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The area of atmospheric optics has continued to flourish and burgeon. When we compiled this report four years ago we screened 400 titles for inclusion; this time the number increased to over 900 items, which were found chiefly by checking the contents lists of the five principal journals and utilizing abstracting journals for the rest. We retained about 750 in the bibliography, including a few reports that are available from the Clearinghouse for Scientific and Technical Information, Springfield, Virginia. We omitted most papers relating to the construction or calibration of equipment for atmospheric optical studies. Many papers appeared during this time period on the atmospheres of other planets; we included only papers closely related to the terrestrial atmosphere.
The area of atmospheric optics has continued to flourish and burgeon. When we compiled this report four years ago we screened 400 titles for inclusion; this time the number increased to over 900 items, which were found chiefly by checking the contents lists of the five principal journals and utilizing abstracting journals for the rest. We retained about 750 in the bibliography, including a few reports that are available from the Clearinghouse for Scientific and Technical Information, Springfield, Virginia. We omitted most papers relating to the construction or calibration of equipment for atmospheric optical studies. Many papers appeared during this time period on the atmospheres of other planets; we included only papers closely related to the terrestrial atmosphere.
Theoretical expressions for the spectral density of amplitude, amplitude-difference, and phase-difference fluctuations of waves propagating over a line-of-sight path in a weakly scattering turbulent medium are derived. Experimental observations made at radio (35 GHz) and acoustic (3 kHz) frequencies are in good agreement with the theoretical predictions under a variety of meteorological conditions. Comparison of experimental and theoretical spectra yields a measure of the average across-the-path wind velocity and the average refractiveindex structure constant C,•. In general, wind speeds and refractive-index structure constants inferred from simultaneous meteorological measurements agree with those obtained from propagation data. rived a theoretical expression for the power spectrum of amplitude fluctuations of a plane wave propagating through a turbulent atmosphere. Later, Tatarskii [1971] extends these results to phase and phasedifference variations; however, he still considers only the plane-wave case. Skrypnik [1966] examines similar spectral expressions for the case of nonuniform wind along the propagation path. Temporal frequency spectra for a spherical wave are obtained by Clifford [1971] and Ishimaru [1972] in the form of double integrals; they also give asymptotic expressions for large and small fluctuation frequencies. Mandics [1971, pp. 17-22] numerically evaluates amplitude and phase spectra for a specific geometry. Numerous workers have calculated fluctuation spectra from measured scintillations of optical, microwave, and acoustic frequencies (e.g., Tatarski [1961], HOhn [1966], Janes et al. [1970], and Golitsyn et al. [1960]). Due to lack of an adequate theoretical framework, however, it has become possible only recently to compare experimentally obtained spectra with the appropriate theory (see Clifford et al. [1971], Ishimaru [1972], and Mandics [1971, pp. 59-74]).The present study will give the results of line-ofsight propagation experiments performed at mm-wave and acoustic frequencies. These experiments are unique in that the incident wavefront is sampled (nearly) simultaneously at several points in space and at a very rapid rate. The sampling rate is set high enough in each case to include all atmosphere-185 of this assumption will have to be examined more closely.Assuming that scatterers of importance lie within the inertial subrange of ,the turbulence spectrum it is possible to express •(•) in the following form [Tatarski, 1961, p. 58] ß ,,(g) = 0.033C,,=(s)t• -•/a 2r/Lo < t• < 2r/go (3) where it is realized that the refractive-index structure constant, C,, may be a function of position SHORT-TERM SIGNAL-FLUCTUATION SPECTRA 157 For the moment, however, the -11/3 exponent indicated in equation 3 is assumed to be valid. It is convenient to normalize the amplitude covariance expression in the following manner' along the path. (Here, l0 and L0 are the inner and that is, it is possible to express the time-lagged autoouter scales of turbulence, respectively.) In addi-covariance function, B•(r), in...
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