International Severe Asthma Registry Canonica, G. Walter; Alacqua, Marianna; Altraja, Alan ...
Chest,
April 2020, 2020-04-00, Volume:
157, Issue:
4
Journal Article
Peer reviewed
Open access
Regional and/or national severe asthma registries provide valuable country-specific information. However, they are often limited in scope within the broader definitions of severe asthma, have ...insufficient statistical power to answer many research questions, lack intraoperability to share lessons learned, and have fundamental differences in data collected, making cross comparisons difficult. What is missing is a worldwide registry which brings all severe asthma data together in a cohesive way, under a single umbrella, based on standardized data collection protocols, permitting data to be shared seamlessly. The International Severe Asthma Registry (ISAR; http://isaregistries.org/) is the first global adult severe asthma registry. It is a joint initiative where national registries (both newly created and preexisting) retain ownership of their own data but open their borders and share data with ISAR for ethically approved research purposes. Its strength comes from collection of patient-level, anonymous, longitudinal, real-life, standardized, high-quality data (using a core set of variables) from countries across the world, combined with organizational structure, database experience, inclusivity/openness, and clinical, academic, and database expertise. This gives ISAR sufficient statistical power to answer important research questions, sufficient data standardization to compare across countries and regions, and the structure and expertise necessary to ensure its continuance and the scientific integrity and clinical applicability of its research. ISAR offers a unique opportunity to implement existing knowledge, generate new knowledge, and identify the unknown, therefore promoting new research. The aim of this commentary is to fully describe how ISAR may improve our understanding of severe asthma.
Three-dimensional ISAR imaging: a review Martorella, Marco; Salvetti, Federica; Staglianò, Daniele ...
Journal of engineering (Stevenage, England),
October 2019, Volume:
2019, Issue:
20
Journal Article
Peer reviewed
Open access
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.
This work investigates the impact of motion estimation errors on passive inverse synthetic aperture radar (ISAR) images of rotating targets when back-projection algorithm (BPA) is employed to focus ...the data. Accurate target motion estimation can be quite challenging, especially in non-cooperative target scenarios. In these cases, BPA is applied under erroneous target kinematics information, entailing defocusing and distortions of the final image product. Starting from the evaluation of the image point spread function (PSF) and the resolution properties of the BPA image under ideally known target motion, it will be analytically shown as, at first order, the PSF under motion estimation errors is approximately a scaled and rotated version of the nominal one. Then, theoretical solutions to predict the location of the scatterers in the image will be provided to characterize in closed-form the distortion of the BPA plane. Numerical results under different use cases of practical interest are provided to analyze the level of accuracy required by the motion estimation task for a reliable focusing in the challenging passive radar scenario. Experimental results using both terrestrial and satellite signals of opportunity are also provided, showing the general validity of the approach in different passive ISAR systems. The present analysis is not limited to passive radars and it can be also applied to active bistatic radars having limited transmitted bandwidth.
Target Classification for 3D-ISAR Using CNNs Pui, Chow Yii; Ng, Brian; Rosenberg, Luke ...
IEEE transactions on aerospace and electronic systems,
02/2024, Volume:
60, Issue:
1
Journal Article
Peer reviewed
In maritime surveillance, inverse synthetic aperture radar (ISAR) is a technique for imaging non-cooperative targets, with classification typically performed by the radar operator. By automating the ...target classification process, the operator workload will be reduced significantly and the classification accuracy can be improved. Traditional classification approaches use geometric features extracted from images of known targets to form a training dataset that is later used to classify an unknown target. While these approaches work reasonably well, deep learning based techniques have recently demonstrated significant improvements over conventional processing schemes in many areas of radar. The classification of traditional 2D-ISAR imagery is difficult due to the motion of the sea causing a wide range of imagery. The 3D-ISAR technique was developed as an alternative representation with the target represented by a three-dimensional point cloud. In this article, we investigate how 3D-ISAR can be used for the classification of maritime targets. The proposed scheme makes use of features extracted from the 3D-ISAR generated point cloud of the target from different perspectives (i.e. side, top and front views) to form three point density images. These are then fed into a convolutional neural network to classify the targets.
Interferometric inverse synthetic aperture radar (InISAR) imaging is capable of retrieving 3-D target information from multichannel inverse synthetic aperture radar (ISAR) images obtained by adjacent ...radars or antennas. The InISAR imaging of space targets is more difficult, compared with that observing short range targets with small radar systems. Considering the practical constraints when observing space targets with multiple large radars, this article establishes a flexible InISAR imaging system that allows for nonperpendicular baselines and observation of targets under squint mode. Based on this, the generalized formulas for calculating scatterers' coordinates from measured interferometric phases are derived. Moreover, a pulse-level image registration method based on joint translational motion compensation is proposed to recover the coherence between multichannel ISAR images, under the condition of inconsistent pulse delays at different radar channels. With the proposed method, promising InISAR imaging results are obtained via two simulation experiments. The first experiment assumes ideal point scattering of the target, which verifies the high accuracy and computational efficiency of the proposed ISAR image registration method; the second experiment considers more practical target scattering using facet target model and physical optics algorithm, which demonstrates the possible deviation in InISAR imaging result caused by scatterer's anisotropic scattering and residual error of translational motion compensation. We believe that the derivation and simulation results in this article would be helpful reference for practical InISAR imaging experiments.
This work investigates the impact of motion estimation errors on passive inverse synthetic aperture radar (ISAR) images of rotating targets when the backprojection algorithm (BPA) is employed to ...focus the data. Accurate target motion estimation can be quite challenging, especially in noncooperative target scenarios. In these cases, BPA is applied under erroneous target kinematics information, entailing defocusing and distortions of the final image product. Starting from the evaluation of the image point spread function (PSF) and the resolution properties of the BPA image under ideally known target motion, it will be analytically shown as, at first order, the PSF under motion estimation errors is approximately a scaled and rotated version of the nominal one. Then, theoretical solutions to predict the location of the scatterers in the image will be provided to characterize in closed form the distortion of the BPA plane. Numerical results under different use cases of practical interest are provided to analyze the level of accuracy required by the motion estimation task for a reliable focus in the challenging passive radar scenario. Experimental results using both terrestrial and satellite signals of opportunity are also provided, showing the general validity of the approach in different passive ISAR systems. The present analysis is not limited to passive radars and it can also be applied to active bistatic radars having limited transmitted bandwidth.
A wide-band radar cross section (RCS) reduction of the elliptic surface at TM polarization is reported in this communication. The main scattering sources and the corresponding scattering mechanisms ...of the elliptic surface are accurately identified based on the ISAR imaging technique and the high-frequency approximation theory. The frequency selective surface (FSS) absorber is employed to suppress the specular reflection, and the tapered resistive sheets (TRSs) are used to handle the scattering from the trailing edges. Samples have been fabricated and measured in the anechoic room, both the simulation and measurement results illustrate that 10-dB RCS reduction is achieved within 1.35-4.9 GHz at TM polarization.
In inverse synthetic aperture radar (ISAR) imaging for a uniformly moving rigid-body target, a finely focused ISAR image can be obtained by using the conventional range-Doppler algorithm. However, ...the ISAR image quality may significantly deteriorate when the time-vary Doppler phases in virtue of target maneuvering motions are present, such as an airplane with nonuniformly rotation and a ship with fluctuation. This has become a challenging task, especially under nonhigh signal-to-noise ratio (SNR) environment. In this article, a novel ISAR imaging algorithm for a maneuvering target with moderate reflection intensity is proposed. After motion compensation, the radar echo signal in a range cell is modeled as a multicomponent cubic phase signal (CPS), in which the chirp rate and the quadratic chirp rate are two important physical quantities that may determine the target ISAR focusing quality. Based on a symmetrical instantaneous autocorrelation function, the received CPSs are transformed into the time and lag-time plane, and then a 2-D coherent integration can be realized after the generalized time-scaled transform and 1-D maximization. This forms a high-quality ISAR image. The effectiveness and superiority of the proposed algorithm are validated by the ISAR imaging results of simulated and real measured data.
Spacecraft Inverse Synthetic Aperture Radar (ISAR) imaging super-resolution aims to enhance the resolution of low-resolution images to produce high-resolution images. However, spacecraft ISAR imaging ...presents challenges such as sparse, fuzzy boundaries, and the intricate differentiation between background and spacecraft, rendering current methods less effective in achieving satisfactory super-resolution results. In this letter, we propose a sparse and selective feature fusion network for super-resolution spacecraft ISAR images. At the heart of our approach lies a multi-scale residual block featuring the following essential components: (a) parallel multi-resolution streams to extract multi-scale features, (b) trainable top-k selection operator that intelligently retains the most critical attention scores from the keys for each query, enhancing the distinction between background and spacecraft information within the local region, and (c) selective cross fusion to discriminatively determine which low-and high-scale information to retain when aggregating multi-scale features. The resulting tightly interlinked architecture, named as SSNet, learns a set of more accurate features. Extensive experiments on real ISAR images of spacecraft unequivocally illustrate the superior performance of the proposed method compared to state-of-the-art approaches, achieving an impressive 33.27dB. The code are released at https://github.com/Tombs98/SSNet.
Vortex electromagnetic (EM) waves carrying orbital angular momentum (OAM) wave, whose infinitely helical wavefront and orthogonal eigenvalues of unique physical properties introduce additional ...rotational degrees of freedom, which has demonstrated superior performance in target detection and azimuthal imaging. In order to enhance the imaging performance for maneuvering targets, this paper offers a solution to develop the vortex inverse synthetic aperture radar (ISAR) technique based on OAM beams design. Firstly, by the space geometry of radar and maneuvering targets, the vortex echo signal model is derived, and the characteristics are analyzed as well. Secondly, pre-processing approach is developed for initial phase compensation by the design of the transmitted OAM beams. Thirdly, the imaging method, based on fractional Fourier transform (FrFT) and Doppler centroid tracking (DCT), is proposed to achieve high-precision range compression and motion compensation to accomplish the range alignment while removing the phases caused by residual azimuth displacements. Finally, after the slow-time pulse compression, the time-invariant Doppler shift is generated, and the well-focused ISAR image can be obtained. The simulation results demonstrate that the proposed vortex ISAR imaging can achieve a higher azimuth resolution than the conventional planar EM ISAR paradigm with the same synthetic aperture length. This discovery provides an approach for OAM-based microwave imaging in a rather efficient manner, which has no harsh requirements for complicated and heavily computational post-processing.
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