter of Fried (1966) which can be related to errors affecting the solar radius measurements (Irbah et al 1994). However, and at least for the time being, this advantages could have only a formal character, since as we have shown in this paper, in practice, CCD measurements of the solar diameter with an astrolabe can be strongly affected by systematic effects that produce quite significant distorsion of the results.…”

Section: Discussionmentioning

confidence: 96%

Visual and CCD astrolabe observations of the solar radius

Noel

2001

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Abstract.Here we discuss and compare two sets of solar semidiameter measurements made with Danjon astrolabes during the period 1997-1999. One is based on 10 522 CCD observations made at Rio de Janeiro, Brazil; the other one is based on 956 visual observations made at Santiago, Chile. Linear fits applied to both data sets give a standard deviation of ±0. 365 and ±0. 360 for each daily mean value of the solar radius for Rio de Janeiro and Santiago respectively. During the period of this analysis, the apparent solar radius had an annual variation of −0. 060 ± 0. 013 according to the CCD observations of Rio de Janeiro and of +0. 213 ± 0. 018 according to the visual observations of Santiago. We show here that this discrepancy could be due to systematic effects, probably of instrumental origin, that produce significant internal inconsistencies in the results of Rio de Janeiro. The drift of the apparent solar radius observed with the astrolabe of Santiago during 1997-1999 is consistent with former results obtained with this instrument since 1990. These results show that the apparent semidiameter of the Sun varies in phase with solar activity (Noël 1997(Noël , 2001).

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Section: Discussionmentioning

confidence: 96%

Visual and CCD astrolabe observations of the solar radius

Noel

2001

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“…In the simulations, we will assume that the only aberrations are those introduced by atmospheric turbulence, setting the ratio of the telescope diameter, D, to the Fried Parameter, r 0 , equal to ten (Fried 1966). We could also generalize the simulations to include static and dynamic telescope aberrations.…”

Section: Reconstruction Resultsmentioning

confidence: 99%

“…Then, we will apply the methods to a complex extended object, once again varying the photons per frame. We assume that the only aberrations are those introduced by atmospheric turbulence setting the ratio of the telescope diameter, D, to the Fried Parameter, r 0 , equal to ten (Fried 1966). Additionally, we assume that the focalplane detector array is photon-noise limited, the illumination is narrow-band (essentially monochromatic) and the atmosphere is Article published by EDP Sciences A58, page 1 of 7 static during each data frame.…”

Section: Introductionmentioning

confidence: 99%

New phasor reconstruction for speckle imaging

Dente¹,

Tilton

2011

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We will develop and then compare object spectrum phasor reconstruction results for several speckle imaging approaches. Each phasor reconstruction algorithm results from minimizing a very naturally defined weighted-least-squares error function. Once we pick a phasor-based error function, the remaining steps in our algorithms are developed by setting the error function variation, with respect to each phasor element, to zero. The resulting coupled nonlinear equations for the minimum error phasor array are then solved iteratively. In the applications, we will specifically compare and contrast three implementations: 1) Knox-Thompson; 2) bispectrum, using only two bispectrum planes; 3) bispectrum, using four bispectrum planes. In each application of the three approaches, we first calculate the modulus of the object spectrum using a Wiener-Helstrom filter to remove the speckle transfer function. The methods then differ only in their object spectrum phasor reconstructions. In the simulations, we will implement all three methods on a simple object at low photon-per-frame light levels. Next, we will apply the methods to a complex extended object. Although we develop and minimize error functions for three specific speckle methods, the approach readily generalizes to other cases.

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“…Consequently, for a given laser wavelength and propagation distance L, the turbulence problem is governed by the three free parameters C 2 n , L 0 and l 0 . An important quantity is the Fried parameter r 0 (coherence length) [10], scaling as 6∕5 ∶ Physically, the Fried parameter may be regarded as the aperture of a fictive telescope over which the rms phase differences between any two points remain in the order of one radian. That means, a telescope with aperture r 0 in the absence of turbulence (i.e., diffraction-limited) has the same image resolution as any telescope under turbulence conditions having an aperture arbitrarily larger than r 0 .…”

Section: Theoretical Basis Of Laser Beam Propagation In Turbulent Atmmentioning

confidence: 99%