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SAR Data Processing and Applications Based on Machine Learning Method

A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Engineering Remote Sensing".

Deadline for manuscript submissions: closed (1 June 2024) | Viewed by 18312

Special Issue Editors


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Guest Editor
School of Electronics and Information Engineering, Beihang University, Beijing 100191, China
Interests: space-borne SAR signal processsing; SAR image quality improvement; SAR imaging understanding
Special Issues, Collections and Topics in MDPI journals
College of Information Engineering, Capital Normal University, Beijing 100048, China
Interests: new space SAR system design; advanced radar signal processing; polar remote sensing
School of Artificial Intelligence, Beijing University of Posts and Telecommunications, Beijing 100876, China
Interests: remote sensing image understing; imaging detection and intelligent perception; trustworthy artificial intelligence
Special Issues, Collections and Topics in MDPI journals

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Guest Editor
School of Electronics and Information Engineering, Beihang University, Beijing 100191, China
Interests: moving target detection; machine learning method on SAR; SAR 3-D imaging

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Guest Editor
Surveying and Geospatial Engineering, School of Civil and Environmental Engineering, The University of New South Wales (UNSW), Sydney, NSW 2052, Australia
Interests: photogrammetry and remote sensing; geospatial information systems; SAR remote sensing; feature extraction from images; sustainable development; ecosystem services
Special Issues, Collections and Topics in MDPI journals

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Guest Editor
Faculty of Electrical Engineering and Computer Science, University of Maribor, Koroška cesta 46, SI-2000 Maribor, Slovenia
Interests: synthetic aperture radar image enhancement; small-radar development; deep learning for SAR image enhancement; data interpretation, short-range radar development, radar signal processing, through the wall imaging, soil moisture estimation, and machine vision
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Due to the explosive growth of data and great advances in computing power, machine learning techniques are having a profound impact on the development of remote sensing. Taking advantage of this, remote sensing technology is transforming from model-driven to data-driven. Due to the unique nature of SAR signals and images, machine learning SAR still offers many opportunities for exploration, which is also an exciting challenge for us. The unique non-linear capability of machine learning has revealed the further potential of SAR processing and application, such as target recognition, feature scene classification, speckle noise and ambiguity energy suppression. Next-generation SAR spacecraft may also carry edge computers based on AI platforms. In the future, machine learning SAR will significantly diminish the workload of scientists and engineers, enhance the application value of SAR data, and even influence the underlying design concepts of novel space SAR systems.

Remote Sensing is an established scientific journal attending to the science and application of remote sensing technologies, and encouraging the presentation of unique processing techniques, applied results, and natural findings. As a crucial aspect of remote sensing, SAR provides the microwave scattering characteristics of terrain, but also poses great difficulties in processing and application due to the great variations in human visual habits. The combination of machine learning and SAR can better bridge this gap, again revealing many opportunities and challenges. We hope that this Special Issue will provide an overview of the impact of this technology and exciting results regarding machine learning on SAR remote sensing.

This Special Issue is dedicated to advancing our knowledge in SAR data processing and applications based on machine learning methods. We invite the submission of review and regular papers on machine learning with SAR systems, 2D/3D/4D imaging methods, SAR image enhancement, SAR target detection and terrain classification, SAR image understanding, and trustworthy intelligence processing.

Prof. Dr. Jie Chen
Dr. Peng Xiao
Dr. Yanan You
Dr. Wei Yang
Prof. Dr. John Trinder
Prof. Dr. Dusan Gleich
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • synthetic aperture radar
  • machine learning
  • trustworthy deep learning
  • convolutional neural network
  • SAR imaging
  • SAR image target recognition
  • SAR image classification
  • SAR image understanding

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Published Papers (10 papers)

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21 pages, 7856 KiB  
Article
DACLnet: A Dual-Attention-Mechanism CNN-LSTM Network for the Accurate Prediction of Nonlinear InSAR Deformation
by Junyu Lu, Yuedong Wang, Yafei Zhu, Jingtao Liu, Yang Xu, Honglei Yang and Yuebin Wang
Remote Sens. 2024, 16(13), 2474; https://doi.org/10.3390/rs16132474 - 5 Jul 2024
Cited by 7 | Viewed by 1362
Abstract
Nonlinear deformation is a dynamically changing pattern of multiple surface deformations caused by groundwater overexploitation, underground coal mining, landslides, urban construction, etc., which are often accompanied by severe damage to surface structures or lead to major geological disasters; therefore, the high-precision monitoring and [...] Read more.
Nonlinear deformation is a dynamically changing pattern of multiple surface deformations caused by groundwater overexploitation, underground coal mining, landslides, urban construction, etc., which are often accompanied by severe damage to surface structures or lead to major geological disasters; therefore, the high-precision monitoring and prediction of nonlinear surface deformation is significant. Traditional deep learning methods encounter challenges such as long-term dependencies or difficulty capturing complex spatiotemporal patterns when predicting nonlinear deformations. In this study, we developed a dual-attention-mechanism CNN-LSTM network model (DACLnet) to monitor and accurately predict nonlinear surface deformations precisely. Using advanced time series InSAR results as input, the DACLnet integrates the spatial feature extraction capability of a convolutional neural network (CNN), the advantages of the time series learning of a long short-term memory (LSTM) network, and the enhanced focusing effect of the dual-attention mechanism on crucial information, significantly improving the prediction accuracy of nonlinear surface deformations. The groundwater overexploitation area of the Turpan Basin, China, is selected to test the nonlinear deformation prediction effect of the proposed DACLnet. The results demonstrate that the DACLnet accurately captures developmental trends in historical surface deformations and effectively predicts surface deformations for the next two months in the study area. Compared to traditional LSTM and CNN-LSTM methods, the root mean square error (RMSE) of the DACLnet improved by 85.09% and 68.57%, respectively. These research results can provide crucial technical support for the early warning and prevention of geological disasters and can serve as an effective alternative tool for short-term ground subsidence prediction in areas lacking hydrogeological and other related data. Full article
(This article belongs to the Special Issue SAR Data Processing and Applications Based on Machine Learning Method)
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<p>Flowchart of the improved IPTA method. The full names of abbreviations such as SLC, DEM, EDAD, and SVD can be found in Abbreviations Section.</p>
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<p>Structure diagram of the DACLnet model.</p>
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<p>The Turpan Basin and SAR data coverage.</p>
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<p>Spatiotemporal baseline maps, where (<b>a</b>) shows the spatiotemporal baseline map for AT41F135 and (<b>b</b>) shows the spatiotemporal baseline map for DT121F449.</p>
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<p>Surface subsidence velocity maps for the Turpan–Hami Basin: (<b>a</b>) AT orbit; (<b>b</b>) DT orbit. Panels (<b>c</b>,<b>d</b>) depict the temporal deformations of feature points P1 and P2, monitored using the AT and DT orbit datasets.</p>
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<p>(<b>a</b>,<b>b</b>) Distribution statistics and (<b>c</b>) correlation between the subsidence rate results on AT143F135 and DT121F449. The black dashed line represents three times the RMSE.</p>
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<p>Loss decrease chart during model training.</p>
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<p>A comparison of sedimentation simulation results between the DACLnet and LSTM as well as CNN-LSTM models under the same training strategy.</p>
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<p>Prediction of nonlinear deformations from historical deformation sequences from 25 March 2015 to 27 February 2020, spanning from 27 February 2020 to 27 April 2020.</p>
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<p>A spatial variation map of surface deformation velocity in the Turpan Basin. (<b>a</b>) Actual deformation results processed with InSAR from the ascending track (AT41F135) of Sentinel-1. (<b>b</b>) The InSAR deformation results predicted using the DACLnet model.</p>
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<p>A comparison between the InSAR deformation velocity observations and DACLnet prediction results, derived from a comprehensive dataset of 574,662 ascending track observations and predictions. The black dashed line indicates a range three times greater than the RMSE.</p>
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24 pages, 18770 KiB  
Article
A Two-Step Phase Compensation-Based Imaging Method for GNSS-Based Bistatic SAR: Extraction and Compensation of Ionospheric Phase Scintillation
by Tao Tang, Pengbo Wang, Jie Chen, Huguang Yao, Ziheng Ren, Peng Zhao and Hongcheng Zeng
Remote Sens. 2024, 16(13), 2345; https://doi.org/10.3390/rs16132345 - 27 Jun 2024
Cited by 1 | Viewed by 1067
Abstract
The GNSS-based bistatic SAR (GNSS-BSAR) system has emerged as a hotspot due to its low power consumption, nice concealment, and worldwide reach. However, the weak landing power density of the GNSS signal often necessitates prolonged integration to achieve an adequate signal-to-noise ratio (SNR). [...] Read more.
The GNSS-based bistatic SAR (GNSS-BSAR) system has emerged as a hotspot due to its low power consumption, nice concealment, and worldwide reach. However, the weak landing power density of the GNSS signal often necessitates prolonged integration to achieve an adequate signal-to-noise ratio (SNR). In this case, the effects of the receiver’s time-frequency errors and atmospheric disturbances are significant and cannot be ignored. Therefore, we propose an ionospheric scintillation compensation-based imaging scheme for dual-channel GNSS-BSAR system. This strategy first extracts the reference phase, which contains the ionospheric phase scintillation and other errors. Subsequently, the azimuth phase of the target is divided into difference phase and reference phase. We apply the two-step phase compensation to eliminate Doppler phase errors, thus achieving precise focusing of SAR images. Three sets of experiments using the GPS L5 signal as the illuminator were conducted, coherently processing a 1.5 km by 0.8 km scene about 300 s. The comparative results show that the proposed method exhibited better focusing performance, avoiding the practical challenges encountered by traditional autofocus algorithms. Additionally, ionospheric phase scintillation extracted at different times of the day suggest diurnal variations, preliminary illustrating the potential of this technology for ionospheric-related studies. Full article
(This article belongs to the Special Issue SAR Data Processing and Applications Based on Machine Learning Method)
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<p>The system configuration of the studied GNSS-BSAR system.</p>
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<p>Typical structure of a GNSS signal (taking GPS as an example).</p>
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<p>Schematic diagram of two-dimensional SAR matrix formation.</p>
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<p>Atmospheric distribution in the GNSS-BSAR system.</p>
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<p>The variation of range delay error and <span class="html-italic">QPE</span> with the <span class="html-italic">TEC</span> of the ionosphere. (<b>a</b>) The variation curve of range delay with <span class="html-italic">TEC</span>; (<b>b</b>) the variation curve of <span class="html-italic">QPE</span> with <span class="html-italic">TEC</span>.</p>
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<p>Ionospheric scintillation phase error (<span class="html-italic">C<sub>k</sub>L</span> = 10<sup>32</sup>, <span class="html-italic">C<sub>k</sub>L</span> = 10<sup>33</sup> and <span class="html-italic">C<sub>k</sub>L</span> = 10<sup>34</sup>).</p>
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<p>Principle diagram of the classic BPA.</p>
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<p>The navigation signal receiving process in the reference channel for the GNSS-BSAR system.</p>
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<p>The diagram of the proposed two-step azimuth phase compensation processing.</p>
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<p>The constructed experimental platform.</p>
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<p>On-site photographs of the experiment taken at different times of the day: (<b>a</b>) in the morning, (<b>b</b>) at midday, (<b>c</b>) in the evening.</p>
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<p>The illustration of the experimental scene.</p>
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<p>GPS satellite acquisition results and sky map. (<b>a</b>) Sky map at the test time; (<b>b</b>) acquisition results at the test time.</p>
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<p>The reference channel carrier frequency tracking results.</p>
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<p>Comparison of the theoretical value and the measured value of the reference phase.</p>
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<p>Reference channel Doppler phase errors extraction results from three sets of experimental results. (<b>a</b>) In the morning; (<b>b</b>) at midday; (<b>c</b>) in the evening.</p>
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<p>Imaging results before and after ionospheric scintillation error compensation: (<b>a1</b>) imaging results before phase error compensation (morning); (<b>a2</b>) imaging results before phase error compensation (midday); (<b>a3</b>) imaging results before phase error compensation (evening); (<b>b1</b>) imaging results after phase error compensation (morning); (<b>b2</b>) imaging results after phase error compensation (midday); (<b>b3</b>) imaging results after phase error compensation (evening).</p>
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<p>Comparative analysis of actual data processing results. (<b>a</b>) Result of the proposed method; (<b>b</b>) result using traditional PGA.</p>
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<p>Comparison of azimuth profiles of strong scattering points. (<b>a</b>) First set of experiments in the morning; (<b>b</b>) second set of experiments at noon; (<b>c</b>) third set of experiments in the evening.</p>
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<p>Incoherent accumulation results of three SAR images (Before phase error compensation).</p>
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<p>Incoherent accumulation results of three SAR images (after phase error compensation).</p>
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<p>Overlapped result of the focused SAR image and the optical image.</p>
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24 pages, 12173 KiB  
Article
Sea Clutter Suppression Based on Chaotic Prediction Model by Combining the Generator and Long Short-Term Memory Networks
by Jindong Yu, Baojing Pan, Ze Yu, Hongling Zhu, Hanfu Li, Chao Li and Hezhi Sun
Remote Sens. 2024, 16(7), 1260; https://doi.org/10.3390/rs16071260 - 2 Apr 2024
Viewed by 1565
Abstract
Sea clutter usually greatly affects the target detection and identification performance of marine surveillance radars. In order to reduce the impact of sea clutter, a novel sea clutter suppression method based on chaos prediction is proposed in this paper. The method combines a [...] Read more.
Sea clutter usually greatly affects the target detection and identification performance of marine surveillance radars. In order to reduce the impact of sea clutter, a novel sea clutter suppression method based on chaos prediction is proposed in this paper. The method combines a generator trained by Generative Adversarial Networks (GAN) with a Long Short-Term Memory (LSTM) network to accomplish sea clutter prediction. By exploiting the generator’s ability to learn the distribution of unlabeled data, the accuracy of sea clutter prediction is improved compared with the classical LSTM-based model. Furthermore, effective suppression of sea clutter and improvements in the signal-to-clutter ratio of echo were achieved through clutter cancellation. Experimental results on real data demonstrated the effectiveness of the proposed method. Full article
(This article belongs to the Special Issue SAR Data Processing and Applications Based on Machine Learning Method)
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<p>An LSTM-based neural network model used for one-step sea clutter prediction. The LSTM network encodes the input sequence <math display="inline"><semantics> <mrow> <mstyle mathvariant="bold" mathsize="normal"> <mi>X</mi> </mstyle> <mfenced> <mi>j</mi> </mfenced> </mrow> </semantics></math> into a vector <math display="inline"><semantics> <mrow> <msub> <mstyle mathvariant="bold" mathsize="normal"> <mi>h</mi> </mstyle> <mrow> <mi>m</mi> <mi>τ</mi> </mrow> </msub> </mrow> </semantics></math> that contains the evolutional law in <math display="inline"><semantics> <mrow> <mstyle mathvariant="bold" mathsize="normal"> <mi>X</mi> </mstyle> <mfenced> <mi>j</mi> </mfenced> </mrow> </semantics></math>. Then, the FC decodes the vector into <math display="inline"><semantics> <mrow> <mover accent="true"> <mi>x</mi> <mo stretchy="false">^</mo> </mover> <mfenced> <mrow> <mi>j</mi> <mo>+</mo> <mi>m</mi> <mi>τ</mi> </mrow> </mfenced> </mrow> </semantics></math>, which is the predicted value of next time. The LSTM network contains the cell, which works in the recurrent mechanism. At the <span class="html-italic">t</span>-th moment, the cell has three inputs. One is <math display="inline"><semantics> <mrow> <mi>x</mi> <mfenced> <mrow> <mi>j</mi> <mo>+</mo> <mi>t</mi> </mrow> </mfenced> </mrow> </semantics></math>. The other two are the hidden vector <math display="inline"><semantics> <mrow> <msub> <mstyle mathvariant="bold" mathsize="normal"> <mi>h</mi> </mstyle> <mi>t</mi> </msub> </mrow> </semantics></math> and the memory cell state vector <math display="inline"><semantics> <mrow> <msub> <mstyle mathvariant="bold" mathsize="normal"> <mi>C</mi> </mstyle> <mi>t</mi> </msub> </mrow> </semantics></math>, which are the outputs of the cell at the time <math display="inline"><semantics> <mrow> <mfenced> <mrow> <mi>t</mi> <mo>−</mo> <mn>1</mn> </mrow> </mfenced> </mrow> </semantics></math>. The cell memorizes the state of the previous input, continuously updates the latest input information, and passes it on, so that the vector <math display="inline"><semantics> <mrow> <msub> <mstyle mathvariant="bold" mathsize="normal"> <mi>h</mi> </mstyle> <mrow> <mi>m</mi> <mi>τ</mi> </mrow> </msub> </mrow> </semantics></math> has the evolutionary information of the whole input sequence <math display="inline"><semantics> <mrow> <mstyle mathvariant="bold" mathsize="normal"> <mi>X</mi> </mstyle> <mfenced> <mi>j</mi> </mfenced> </mrow> </semantics></math>.</p>
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<p>A GLSTM-based model for one-step prediction of sea clutter sequences. The input of the model is a sea clutter sequence that is encoded into a vector <math display="inline"><semantics> <mrow> <msub> <mstyle mathvariant="bold" mathsize="normal"> <mi>h</mi> </mstyle> <mrow> <mi>m</mi> <mi>τ</mi> </mrow> </msub> </mrow> </semantics></math>. Then, the generator obtained by adversarial training decodes <math display="inline"><semantics> <mrow> <msub> <mstyle mathvariant="bold" mathsize="normal"> <mi>h</mi> </mstyle> <mrow> <mi>m</mi> <mi>τ</mi> </mrow> </msub> </mrow> </semantics></math> into the predicted element.</p>
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<p>The training process involves a generator and a discriminator to learn the distribution of sea clutter. The generator accepts a fixed dimensional vector and generates data, while the discriminator evaluates whether the input is real sea clutter or generated data and provides the corresponding judgment results.</p>
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<p>Sea clutter suppression using chaotic prediction. The range cells are processed one by one. Firstly, the real and imaginary components are normalized. Subsequently, the normalized parts are put into the sea clutter prediction model, which generates the predicted clutter. At last, the predicted clutter is subtracted from the original data to get the sea clutter-suppressed result.</p>
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<p>Training dataset. With an original sequence of length <span class="html-italic">N</span>, the training dataset is created by obtaining short sequences of length <math display="inline"><semantics> <mrow> <mi>N</mi> <mo>−</mo> <mi>m</mi> <mi>τ</mi> </mrow> </semantics></math> and their corresponding labels.</p>
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<p>The curve corresponding to the normalized autocorrelation function. The delay time <span class="html-italic">τ</span> must be an integer. The horizontal line represents <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="normal">R</mi> <mi>x</mi> </msub> <mfenced> <mi>τ</mi> </mfenced> <mo>=</mo> <mn>1</mn> <mo>−</mo> <msup> <mi>e</mi> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </mrow> </semantics></math>, and the vertical line represents <span class="html-italic">m</span> = 5. <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="normal">R</mi> <mi>x</mi> </msub> <mfenced> <mi>τ</mi> </mfenced> </mrow> </semantics></math> is nearest to <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>−</mo> <msup> <mi>e</mi> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </mrow> </semantics></math> when <span class="html-italic">τ</span> is set to 5, which is shown in the gray circle.</p>
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<p>The variation of <math display="inline"><semantics> <mrow> <msub> <mi>E</mi> <mn>1</mn> </msub> <mfenced> <mi>m</mi> </mfenced> </mrow> </semantics></math> increases as the embedding dimension <span class="html-italic">m</span> increases. The growth rate of the curve becomes very slow when <span class="html-italic">m</span> is greater than 9. The gray circle indicates the position of the curve at <span class="html-italic">m</span> = 9.</p>
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<p>Range compression amplitude image of radar echoes. (<b>a</b>) Range compression amplitude image of the original radar data. (<b>b</b>) Range compression amplitude image of the LSTM-based method-suppressed result. (<b>c</b>) Range compression amplitude image of the GLSTM-based method-suppressed result.</p>
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<p>Image of radar echoes. (<b>a</b>) Image of the original data. (<b>b</b>) Image of the LSTM-based method suppressed result. (<b>c</b>) Image of the GLSTM-based method suppressed result.</p>
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<p>R-square curves obtained by processing data block I in the 2–100 range cells based on the LSTM-based and GLSTM-based models.</p>
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<p>Sea clutter suppression results of data block I. (<b>a</b>) The comparison of the original data and the clutter suppression result of the LSTM-based method. (<b>b</b>) The comparison of the original data and the clutter suppression result of the GLSTM-based method.</p>
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<p>Sea clutter suppressed results of data block II. (<b>a</b>) The comparison of the original data and the clutter suppression result of the LSTM-based method. (<b>b</b>) The comparison of the original data and the clutter suppression result of the GLSTM-based method.</p>
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<p>The sea clutter suppressed results for data block I in the 4000th pulse.</p>
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<p>The sea clutter suppressed result for data block II in the 2204th pulse.</p>
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<p>The variation of suppressed energy with different noise levels.</p>
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<p>The variation of R-square with different noise levels.</p>
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<p>The variation of MSE with different noise levels.</p>
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<p>The relationship between the input SCR and output SCR of the proposed method.</p>
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<p>The PDF results of the original sea clutter data, the predicted sea clutter result, and the suppressed sea clutter result.</p>
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<p>Sea clutter suppression results of IPIX X-band polarimetric coherent radar data. (<b>a</b>) The original signal in the range compression domain. (<b>b</b>) The original imaging result. (<b>c</b>) The sea clutter suppressed result in the range compression domain. (<b>d</b>) The sea clutter suppressed result in the imaging domain.</p>
Full article ">Figure 20 Cont.
<p>Sea clutter suppression results of IPIX X-band polarimetric coherent radar data. (<b>a</b>) The original signal in the range compression domain. (<b>b</b>) The original imaging result. (<b>c</b>) The sea clutter suppressed result in the range compression domain. (<b>d</b>) The sea clutter suppressed result in the imaging domain.</p>
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<p>Sea clutter suppression results of the data with sea state 5. (<b>a</b>) The original signal in the range compression domain. (<b>b</b>) The original imaging result. (<b>c</b>) The sea clutter suppressed result in the range compression domain. (<b>d</b>) The sea clutter suppressed result in the imaging domain.</p>
Full article ">Figure 21 Cont.
<p>Sea clutter suppression results of the data with sea state 5. (<b>a</b>) The original signal in the range compression domain. (<b>b</b>) The original imaging result. (<b>c</b>) The sea clutter suppressed result in the range compression domain. (<b>d</b>) The sea clutter suppressed result in the imaging domain.</p>
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<p>Sea clutter suppression results of data with sea state 3. (<b>a</b>) The original signal in the range compression domain. (<b>b</b>) The original imaging result. (<b>c</b>) The sea clutter suppressed result in the range compression domain. (<b>d</b>) The sea clutter suppressed result in the imaging domain.</p>
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<p>The effect of white caps on training. (<b>a</b>) Original sea clutter signal in range compression domain. (<b>b</b>) Sea clutter suppressed result obtained by the model trained in the 74th range cell data. (<b>c</b>) Sea clutter suppressed result obtained by the model trained in the 1st range cell data.</p>
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<p>The sea clutter suppressed the result of wind seas data. (<b>a</b>) The original data. (<b>b</b>) The sea clutter suppressed result.</p>
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<p>The sea clutter suppressed the result of swell dominant seas data. (<b>a</b>) The original data. (<b>b</b>) The sea clutter suppressed result.</p>
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25 pages, 16942 KiB  
Article
TAG-Net: Target Attitude Angle-Guided Network for Ship Detection and Classification in SAR Images
by Dece Pan, Youming Wu, Wei Dai, Tian Miao, Wenchao Zhao, Xin Gao and Xian Sun
Remote Sens. 2024, 16(6), 944; https://doi.org/10.3390/rs16060944 - 7 Mar 2024
Cited by 1 | Viewed by 1611
Abstract
Synthetic aperture radar (SAR) ship detection and classification has gained unprecedented attention due to its important role in maritime transportation. Many deep learning-based detectors and classifiers have been successfully applied and achieved great progress. However, ships in SAR images present discrete and multi-centric [...] Read more.
Synthetic aperture radar (SAR) ship detection and classification has gained unprecedented attention due to its important role in maritime transportation. Many deep learning-based detectors and classifiers have been successfully applied and achieved great progress. However, ships in SAR images present discrete and multi-centric features, and their scattering characteristics and edge information are sensitive to variations in target attitude angles (TAAs). These factors pose challenges for existing methods to obtain satisfactory results. To address these challenges, a novel target attitude angle-guided network (TAG-Net) is proposed in this article. The core idea of TAG-Net is to leverage TAA information as guidance and use an adaptive feature-level fusion strategy to dynamically learn more representative features that can handle the target imaging diversity caused by TAA. This is achieved through a TAA-aware feature modulation (TAFM) module. It uses the TAA information and foreground information as prior knowledge and establishes the relationship between the ship scattering characteristics and TAA information. This enables a reduction in the intra-class variability and highlights ship targets. Additionally, considering the different requirements of the detection and classification tasks for the scattering information, we propose a layer-wise attention-based task decoupling detection head (LATD). Unlike general deep learning methods that use shared features for both detection and classification tasks, LATD extracts multi-level features and uses layer attention to achieve feature decoupling and select the most suitable features for each task. Finally, we introduce a novel salient-enhanced feature balance module (SFB) to provide richer semantic information and capture the global context to highlight ships in complex scenes, effectively reducing the impact of background noise. A large-scale ship detection dataset (LSSDD+) is used to verify the effectiveness of TAG-Net, and our method achieves state-of-the-art performance. Full article
(This article belongs to the Special Issue SAR Data Processing and Applications Based on Machine Learning Method)
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Graphical abstract

Graphical abstract
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<p>The imaging results of three different types of ships in SAR images and their corresponding target attitude angles. From left to right, they are a container ship, bulk carrier, and oil tanker. The target attitude angle is defined as the deflection angle of the target relative to the horizontal direction, where the horizontal direction is 0° and the counterclockwise rotation ranges from 0° to 180°.</p>
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<p>The overview of TAG-Net.</p>
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<p>Representation of the oriented bounding box.</p>
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<p>Structure of the TAFM.</p>
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<p>(<b>a</b>) Ground truth bounding box. (<b>b</b>) Ground truth of TAA map.</p>
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<p>Structure of the LATD.</p>
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<p>Structure of the SFB.</p>
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<p>Number of instances per category in LSSDD+.</p>
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<p>Example images of civil ships in LSSDD+.</p>
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<p>Visual comparison of detection results without and with LATD. The bounding boxes show the detected objects, with different colors indicating different categories: the yellow circles, blue circles, and red circles denote the objects with inaccurate localization, category errors, and missing ships, respectively. (<b>a</b>,<b>d</b>,<b>g</b>) Ground truth, (<b>b</b>,<b>e</b>,<b>h</b>) baseline without LATD, (<b>c</b>,<b>f</b>,<b>i</b>) baseline with LATD.</p>
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<p>Visualization of feature maps extracted by different methods. The orange boxes indicate the positions of ships. (<b>a</b>,<b>d</b>) the positions of the ships, (<b>b</b>,<b>e</b>) baseline without SFB, (<b>c</b>,<b>f</b>) baseline with SFB.</p>
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<p>Detection results of different methods on LSSDD+. The bounding boxes show the detected objects, with different colors indicating different categories: the yellow circles, blue circles, and red circles denote the objects with inaccurate localization, category errors, and missing ships, respectively. (<b>a</b>,<b>g</b>) Ground truth, (<b>b</b>,<b>h</b>) Rotated FCOS, (<b>c</b>,<b>i</b>) Rotated ATSS, (<b>d</b>,<b>j</b>) ROI Trans, (<b>e</b>,<b>k</b>) Oriented R-CNN, (<b>f</b>,<b>l</b>) TAG-Net.</p>
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<p>Detection results in large-scale SAR images. The bounding boxes show the detected objects, with different colors indicating different categories: the yellow circles, blue circles, and red circles denote the objects with inaccurate localization, category errors, and missing ships, respectively. (<b>a</b>) Oriented R-CNN, (<b>b</b>) TAG-Net.</p>
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20 pages, 7264 KiB  
Article
Synthetic Aperture Radar Image Compression Based on Low-Frequency Rejection and Quality Map Guidance
by Jiawen Deng and Lijia Huang
Remote Sens. 2024, 16(5), 891; https://doi.org/10.3390/rs16050891 - 2 Mar 2024
Viewed by 2026
Abstract
Synthetic Aperture Radar (SAR) images are widely utilized in the field of remote sensing. However, there is a limited body of literature specifically addressing the compression of SAR learning images. To address the escalating volume of SAR image data for storage and transmission, [...] Read more.
Synthetic Aperture Radar (SAR) images are widely utilized in the field of remote sensing. However, there is a limited body of literature specifically addressing the compression of SAR learning images. To address the escalating volume of SAR image data for storage and transmission, which necessitates more effective compression algorithms, this paper proposes a novel framework for compressing SAR images. Experimental validation is performed using a representative low-resolution Sentinel-1 dataset and the high-resolution QiLu-1 dataset. Initially, we introduce a novel two-stage transformation-based approach aimed at suppressing the low-frequency components of the input data, thereby achieving a high information entropy and minimizing quantization losses. Subsequently, a quality map guidance image compression algorithm is introduced, involving the fusion of the input SAR images with a target-aware map. This fusion involves convolutional transformations to generate a compact latent representation, effectively exploring redundancies between focused and non-focused areas. To assess the algorithm’s performance, experiments are carried out on both the low-resolution Sentinel-1 dataset and the high-resolution QiLu-1 dataset. The results indicate that the low-frequency suppression algorithm significantly outperforms traditional processing algorithms by 3–8 dB when quantifying the input data, effectively preserving image features and improving image performance metrics. Furthermore, the quality map guidance image compression algorithm demonstrates a superior performance compared to the baseline model. Full article
(This article belongs to the Special Issue SAR Data Processing and Applications Based on Machine Learning Method)
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<p>The framework of the hyperprior compression algorithm.</p>
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<p>The framework of the designed compression algorithm.</p>
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<p>The framework of the low-frequency suppression algorithm model.</p>
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<p>The network of the quality-map-guided image compression model.</p>
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<p>SFT feature fusion module.</p>
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<p>Fitting curves. (<b>a</b>) Sentinel-1 image with σ = 6.42; (<b>b</b>) QiLu-1 image with σ = 0.32.</p>
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<p>Loss surface chart results and PDF of <a href="#remotesensing-16-00891-f006" class="html-fig">Figure 6</a> after low-frequency suppression transformation. (<b>a</b>) Loss surface chart results of Sentinel-1; (<b>b</b>) loss surface chart results of QiLu-1; (<b>c</b>) PDF of Sentinel-1; (<b>d</b>) PDF of QiLu-1.</p>
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<p>Preprocessing result of Sentinel-1. (<b>a</b>,<b>d</b>) Traditional linear method; (<b>b</b>,<b>e</b>) traditional power method; (<b>c</b>,<b>f</b>) proposed method.</p>
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<p>Preprocessing result of QiLu-1. (<b>a</b>,<b>d</b>) Traditional linear method; (<b>b</b>,<b>e</b>) traditional power method; (<b>c</b>,<b>f</b>) proposed method.</p>
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<p>Attention feature maps. (<b>a</b>–<b>d</b>) Attention features of raw data, the traditional linear method, the traditional power method, and the proposed method.</p>
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<p>Visual display of compression model results. (<b>a</b>,<b>d</b>) Ground truth and subgraphs; (<b>b</b>,<b>e</b>) JPEG and subgraphs; (<b>c</b>,<b>f</b>) proposed method and subgraphs.</p>
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19 pages, 4803 KiB  
Article
Pseudo-L0-Norm Fast Iterative Shrinkage Algorithm Network: Agile Synthetic Aperture Radar Imaging via Deep Unfolding Network
by Wenjiao Chen, Jiwen Geng, Fanjie Meng and Li Zhang
Remote Sens. 2024, 16(4), 671; https://doi.org/10.3390/rs16040671 - 13 Feb 2024
Viewed by 1268
Abstract
A novel compressive sensing (CS) synthetic-aperture radar (SAR) called AgileSAR has been proposed to increase swath width for sparse scenes while preserving azimuthal resolution. AgileSAR overcomes the limitation of the Nyquist sampling theorem so that it has a small amount of data and [...] Read more.
A novel compressive sensing (CS) synthetic-aperture radar (SAR) called AgileSAR has been proposed to increase swath width for sparse scenes while preserving azimuthal resolution. AgileSAR overcomes the limitation of the Nyquist sampling theorem so that it has a small amount of data and low system complexity. However, traditional CS optimization-based algorithms suffer from manual tuning and pre-definition of optimization parameters, and they generally involve high time and computational complexity for AgileSAR imaging. To address these issues, a pseudo-L0-norm fast iterative shrinkage algorithm network (pseudo-L0-norm FISTA-net) is proposed for AgileSAR imaging via the deep unfolding network in this paper. Firstly, a pseudo-L0-norm regularization model is built by taking an approximately fair penalization rule based on Bayesian estimation. Then, we unfold the operation process of FISTA into a data-driven deep network to solve the pseudo-L0-norm regularization model. The network’s parameters are automatically learned, and the learned network significantly increases imaging speed, so that it can improve the accuracy and efficiency of AgileSAR imaging. In addition, the nonlinearly sparsifying transform can learn more target details than the traditional sparsifying transform. Finally, the simulated and data experiments demonstrate the superiority and efficiency of the pseudo-L0-norm FISTA-net for AgileSAR imaging. Full article
(This article belongs to the Special Issue SAR Data Processing and Applications Based on Machine Learning Method)
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<p>The imaging geometry. <math display="inline"><semantics> <mi>η</mi> </semantics></math> is the slow time along the azimuth and <math display="inline"><semantics> <mrow> <msub> <mi>R</mi> <mi>i</mi> </msub> <mfenced> <mi>η</mi> </mfenced> </mrow> </semantics></math> represents the range between the radar and the point target located at the coordinate <math display="inline"><semantics> <mrow> <mfenced> <mrow> <msub> <mi>x</mi> <mi>i</mi> </msub> <mo>,</mo> <msub> <mi>y</mi> <mi>i</mi> </msub> <mo>,</mo> <mn>0</mn> </mrow> </mfenced> </mrow> </semantics></math> at the azimuth time <math display="inline"><semantics> <mi>η</mi> </semantics></math>. <math display="inline"><semantics> <mrow> <msub> <mi>x</mi> <mi>i</mi> </msub> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>y</mi> <mi>i</mi> </msub> </mrow> </semantics></math> denote the azimuth and range coordinates, respectively. Because a two-dimensional image, i.e., azimuth and range, is considered, the coordinate <math display="inline"><semantics> <mrow> <mfenced> <mrow> <msub> <mi>x</mi> <mi>i</mi> </msub> <mo>,</mo> <msub> <mi>y</mi> <mi>i</mi> </msub> <mo>,</mo> <mn>0</mn> </mrow> </mfenced> </mrow> </semantics></math> is simplified as <math display="inline"><semantics> <mrow> <mfenced> <mrow> <msub> <mi>x</mi> <mi>i</mi> </msub> <mo>,</mo> <msub> <mi>y</mi> <mi>i</mi> </msub> </mrow> </mfenced> </mrow> </semantics></math> <span class="html-fig-inline" id="remotesensing-16-00671-i001"><img alt="Remotesensing 16 00671 i001" src="/remotesensing/remotesensing-16-00671/article_deploy/html/images/remotesensing-16-00671-i001.png"/></span> denotes the Nyquist samples. <span class="html-fig-inline" id="remotesensing-16-00671-i002"><img alt="Remotesensing 16 00671 i002" src="/remotesensing/remotesensing-16-00671/article_deploy/html/images/remotesensing-16-00671-i002.png"/></span> demonstrates the real azimuthal samples chosen randomly from Nyquist samples in the AgileSAR system.</p>
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<p>The overall framework of the proposed pseudo-<math display="inline"><semantics> <mrow> <msub> <mi mathvariant="script">L</mi> <mn>0</mn> </msub> </mrow> </semantics></math>-norm FISTA-net. Specifically, the pseudo-<math display="inline"><semantics> <mrow> <msub> <mi mathvariant="script">L</mi> <mn>0</mn> </msub> </mrow> </semantics></math>-norm FISTA-net consists of four main modules, i.e., gradient descenting, reweight updating, proximal mapping, and momentum updating.</p>
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<p>The reconstructed results: (<b>a</b>) the result reconstructed by RDA with Nyquist sampling raw data; (<b>b</b>) the result reconstructed by the OMP algorithm with 20% sub-Nyquist sampling raw data in AgileSAR; (<b>c</b>) the result reconstructed by the <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="script">L</mi> <mn>1</mn> </msub> </mrow> </semantics></math>-norm optimization algorithm with 20% sub-Nyquist sampling raw data in AgileSAR; (<b>d</b>) the result reconstructed by the Bayesian-based algorithm with 20% sub-Nyquist sampling raw data in AgileSAR; (<b>e</b>) the result reconstructed by the pseudo-<math display="inline"><semantics> <mrow> <msub> <mi mathvariant="script">L</mi> <mn>0</mn> </msub> </mrow> </semantics></math>-norm FISTA-net with 20% sub-Nyquist sampling raw data in AgileSAR.</p>
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<p>The reconstructed results: (<b>a</b>) the result reconstructed by RDA with Nyquist sampling raw data; (<b>b</b>) the result reconstructed by the OMP algorithm with 20% sub-Nyquist sampling raw data in AgileSAR; (<b>c</b>) the result reconstructed by the <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="script">L</mi> <mn>1</mn> </msub> </mrow> </semantics></math>-norm optimization algorithm with 20% sub-Nyquist sampling raw data in AgileSAR; (<b>d</b>) the result reconstructed by the Bayesian-based algorithm with 20% sub-Nyquist sampling raw data in AgileSAR; (<b>e</b>) the result reconstructed by the pseudo-<math display="inline"><semantics> <mrow> <msub> <mi mathvariant="script">L</mi> <mn>0</mn> </msub> </mrow> </semantics></math>-norm FISTA-net with 20% sub-Nyquist sampling raw data in AgileSAR.</p>
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<p>The reconstructed results: (<b>a</b>) the result reconstructed by RDA with Nyquist sampling raw data; (<b>b</b>) the result reconstructed by the OMP algorithm with 20% sub-Nyquist sampling raw data in AgileSAR; (<b>c</b>) the result reconstructed by the <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="script">L</mi> <mn>1</mn> </msub> </mrow> </semantics></math>-norm optimization algorithm with 20% sub-Nyquist sampling raw data in AgileSAR; (<b>d</b>) the result reconstructed by the Bayesian-based algorithm with 20% sub-Nyquist sampling raw data in AgileSAR; (<b>e</b>) the result reconstructed by the pseudo-<math display="inline"><semantics> <mrow> <msub> <mi mathvariant="script">L</mi> <mn>0</mn> </msub> </mrow> </semantics></math>-norm FISTA-net with 20% sub-Nyquist sampling raw data in AgileSAR.</p>
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<p>The curves (<b>a</b>), (<b>b</b>) and (<b>c</b>) of performance indexes for the first, second and third testing scenes with respect to different phase numbers, respectively.</p>
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<p>The curves (<b>a</b>), (<b>b</b>) and (<b>c</b>) performance indexes for the first, the second and the third testing scenes with respect to different epoch numbers, respectively.</p>
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<p>The curves (<b>a</b>), (<b>b</b>) and (<b>c</b>) performance indexes for the first, the second and the third testing scenes with respect to different epoch numbers, respectively.</p>
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19 pages, 8454 KiB  
Article
DeepRED Based Sparse SAR Imaging
by Yao Zhao, Qingsong Liu, He Tian, Bingo Wing-Kuen Ling and Zhe Zhang
Remote Sens. 2024, 16(2), 212; https://doi.org/10.3390/rs16020212 - 5 Jan 2024
Cited by 5 | Viewed by 1727
Abstract
The integration of deep neural networks into sparse synthetic aperture radar (SAR) imaging is explored to enhance SAR imaging performance and reduce the system’s sampling rate. However, the scarcity of training samples and mismatches between the training data and the SAR system pose [...] Read more.
The integration of deep neural networks into sparse synthetic aperture radar (SAR) imaging is explored to enhance SAR imaging performance and reduce the system’s sampling rate. However, the scarcity of training samples and mismatches between the training data and the SAR system pose significant challenges to the method’s further development. In this paper, we propose a novel SAR imaging approach based on deep image prior powered by RED (DeepRED), enabling unsupervised SAR imaging without the need for additional training data. Initially, DeepRED is introduced as the regularization technique within the sparse SAR imaging model. Subsequently, variable splitting and the alternating direction method of multipliers (ADMM) are employed to solve the imaging model, alternately updating the magnitude and phase of the SAR image. Additionally, the SAR echo simulation operator is utilized as an observation model to enhance computational efficiency. Through simulations and real data experiments, we demonstrate that our method maintains imaging quality and system downsampling rate on par with deep-neural-network-based sparse SAR imaging but without the requirement for training data. Full article
(This article belongs to the Special Issue SAR Data Processing and Applications Based on Machine Learning Method)
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<p>Framework of ADMM Solution for SAR Imaging Leveraging DeepRED.</p>
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<p>Reconstruction results of simulated scenes at SNR = 30 dB. (<b>a</b>) GT; (<b>b</b>) RDA; (<b>c</b>) <math display="inline"><semantics> <msub> <mi>L</mi> <mn>1</mn> </msub> </semantics></math> regularization; (<b>d</b>) <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>&amp;</mo> <mi>T</mi> <mi>V</mi> </mrow> </semantics></math> regularization; (<b>e</b>) CNN; (<b>f</b>) DeepRED. All images were simulated under the same conditions and plotted with the same color map to maintain consistency for comparison.</p>
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<p>The range and azimuth direction slices of the results obtained by the five methods in processing the simulated data when SNR = 30 dB. (<b>a</b>) The slice along the range direction. (<b>b</b>) The slice along the azimuth direction.</p>
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<p>Reconstruction results of simulated scenes at SNR = 0 dB. (<b>a</b>) GT; (<b>b</b>) RDA; (<b>c</b>) <math display="inline"><semantics> <msub> <mi>L</mi> <mn>1</mn> </msub> </semantics></math> regularization; (<b>d</b>) <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>&amp;</mo> <mi>T</mi> <mi>V</mi> </mrow> </semantics></math> regularization; (<b>e</b>) CNN; (<b>f</b>) DeepRED. All images were simulated under the same conditions and plotted with the same color map to maintain consistency for comparison.</p>
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<p>The range and azimuth direction slices of the results obtained by the five methods in processing the simulated data when SNR = 0 dB. (<b>a</b>) The slice along the range direction. (<b>b</b>) The slice along the azimuth direction.</p>
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<p>Reconstruction Results of Real Scene Point Target from Full Sampling. (<b>a</b>) RDA; (<b>b</b>) <math display="inline"><semantics> <msub> <mi>L</mi> <mn>1</mn> </msub> </semantics></math> regularization; (<b>c</b>) <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>&amp;</mo> <mi>T</mi> <mi>V</mi> </mrow> </semantics></math> regularization; (<b>d</b>) CNN; (<b>e</b>) DeepRED.</p>
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<p>Slices of the reconstructed point target results along the range and azimuth directions under full sampling conditions. (<b>a</b>) The slice along the azimuth direction. (<b>b</b>) The slice along the range direction.</p>
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<p>Reconstruction Results of Real Scene Point Target from Random Sampling at 60% Rate. (<b>a</b>) RDA; (<b>b</b>) <math display="inline"><semantics> <msub> <mi>L</mi> <mn>1</mn> </msub> </semantics></math> regularization; (<b>c</b>) <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>&amp;</mo> <mi>T</mi> <mi>V</mi> </mrow> </semantics></math> regularization; (<b>d</b>) CNN; (<b>e</b>) DeepRED.</p>
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<p>Slices of the reconstructed point target results along the range and azimuth directions under <math display="inline"><semantics> <mrow> <mn>60</mn> <mo>%</mo> </mrow> </semantics></math> downsampling conditions. (<b>a</b>) The slice along the azimuth direction. (<b>b</b>) The slice along the range direction.</p>
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<p>Reconstruction results of Experiment 2. (<b>a</b>) RDA; (<b>b</b>) <math display="inline"><semantics> <msub> <mi>L</mi> <mn>1</mn> </msub> </semantics></math> regularization; (<b>c</b>) <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>&amp;</mo> <mi>T</mi> <mi>V</mi> </mrow> </semantics></math> regularization; (<b>d</b>) CNN; (<b>e</b>) DeepRED.</p>
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<p>Reconstruction results of Experiment 3. (<b>a</b>) RDA; (<b>b</b>) <math display="inline"><semantics> <msub> <mi>L</mi> <mn>1</mn> </msub> </semantics></math> regularization; (<b>c</b>) <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>&amp;</mo> <mi>T</mi> <mi>V</mi> </mrow> </semantics></math> regularization; (<b>d</b>) CNN; (<b>e</b>) DeepRED.</p>
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28 pages, 17240 KiB  
Article
OEGR-DETR: A Novel Detection Transformer Based on Orientation Enhancement and Group Relations for SAR Object Detection
by Yunxiang Feng, Yanan You, Jing Tian and Gang Meng
Remote Sens. 2024, 16(1), 106; https://doi.org/10.3390/rs16010106 - 26 Dec 2023
Cited by 11 | Viewed by 2519
Abstract
Object detection in SAR images has always been a topic of great interest in the field of deep learning. Early works commonly focus on improving performance on convolutional neural network frameworks. More recent works continue this path and introduce the attention mechanisms of [...] Read more.
Object detection in SAR images has always been a topic of great interest in the field of deep learning. Early works commonly focus on improving performance on convolutional neural network frameworks. More recent works continue this path and introduce the attention mechanisms of Transformers for better semantic interpretation. However, these methods fail to treat the Transformer itself as a detection framework and, therefore, lack the development of various details that contribute to the state-of-the-art performance of Transformers. In this work, we first base our work on a fully multi-scale Transformer-based detection framework, DETR (DEtection TRansformer) to utilize its superior detection performance. Secondly, to acquire rotation-related attributes for better representation of SAR objects, an Orientation Enhancement Module (OEM) is proposed to facilitate the enhancement of rotation characteristics. Then, to enable learning of more effective and discriminative representations of foreground objects and background noises, a contrastive-loss-based GRC Loss is proposed to preserve patterns of both categories. Moreover, to not restrict comparisons exclusively to maritime objects, we have also developed an open-source labeled vehicle dataset. Finally, we evaluate both detection performance and generalization ability on two well-known ship datasets and our vehicle dataset. We demonstrated our method’s superior performance and generalization ability on both datasets. Full article
(This article belongs to the Special Issue SAR Data Processing and Applications Based on Machine Learning Method)
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<p>Different patterns of ships in SAR images. (<b>a</b>) In row order, ships of different orientations have distinct cross-bright spot patterns that can be easily recognized. In column order, ships with the same orientation have differences within the foreground class. It can be concluded that integrating rotation information of ships into the memory sequence can enable better feature representation ability in the model. (<b>b</b>) Diversity of background noises and visual confusion of foreground ships and background noises. Red boxes represent zoomed areas shown in the next column.</p>
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<p>An exemplary case of rotation-invariant property in both optical images and the lack of such property in SAR images. (<b>a</b>) Despite the clear directional attributes of objects in optical images, characteristics of these objects remain consistent with their rotated versions. (<b>b</b>) Characteristics of objects in SAR images usually vary significantly with respect to different oriented conditions due to the imaging mechanism of SAR.</p>
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<p>The aggregation-suppression effect of attention mechanism. This effect is observed in three different kinds of scenes (offshore, near shore with fewer and more buildings) We initialize query locations for every experiment setting with 2-D uniform distribution, as is shown in the first row. Red spots are visualized 2-D coordinates of each query. Object-related queries are clustered around objects and irrelevant ones are dispelled to the border of each image.</p>
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<p>General architecture of our proposed method (Blue boxes denote modifications we proposed to the original structure). The entirety of our method mainly consists of an Encoder and a Decoder. The encoder takes a flattened sequence from multi-scale outputs of the FPN network at Feature Extraction procedures. The Orientation Enhancement Module (OEM) computes channel-wise attention weights for each layer and then adjusts the relevance of rotation information by re-weighting the feature sequence. The feature sequence is also used to generate initial proposals and CDN queries for Decoder. In the loss calculation part, the GRC Loss is calculated and used for backward propagation.</p>
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<p>Structure of Orientation Enhancement Module (OEM) and the structure of Rotation-Sensitive Module. (<b>a</b>) The OEM consists of the feature enhancement (FE) branch and the encoder branch. Multi-scale feature maps are directly acquired from the Feature Pyramid Network (FPN). Feature maps for the encoder branch are flattened at spatial dimensions. Features for the FE branch are first processed by Rotation-Sensitive convolution layers and then spatially flattened to calculate layer attention weights. The enhanced memory sequence is the product of attention weights and the original sequence. (<b>b</b>) The Rotation-Sensitive Module (RSM) extracts rotation information by leveraging the Oriented Response Convolution (ORConv) [<a href="#B52-remotesensing-16-00106" class="html-bibr">52</a>], which calculates standard convolution feature maps with rotated convolution kernels of different angles. The ORPool is a simple max pooling function to select the maximum response from activation maps of all rotated kernels.</p>
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<p>Values decrease in the Confusion Matrix (CM) tested on the DOTA dataset after additionally regulating relations among representations from the label book. (<b>a</b>) Differences between the CM with and without regulating cross-relations among queries and label book representations at the same training epoch. (<b>b</b>) Differences between the CM with additional regulation at different epochs. (<b>c</b>) Differences between the CM with additional self-relations and cross-relations at different epochs.</p>
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<p>Overview of GRC Loss. Given groups per class <math display="inline"><semantics> <mrow> <mi>K</mi> <mo>=</mo> <mn>3</mn> </mrow> </semantics></math>, the number of classes <math display="inline"><semantics> <mrow> <msub> <mi>N</mi> <mi>c</mi> </msub> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math> and we display here 4 matched samples selected by the Hungarian matcher. Groups with the least and the most similarity are selected for matched and un-matched queries respectively, breaking the previous limitation that intra-class representations can only match with themselves in contrastive loss while enabling more choices to distinguish from inter-class representations via more thorough comparisons.</p>
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<p>Partial samples from the three datasets. (<b>a</b>) Samples from the HRSID dataset featuring ship objects from offshore areas to nearshore areas. (<b>b</b>) Samples from the SSDD dataset featuring offshore and inshore ship objects. (<b>c</b>) Samples from our SAR Vehicle Dataset featuring vehicles from different noise conditions and scales.</p>
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<p>Correct predictions of our method on HRSID, SSDD and SAR Vehicle Dataset. Various samples are chosen from diverse scenes and organized in a sequence where the background disturbance progressively increases.</p>
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<p>Visualization of offshore detection results on HRSID dataset. (<b>a</b>) An offshore scene with negligible noises and isolated ships. (<b>b</b>) An offshore scene with ships on the harbor and away from land. This scene introduces mixed background patterns from both land clutters and sea clutters.</p>
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<p>Visualization of inshore detection results on HRSID dataset. (<b>a</b>) A nearshore scene with less noise, featuring small ships. (<b>b</b>) A nearshore scene with more noise, featuring small and medium-sized ships.</p>
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<p>Visualization of partial detection results of vehicles in open fields.</p>
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<p>Visualization of partial detection results of vehicles beside buildings.</p>
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<p>Visualization of several different activation maps in OEM module. We forward three SAR images of different near-shore and offshore scenes. We set the first column of each row as the input image, the second as the feature map acquired from direct FPN output, the third as the feature map acquired from the Rotation-Sensitive Module, and the last as the rearranged 1-dimensional output sequence of self-attention calculation. (<b>a</b>) A nearshore scene with no land area in sight. (<b>b</b>) A nearshore scene with land area. (<b>c</b>) An offshore scene.</p>
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<p>tSNE visualization of prediction queries taken from 20 iterations; red crosses mark foreground objects, and blue spots are background queries. Red contours represent different point densities of foreground queries. tSNE settings for every result are 2 for the number of components and 0 for the random state. Settings for point density contour lines are in 5 levels, with 0.1 as the minimum threshold.</p>
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<p>Visualization of how GRC Loss works during training. (<b>a</b>) When calculating GRC Loss, patterns of each class operate differently. Patterns, or groups of the same class are considered as inner groups and do not largely interfere with learning behaviors of other patterns to distinguish from patterns of different classes. Patterns from different groups are called intersections and are aimed to separate from each other as much as possible (denoted as blue, representing value decreases in confusion matrices). (<b>b</b>) GRC Loss applied on FG-BG classes with 2 groups (K = 2). (<b>c</b>) GRC Loss applied on FG-BG classes with 3 groups (K = 3). (<b>d</b>) GRC Loss applied on FG-BG classes with 4 groups (K = 4).</p>
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26 pages, 36367 KiB  
Article
Intelligent Detection and Segmentation of Space-Borne SAR Radio Frequency Interference
by Jiayi Zhao, Yongliang Wang, Guisheng Liao, Xiaoning Liu, Kun Li, Chunyu Yu, Yang Zhai, Hang Xing and Xuepan Zhang
Remote Sens. 2023, 15(23), 5462; https://doi.org/10.3390/rs15235462 - 22 Nov 2023
Cited by 4 | Viewed by 1605
Abstract
Space-borne synthetic aperture radar (SAR), as an all-weather observation sensor, is an important means in modern information electronic warfare. Since SAR is a broadband active radar system, radio frequency interference (RFI) in the same frequency band will affect the normal observation of the [...] Read more.
Space-borne synthetic aperture radar (SAR), as an all-weather observation sensor, is an important means in modern information electronic warfare. Since SAR is a broadband active radar system, radio frequency interference (RFI) in the same frequency band will affect the normal observation of the SAR system. Untangling the above problem, this research explores a quick and accurate method for detecting and segmenting RFI-contaminated images. The purpose of the current method is to quickly detect the existence of RFI and to locate it in massive SAR data. Based on deep learning, the method shown in this paper realizes the existence of RFI by determining the presence or absence of interference in the image domain and then performs pixel-level image segmentation on Sentinel-1 RFI-affected quick-look images to locate RFI. Considering the need to quickly detect RFI in massive SAR data, an improved network based on MobileNet is proposed, which replaces some inverted residual blocks in the network with ghost blocks, reducing the number of network parameters and the inference time to 6.1 ms per image. Further, this paper also proposes an improved network called the Smart Interference Segmentation Network (SISNet), which is based on U2Net and replaces the convolution of the VGG blocks in U2Net with a residual convolution and introduces attention mechanisms and a modified RFB module to improve the segmentation mIoU to 87.46% on average. Experiment results and statistical analysis based on the MID dataset and PAIS dataset show that the proposed methods can achieve quicker detection than other CNNs while ensuring a certain accuracy and can significantly improve segmentation performance under the same conditions compared to the original U2Net and other semantic segmentation networks. Full article
(This article belongs to the Special Issue SAR Data Processing and Applications Based on Machine Learning Method)
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Graphical abstract

Graphical abstract
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<p>RFI-contaminated Sentinel-1 data examples.</p>
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<p>A rough classification of SAR interference [<a href="#B26-remotesensing-15-05462" class="html-bibr">26</a>].</p>
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<p>Some samples of the MID dataset. (<b>left</b>) RFI-contaminated images. (<b>right</b>) RFI-free images.</p>
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<p>The data augmentations performed, including flipping, blurring, translating, and affiliating.</p>
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<p>Some augmented data samples of PAIS dataset show from left to right in columns that the original image has been flipped, translated and blurred, and noise has been added, respectively.</p>
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<p>Samples of PAIS dataset. (<b>a</b>,<b>c</b>,<b>e</b>,<b>g</b>) are quick-look images contaminated by RFI. (<b>b</b>,<b>d</b>,<b>f</b>,<b>h</b>) are the annotated segmentation labels.</p>
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<p>Schematic diagram of FCN network.</p>
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<p>Schematic diagram of UNet.</p>
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<p>Architecture of proposed IQDN.</p>
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<p>Ghost module: replacing convolution operation with linear transformation.</p>
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<p>Max-Blur-Pooling: an anti-aliasing max-pooling method implemented by applying low-pass filters before down-sampling.</p>
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<p>The architecture of the modified receptive field block with larger dilation rates.</p>
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<p>The framework of the channel weighting module.</p>
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<p>Modified convolutional layer with shortcut layer between input and output.</p>
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<p>The network structure of proposed SISNet.</p>
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<p>The training accuracy and loss curve with training steps: (<b>a</b>) training accuracy; (<b>b</b>) loss.</p>
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<p>The average training loss curve and evaluation indicators of different networks with training epochs. Error bars were added in the last 10 epochs: (<b>a</b>) average training loss, (<b>b</b>) average training mIoU, (<b>c</b>) average training precision, and (<b>d</b>) average training F1.</p>
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<p>The SISNet training mIoU curve and loss curve with training epochs in the five-fold cross-validation experiments: (<b>a</b>) the mIoU results of five subtests and the average mIoU and (<b>b</b>) the loss of five subtests and the average loss.</p>
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<p>Comparison of average mIoU results of different semantic segmentation networks. Validation method: 5-fold cross-validation. (<b>a</b>) SISNet vs. FCN8s, (<b>b</b>) SISNet vs. UNet, (<b>c</b>) SISNet vs. UNet++, and (<b>d</b>) SISNet vs. U2Net.</p>
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<p>Comparison of interference segmentation experiment results: (<b>a1</b>–<b>a6</b>) original quick-look images (the numbering sequence is consistent with <a href="#remotesensing-15-05462-t005" class="html-table">Table 5</a> above); (<b>b1</b>–<b>b6</b>) label image; (<b>c1</b>–<b>c6</b>) FCN8s outputs; (<b>d1</b>–<b>d6</b>) UNet++ outputs; (<b>e1</b>–<b>e6</b>) U2Net outputs; (<b>f1</b>–<b>f6</b>) our proposed SISNet outputs.</p>
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20 pages, 13392 KiB  
Technical Note
A GAN-Based Augmentation Scheme for SAR Deceptive Jamming Templates with Shadows
by Shinan Lang, Guiqiang Li, Yi Liu, Wei Lu, Qunying Zhang and Kun Chao
Remote Sens. 2023, 15(19), 4756; https://doi.org/10.3390/rs15194756 - 28 Sep 2023
Cited by 2 | Viewed by 1397
Abstract
To realize fast and effective synthetic aperture radar (SAR) deception jamming, a high-quality SAR deception jamming template library can be generated by performing sample augmentation on SAR deception jamming templates. However, the current sample augmentation schemes of SAR deception jamming templates face certain [...] Read more.
To realize fast and effective synthetic aperture radar (SAR) deception jamming, a high-quality SAR deception jamming template library can be generated by performing sample augmentation on SAR deception jamming templates. However, the current sample augmentation schemes of SAR deception jamming templates face certain problems. First, the authenticity of the templates is low due to the lack of speckle noise. Second, the generated templates have a low similarity to the target and shadow areas of the input templates. To solve these problems, this study proposed a sample augmentation scheme based on generative adversarial networks, which can generate a high-quality library of SAR deception jamming templates with shadows. The proposed scheme solved the two aforementioned problems from the following aspects. First, the influence of the speckle noise was considered in the network to avoid the problem of reduced authenticity in the generated images. Second, a channel attention mechanism module was used to improve the network’s learning ability of the shadow features, which improved the similarity between the generated template and the shadow area in the input template. Finally, the single generative adversarial network (SinGAN) scheme, which is a generative adversarial network capable of image sample augmentation for a single SAR image, and the proposed scheme were compared regarding the equivalent number of looks and the structural similarity between the target and shadow in the sample augmentation results. The comparison results demonstrated that, compared to the templates generated by the SinGAN scheme, those generated by the proposed scheme had targets and shadow features similar to those of the original image and could incorporate speckle noise characteristics, resulting in a higher authenticity, which helps to achieve fast and effective SAR deception jamming. Full article
(This article belongs to the Special Issue SAR Data Processing and Applications Based on Machine Learning Method)
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Figure 1

Figure 1
<p>Structure of the network. <math display="inline"><semantics> <mi>Z</mi> </semantics></math> is the noise, <math display="inline"><semantics> <mi>u</mi> </semantics></math> is the input image, <math display="inline"><semantics> <mrow> <mover accent="true"> <mi>u</mi> <mo stretchy="true">˜</mo> </mover> </mrow> </semantics></math> is the generated image, <math display="inline"><semantics> <mi>G</mi> </semantics></math> is the generator, <math display="inline"><semantics> <mi>N</mi> </semantics></math> is the number of layers, and <math display="inline"><semantics> <mi>D</mi> </semantics></math> is the discriminator.</p>
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<p>SAR images with speckle noise.</p>
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<p>SAR image tanks and its shadow.</p>
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<p>Block diagram of the generator.</p>
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<p>Structural diagram of the discriminator.</p>
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<p>The loss variation curve.</p>
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<p>48 SAR deception jamming templates with shadows of the T72 tank generated by the proposed network.</p>
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<p>Real image and three generated samples. (<b>a</b>) Real image; (<b>b</b>) sample 1; (<b>c</b>) sample 2; (<b>d</b>) sample 3.</p>
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<p>50 SAR deception jamming templates with shadows of the trucks (ZIL-131) generated by the proposed network.</p>
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<p>Real image and three generated samples. (<b>a</b>) Real image; (<b>b</b>) sample 1; (<b>c</b>) sample 2; (<b>d</b>) sample 3.</p>
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<p>48 SAR deception jamming templates with shadows of the T72 tank generated by the SinGAN.</p>
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<p>Real image and three generated samples. (<b>a</b>) Real image; (<b>b</b>) sample 1; (<b>c</b>) sample 2; (<b>d</b>) sample 3.</p>
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<p>50 SAR deception jamming template with shadows of the trucks (ZIL-131) generated by the SinGAN scheme.</p>
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<p>Real image and three generated samples. (<b>a</b>) Real image; (<b>b</b>) sample 1; (<b>c</b>) sample 2; (<b>d</b>) sample 3.</p>
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<p>Generated samples without the spatial attention mechanism block.</p>
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<p>Real image and three generated samples. (<b>a</b>) Real image; (<b>b</b>) sample 1; (<b>c</b>) sample 2; (<b>d</b>) sample 3.</p>
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<p>Generated samples using the scheme without speckle noise.</p>
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<p>Real image and three generated samples. (<b>a</b>) Real image; (<b>b</b>) sample 1; (<b>c</b>) sample 2; (<b>d</b>) sample 3.</p>
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