High Multiple Radio Reflections from the F2 Layer of the Ionosphere at Brisbane

1954 ◽  
Vol 7 (1) ◽  
pp. 165 ◽  
Author(s):  
K Baird
Keyword(s):  
Normal Incidence ◽  
Reflection Coefficients ◽  
Fixed Frequency ◽  
Night Time ◽  
Variable Gain

Continuous night-time records of multiple F2 reflections at normal incidence have been made at a fixed frequency. The echo patterns have been classified, and qualitative explanations given in terms of humped ionization contours, extending the work of Pierce and Mimno (1940). These patterns have been studied also by a variable gain technique. It is concluded that accurate measurements of reflection coefficients cannot be made by this means.

REFLECTION COEFFICIENTS AND BOTTOM LOSSES AT NORMAL INCIDENCE COMPUTED FROM PACIFIC SEDIMENT PROPERTIES

Geophysics ◽  
1970 ◽  
Vol 35 (6) ◽  
pp. 995-1004 ◽  
Author(s):  
Edwin L. Hamilton
Keyword(s):  
Normal Incidence ◽  
Silty Sand ◽  
Reflection Coefficients ◽  
Silty Clay ◽  
Sediment Properties ◽  
Compressional Waves ◽  
Sea Floor ◽  
Sediment Types ◽  
The Pacific ◽  
Clayey Silt

Rayleigh reflection coefficients and bottom losses of compressional waves at normal incidence on the water‐sediment interface are computed with values of density and velocity measured in sea‐floor sediment samples; main sediment types in three major environments of the Pacific and adjacent areas are included. Some typical average computed values of acoustic bottom loss at normal incidence in db are (1) continental shelf: sands, 8; silty sand, 10; sandy silt, 14; silty clay, 16; (2) abyssal plain: clayey silt, 17; silty clay and clay, 21; and (3) abyssal hill: silty clay and clay, 17. Comparisons with actual measurements at sea by several investigators demonstrate the validity of the approach.

Data‐matrix asymmetry and polarization changes from multicomponent surface seismics

Geophysics ◽  
1997 ◽  
Vol 62 (2) ◽  
pp. 630-643 ◽  
Author(s):  
Xiang‐Yang Li ◽  
Colin MacBeth
Keyword(s):  
Normal Incidence ◽  
Geological Structure ◽  
South Texas ◽  
Data Matrix ◽  
Reflection Coefficients ◽  
Incidence Plane ◽  
Degree Of Anisotropy ◽  
The Asymmetry ◽  
The Time Domain ◽  
Value Decomposition

We present methods for interpreting data‐matrix asymmetry and polarization changes with depth from multicomponent surface seismics. There are two main sources of data matrix asymmetry in four component shear‐wave seismics: that arising from the acquisition geometry caused by source and receiver misorientation, misalignment, imbalance, and cross‐coupling, and that arising from the medium caused by variations in the geological structure, lithology, or stress. The asymmetry caused by acquisition geometry is more significant than that from the medium. Two asymmetry indices are used to quantify these medium and acquisition asymmetries separately. Their behavior may be used to identify the origin of the asymmetry. The asymmetry caused by the medium is studied by deriving approximate normal‐incidence, plane‐wave reflection coefficients for an interface separating two anisotropic media with differenfly oriented symmetry axes. The degree of asymmetry in the reflectivity is proportional to the product of the degree of anisotropy in the layers above and below the reflector, and is thus small for most realistic cases. Consequently, the reflection coefficients can be approximated by a similarity transform of the principal reflection coefficients using the expected polarization difference. These equations can then be used to formulate a singular‐value decomposition (SVD) in the time‐domain to recover both the principal reflectivity and the changes of polarizations with depth. Applications to field data in south Texas reveal the potential of the technique, and zones of polarization changes in the Austin Chalk are identified that may be correlated with fracture swarms.

scholarly journals Transmission of Normal P-Waves across a Single Joint Based ong‐λModel

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Zhanfeng Fan ◽  
Jichun Zhang ◽  
Hua Xu ◽  
Jianhua Cai
Keyword(s):  
Particle Velocity ◽  
Normal Incidence ◽  
Exponential Model ◽  
P Wave ◽  
Displacement Discontinuity ◽  
Reflection Coefficients ◽  
Joint Stress ◽  
Limit Values ◽  
Transmission And Reflection Coefficients ◽  
Transmission And Reflection

This paper investigates the wave transmission and reflection of an elastic P-wave at a single joint for normal incidence. First, considering a coupled joint (correction parameterλ,0<λ<1), a normal deformation constitutive model of the joint (g‐λmodel) under static or quasi-static loading is introduced and then extended to dynamic loading. The nonlinearity of the joint stress-deformation curve increases with increasingλ. Second, the interaction between the P-wave and the joint is investigated by using the method of characteristics and the displacement discontinuity method to deduce the differential expression of the transmitted wave’s particle velocity. The approximate analytical expressions of the transmission and reflection coefficients are obtained according to the Lemaitre equivalent strain assumption. Third, parametric studies are conducted to evaluate the effects ofλon transmission characteristics for a normally incident P-wave at a single joint. The results show that the particle velocity of the transmitted wave depends onλ. Whenλtakes the limit values 0 and 1, the transmitted wave’s particle velocities are then consistent with the conclusions of the classical exponential model and the Barton–Bandis model. In addition, the transmission and reflection coefficients are discussed with respect toλand also to the ratio of the joint closure to the maximum allowable joint closure.

Amplitude responses of thin beds: Sinusoidal approximation versus Ricker approximation

Geophysics ◽  
1995 ◽  
Vol 60 (1) ◽  
pp. 223-230 ◽  
Author(s):  
Hai‐Man Chung ◽  
Don C. Lawton
Keyword(s):  
Numerical Modeling ◽  
Normal Incidence ◽  
Reflection Coefficients ◽  
Amplitude Dependence ◽  
Dominant Wavelength ◽  
Amplitude Response ◽  
Analytical Expression ◽  
Ricker Wavelet ◽  
Analytical Expressions

The amplitude response of a thin bed with arbitrary upper and lower normal incidence reflection coefficients is studied. Two analytical expressions for the normal incidence amplitude response as a function of the thickness are derived and are both valid for weak reflectivities and for thicknesses below [Formula: see text], where [Formula: see text] is the dominant wavelength. The first expression is based on the substitution of a cosine wave for the source wavelet, and the second is based directly on the analytical expression for a Ricker wavelet. The results calculated from these two expressions are compared to numerical modeling results for a Ricker wavelet for several models. We found that the differences between the two expressions are small, and both are good approximations. Above the [Formula: see text] thickness, the percentage differences increase rapidly for both expressions, implying that the thin‐bed assumptions in both derivations break down rapidly beyond the [Formula: see text] thickness. Below the [Formula: see text] thickness, except in the case where the two reflection coefficients are equal in magnitude but opposite in sign, the amplitude dependence on the thickness is nonlinear.

scholarly journals A Study of "Spread?F" Ionospheric Echoes at Night at Brisbane. I. Range Spreading (Experimental)

1956 ◽  
Vol 9 (2) ◽  
pp. 247 ◽  
Author(s):  
RWE McNicol ◽  
HC Webster ◽  
GG Bowman
Keyword(s):  
Critical Frequency ◽  
Fixed Frequency ◽  
Night Time ◽  
Range Measurements ◽  
Phase Path ◽  
Spread F

At frequencies well below the critical frequency, satellite echoes sometimes accompany the night-time F2 echo, sometimes clearly separated, sometimes overlapping. In an investigation of these range multiplets, in addition to routine P'f sounding records, continuous virtual range measurements at fixed frequency (at stations of various separations), and measurements of mean intensities, phase-path changes, and directions of arrival, have been carried out.

Impedance‐type approximations of the P–P elastic reflection coefficient: Modeling and AVO inversion

Geophysics ◽  
2004 ◽  
Vol 69 (2) ◽  
pp. 592-598 ◽  
Author(s):  
Lúcio T. Santos ◽  
Martin Tygel
Keyword(s):  
Reflection Coefficient ◽  
Normal Incidence ◽  
Simple Expression ◽  
P Wave ◽  
Reflection Coefficients ◽  
Seismic Reflection Data ◽  
Acoustic Reflection ◽  
Reflection Data ◽  
Avo Inversion ◽  
Elastic Impedance

The normal‐incidence elastic compressional reflection coefficient admits an exact, simple expression in terms of the acoustic impedance, namely the product of the P‐wave velocity and density, at both sides of an interface. With slight modifications a similar expression can, also exactly, express the oblique‐incidence acoustic reflection coefficient. A severe limitation on the use of these two reflection coefficients in analyzing seismic reflection data is that they provide no information on shear‐wave velocities that refer to the interface. We address the natural question of whether a suitable impedance concept can be introduced for which arbitrary P–P reflection coefficients can be expressed in a form analogous to their acoustic counterparts. Although no closed‐form exact solution exists, our analysis provides a general framework for which, under suitable restrictions of the medium parameters, possible impedance functions can be derived. In particular, the well‐established concept of elastic impedance and the recently introduced concept of reflection impedance can be better understood. Concerning these two impedances, we examine their potential for modeling and for estimating the AVO indicators of intercept and gradient. For typical synthetic examples, we show that the reflection impedance formulation provides consistently better results than those obtained using the elastic impedance.

The generalized one‐dimensional synthetic seismogram

Geophysics ◽  
1987 ◽  
Vol 52 (5) ◽  
pp. 589-605 ◽  
Author(s):  
P. R. Gutowski ◽  
S. Treitel
Keyword(s):  
Moving Average ◽  
Normal Incidence ◽  
Synthetic Seismogram ◽  
Stratified Medium ◽  
Autoregressive Moving Average ◽  
Reflection Coefficients ◽  
Source Surface ◽  
Theoretical Treatment ◽  
Surface Source ◽  
Ar Representations

The normal‐incidence synthetic seismogram for an elastic and horizontally stratified medium has been thoroughly studied for a relatively restricted number of source and receiver locations. Most existing treatments are concerned with the special case in which the source as well as the receiver are situated at the surface; few attempts have dealt with completely arbitrary source and receiver geometries. Here we examine arbitrary geometries with the aid of the layer matrix approach, in which upgoing and downgoing wave motion at each interface is expressed in terms of z-transform polynomials. Such an approach brings to light a number of physically important relations that the model satisfies. For example, the synthetic seismograms generally have the familiar autoregressive‐moving average (ARMA) structure for the surface‐source, surface‐receiver case. For particular combinations of reflection coefficients, however, the seismograms reduce to purely autoregressive (AR) representations. In all cases, we work out the delay properties that the respective autoregressive and moving average components must obey. The present solutions are easily reduced to a useful form for practical computation. One application of particular current interest is the simulation of vertical seismic profiling (VSP) surveys, where we have extended the theoretical treatment to include expressions for the derivatives of the seismograms with respect to the reflection coefficients. The resulting time series, which we call Jacobograms, are indicative of the sensitivity of the seismogram to the various reflection coefficients and are thus diagnostic of the model’s behavior.

Acoustical Reflection and Scattering from the Underside of Laboratory-Grown Sea Ice: Measurements and Predictions (Abstract)

1987 ◽  
Vol 9 ◽  
pp. 238
Author(s):  
K.C. Jezek ◽  
T.K. Stanton ◽  
A.J. Gow
Keyword(s):  
Sea Ice ◽  
Impedance Matching ◽  
Dendritic Structure ◽  
Acoustic Scattering ◽  
Statistical Parameter ◽  
Normal Incidence ◽  
Reflection Coefficients ◽  
Cross Sectional ◽  
Thin Sections ◽  
Using Data

We have studied acoustical reflection and scattering properties of the underside of laboratory-grown sea ice. Our purpose was to determine the morphologic characteristics of undeformed sea ice that control acoustic scattering and reflection. So our experiments included both detailed studies of the structure of the ice as well as the application of a variety of acoustic methods. Ice sheets were grown in an outdoor pond (about 6 m by 13 m by 1.5 m) and exhibited features characteristic of undeformed, cold sea ice: an upper granular zone; a columnar zone of crystals with cross-sectional areas of about 1 cm2; vertical sheets of brine pockets; a bulk salinity of 9.1‰ distributed over 9 cm of ice; a dendritic interface at the ice/water boundary with dendrites about 0.5 mm across at the time of our measurements. Echo-amplitude fluctuations of normal-incidence sonar pings (100 kHz to 800 kHz) were measured as the sonars moved horizontally under the ice and accumulated into echo-amplitude histograms. (Data from a deteriorating ice sheet as well as data on lake ice were also collected.) We fitted the Rice probability density function (PDF) to the data and combined the resultant statistical parameter with Eckart acoustic scattering theory. The reflection coefficients calculated using this method ranged from 0.06 to 0.12, depending on environmental conditions. RMS roughness calculated using data from new sea ice was estimated to be about 0.3 mm. Because our ice thin sections show the ice to be porous and permeable at the interface with dendrites 0.5 mm thick, we suspect that the dendrites control the scattering as described by the echo-amplitude histograms. Further, we attribute the low reflection coefficients to the dendritic structure which may act as an impedance-matching zone into the columnar section of the sea ice. Transmission measurements were performed by positioning a transducer located at the ice/air interface directly over the transducer located in the water. The total attenuation through 18 cm of ice ranged from 12 dB at 50 kHz to 70 dB at 420 kHz (signal levels were measured relative to the same path in water).

Fast seismic inversion

Geophysics ◽  
1983 ◽  
Vol 48 (10) ◽  
pp. 1371-1372 ◽  
Author(s):  
W. Keith McClary
Keyword(s):  
Inverse Problem ◽  
Layered Medium ◽  
Normal Incidence ◽  
Seismic Inversion ◽  
Reflection Coefficients ◽  
Type B ◽  
Layer Model ◽  
Type C ◽  
Layer Problem

The equal traveltime layer model of a horizontally layered medium with waves at normal incidence is used to solve the inverse problem (determination of the reflection coefficients and fundamental polynomials from the surface response) by an efficient algorithm using [Formula: see text] computations for N layers. The idea is to reduce the N‐layer problem to two similar problems of N/2 layers each plus additional computations of type B and C. Type B computes the data for the second problem from the result of the first and type C combines the results. For [Formula: see text] the reduction is carried out k times leading to N trivial one‐layer problems plus more computations of type B and C, which are polynomial multiplications or discrete convolutions. The improvement over the [Formula: see text] computations required by recursive methods comes from using the fast Fourier transform to perform the convolutions.

scholarly journals Acoustical Reflection and Scattering from the Underside of Laboratory-Grown Sea Ice: Measurements and Predictions (Abstract)

1987 ◽  
Vol 9 ◽  
pp. 238-238
Author(s):  
K.C. Jezek ◽  
T.K. Stanton ◽  
A.J. Gow
Keyword(s):  
Sea Ice ◽  
Impedance Matching ◽  
Dendritic Structure ◽  
Acoustic Scattering ◽  
Statistical Parameter ◽  
Normal Incidence ◽  
Reflection Coefficients ◽  
Cross Sectional ◽  
Thin Sections ◽  
Using Data

We have studied acoustical reflection and scattering properties of the underside of laboratory-grown sea ice. Our purpose was to determine the morphologic characteristics of undeformed sea ice that control acoustic scattering and reflection. So our experiments included both detailed studies of the structure of the ice as well as the application of a variety of acoustic methods.Ice sheets were grown in an outdoor pond (about 6 m by 13 m by 1.5 m) and exhibited features characteristic of undeformed, cold sea ice: an upper granular zone; a columnar zone of crystals with cross-sectional areas of about 1 cm2; vertical sheets of brine pockets; a bulk salinity of 9.1‰ distributed over 9 cm of ice; a dendritic interface at the ice/water boundary with dendrites about 0.5 mm across at the time of our measurements. Echo-amplitude fluctuations of normal-incidence sonar pings (100 kHz to 800 kHz) were measured as the sonars moved horizontally under the ice and accumulated into echo-amplitude histograms. (Data from a deteriorating ice sheet as well as data on lake ice were also collected.) We fitted the Rice probability density function (PDF) to the data and combined the resultant statistical parameter with Eckart acoustic scattering theory. The reflection coefficients calculated using this method ranged from 0.06 to 0.12, depending on environmental conditions. RMS roughness calculated using data from new sea ice was estimated to be about 0.3 mm. Because our ice thin sections show the ice to be porous and permeable at the interface with dendrites 0.5 mm thick, we suspect that the dendrites control the scattering as described by the echo-amplitude histograms. Further, we attribute the low reflection coefficients to the dendritic structure which may act as an impedance-matching zone into the columnar section of the sea ice.Transmission measurements were performed by positioning a transducer located at the ice/air interface directly over the transducer located in the water. The total attenuation through 18 cm of ice ranged from 12 dB at 50 kHz to 70 dB at 420 kHz (signal levels were measured relative to the same path in water).

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