Three-dimensional ISAR imaging: a review

Three-dimensional (3D) inverse synthetic aperture radar (ISAR) imaging has been proven feasible by combining traditional ISAR imaging and interferometry. Such technique, namely inteferometric ISAR (In-ISAR), allows for the main target scattering centres to be mapped into a 3D spatial domain as point clouds. Specifically, the use of an In-ISAR system can overcome the main geometrical interpretation issues imposed by the monostatic acquisition geometry as the problem of cross-range scaling and unknown image projection plane (IPP). However, some issues remain such as scatterer scintillation, shadowing effects, poor SNR etc., which limit the effectiveness of 3D imaging. A solution to such unsolved issues can be found in the use of multiple 3D views, which can be obtained exploiting either multi-temporal or multi-perspective configurations or a combination of both. This study aims to review the main concepts to produce multi-view 3D ISAR images by using In-ISAR systems also presenting real data collected with a multi-static In-ISAR system

Proportional similarity-based Openmax classifier for open set recognition in SAR images

Most of the existing Non-Cooperative Target Recognition (NCTR) systems follow the “closed world” assumption, i.e., they only work with what was previously observed. Nevertheless, the real world is relatively “open” in the sense that the knowledge of the environment is incomplete. Therefore, unknown targets can feed the recognition system at any time while it is operational. Addressing this issue, the Openmax classifier has been recently proposed in the optical domain to make convolutional neural networks (CNN) able to reject unknown targets. There are some fundamental limitations in the Openmax classifier that can end up with two potential errors: (1) rejecting a known target and (2) classifying an unknown target. In this paper, we propose a new classifier to increase the robustness and accuracy. The proposed classifier, which is inspired by the limitations of the Openmax classifier, is based on proportional similarity between the test image and different training classes. We evaluate our method by radar images of man-made targets from the Moving and Stationary Target Acquisition and Recognition (MSTAR) dataset. Moreover, a more in-depth discussion on the Openmax hyper-parameters and a detailed description of the Openmax functioning are given

Optimized Nonlinear PRI Variation Strategy Using Knowledge-Guided Genetic Algorithm for Staggered SAR Imaging

Staggered synthetic aperture radar (SAR), which operates with variable pulse repetition interval (PRI), staggers blind areas to solve the blind range problem caused by constant PRI in conventional high-resolution wide-swath SAR imaging. The PRI variation strategy determines the blind area distribution, and thus has a significant influence on the imaging performance in staggered mode. Generally, the existing strategies based on linear PRI variation can control the blind areas in a straightforward way, which has achieved impressive results. However, the linearity of the PRI variation imposes regularity or even periodicity on the locations of the blind areas, which limits the distribution of the blind areas. The imaging performance has the potential to be further improved by introducing much more irregularity into the PRI sequences. To this end, this article proposes an optimized nonlinear PRI variation strategy for staggered SAR mode. First, a novel objective function is defined that quantitatively measures the uniformity of the blind area distribution along the slant range and the discontinuity of the blind area distribution along the azimuth. Subsequently, the optimum nonlinear PRI variation strategy is found using an optimization problem and the proposed objective function. A knowledge-guided genetic algorithm is proposed to solve the optimization problem. Comparisons with the existing linear variation strategies show that the proposed strategy can provide a superior imaging performance after reconstruction with a lower objective function value. Simulations and experiments on raw data generated in staggered SAR mode are performed to verify the effectiveness of the optimized nonlinear PRI variation strategy

Compressive sensing for interferometric inverse synthetic aperture radar applications

The applicability of interferometric inverse synthetic aperture radar (InISAR) techniques to images reconstructed via compressive sensing (CS)-based algorithms is investigated. Specifically, the three-dimensional (3D) reconstruction algorithm is applied after exploiting CS for data compression and image reconstruction. The InISAR signal model is derived and formalised in a CS framework. A comparison between conventional CS reconstruction and global sparsity constrained reconstruction techniques is performed for different compression rates and different signal-to-noise ratio conditions. Performances on the 2D and 3D reconstructions are evaluated. Results obtained on real data acquired during the NATO-SET 196 trial are shown

Three-Dimensional Polarimetric InISAR Imaging of Non-Cooperative Targets

A new Polarimetric Interferometry Inverse Synthetic Aperture Radar (Pol-InISAR) 3D imaging method for non-cooperative targets is proposed in this paper. 3D imaging of non-cooperative targets becomes possible by combining additional information of interferometric phase along with conventional 2D ISAR imaging. In the previously reported single-polarimetry InISAR based 3D imaging, only a single-channel based interferometric phase is available that can be exploited to reconstruct the 3D ISAR image. This limits the ability to obtain a full target's scattering response and therefore limits the estimation of an accurate interferometric phase. To overcome this constraint, full-polarimetry information is being exploited in this paper, which allows to select the optimal polarimetric combination through which the highest coherence can be obtained. A higher coherence leads to a reduction (optimally a minimization) of the phase estimation error. Consequently, with an optimal phase estimation, an accurate 3D imaging of the target is possible. To validate this proposed Pol-InISAR based 3D imaging approach, both simulated and real datasets are taken under consideration

Non-traumatic splenic rupture on dual antiplatelet therapy with aspirin and ticagrelor after stenting for acute coronary syndrome

AbstractWe report a case of non-traumatic splenic rupture in a 57-year-old man on dual antiplatelet therapy (DAPT) with aspirin and ticagrelor, seven months after percutaneous coronary intervention and drug-eluting stent implantation for non-ST elevation myocardial infarction. No splenic abnormalities were found at histopathological analysis after splenectomy, and no history of recent trauma was reported. Once restarted, DAPT after splenectomy, assessment of platelet function was performed by light transmittance aggregometry, showing a profound inhibition of platelet function by adenosine diphosphate, arachidonic acid, and collagen. Taking into account the bleeding risk associated with low on-treatment platelet reactivity, and to switch the patient from ticagrelor to a less potent P2Y12 inhibitor such as clopidogrel, cytochrome P450, genetic polymorphisms accounting for clopidogrel response variability were analyzed. The polymorphisms associated with lower response (CYP2C19*2, CYP2C19*3) were absent. Therefore, ticagrelor was withdrawn, and DAPT was continued with aspirin and clopidogrel. Rupture of the spleen may occur in the absence of major trauma or previous splenic diseases, and could be a complication of antithrombotic treatments. Moreover, low on-treatment platelet reactivity during DAPT is emerging as a possible risk factor for bleeding complications, so underlining the usefulness of assessing platelet function in special conditions to ensure that the patient receives the best tailored antiplatelet therapy.<Learning objective: Non-traumatic splenic rupture is a rare event, and is more often associated with pre-existing splenic abnormalities. However, it may be also a complication of medical treatments, especially with antithrombotic drugs. Low on-treatment platelet reactivity is emerging as a possible risk factor for bleeding complications; therefore, assessing platelet function in special conditions could be useful to ensure the patient receives the best-tailored antiplatelet therapy.

Image Based Robust Target Classification For Passive ISAR

This paper presents an automatic and robust, image feature-based target extraction, and classification method for multistatic passive inverse synthetic aperture radar range/cross-range images. The method can be used as a standalone solution or for augmenting classical signal processing approaches. By extracting textural, directional, and edge information as low-level features, a fused saliency map is calculated for the images and used for target detection. The proposed method uses the contour and the size of the detected targets for classification, is lightweight, fast, and easy to extend. The performance of the approach is compared with machine learning methods and extensively evaluated on real target images

O conceito de proporcionalidade direta de alunos brasileiros de 16 -17 anos na perspectiva dos três mundos da matemática

Teve-se por objetivo investigar as definições de conceito e as imagens de conceito de proporcionalidade direta de um grupo de alunos brasileiros do último ano do Ensino Médio (16-17 anos de idade) de uma escola pública do Estado de São Paulo. Escolheu-se os três mundos da matemática para elaborar e analisar as questões do diagnóstico e buscou-se respostas para duas questões: Qual a definição de conceito de proporcionalidade direta de alunos do Ensino Médio? Com que características, entre formais, simbólicas e corporificadas, trabalham questionamentos que envolvem a proporcionalidade direta? Verificou-se que as definições de conceito e as resoluções dadas aos problemas propostos têm essencialmente características corporificadas; não apresentam características simbólicas; poucos explicitam características formais. Conclui-se que esses participantes não transitaram pelos Três Mundos da Matemática e nem desenvolveram o pensamento proporcional

O conceito de proporcionalidade direta de alunos brasileiros de 16-17 anos na perspectiva dos três mundos da matemática

Teve-se por objetivo investigar as definições de conceito e as imagens de conceito de proporcionalidade direta de um grupo de alunos brasileiros do último ano do ensino médio (16-17 anos de idade) de uma escola pública do Estado de São Paulo. Escolheu-se os Três Mundos da Matemática para elaborar e analisar as questões do diagnóstico e buscou-se respostas para duas questões: Qual a definição de conceito de proporcionalidade direta de alunos do ensino médio? Com que características, entre formais, simbólicas e corporificadas, trabalham questionamentos que envolvem a proporcionalidade direta? Verificou-se que as definições de conceito e as resoluções dadas aos problemas propostos têm essencialmente características corporificadas; não apresentam características simbólicas; poucos explicitam características formais. Conclui-se que esses participantes não transitaram pelos três mundos da matemática e nem desenvolveram o pensamento proporcional