Showing papers on "Amplitude published in 1986"

P-SV wave propagation in heterogeneous media: Velocity‐stress finite‐difference method

Abstract: I present a finite-difference method for modeling P-SV wave propagation in heterogeneous media This is an extension of the method I previously proposed for modeling SH-wave propagation by using velocity and stress in a discrete grid The two components of the velocity cannot be defined at the same node for a complete staggered grid: the stability condition and the P-wave phase velocity dispersion curve do not depend on the Poisson's ratio, while the S-wave phase velocity dispersion curve behavior is rather insensitive to the Poisson's ratio Therefore, the same code used for elastic media can be used for liquid media, where S-wave velocity goes to zero, and no special treatment is needed for a liquid-solid interface Typical physical phenomena arising with P-SV modeling, such as surface waves, are in agreement with analytical results The weathered-layer and corner-edge models show in seismograms the same converted phases obtained by previous authors This method gives stable results for step discontinuities, as shown for a liquid layer above an elastic half-space The head wave preserves the correct amplitude Finally, the corner-edge model illustrates a more complex geometry for the liquid-solid interface As the Poisson's ratio v increases from 025 to 05, the shear converted phases are removed from seismograms and from the time section of the wave field

Volume dependence of the energy spectrum in massive quantum field theories. II. Scattering states

Abstract: The low-lying energy values associated to energy eigenstates describing two stable particles enclosed in a (space-like) box of sizeL are shown to be expandable in an asymptotic power series of 1/L The coefficients in these expansions are related to the appropriate elastic scattering amplitude in a simple and apparently universal manner At low energies, the scattering amplitude can thus be determined, if an accurate calculation of two-particle energy values is possible (by numerical simulation, for example)

Amplitude for n-gluon scattering.

Abstract: A nontrivial squared helicity amplitude is given for the scattering of an arbitrary number of gluons to lowest order in the coupling constant and to leading order in the number of colors.

Modulation instability and periodic solutions of the nonlinear Schrödinger equation

Abstract: A very simple exact analytic solution of the nonlinear Schroedinger equation is found in the class of periodic solutions. It describes the time evolution of a wave with constant amplitude on which a small periodic perturbation is superimposed. Expressions are obtained for the evolution of the spectrum of this solution, and these expressions are analyzed qualitatively. It is shown that there exists a certain class of periodic solutions for which the real and imaginary parts are linearly related, and an example of a one-parameter family of such solutions is given.

Exact and Approximate Construction of Digital Phase Modulations by Superposition of Amplitude Modulated Pulses (AMP)

Abstract: Minimum shift keying and offset QPSK are two well-known modulations which can be interpreted as a set of time/phase-shifted AM pulses. We show in this paper that any constant amplitude binary phase modulation can also be expressed as a sum of a finite number of time limited amplitude modulated pulses (AMP decomposition). New methods for computing autocorrelation and power frequency spectrum are derived, which give very simple results for half-integer index modulations. We also show that the signal can be built with good accuracy using only one optimized pulse ("main pulse"). This synthesis is particularly satisfactory for modulations that have good spectral characteristics and/ or low index.

Viscous flows in two dimensions

Abstract: This review is an expository treatment of the displacement of one fluid by another in a two-dimensional geometry (a Hele-Shaw cell). The Saffman-Taylor equations modeling this system are discussed. They are simulated by random-walk techniques and studied by methods from complex analysis. The stability of the generated patterns (fingers) is studied by a WKB approximation and by complex analytic techniques. The primary conclusions reached are that (a) the fingers are linearly stable even at the highest velocities, (b) they are nonlinearly unstable against noise or an external perturbation, the critical amplitude for the noise being an exponential function of a power of the velocity for high velocities, (c) such exponentials seem to dominate high-velocity behavior, as can be seen from a WKB analysis, and (d) the results of the Saffman-Taylor equations disagree with experiments, apparently because they leave out film-flow phenomena.

Viscous flows in two dimensions

Abstract: This review is an expository treatment of the displacement of one Ouid by another in a two-dimensional geometry (a Hele-Shaw cell). The Saffman-Taylor equations modeling this system are discussed. They are simulated by random-walk techniques and studied by methods from complex analysis. The stability of the generated patterns (fingers) is studied by a WKB approximation and by complex analytic techniques. The primary conclusions reached are that (a) the fingers are linearly stable even at the highest velocities, (b) they are nonlinearly unstable against noise or an external perturbation, the critical amplitude for the noise being an exponential function of a power of the velocity for high velocities, (c) such exponentials seem to dominate high-velocity behavior, as can be seen from a WKB analysis, and (d) the results of the SaffmanTaylor equations disagree with experiments, apparently because they leave out film-flow phenomena.

Anisotropy of the inner core inferred from PKIKP travel times

Abstract: Travel-time residuals of the PKIKP phase observed between 170° and 180° show an axisymmetric pattern of degree 2 with an amplitude of about 2 seconds. The effect at shorter distances is much less pronounced and the entire data set cannot be explained by a physically realistic radial distribution of (isotropic) heterogeneity. We propose that, in addition to the general (isotropic) heterogeneity, the inner core is anisotropic with cylindrical symmetry aligned with the earth's rotation axis. Average P-velocity along this axis is about 1 percent faster than in the equatorial plane.

Saturation and the “universal” spectrum for vertical profiles of horizontal scalar winds in the atmosphere

Abstract: A theory is presented which explains the universal nature of one-dimensional vertical wave number, k, power spectral densities (PSDs) of horizontal winds as measured in the atmosphere and predicted by VanZandt. The theory is that the PSD amplitude at any given wave number (greater than a certain minimum, k*) is determined by its saturation value due either to shear instability (i.e., critical Richardson Number) or, more likely, to convective instability. This explains why the PSD amplitudes observed do not grow exponentially with increasing altitude. This saturation theory assumption plus other considerations leads to a PSD of the form N2/kn, where n is in the range of about 2.5 to 3 and N is the Brunt frequency. A simplified model involving superimposed narrow bands of gravity waves as well as a model based merely on dimensional arguments both lead to n = 3. The full model not only explains the observed spectral slopes but also predicts the PSD amplitude in the troposphere to be 3.5 times smaller than in the stratosphere. The derivation of the model is based on the saturation condition that ∫ k2PSD(k) dk = N2. The model may also apply to the ocean and explain the Garrett-Munk vertical wave number spectrum.

Decay instability of finite-amplitude circularly polarized Alfven waves - A numerical simulation of stimulated Brillouin scattering

Abstract: By means of a numerical simulation, nonlinear evolution of large amplitude dispersive Alfven waves is studied. An energy transfer from the parent wave to two daughter Alfven-like waves and a soundlike wave is observed (a stimulated Brillouin scattering process). The observed growth rates and propagation characteristics of these daughter waves agree with the analytical results, which we obtain by extending the previous treatments by Goldstein, Derby, Sakai, and Sonnerup. Ions are first trapped by the electrostatic potential of the daughter soundlike waves. Along with the eventual decay (ion Landau damping) of the soundlike waves, ions are phase-mixed and left heated in the parallel direction. The increased parallel energy of ions is transferred to the perpendicular thermal energy through the nonresonant scattering process in the colliding Alfven waves (parent and daughter waves). We further observe that the daughter Alfven waves, which still have a large amplitude, are also unstable for further decay, and that the wave energy is continuously transferred to the longer wavelength regime (inverse cascading process).

A general wave equation for waves over rippled beds

Abstract: A time-dependent extension of the reduced wave equation of Berkhoff is developed for the case of waves propagating over a bed consisting of ripples superimposed on an otherwise slowly varying mean depth which satisfies the mild-slope assumption. The ripples are assumed to have wavelengths on the order of the surface wavelength but amplitudes which scale as a small parameter along with the bottom slope. The theory is verified by showing that it reduces to the case of plane waves propagating over a patch of sinusoidal ripples, which vary in one direction and extend to ± ∞ in the transverse direction, studied recently by Davies & Heathershaw and Mei. We then formulate and use coupled parabolic equations to study propagation over patches of arbitrary form in order to study wave reflection.

Amplitude squeezing in a pump-noise-suppressed laser oscillator.

Abstract: This paper clarifies the origins of the standard quantum limit for the amplitude noise of a laser-oscillator outgoing field. The amplitude noise within the cavity bandwidth, \ensuremath{\Omega}\ensuremath{\le}\ensuremath{\omega}/Q, is ultimately caused by the pump amplitude fluctuation, while that above the cavity bandwidth, \ensuremath{\Omega}\ensuremath{\ge}\ensuremath{\omega}/Q, is due to the field zero-point fluctuation. The uncertainty product of the amplitude- and phase-noise spectra at an extremely high pumping level is still larger than the Heisenberg minimum-uncertainty product because of the presence of nonstationary phase-diffusion noise. In this sense, an ordinary laser oscillator is not a quantum-limited device. This paper suggests that a laser oscillator can produce an amplitude-squeezed state in itself if the pump amplitude fluctuation is suppressed below the ordinary shot-noise level. The paper discusses possible schemes for suppressing pump fluctuation, commutator bracket preservation without pump fluctuation, and resulting amplitude and phase spectra. The similarity of and difference between a pump-noise-suppressed laser and a cavity degenerate parametric amplifier are delineated.

Amplitude, phase and path anomalies of mantle waves

Abstract: Summary. The amplitude and phase anomalies observed in long period Rayleigh and Love waves (T> 150 s) show definite patterns of variation from orbit to orbit. In some cases the phase anomalies agree with the prediction of linear perturbation theory applied to a spherical reference model (Fermat’s Principle), namely that each complete orbit of the earth in either direction corresponds to a constant phase anomaly increment. The corresponding approximation for amplitude anomaly is derived in this study; it is shown that orbits of one sense are amplified (or deamplified) by a constant factor for each complete orbit, and that orbits of the opposite sense are amplified or deamplified) by the reciprocal factor. This amplification is due to partial establishing that the large observed anomalies are caused by focusing and defocusing due to heterogeneity. Some of the data, however, show substantial deviations from these approximations, indicating that lateral refraction is sometimes a large effect for high orbits. Evidence is presented for orbits which have paths deviating from the great circle by more than 1000km. A technique is outlined for making use of such data to constrain lateral variations in earth structure. i ocusing and defocusing of a ray bundle. The data often show such behaviour,

Pore fluids and frequency-dependent wave propagation in rocks

Abstract: Attenuation is the anelastic process which dissipates seismic energy by conversion to heat, thus decreasing the amplitude and modifying the frequency and phase content of a propagating wavelet. Laboratory measurements show seismic phase velocity and attenuation are dependent upon the fluid saturation and the product of frequency and pore‐fluid viscosity, with a peak in attenuation between the seismic and sonic bands. The dominant mechanism by which seismic energy is dissipated in the upper crust is local viscous fluid flow in pores of small aspect ratio. Phenomenologically, this behavior is modeled as a series of linear viscoelastic elements with a narrow distribution of relaxation times, where velocity and attenuation are related through the Hilbert transform. This model may be generalized to include constant-Q behavior, as observed in dry rocks. Solutions to the wave equation may be generated for an arbitrary frequency dependence of phase velocity and Q. When Q is nearly independent of frequency, the im...

The Effects of Porosity And Clay Content On Wave Velocities In Sandstones

Abstract: The ultrasonic compressional (Vp) and shear (V,) ve­ locities and first-arrival peak amplitude (A p ) were mea­ sured as functions of differential pressure to 50 MPa and to a state of saturation on 75 different sandstone samples, with porosities ranging from 2 to 30 percent and volume clay content C ranging from 0 to 50 per­ cent, respectively. Both V p and V, were found to corre­ late linearly with porosity and clay content in shaly sandstones, At confining pressure of 40 MPa and pore pressure of 1.0 MPa, the best least-squares fits to the velocity data are

On long nonlinear internal waves over slope-shelf topography

Abstract: An experimental and theoretical study of the propagation and stability of long nonlinear internal waves over slope-shelf topography is presented. A generalised Korteweg-de Vries (KdV) equation, including the effects of nonlinearity, dispersion, dissipation and varying bottom topography, is formulated and solved numerically for single and rank-ordered pairs of solitary waves incident on the slope. The results of corresponding laboratory experiments in a salt-stratified system are reported. Very good agreement between theory and experiment is obtained for a range of stratifications, topography and incident-wave amplitudes. Significant disagreement is found in some cases if the effects of dissipation and higher-order (cubic) nonlinearity are not included in the theoretical model. Weak shearing and strong breaking (overturning) instabilities are observed and found to depend strongly on the incident-wave amplitude and the stratification on the shelf. In some cases the instability of the lowest-mode wave leads to the generation of a second-mode solitary wave. The application of these findings to the prediction and interpretation of field data is discussed.

Late stage spinodal decomposition of a binary polymer mixture. II. Scaling analyses on Qm(τ) and Im(τ)

Abstract: The early‐to‐late stage of the spinodal decomposition (SD) of the critical mixtures of polystyrene and poly(vinyl methyl ether) was investigated by the time‐resolved light scattering technique. The early stage SD where the time evolution of the fluctuations can be described, at least with a good approximation, by the linearized theory of Cahn was found to exist in the reduced time scale τ approximately less than 2. The later stage unmixing process (τ>2) was found to give the scaling laws on the reduced wave number of the dominant Fourier component of the fluctuations Qm and on the reduced maximum scattered intensity Im as given by Qm∼τ−α and Im∼τ β over narrow time scales. In the intermediate stage (2 3α was found, indicating that both the wavelength and amplitude of the dominant mode of fluctuations grow with time. In the late stage (60≲τ), the scaling relation of β=3α was found and dynamical scaling relation was found on the scattering function, indicating that there exists ...

Low-amplitude breather and envelope solitons in quasi-one-dimensional physical models.

Abstract: In the low-amplitude limit we examine the breather- and envelope-soliton solutions of the generalized nonlinear Klein-Gordon system as nonlinear Schr\"odinger solitons. The existence of breather and envelope solutions is determined in the continuum and quasidiscrete limit; in this case the oscillations of the carrier in the envelope are treated exactly. The results are applied to the perturbed sine-Gordon and ${\ensuremath{\varphi}}^{4}$ systems; in both cases the asymmetry of the breathers is controlled by the amplitude of the external force. The study is generalized to the calculations of low-amplitude breather modes in a ferromagnetic chain with a small out-of-plane angle.

Inward rectification and low threshold calcium conductance in rat cerebellar Purkinje cells. An in vitro study.

Abstract: The bioelectrical properties of Purkinje cells were analysed in sagittal slices of adult rat cerebellum by the use of intracellular recordings performed at a somatic level in current or in voltage clamp. The passive electrical constants of Purkinje cells were determined by measuring the time course and the amplitude of the voltage responses induced by hyperpolarizing current pulses. The mean value of input resistance was 21 +/- 1 M omega. Mean values of the membrane time constant and of the total electrotonic length of Purkinje cells were 19.5 +/- 1.7 ms and 0.59 +/- 0.01 ms respectively. A time dependent inward rectification was present in all cells. In current-clamp experiments it appeared as a sag in hyperpolarizing voltage responses which were followed by well developed anodal breaks. In voltage-clamped cells, the inward relaxation induced by hyperpolarizing commands fitted to a single exponential. It was already present near resting potential and could reach an amplitude of up to 4 nA for jumps near to -120 mV. This relaxation was provisionally termed Ih. Tail current relaxations also fitted to a single exponential when they were recorded in the presence of tetrodotoxin (TTX) and of Co. The inward relaxation induced by hyperpolarizing commands was readily blocked by Cs, whereas it was unaffected when Ba replaced Ca in the bath, except near rest where it was strongly reduced. The Ca channel blockers Cd, Co and D600 also markedly depressed or even suppressed the inward rectification near resting potential, and up to about -85 mV, whereas this blocking effect was much less apparent or even absent at more negative potentials. Ih was clearly enhanced when the external K concentration was raised up to 20 mM. In the presence of TTX and Co in the bath, inward relaxations induced by hyperpolarizing jumps were unaffected in Na-free solution, whereas the amplitude of tail currents was reduced. Furthermore, the reversal potential of Ih which ranged between -45 and -56 mV in the Co plus TTX containing solution, shifted toward more negative values in the Na-free medium. In contrast, Ih remained unchanged in low Cl solution. From these experiments, it is likely that K and Na are the main charge carriers of Ih. Furthermore, this current seems to be contaminated near resting potential by a Ca-dependent K current. Anodal breaks following hyperpolarizing commands were slightly attenuated when Cd or TTX were added to the bath.(ABSTRACT TRUNCATED AT 400 WORDS)

Processing of acoustic waveforms

Abstract: A sinusoidal model for acoustic waveforms is applied to develop a new analysis/synthesis technique which characterizes a waveform by the amplitudes, frequencies, and phases of component sine waves. These parameters are estimated from a short-time Fourier transform. Rapid changes in the highly-resolved spectral components are tracked using the concept of "birth" and "death" of the underlying sine waves. The component values are interpolated from one frame to the next to yield a representation that is applied to a sine wave generator. The resulting synthetic waveform preserves the general waveform shape and is perceptually indistinguishable from the original. Furthermore, in the presence of noise the perceptual characteristics of the waveform as well as the noise are maintained. The method and devices disclosed herein are particularly useful in speech coding, time-scale modification, frequency scale modification and pitch modification.

Short-period P- and S-wave radiation from large earthquakes: Implications for spectral scaling relations

Abstract: Recent measurements of peak P-wave amplitudes on World Wide Standardized Seismographic Network short-period instruments by Houston and Kanamori (1986) provided the opportunity to investigate source radiation from great earthquakes at higher frequencies than have previously been available. The dependence on moment magnitude (M) of the amplitude measurements (A) and the dominant period (T) in the P-wave seismograms are compared to predictions from several source-scaling relations. For all of the relations, the radiated energy was assumed to be randomly distributed over a duration proportional to the inverse corner frequency. An w-square source-scaling relation with a constant stress parameter of 50 bars gives a good fit to both observed quantities (A and T) for earthquakes up to M 9.5. This model, with the same stress parameter, also fits peak acceleration and peak velocity data for earthquakes with moment magnitude as low as 0.5. Predictions using the source spectra derived by Gusev (1983), which are representative of several published relations featuring regions of reduced spectral decay after an initial ~-2 attenuation beyond the corner frequency, do not fit the various high-frequency observations quite as well as do those using the ~-square model, although the differences between the predicted motions are generally within a factor of 2 to 3. Although the w-square model successfully predicts a wide variety of time-domain measures over an extraordinary magnitude range, it fails to fit the Ms, M correlation for large earthquakes; Gusev's spectral scaling relation, on the other hand, fits this correlation, but was constrained in advance to do so. This failure of the w-square model is of little practical concern, occurring as it does at periods longer than those of usual engineering importance. An ~-cube model fails completely to explain the seismic moment dependence of the observations.

Large amplitude ion‐acoustic double layers in a double Maxwellian electron plasma

Abstract: A finite amplitude theory for an ion‐acoustic double layer (DL) in a plasma with cold ions and two distinct groups of Boltzmann–Maxwellian distributed hot electrons is presented. Conditions are obtained under which large amplitude stationary double layers can exist. For physical parameters of interest, the DL profiles and the relationship between the maximum DL amplitude and the Mach number are found. A perturbation technique is introduced to derive a modified Korteweg–de Vries (MKdV) equation which governs the dynamics of a weak double layer. It is found that the parameter regimes for the existence of small and finite amplitude DL are not complementary to each other. The relevance of this investigation to space and laboratory plasmas is pointed out.

Yield estimates of nevada test site explosions obtained from seismic Lg waves

Abstract: A methodology is presented for determining the yield of underground nuclear explosions from Lg wave amplitudes. The methodology is applied to Nevada Test Site (NTS) explosions, for which the data from short-period, vertical component analog seismographs at three stations are used to develop calibration curves for unsaturated material and water-saturated rock source conditions. The latter curves are found to provide reasonably accurate estimates of the yields of explosions in other areas of the United States and in the French Sahara, suggesting that they may be applicable to all continental areas. If so, they also can provide an estimate of the bias of mb(P) magnitudes between different continental sites. For example, the Lg data from NTS explosions indicate a 0.31±0.02 magnitude unit bias between NTS and eastern North America, similar to the approximately 0.33 unit bias found between western and eastern North America previously by use of earthquake data.

Quantum nondemolition detection of optical quadrature amplitudes.

Abstract: In an optical fiber, nonlinear optical interactions couple the sideband modes of two strong pump waves at different frequencies just as required for a quantum nondemolition measurement. Experimental measurements demonstrate that 37% of the rms phase fluctuations of one wave are caused by the quantum amplitude fluctuations of the other.

Source spectra of great earthquakes: Teleseismic constraints on rupture process and strong motion

Abstract: Short-period body waves recorded at teleseismic distances from great earthquakes provide information about source rupture processes and strong motions First, we examine mostly WWSSN records of 19 earthquakes of moment magnitude M_w of 65 to 95 Four parameters are measured from the short-period P-wave train: the maximum amplitude; the period at maximum amplitude; the time between the first arrival and when the maximum amplitude is attained; and coda length An extension, m_b, of the teleseismic magnitude, m_b, is defined using the maximum amplitude of the entire short-period P-wave rather than the amplitude achieved in the first few P-wave cycles A least-squares fit to the data yields the following relationship between m_b and M_w: m_b = 053 M_w + 270 for M_w 65 to 95 The time from the first arrival until the maximum amplitude is achieved and the coda length are roughly proportional to M_w, but are further interpreted by a simple asperity model of the rupture process These data support that short-period waves are, on average, generated preferentially in the same regions of the fault plane as long-period waves (with periods of 10 to 50 sec) We analyze the spectra of short- and intermediate-period teleseismic GDSN records for seven earthquakes with M_w's of 64 to 78 and hand-digitized short-period WWSSN records of the 1971 San Fernando earthquake Significant differences exist between the spectra of different events, due partly to variations in tectonic setting or seismic coupling Using the digital data, we also investigate the relationship between time-domain amplitude and spectral amplitude for short-period P waves From our empirical relation between spectral amplitude and time-domain amplitude, we estimate the spectral amplitudes implied by the m_b data We compare our results to the ω^(−2) and Gusev spectral models Neither model can completely represent the data Nevertheless, we consider the ω^(−2) model a useful reference model for comparing different events The average source spectrum of six large events with M_w 74 to 78 does not have the spectral structure suggested by Gusev An application to strong motion modeling is presented in which a 1971 San Fernando teleseismic short-period record is summed up to simulate teleseismic records produced by five great earthquakes The summation procedure matches the moment of the event to be simulated, and includes rupture propagation, fault plane roughness, and randomness The m_b data provide an important constraint on the summation procedures Thus constrained, this summation procedure can be more confidently used with near-field strong motion records as Green's functions to predict strong motions from great earthquakes

Direct observation of ensemble averaging of the Aharonov-Bohm effect in normal-metal loops.

Abstract: Aharonov-Bohm magnetoconductance oscillations have been measured in series arrays of 1, 3, 10, and 30 submicron-diameter Ag loops. At constant temperature, the amplitude of the h/e oscillations is observed to decrease as the square root of number of loops, while the amplitude of h/2e conductance oscillations, measured in the same samples, is independent of the number of series loops. This is direct confirmation of the ensemble averaging properties of h/e oscillations in multiloop systems. The amplitude of the h/e oscillations is in good agreement with recent calculations.

Synthesis of phase-coherent, picosecond optical square pulses.

Abstract: We report the generation of Fourier-transform-limited, picosecond optical square pulses (with a duration of ~6 psec full width at half-maximum and a rise time of ~1 psec). Control of the pulse temporal profile is achieved by masking the amplitude and the phase of the optical frequency components, which are spatially dispersed within a grating pulse compressor.

Acoustic emissions by vortex motions

Abstract: Fundamental aspects of the acoustic emission by vortex motions are considered by summarizing our recent work. Three typical cases are presented as illustrative examples: (i) head-on collision of two vortex rings, (ii) a vortex ring moving near a circular cylinder, and (iii) a vortex ring moving near a sharp edge of a semi-infinite plate. The theory of aerodynamic sound for low-Mach-number motion of an inviscid fluid predicts that the amplitude of the acoustic pressure in the far field is proportional to U4, U3 and U2.5 for (i)-(iii) respectively, where U is the translation velocity of a single vortex ring. Therefore the vortex-edge interaction generates the most powerful sound among the three cases at low Mach numbers. Our observations have confirmed these scaling laws. In addition to the scaling properties, we show the wave profiles of the emission as well as the directionality pattern. The head-on collision radiates waves of quadrupole directionality, whereas waves of dipole property are originated by the vortex-cylinder interaction. The third, vortex-edge, interaction generates waves of a cardioid directionality pattern. The wave profiles of all three cases are related to the time derivatives of the volume flux (through the vortex ring) of an imaginary potential flow which is characteristic of each configuration, although the orders of the time derivatives are different for each case. The observed profiles are surprisingly well fitted to the curves predicted by the theory, except the final period of the first case, in which viscosity is assumed to play an important role. The observed wave profiles are shown in a perspective diagram.

Measurement and Modeling of Amplitude Scintillations on Low-Elevation Earth-Space Paths and Impact on Communication Systems

Abstract: Amplitude scintillations occurring on low-elevation earthspace paths can be large enough to significantly degrade the quality of satellite communications links at X -band and higher frequencies. This paper presents measurements of amplitude scintillations on low-elevation (7.1° and 8.9°) satellite downlinks at X -band. The statistical distributions of scintillation amplitude and rms intensity are approximated using the Moulsley-Vilar model [1]. An analytical approximation of this model is presented and is shown to be an easy means of predicting system outage time due to scintillations. Theoretical estimates of the average bit error rate for a digital satellite link subject to scintillation fading are presented for NCFSK and CPSK modulations. Other ways in which scintillations can affect a satellite communication link are discussed, and results are also presented showing the seasonal and diurnal variability of the scintillation intensity and long-term correlation with ground temperature.