摘要:

AbstractIn many fields of imaging, the shape of the function describing the incident source wave (“the wavelet”) is known. In seismic exploration, this luxury is not available since seismic sources are affected by their environment. The resultant wavelet that is transmitted into the earth is quite different from any measurement that may be conducted near the source. To many seismic explorationists the wavelet has almost taken a mythical position of stature. More Black Art, mysterious assumptions, advanced mathematics, and handwaving go into wavelet estimation than any other aspect of seismic exploration. The reason for all the effort stems from the need to explore targets that are fractions of wavelengths. This presentation describes some of the methods used in seismic exploration to preserve bandwidth, estimate the wavelet shape, and invert the data to obtain a sharp im

ISSN:0899-9457    

DOI:10.1002/ima.1850020102

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

ISSN:0899-9457    

DOI:10.1002/ima.1850020103

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractWhen the product of contrast and size of an object, which is to be reconstructed by using the ultrasound inverse scattering tomography algorithm, is large, it is well known that those algorithms fail to converge to a unique global minimum. In order to solve this well known and difficult convergence problem, in this paper we present a new method, which converges to the true solution, for obtaining the scattering potential without using the Born or Rytov approximation. This method converts the nonlinear nature of the problem into a linear one. Through computer simulations we will show the validity of the new approach for high contrast two‐dimensional scattering objects which are insonified by an incident ultrasound plane wave. Numerical results show that the reconstruction error is very small for circularly symmetric two‐dimensional cylindrical objects whose refractive indices range from small to even sufficiently large values for which the previous inverse scattering algorithms fail to conve

ISSN:0899-9457    

DOI:10.1002/ima.1850020104

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractAlgorithms for extrapolating the scattered field along the frequency direction and the azimuthal direction are developed and analyzed. Their effects on the image resolution for polar format processing and rectangular format processing are discussed. Simulation and experimental results show that extrapolation along the frequency direction does increase the range resolution. While extrapolation along the azimuthal direction improves the cross‐range resolution for small angle imaging, it does not improve image resolution of complex‐shaped objects for wide angle imaging. Both range and cross‐range resolutions can be improved simultaneously for small angle imaging using rectangular format processing if the angular interval and the resolution cells are suitably chosen. A promising application for the algorithms developed is in microwave dynamic im

ISSN:0899-9457    

DOI:10.1002/ima.1850020105

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe application of solid echoes to the nuclear magnetic resonance (NMR) imaging of shortT2materials is demonstrated by means of two‐dimensional (19F) images. A closed‐form, exact and generally applicable expression for solid echo imaging is derived and a procedure for on‐the‐fly data analysi

ISSN:0899-9457    

DOI:10.1002/ima.1850020106

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractIt was previously shown that the sonic echo wave pattern from a thin layer embedded between two thick layers can be readily and accurately calculated using a recursive expression (1). Two three‐layered experimental structures were described where the calculated and experimental wave patterns were successfully compared. It was shown that marked drastic changes in the echo wave pattern result from a layer much thinner than the pulse length.The mathematical technique lends itself readily to computer calculation and can be employed in situations with an arbitrary number of layers. The power of the algorithm will be demonstrated here on a four‐layered structure. The material in the next section is taken directly from Ref

ISSN:0899-9457    

DOI:10.1002/ima.1850020107

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe estimation of the three‐dimensional (3‐D) motion parameters of a rigid body is a very important subject in scene analysis and trajectory prediction. Motion parameters can be estimated from two sets of object feature points before and after the motion. In general, the matching correspondences of the feature points are available, and the motion parameters can be estimated by solving equations associated with the correspondences. In this paper, we present a new method for motion estimation from 3‐D data without requiring the knowledge of matching correspondences.In the noise‐free case, this approach identifies four candidates for the rotation matrix. The rotation matrix giving the best match of the point features can then be selected from the four candidates, and the matching correspondences are subsequently established. Possible ambiguities due to symmetrical feature points are also discussed in this paper. In the presence of noise, this method provides an initial estimate of the motion, which is then used to establish the matching correspondences. Subsequently, a new estimate of the motion parameters can be obtained with the established matching correspondence information. The effects of random zero‐mean noise are studied. Simulated results are shown to demonstrate the effectiveness and accuracy of this

ISSN:0899-9457    

DOI:10.1002/ima.1850020108

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

ISSN:0899-9457    

DOI:10.1002/ima.1850020109

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

ISSN:0899-9457    

DOI:10.1002/ima.1850020101

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY