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  • 2015-2019  (561)
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  • 1
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    Unknown
    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2017-12-30
    Description: While attitude steering in the yaw and pitch axes effectively minimizes a residual Doppler centroid in spaceborne synthetic aperture radar systems, it can induce a ground–target pointing error due to the steered radar boresight. In other words, the beams after steering may no longer illuminate the desired target. In this letter, a novel method is proposed to compensate for the target error. The roll angle and image start time, the two degrees of freedom that may be modified while maintaining the zero Doppler centroid condition, are utilized as control parameters. By correcting the roll and time, the associated target error can be significantly reduced. Two solutions are proposed in this letter. The first is a numerical accurate solution, and the second is an analytical approximate solution. One of the solutions can be implemented on-board after a tradeoff study is performed between the remaining target error and computational load. Simulation results verify that the target error is considerably reduced while the Doppler centroid is minimized with the proposed methods.
    Print ISSN: 1545-598X
    Electronic ISSN: 1558-0571
    Topics: Architecture, Civil Engineering, Surveying , Geography , Geosciences
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  • 2
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2017-12-30
    Description: Focusing moving targets with frequency-domain algorithms may suffer from azimuth spectrum not entirely contained within a pulse-repetition frequency band, which may lead to degraded detection performance due to distributing the energy to the artifacts. In order to avoid this problem, a refocusing algorithm after back-projection integral is proposed. The main idea is first to uniformly and coarsely focus moving targets for detection, and then extract the detected targets for refocusing. By deriving the exact analytic expression of the wavenumber spectrum, motion parameter estimation and motion compensation are directly carried out on the 2-D wavenumber domain of the small-sized extracted data, which involves fast Fourier transform and Inverse Fast Fourier Transform operations only with no interpolation, thus reduces the computational complexity. Then, the final refocused image of the moving target is achieved. Refocusing results of both airborne and spaceborne synthetic aperture radar data are shown to validate the effectiveness of the proposed method.
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    Topics: Architecture, Civil Engineering, Surveying , Geography , Geosciences
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  • 3
    Publication Date: 2017-12-30
    Description: Persistent scatterer (PS) pixels contain highly coherent information, which is used in the estimation of geophysical parameters of interest. Conventionally, PS pixels are selected on the basis of the estimated noise present in the spatially uncorrelated phase component along with look-angle error. The phase history of selected PS pixels is corrected for the look-angle error followed by phase unwrapping and extraction of spatially correlated nuisance phase component leading to displacement estimation. In this letter, a novel PS selection method, which is based on a new index called the similar time-series interferometric pixels (STIPs) representing the number of neighborhood pixels with similar phase history, is proposed. In this approach, apart from PS selection, corresponding set of STIP is also used in refining look-angle error estimation. The efficiency of the proposed InSAR processing chain is demonstrated for the Sentinel-1A single look complex images of Rajmahal, Jharkhand, India, predominantly a coal mines area. Results, when compared with the conventional PS processing technique, reveal substantial improvement in terms of extracting more number of reliable PS with enhanced density.
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  • 4
    Publication Date: 2017-12-30
    Description: In this letter, we propose a novel technique for obtaining scattering components from polarimetric synthetic aperture radar (PolSAR) data using the geodesic distance on the unit sphere. This geodesic distance is obtained between an elementary target and the observed Kennaugh matrix, and it is further utilized to compute a similarity measure between scattering mechanisms. The normalized similarity measure for each elementary target is then modulated with the total scattering power (Span). This measure is used to categorize pixels into three categories, i.e., odd-bounce, double-bounce, and volume, depending on which of the above scattering mechanisms dominate. Then the maximum likelihood classifier of Lee et al . based on the complex Wishart distribution is iteratively used for each category. Dominant scattering mechanisms are thus preserved in this classification scheme. We show results for L-band AIRSAR and ALOS-2 data sets acquired over San Francisco and Mumbai, respectively. The scattering mechanisms are better preserved using the proposed methodology than the unsupervised classification results using the Freeman–Durden scattering powers on an orientation angle corrected PolSAR image. Furthermore: 1) the scattering similarity is a completely nonnegative quantity unlike the negative powers that might occur in double-bounce and odd-bounce scattering component under Freeman–Durden decomposition and 2) the methodology can be extended to more canonical targets as well as for bistatic scattering.
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  • 5
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2017-12-30
    Description: Presents the cover/table of contents for this issue of the periodical.
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  • 6
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2017-12-30
    Description: Provides a listing of current committee members and society officers.
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  • 7
    Publication Date: 2017-12-30
    Description: In our previous work, a tensor decomposition-based anomaly detection algorithm has been proposed. However, determining $K_{1}$ , $K_{2}$ , and $K_{3}$ (i.e., the major principal component numbers along the three modes of hyperspectral data) has not been settled satisfactorily. In this letter, a fast and adaptive method for determining $K_{1}$ , $K_{2}$ , and $K_{3}$ is proposed. In the proposed method, the determination problem is converted into an optimization problem by constructing the energy function by maximizing the anomalous degree of the reconstructed anomaly data in both spectral and spatial domains. In order to reduce the computational complexity, a fast initialization strategy is introduced to initialize those parameters in the feature space directly. In addition, to avoid the problem of parameter selection, an adaptive strategy is utilized. Furthermore, $K_{1}$ and $K_{2}$ are considered to be independent, making the degree of freedom of the three parameters conform with the actual. Experiments with three hyperspectral data sets reveal that the proposed method works effectively.
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  • 8
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2017-12-30
    Description: Scale is of great significance in image analysis and interpretation. In order to utilize scale information, multiscale fusion is usually employed to combine change detection (CD) results from different scales. However, CD results from different scales are usually treated independently, which ignores the scale contextual information. To overcome this drawback, this letter introduces a novel object-based change detection (OBCD) technique for unsupervised CD in very high-resolution (VHR) images by incorporating multiscale uncertainty analysis. First, two temporal images are stacked and segmented using a series of optimal segmentation scales ranging from coarse to fine. Second, an initial CD result is obtained by fusing the pixel-based CD result and OBCD result based on Dempter–Shafer (DS) evidence theory. Third, multiscale uncertainty analysis is implemented from coarse scale to fine scale by support vector machine classification. Finally, a CD map is generated by combining all the available information in all the scales. The experimental results employing SPOT5 and GF-1 images demonstrate the effectiveness and superiority of the proposed approach.
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  • 9
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2017-12-30
    Description: Unsupervised learning of a convolutional neural network (CNN) is a feasible method to represent and classify remote sensing images, where labeling the observed data to prepare training samples is a highly expensive and time-consuming task. In this letter, we propose an unsupervised convolutional feature fusion network to formulate an easy-to-train but effective CNN representation of remote sensing images. The efficiency and effectiveness are derived from the following two aspects. First, the proposed method trains a deep CNN through unsupervised learning of each CNN layer in a greedy layer-wise manner, which makes the training relatively easy and efficient. Second, the feature fusion strategy in the proposed network can effectively use both the information from individual layers and the important interactions between different layers. As a result, the proposed network requires only several layers to obtain comparable or even better results than very deep networks. The experiments on unsupervised deep representations and the classification of remote sensing images demonstrate the efficiency and effectiveness of the proposed method.
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  • 10
    Publication Date: 2017-12-30
    Description: Near real-time building damage mapping is an indispensable prerequisite for governments to make decisions for disaster relief. With high-resolution synthetic aperture radar (SAR) systems, such as TerraSAR-X, the provision of such products in a fast and effective way becomes possible. In this letter, a deep learning-based framework for rapid regional tsunami damage recognition using post-event SAR imagery is proposed. To perform such a rapid damage mapping, a series of tile-based image split analysis is employed to generate the data set. Next, a selection algorithm with the SqueezeNet network is developed to swiftly distinguish between built-up (BU) and nonbuilt-up regions. Finally, a recognition algorithm with a modified wide residual network is developed to classify the BU regions into wash away, collapsed, and slightly damaged regions. Experiments performed on the TerraSAR-X data from the 2011 Tohoku earthquake and tsunami in Japan show a BU region extraction accuracy of 80.4% and a damage-level recognition accuracy of 74.8%, respectively. Our framework takes around 2 h to train on a new region, and only several minutes for prediction.
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