Pdf 3d description of normal moveout in anisotropic. Apr 23, 2012 depth conversion of selected seismic reflections is a valuable procedure to position key reflectors in depth in a process of constructing or refining a depthvelocity model. This survey uses one sourcereceiver pair, and the receiver is always at the same location as the source. For the dipping layer sketched in figure the reflection point for the sourcereceiver ray is r. From the 3d wave equation, the seismic data collected over a dipping planar reflector is given by py,t y r.
As the input data we use the pwave nmo ellipses from a horizontal and a dipping reflector dip. The reflection point r is seen in the zerooffset case from the surface point j. For dipping reflectors, as shown in figure 3, the residual. Higherresolution determination of zerooffset common. Figure 1 raypaths and wavefronts for a zerooffset seismic line shot above a dipping reflector. Normal moveout from dipping reflectors in anisotropic media. Inversion for thomsens parameters using shifted hyperbola. If the medium above a dipping reflector is horizontally stratified, the effective nmo velocity is determined through a dixtype average of the matrices responsible for the interval nmo ellipses in the individual layers. Download scientific diagram normal moveout for a dipping reflector. The nmo velocity for a dipping reflector is greater than that for a horizontal reflector. Nonstretch nmo of prestack migrated gathers programs. The traveltime equation 10 for a dipping reflector represents a hyperbola as for the flat reflector equation 1. The models consist of 1 a dipping planar reflector, within a homogeneous overburden, for which the time eq. This wave now gets reflected as collimated wave front, as discussed previously.
This point is positioned updip relative to the intersection o of the zerooffset ray from the commonmidpoint f with the dipping reflector. At each position, denoted by in the figure, the source emits waves and the receiver records the echoes as a single seismic trace. Dippingreflector shifts a little geometry gives simple expressions for the horizontal and vertical position errors on the zerooffset section, which are to be corrected by migration. Reflection traveltime inversions in vti media chunyan mary xiao, john c. For the model of a single homogeneous layer above a dipping reflector, we obtain an explicit nmo expression valid for all pure modes and any. In reflection seismology, normal moveout nmo describes the effect that the distance between. The second order nmo equation is derived from the raypath geometry of this simple single horizontal layer model. These two equations are used for the parameter estimation in this study.
Seismic experiment conducted over a halfspace with a constant velocity medium and a dipping reflector. Nmo mount connectors from pasternack enterprises ship same day. The relationship between arrival time and offset is hyperbolic and it is the principal criterion that a geophysicist uses to decide whether an event is a reflection or not. It means that, the waves come out of the focal point and strike the paraboloidal reflector. Castle 1994 proposed shifted hyperbola nmo equation, which is a better approximation to the moveout than the dixs nmo dix, 1955 equation.
We show that pwave nmo velocity for dipping reflectors in homogeneous ti media with a vertical symmetry axis depends just on the zerodip value v nmo 0 and a new effective parameter eta that. The traveltimes for these two events are described by the ordinary nmo equations where the velocity coefficients for the diffractor, and dipping reflector, are given by here, and represent the root mean square rms velocity and the dip angle, respectively. Nmo correction in anisotropic media using ray velocity. Velocity analysis for transversely isotropic media. Optical system design s15 reflector telescopes joseph a. Therefore, apriori knowledge of the velocity trend is important to establish the best nmo approximation to obtain the interval velocities. With the introduction of the rms velocity, the second order nmo equation becomes a useful approximation to the re. This arrival time is depicted on the time section in figure 5. The raypath from the source to the receiver is sketched by the segments ar and rb. In reflection seismology, normal moveout nmo describes the effect that the distance between a seismic source and a receiver the offset has on the arrival time of a reflection in the form of an increase of time with offset.
Travel time for single plane dipping layer the length of the reflection path, scr, from source to receiver is the same as path ir. Generalized dix equation and analytic treatment of. Ppps processing datum, nmo and velocity analysis from topography the conventional pp and ps nmo equations assume that all shotreceiver pairs for traces within a midpoint gather are at the same elevation. For a flat, horizontal reflector, the traveltime equation is. A method and apparatus for carrying out dip moveout correction on seismic data to provide trueamplitude seismic images use a calibration process to design a set of filters that correct the seismic amplitudes during dip moveout correction so as to provide trueamplitude imaging. Depth conversion of selected seismic reflections is a valuable procedure to position key reflectors in depth in a process of constructing or refining a depthvelocity model. Small errors for the other two models pierre mains significantly higher than the nmo velocity for a shale and bereasandstone are not surprising since both are horizontal reflector. A dipping reflector leads to asymmetric arrival times for shots recorded in. Here, i present a concise analytic expression for normalmoveout nmo velocities valid for a wide range of. Normal moveout for a dipping reflector beneath a vertically. These filters can be designed and applied in any known implementation of dipmoveout, in three or two dimensions.
Inverse commonreflectionsurface geophysical journal. Consider the zerooffset seismic survey shown in figure 5. More special to figure, suppose we have recorded data from the dipping reflector as. What is nmo from the guthyjackson charitable foundation neuromyelitis optica nmo is an uncommon disease syndrome of the central nervous system cns that affects the optic nerves and spinal cord. Badawy page46 how geologic features appear after migration. Shaw montana state university conics a conic is a surface of revolution formed by spinning a conic section around the axis. Tsvankin and thomsen 1994 described a nmo equation for ti media in terms of the thomsens parameters. Consider the zerooffset seismic survey shown in figure 1. Moon dipmoveout by fourier transform 339 y source receiver midpoint, yo the point where the dipping reflector meets the surface. Since the late seventies and early eighties, under the assumption of. And after the migration applied, mean dipping reflector moved upward,same way reflection traces also moves up. Individuals with nmo develop optic neuritis, which causes pain in the eye and vision loss, and transverse myelitis, which causes weakness.
The fact that this nmo equation is the best for model 2 does not mean that it can perform equally well in other cases. Net reflector is a paid development application that is compatible with windowsbased computers. Traveltime curve for a flat reflector is a hyperbola with its apex at zerooffset trace. It is distinguished from dip moveout dmo, the systematic change in arrival time due to a dipping layer. The traveltime equation for a dipping reflector represents a hyperbola as for the flat reflector equation 1. The influence of anisotropy on normalmoveout velocity is absorbed by the slowness components of the zerooffset ray. Neuromyelitis optica nmo is an uncommon disease syndrome of the central nervous system cns that affects the optic nerves and spinal cord. Neuromyelitis optica nmo is a heterogeneous condition consisting of the inflammation and demyelination of the optic nerve optic neuritis and the spinal cord myelitis. Crains petrophysical handbook chapter and topic index. The total reflection or offset time t r is given by the nmo or zerooffset time t n, the offset x and the velocity of the medium v.
For a flat reflector with an overlying homogeneous medium, the reflection hyperbola can be corrected for offset if the correct medium velocity is used in the nmo equation. If a parabolic reflector antenna is used for transmitting a signal, the signal from the feed, comes out of a dipole or a horn antenna, to focus the wave on to the parabola. Estimation of geological dip and reflector curvature from. Its not very common only about 4,000 people in the united states have it. Migration using a transversely isotropic medium with symmetry. Both ellipses were distorted by random noise with a variance of 2%. This process is constrained by two kinematic equations, one for perturbations in the normalmoveout nmo velocity and the other for. The need for dmo the nmo velocity figure shows a dipping reflector and the position of the source, geophone and cmp. What is nmo from the guthyjackson charitable foundation. The results of the different velocities are compared and the velocity that results in a flattening of the hyperbolas is the velocity for a certain reflector. Pasternack nmo mount connectors are part of over 30,000 rf, microwave and fiber optics products available for same day shipment. The most widespread example of such procedure is the socalled map migration, in which normalincidence, zerooffset stacked seismic data are employed. Dec 15, 2016 principles of seismic data processing m.
Velocity analysis for transversely isotropic media inside mines. On optimal nmo and generalised dix equations for velocity. Reflection traveltime inversions in vti media cseg. The offset wave number is given now by a simpler equation for completeness, the laterally varying phase velocity for ti media is given as where, is the velocity in the symmetry direction, is the nmo velocity with respect to the symmetry axis, and is the anisotropy parameter relating the nmo velocity to the velocity normal to the symmetry axis. Here, t n is the event time after nmo correction using the flatevent velocity v nmo, h is the halfoffset and. In this paper, a new nmo correction method has been developed for a horizontal layer in vti media based on ray velocity. The basic components of residual migration in vti media using.
Travel time for single plane dipping layer the length of the reflection path, scr, from source to receiver is the same as path ir, from an imaginary source, i, obtained by reflecting the surface source, s, in the interface. C combined effects of reflector depth and velocity on the nmo time for four different reflector depths with increasing velocities. Since the late seventies and early eighties, under the. Data are typically processed to meet this assumption by the application of statics. The following notations will used throughout this page. To circumvent this requirement, we use the relation section d.
James brown, university of calgary, calgary abstract anisotropy parameters in a vti medium can be obtained by normalmoveout velocity analysis performed on shortspread or longspread reflectionseismic data, in combination with checkshot or welllog data. Introduction highgain antennas are required for longdistance radio communications radiorelay links and satellite links, highresolution radars, radioastronomy, etc. Dipping events appear to be steeper migration moves events up dip migration steepness events migration shortens even anticline. For a horizontal layer, the reflection point is situated right under the location of the commonmidpoint cmp. And it may not necessary be in the same phase as the first reflect. The mcs reflection profile re23 depicts two sets of westerly dipping reflector sequences u1 and u2 separated by 5 km figure 6. Pdf inversion of azimuthally dependent nmo velocity in.
Design of 3d geometry reflection seismology reflection. In this part, we will derive the equation which links the reflector shape ux to the parallel beam of source light and to a specified output intensity distribution in the far field. The choice of these models reflects our assumption that. The reflector uses a parabolic shape to ensure that all the power is reflected in a beam in which the wave traces run parallel to each other. Neuromyelitis optica nmo is a heterogeneous condition consisting of the inflammation and demyelination of the optic nerve optic neuritis and the spinal cord. Cvs constant velocity stacks similar to the cvpmethod the data is nmocorrected. Neuromyelitis optica, or nmo, is a disease that affects your eyes and spinal cord. Follow bugs through your application to see where the problem is your own code, thirdparty libraries, or components used by your application. However, the nmo velocity now is given by the medium velocity divided by the cosine of the dip angle as defined by equation. This equation indicates that proper stacking of a dipping event requires a velocity that is greater than the. Nmo mount connectors and other rf, microwave and fiber optic products from pasternack ship same day worldwide. Dec 26, 2000 dipping reflector shifts a little geometry gives simple expressions for the horizontal and vertical position errors on the zerooffset section, which are to be corrected by migration. As shown in the figure, the source at s 2 emits a sphericallyspreading wave that bounces off the reflector and then returns to the receiver at s 2. Blias 2009 has also shown that the nmo approximations are modeldependent.
Migration using a transversely isotropic medium with. Reflector 2 uses the builtin airplay functionality of ios to mirror your ios device on a big screen or tablet without wires or complicated setups. The normal moveout depends on complex combination of factors including the velocity above the reflector, offset, dip of the reflector and the source receiver azimuth in relation to the dip of the reflector. Reflector antennas national radio astronomy observatory. The zerooffset raypath from j is equal to the segment jk. The nmocorrection is applied for a cmp using different constant velocities.
The dipping reflectors are a stack of laterally discontinuous to continuous, high amplitude, divergent and offlapping, westerly dipping reflectors figures 6. Also all the reflected power is in the same phase, because the path length from the source to the reflector and then outwards is the same wherever it is reflected on the surface of the parabola. Generalized dix equation and analytic treatment of normalmoveout. Currently at least three different kinds are proposed based on the presence of autoantibodies thought to produce the disease.
Horizontally layered medium above a dipping reflector generalized dix equation here, we show that the nmo ellipse for vertically inhomogeneous arbitrarily anisotropic media above a dipping reflector fig. The nmo equation defines the normal moveout function. Dix 1955 nmo equation to models consisting of a stack of anisotropic horizontal layers above a dipping reflector. The zerooffset traveltime from the cmp to the reflector and back is given by the segment fg. The cosine rule in the triangle irs gives the travel time, t, as vt, which is the distance. To account for this effect a technique called migration is used. As discussed in principles of dip moveout correction, the integral transform factor a given by equation requires knowledge of the reflector dip. Figure 2 defines the required quantities for a reflection event recorded at s corresponding to the reflectivity at r. The inversion technique is based on the exact analytic equation for the normalmoveout nmo velocity for dipping reflectors in anisotropic media.
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