Data are typically processed to meet this assumption by the application of statics. And after the migration applied, mean dipping reflector moved upward,same way reflection traces also moves up. Badawy page46 how geologic features appear after migration. The following notations will used throughout this page. It is distinguished from dip moveout dmo, the systematic change in arrival time due to a dipping layer.
Neuromyelitis optica, or nmo, is a disease that affects your eyes and spinal cord. To account for this effect a technique called migration is used. 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. And it may not necessary be in the same phase as the first reflect.
Pasternack nmo mount connectors are part of over 30,000 rf, microwave and fiber optics products available for same day shipment. Design of 3d geometry reflection seismology reflection. Optical system design s15 reflector telescopes joseph a. Currently at least three different kinds are proposed based on the presence of autoantibodies thought to produce the disease. 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. Nonstretch nmo of prestack migrated gathers programs. Estimation of geological dip and reflector curvature from. The mcs reflection profile re23 depicts two sets of westerly dipping reflector sequences u1 and u2 separated by 5 km figure 6. Neuromyelitis optica nmo is an uncommon disease syndrome of the central nervous system cns that affects the optic nerves and spinal cord. Castle 1994 proposed shifted hyperbola nmo equation, which is a better approximation to the moveout than the dixs nmo dix, 1955 equation. Reflector antennas national radio astronomy observatory. 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.
These filters can be designed and applied in any known implementation of dipmoveout, in three or two dimensions. Dec 15, 2016 principles of seismic data processing m. Crains petrophysical handbook chapter and topic index. 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. Its not very common only about 4,000 people in the united states have it.
This wave now gets reflected as collimated wave front, as discussed previously. 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. 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. Here, t n is the event time after nmo correction using the flatevent velocity v nmo, h is the halfoffset and. Velocity analysis for transversely isotropic media. The need for dmo the nmo velocity figure shows a dipping reflector and the position of the source, geophone and cmp. 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. 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.
The models consist of 1 a dipping planar reflector, within a homogeneous overburden, for which the time eq. These two equations are used for the parameter estimation in this study. Figure 1 raypaths and wavefronts for a zerooffset seismic line shot above a dipping reflector. The cosine rule in the triangle irs gives the travel time, t, as vt, which is the distance. Reflection traveltime inversions in vti media chunyan mary xiao, john c. A dipping reflector leads to asymmetric arrival times for shots recorded in. Nmo correction in anisotropic media using ray velocity. To circumvent this requirement, we use the relation section d.
Consider the zerooffset seismic survey shown in figure 1. With the introduction of the rms velocity, the second order nmo equation becomes a useful approximation to the re. Moon dipmoveout by fourier transform 339 y source receiver midpoint, yo the point where the dipping reflector meets the surface. Migration using a transversely isotropic medium with symmetry. 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. This arrival time is depicted on the time section in figure 5. For dipping reflectors, as shown in figure 3, the residual. Consider the zerooffset seismic survey shown in figure 5. 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. Here, i present a concise analytic expression for normalmoveout nmo velocities valid for a wide range of. 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. 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 traveltime equation for a dipping reflector represents a hyperbola as for the flat reflector equation 1. For the dipping layer sketched in figure the reflection point for the sourcereceiver ray is r.
The second order nmo equation is derived from the raypath geometry of this simple single horizontal layer model. Neuromyelitis optica nmo is a heterogeneous condition consisting of the inflammation and demyelination of the optic nerve optic neuritis and the spinal cord myelitis. Download scientific diagram normal moveout for a dipping reflector. Dix 1955 nmo equation to models consisting of a stack of anisotropic horizontal layers above a dipping reflector. Higherresolution determination of zerooffset common. 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. Traveltime curve for a flat reflector is a hyperbola with its apex at zerooffset trace. In this paper, a new nmo correction method has been developed for a horizontal layer in vti media based on ray velocity. Pdf inversion of azimuthally dependent nmo velocity in. Blias 2009 has also shown that the nmo approximations are modeldependent. As discussed in principles of dip moveout correction, the integral transform factor a given by equation requires knowledge of the reflector dip. Seismic experiment conducted over a halfspace with a constant velocity medium and a dipping reflector.
Inversion for thomsens parameters using shifted hyperbola. 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. The zerooffset traveltime from the cmp to the reflector and back is given by the segment fg. However, the nmo velocity now is given by the medium velocity divided by the cosine of the dip angle as defined by equation.
The nmo velocity for a dipping reflector is greater than that for a horizontal reflector. The traveltime equation 10 for a dipping reflector represents a hyperbola as for the flat reflector equation 1. Figure 2 defines the required quantities for a reflection event recorded at s corresponding to the reflectivity at r. What is nmo from the guthyjackson charitable foundation.
Tsvankin and thomsen 1994 described a nmo equation for ti media in terms of the thomsens parameters. This process is constrained by two kinematic equations, one for perturbations in the normalmoveout nmo velocity and the other for. Introduction highgain antennas are required for longdistance radio communications radiorelay links and satellite links, highresolution radars, radioastronomy, etc. The zerooffset raypath from j is equal to the segment jk. For a horizontal layer, the reflection point is situated right under the location of the commonmidpoint cmp. 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. This survey uses one sourcereceiver pair, and the receiver is always at the same location as the source. At each position, denoted by in the figure, the source emits waves and the receiver records the echoes as a single seismic trace. 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 inversion technique is based on the exact analytic equation for the normalmoveout nmo velocity for dipping reflectors in anisotropic media. Generalized dix equation and analytic treatment of normalmoveout.
Normal moveout for a dipping reflector beneath a vertically. The basic components of residual migration in vti media using. C combined effects of reflector depth and velocity on the nmo time for four different reflector depths with increasing velocities. Neuromyelitis optica nmo is a heterogeneous condition consisting of the inflammation and demyelination of the optic nerve optic neuritis and the spinal cord.
Migration using a transversely isotropic medium with. Individuals with nmo develop optic neuritis, which causes pain in the eye and vision loss, and transverse myelitis, which causes weakness. On optimal nmo and generalised dix equations for velocity. From the 3d wave equation, the seismic data collected over a dipping planar reflector is given by py,t y r.
Since the late seventies and early eighties, under the assumption of. Follow bugs through your application to see where the problem is your own code, thirdparty libraries, or components used by your application. Net reflector is a paid development application that is compatible with windowsbased computers. The nmo equation defines the normal moveout function. The nmocorrection is applied for a cmp using different constant velocities. 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. Pdf 3d description of normal moveout in anisotropic. Both ellipses were distorted by random noise with a variance of 2%. This equation indicates that proper stacking of a dipping event requires a velocity that is greater than the. Nmo mount connectors from pasternack enterprises ship same day. Reflection traveltime inversions in vti media cseg. Travel time for single plane dipping layer the length of the reflection path, scr, from source to receiver is the same as path ir. The raypath from the source to the receiver is sketched by the segments ar and rb. It means that, the waves come out of the focal point and strike the paraboloidal reflector.
The most widespread example of such procedure is the socalled map migration, in which normalincidence, zerooffset stacked seismic data are employed. The dipping reflectors are a stack of laterally discontinuous to continuous, high amplitude, divergent and offlapping, westerly dipping reflectors figures 6. 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. Velocity analysis for transversely isotropic media inside mines. For a flat, horizontal reflector, the traveltime equation is. 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. As the input data we use the pwave nmo ellipses from a horizontal and a dipping reflector dip. Therefore, apriori knowledge of the velocity trend is important to establish the best nmo approximation to obtain the interval velocities. 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. The reflection point r is seen in the zerooffset case from the surface point j. 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.
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. Nmo mount connectors and other rf, microwave and fiber optic products from pasternack ship same day worldwide. 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. Generalized dix equation and analytic treatment of. Cvs constant velocity stacks similar to the cvpmethod the data is nmocorrected. 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. This point is positioned updip relative to the intersection o of the zerooffset ray from the commonmidpoint f with the dipping reflector.
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. 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. 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. 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. Normal moveout from dipping reflectors in anisotropic media. Dipping events appear to be steeper migration moves events up dip migration steepness events migration shortens even anticline.
The influence of anisotropy on normalmoveout velocity is absorbed by the slowness components of the zerooffset ray. Inverse commonreflectionsurface geophysical journal. The fact that this nmo equation is the best for model 2 does not mean that it can perform equally well in other cases. Since the late seventies and early eighties, under the. Shaw montana state university conics a conic is a surface of revolution formed by spinning a conic section around the axis. The choice of these models reflects our assumption that. More special to figure, suppose we have recorded data from the dipping reflector as. In reflection seismology, normal moveout nmo describes the effect that the distance between.
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