ISSN:0899-9457    

DOI:10.1002/ima.1850040402

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThree methods of producing microwave images of rotating objects are reviewed and correlated. These are range Doppler processing, coherent tomographic imaging, and a physical optics‐based technique using the Bojarski identity. We use an understanding of these processes to interpret and predict the appearances of images reconstructed from data collected over specified frequency and angular windows. Based on the understanding of the fundamental image formation processes, we have developed several image reconstruction algorithms applicable when objects are situated in different environments. Examples are bistatic imaging, near field imaging, moving target imaging, irregularly spaced array imaging, and imaging of objects embedded in a homogeneous dielectric background. Numerical and experimental results have verified the effectiveness of our proposed algorithms.©1993 John Wiley&Sons

ISSN:0899-9457    

DOI:10.1002/ima.1850040403

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractIn coherent imaging the object of interest is complex but only its amplitude is to be estimated. The object phase yields nuisance variables and in a proper Bayesian approach it is necessary to obtain a phaseless likelihood function. We investigate a two‐dimensional case in which the target object is modelled as a collection of point scatterers having independent random phases. The phaseless likelihood function is determined exactly for a configuration of data samples in a uniformly spaced square array in spatial frequency when the target scatterers are confined to lattice positions of a “matched” spatial array. It is determined approximately when the target scatterers are arbitrarily positioned, at most one per conventional resolution cell. The relation between maximum likelihood and conventional Fourier transform imaging is explored and the feasibility of a CLEAN algorithmic technique in coherent imaging is considered.©1993 John Wiley&S

ISSN:0899-9457    

DOI:10.1002/ima.1850040404

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractRecent results in radar imaging using estimation theoretic techniques are applied to forming images from data from a compact radar range. Nonparametric maximum likelihood methods based on spline approximations are used. The object imaged is a one meter diameter sphere covered with wrinkled aluminum foil. This rough sphere approximately fits the diffuse model and the ideal scattering function for a rough rotating sphere is known. The results shown demonstrate that the proposed algorithm is realizable and that the image are comparable to simulations.©1993 John Wiley&Sons In

ISSN:0899-9457    

DOI:10.1002/ima.1850040405

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractReported herein is the estimation of the residual error of the reflectivity displacement method (RDM) and the dependence of RDM on terrain characteristics. The RDM is a method to be implemented on airborne synthetic aperture radars (SAR). It extracts the motion of the aircraft from the radar backscatter signal, allowing for motion compensation without using an inertial navigation system. An extended error analysis of this method and its dependence on the terrain type and contrast is performed. Results proving the estimated performance are shown.

ISSN:0899-9457    

DOI:10.1002/ima.1850040406

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractSelf‐calibration of a phased antenna array is required when distortions in the array are not knowna prioriand cannot be measured, or when turbulence in the propagation medium perturbs the radiation field. Two types of self‐calibration procedures are discussed that have proved successful in experimental high‐resolution two‐dimensional microwave radar imaging. Each extracts information from the backscattered reradiation field to deduce a compensating weight vector for the phased array antenna. The first depends upon the presence of a strong reflector in the field of view of the transmitter. The second calibrates the array from correlation estimates of wavefront samples in the array. The basic algorithm in each group is described, along with two more sophisticated algorithms in the latter class. Two‐dimensional radar images of airplanes are shown with resolution comparable to human vision. The performance of each algorithm and comparisons between them are illustrated by these images of targets and by simulation experiments.©1993 John Wil

ISSN:0899-9457    

DOI:10.1002/ima.1850040407

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractInverse synthetic aperture radar (ISAR) is an imaging technique that shows great promise in classifying airborne targets in real‐time under all weather conditions. The success of classifying targets using ISAR is predicated upon forming highly focused radar images of these target. Efforts to develop highly focused radar imaging computer software have been challenging, mainly because the imaging depends on and is affected by the motion of the target. Computationally intensive motion compensation algorithms have been developed to remove the unwanted degrading effects of target motion. Those particular motion compensation algorithms which require the use of a space domain focal quality indicator (e.g., entropy) to determine image sharpness as processing proceeds pay a severe computational penalty due to the large number of two‐dimensional fast Fourier transforms (2D‐FFTs) which must be computed. This is due to the fact that the actual processing of ISAR data is done primarily in the spatial frequency domain and not in the space domain where the final ISAR image is displayed. If a focal quality indicator could be developed to measure image sharpness in the spatial frequency domain, then the computational burden introduced by the numerous 2D‐FFTs could be greatly relaxed. This article describes the use of a new focal quality indicator called the burst derivative measure for determining ISAR image sharpness in the spatial frequency domain. Tests have been performed on simulated as well as actual ISAR data using both the burst derivative measure and the entropy measure. Results indicate that the burst derivative measure, when used in conjunction with the entropy measure, can greatly reduce the number of 2D‐FFTS presently required in these motion compensation algorithms.©1993 John Wil

ISSN:0899-9457    

DOI:10.1002/ima.1850040408

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractSpeckle in radar images has the characteristic of a multiplicative noise. In this article, two unsupervised methods are introduced to estimate the speckle noise statistics using the mean and the standard deviation of small image blocks (4 × 4, or 6 × 6 pixels). Since most radar images contain many small homogeneous areas, a scatter plot of the standard deviation versus the mean can reveal the characteristic of the noise. The blocks from inhomogeneous areas have higher values for the standard deviation, and they are scattered above the main cluster. They are considered as outliers, and should be excluded in the statistical estimation. These two methods are designed for obtaining a linear fit in the scatter plot by ignoring outliers. Several synthetic aperture radar(SAR) images are used for illustratio

ISSN:0899-9457    

DOI:10.1002/ima.1850040409

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractMIT Lincoln Laboratory in investigating the detection and identification of stationary ground targets in high resolution, fully polarimetric, synthetic aperture radar (SAR) imagery. This article (1) provides a brief description of the Lincoln Laboratory SAR, (2) describes an optimum polarimetric processing technique used to construct minimum‐speckle SAR intensity imagery, and (3) presents examples of polarimetrically processed imagery.©1993 John Wiley&Sons

ISSN:0899-9457    

DOI:10.1002/ima.1850040410

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractMultiresolution representation of images using the wavelet transform is a new approach for the analysis of image information content. The transform can be computed efficiently by a pyramidal algorithm based on convolution with quadrature mirror filters. The result is a set of subband images which consists of a lower resolution version of the original image and a sequence of detail images containing higher frequency spectral information. We used this representation for the supervised segmentation of polarimetric SAR images of the San Francisco Bay area acquired by the airborne JPL system for identifying various terrain covers. Since the wavelet transform generates the localized spatial and spectral information simultaneously, detailed knowledge of the texture variations within an image can be extracted from the data in the spectral subbands. The segmentation algorithm developed in this paper is formulated by taking into consideration both the intensity and the texture information. For polarimetric SAR images, the classification accuracy can be enhanced, if the combined data from copolarized and cross‐polarized images are used in the discrimination process. In contrast to other texture segmentation approaches, this algorithm does not require extensive calculations.©1993 John Wiley&Sons

ISSN:0899-9457    

DOI:10.1002/ima.1850040411

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY