Report on the Maidanak site testing campaign in July 1998 (Maidanak-98)

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ABSTRACT Various parameters of the atmospheric turbulence above the Maidanak observatory located in Uzbekistan Republik were measured on 9 nights in July 1998 with three complementary instruments: Differential Image Motion Monitor (DIMM), Generalized Seeing Monitor (GSM) and two Scintillation Photometers (SP). Median FWHM seeing was equal to 0:64 00 , the median wavefront outer scale L 0 = 25:9 m, median isoplanatic angle ` 0 = 2:48 00 . Temporal evolution of the wavefront can be described by several layers moving at slow velocities (mostly less than 2 m=s and never exceeding 10 m=s) with predominant direction from the West. There was no correlation between wavefront velocity and the wind velocity at ground level. Turbulence in the 3 Gamma 30 m surface layer was not important, contributing on the average 10% to the total C 2 n integral (except on one occasion when it was very strong and dominant). Independent measurements of the free-atmosphere seeing (excluding the first kilometer above...

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    ABSTRACT: A better understanding of the behavior of wavefronts perturbed by the atmospheric turbulence is vital for the progress in the High Angular Resolution (H.A.R) observing techniques, namely long baseline interferometry and adaptive optics. A new instrument called G.S.M. was built for the study of spatial and temporal properties of wavefronts by means of angle of arrival fluctuation measurements in two (or more) spatially separated points. The Fried parameter r_o_, the wavefront outer scale L_0_ and the speckle lifetime tau can be deduced from these data. In the first part of this paper the instrument itself is described. It is based on the modulation of a stellar image formed in a small telescope by a Ronchi grating together with a fast scanning mirror. High sampling rate (up to 5 ms), high precision (rms photon noise 0.08" on alpha UMi) and the possibility to have long uninterrupted data sequence are achieved. Examples of the first results include r_o_ and tau estimates.
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    ABSTRACT: We examine the consequences for an adaptive-optics system of the fact that the turbulence-induced wave-front distortion for two propagation paths with only slightly different propagation directions can be significantly different. We consider the implications of this fact for a compensated imaging system and for an adaptive-optics laser transmitter. Theory and numerical results are presented. The basic results are presented in terms of the average optical transfer function of a compensated imaging system and in terms of the average antenna gain of an adaptive-optics laser transmitter, each expressed as a function of the angular separation ϑ between the propagation path along which the reference signal arrives and the propagation path along which the adaptive-optics system is to provide performance. It is shown that for high spatial frequencies (for the compensated imaging system) and for large-aperture diameters (for the adaptive-laser optics transmitter), i.e., large compared with r0/λ and with r0, respectively, the magnitude of the anisoplanatism effect can be characterized by an isoplanatic patch angular size, which we denote by ϑ0. If the angular separation between the two propagation paths is ϑ, it is shown that the optical transfer function and the antenna gain are each reduced by a factor of exp[-(ϑ/ϑ0)5/3]. This simply expressed performance-reduction factor represents an asymptotic limit for high spatial frequencies and for large transmitter diameters. For lower spatial frequencies and smaller transmitter diameters the reduction factor is not so severe. Numerical results are presented to illustrate this.
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    ABSTRACT: We report the results of 1,049 measurements of the vertical profile of optical turbulence as recorded by a scintillometer above a site at White Sands Missile Range. The distributional law for these measurements is shown to be approximately log normal and examples of monthly to hourly variations in profile structure are presented. An estimate is formed for the isoplanatic angle for wave propagation through each profile by calculating its five-third moment. The ensemble of these calculations is found to be log normally distributed with a mean of 7.2 microrad at a wavelength of 0.5 microm. A strong temporal correction is observed between the size of the isoplanatic angle and the intensity of scintillations. We develop a theory based upon aperture averaging to account for this phenomenon and propose the use of scintillometry to make direct measurements of isoplanatism.
    Applied Optics 08/1979; 18(15):2654-61. DOI:10.1364/AO.18.002654 · 1.78 Impact Factor


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