摘要:

AbstractMigration and dip‐moveout (partial prestack migration) are two‐dimensional (space and time) processes of fundamental importance in digital processing of seismic data. Their goal is to make the seismic section appear similar to the geological image along the seismic line subsurface. In this article we study migration and dip‐movement processes from the point of view of their impulse responses. The constant‐velocity migration process is a space‐invariant and time‐variant operator. We demonstrate and illustrate by examples of synthetic and real seismic sections that by transforming the time axis with a square function the constant‐velocity migration operator becomes temporally stationary as well as spatially stationary, that is, it can be expressed as an invariant two‐dimensional convolution. The dip‐moveout seismic process can be applied to constant‐offset seismic sections or to shot seismic profiles. The application of dip‐moveout process to constant‐offset sections is also a temporally varying and spatially stationary operator. By transforming the time axis with a logarithmic function the constant‐offset dip‐moveout operator becomes temporally stationary as well as spatially stationary. The shot dip‐moveout operator is space variant and time variant. After a logarithmic transformation of both the time and the space coordinates, it becomes time invariant and space invariant. Therefore the dip‐moveout seismic processes can be also expressed as an invariant two‐dimensional convolution. We illustrate this by examp

ISSN:0899-9457    

DOI:10.1002/ima.1850040202

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractWe propose a motion estimation system that uses stereo image pairs as the input data. To perform experimental work, we also obtain a sequence of outdoor stereo images taken by two metric cameras. The system consists of four main stages, which are (1) determination of point correspondences on the stereo images, (2) correction of distortions in image coordinates, (3) derivation of 3D point coordinates from 2D correspondences, and (4) estimation of motion parameters based on 3D point correspondences. For the first stage of the system, we use a four‐way matching algorithm to obtain matched point on two stereo image pairs at two consecutive time instants (tiandti+ 1). Since the input data are stereo images taken by cameras, it has two types of distortions, which are (i) film distortion and (ii) lens distortion. These two distortions must be corrected before any process can be applied on the matched points. To accomplish this goal, we use (i) bilinear transform for film distortion correction and (ii) lens formulas for lens distortion correction. After correcting the distortions, the results are 2D coordinates of each matched point that can be used to derive 3D coordinates. However, due to data noise, the calculated 3D coordinates to not usually represent a consistent rigid structure that is suitable for motion estimation; therefore, we suggest a procedure to select good 3D point sets as the input for motion estimation. The procedure exploits two constraints, rigidity between different time instants and uniform point distribution across the object on the image. For the last stage, we use an algorithm to estimate the motion parameters. We also wish to know what is the effect of quantization error on the estimated results; therefore an error analysis based on quantization error is performed on the estimated motion parameters. In order to test our system, eight sets of stereo image pairs are extracted from an outdoor stereo image sequence and used as the input data. The experimental results indicate that the proposed system does provide reasonable estimated motion parameter

ISSN:0899-9457    

DOI:10.1002/ima.1850040203

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractMany imaging devices have been constructed that use fourier transform techniques for image reconstruction as well as for image analysis. The basis functions in the fourier transform space are sinusoids. These are not localized. Therefore it should not be expected that highly localized behavior of a signal be characterized well using functions distributed evenly throughout the interval of the integral transform. Also, the phase cancellations of a conventional impulse signal are not handled well by fourier techniques. On the other hand, the basis functions of the wavelet transformation are highly localized, i.e., these exhibit compact support, yet are orthonormal. The multispectral decomposition algorithm of the wavelet transformation is used to analyze the signal returning from the reflections of a single ultrasonic transducer with a focused beam and operated in the focal zone. The choice of frequency depends upon the mutually antagonistic factors of penetration (αf–2) and resolution (αf). The signal sent into the sample should not be the impulse response signal used in conventional devices; rather, it should be a time‐reversed replica of a single or a linear combination of the most highly localized basis function wavelets. The returning signal is a sequence of translates of the wavelets plus perhaps some lower‐resolution wavelets. The translations are proportational to the time of flight of the signal. The wavelet transformation is superb at discriminating the population of each of these translates which is identically the A‐scan signal. The transmitted signal, which is a time‐reversed single wavelet or a linear combination of wavelets, is not easy to produce. Inexpensive ultrasound transducers have resonances which make it difficult to produce any desired wave form. Wavelet shape is far from arbitrary. Precise wave shaping is performed by measuring the impulse response function of the transducer; then, the desired wave shape is convolved with the inverse of the measured impulse response function of the transducer. This produces the signal to be presented to the pulse generation circuit. Care is taken to damp the impulse response so that there are no zeros. The received signal is sampled at an even rate which is carefully chosen to match the time delay of one wavelet translate to the next. B‐scan, C‐scan, and volume imaging are easily accomplished using a sequence of A‐scan data, all by conventional techniques. A single A‐scan requires less than 2 ms to perform and reconstruct with a high‐speed arithmetic unit which was designed in conjunction with this work and is now c

ISSN:0899-9457    

DOI:10.1002/ima.1850040204

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA summary of the results of an extensive comparative experimental study of Fourier transformation and model‐fitting methods of spectral analysis of random time‐series data is presented. It is illustrated that Fourier transformation methods can be an essential companion to model‐fitting methods even for short data segments with underlying sharp spectral peaks. The best spectrum estimates can be obtained by taking advantage of the strengths of both types of methods. For example, it is shown that detection and estimation of the frequencies of spectral lines for short data segments can be best accomplished using certain parametric methods in conjunction with Fourier transformation methods to aid in model‐order selection and identification of spurious peaks in the parametric spectrum estimate, and that estimation of amplitude and phase for sine‐wave removal, given frequency estimates, and spectrum estimation after sine‐wave removal can often be best accomplished with Fourier transformation me

ISSN:0899-9457    

DOI:10.1002/ima.1850040205

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractOne of the central problems in dynamic computer vision is the determination of motion from correspondence of points on the visible surface of a moving object obtained at two different times. In the problem we consider, the initial position of several feature points on some object is assumed to be known. Then at some later time instant the corresponding perspective projection of those points is given. The moving body may be nonrigid or the measurements may be corrupted with noise. In either case, we determine the multiplicity of possible solution for the best‐fitting rigid motion. We show that whenever at least three point correspondences are given, there are at most two possible solutions for the best‐fitting rigid motion if the object space is two‐dimensional, while there are at most forty possible solutions if the object space is three‐dimensional. In the latter case the number of possible solutions drops to four if three point correspondence are known, the body is rigid, and the measurements are noise‐free. Several examples are worked out to illustrate our results.©1994 John Wil

ISSN:0899-9457    

DOI:10.1002/ima.1850040206

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA novel image segmentation scheme based on a neural network has been implemented to segment magnetic resonance head images. A three‐layer perceptron‐type neural network, trained with backward error propagation algorithm was used. The scheme utilizes first‐echo intensity and computedT2values to construct a two‐parameter space for classification. After training on a selected slice, the method successfully segments all slices for a given subject without any further human inte

ISSN:0899-9457    

DOI:10.1002/ima.1850040207

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

ISSN:0899-9457    

DOI:10.1002/ima.1850040201

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY