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Aiming at the problems such as long production cycle, low utilization rate of carbon dioxide and difficult to meet the standard requirements of battery grade lithium carbonate produced by traditional carbonization decomposition method, the preparation of battery grade lithium carbonate by sodium carbonate--shear carbonization--ion exchange--heating decomposition process was studied using low-grade leachite ore as raw material. The results show that the removal rates of calcium, magnesium and manganese are 97.26%, 81.82% and 95.73 %, respectively, under the conditions of 30 °C, liquid volume/solid mass ratio of 25/1, carbon dioxide input rate of 0.5 L/rnin and shear speed of 6 000 r/min. The shear assisted carbonization method can significantly improve the carbonization reaction rate, shorten the reaction time, save more than 70% of CO2, and is more conducive to the production of battery grade lithium carbonate. The prepared lithium carbonate can meet the standard of battery grade lithium carbonate. [ABSTRACT FROM AUTHOR]

A shear-enhanced method based on strong homogenization was proposed and applied in the goethite process for iron removal from the zinc process solution to overcome the low reaction efficiency and the difficulty in residue filtration. A 3D shear-enhanced rector model was designed, and the process was simulated to reveal the characteristics of fluid flow, gas mass transfer, and goethite particle movement under the coupling multi-physical field at different shearing speeds. The results showed that the homogenization of the solution in the reactor is improved by increasing the flow rate of fluids. The gas dispersion is strengthened to increase the mass transfer rate, further accelerating the iron removal reaction. In addition, after iron precipitation, the formed goethite particles and grains can be broken and refined at a high shearing speed. Zinc in the iron precipitation residue is present in adsorption instead of incorporation, indicating fewer zinc losses. Finally, the reliability of the model was verified by experiments. The shear-enhanced goethite process was suggested to improve iron removal efficiency, and it obtains the iron precipitation residue with the crystal structure of α-FeOOH, suggesting further good filtration performance in the following solid/liquid separation stages. [ABSTRACT FROM AUTHOR]

Background: Pyroptosis has been implicated in the development of human diseases, including vitiligo. TanshinoneIIA has been confirmed to play anti‐vitiligo role. However, whether tanshinoneIIA inhibits vitiligo progression via regulating cell pyroptosis remains unclear. Methods: Hydrogen peroxide (H2O2)‐induced melanocytes were used to mimic vitiligo cell model in vitro. Cell viability was assessed by cell counting kit 8 assay, and reactive oxygen species (ROS) production was detected by DCFH‐DA staining. Nod‐like receptor protein 3 (NLRP3) expression was detected by quantitative real‐time PCR, western blot and immunofluorescence staining. Cell pyroptosis was measured using flow cytometry, and the contents of interleukin‐1β and interleukin‐18 were determined by ELISA. Besides, the protein levels of apoptosis‐associated speck‐like protein containing CARD (ASC) and cleaved‐Caspase‐1 were examined by western blot analysis. Results: H2O2 could induce ROS production, NLRP3 expression and pyroptosis in melanocytes. TanshinoneIIA inhibited ROS production, pyroptosis, and the expression of NLRP3, ASC and cleaved‐caspase‐1 in H2O2‐induced melanocytes. Compared with the function of ROS inhibitor (NAC), tanshinoneIIA acted as a ROS scavenger to relieve melanocyte pyroptosis. In addition, NLRP3 inhibitor (MCC950) also could aggravate the inhibition effect of tanshinoneIIA on melanocyte pyroptosis. Conclusion: TanshinoneIIA suppressed melanocyte pyroptosis probably through modulating the ROS/NLRP3 signaling axis, which provides the evidence for therapeutic effect in vitiligo. [ABSTRACT FROM AUTHOR]

Airborne synthetic aperture radar (SAR) is susceptible to atmospheric disturbance and other factors that cause the position offset error of the antenna phase center and motion error. In close-range detection scenarios, the large elevation angle may make it impossible to directly observe areas near the underlying plane, resulting in observation blind spots. In cases where the illumination elevation angle is extremely large, the influence of range variant envelope error and phase modulations becomes more serious, and traditional two-step motion compensation (MOCO) methods may fail to provide accurate imaging. In addition, conventional phase gradient autofocus (PGA) algorithms suffer from reduced performance in scenes with few strong scattering points. To address these practical challenges, we propose an improved phase-weighted estimation PGA algorithm that analyzes the motion error of UAV SAR under a large elevation angle, providing a solution for high-order range variant motion error. Based on this algorithm, we introduce a combined focusing method that applies a threshold value for selection and optimization. Unlike traditional MOCO methods, our proposed method can more accurately compensate for spatially variant motion error in the case of scenes with few strong scattering points, indicating its wider applicability. The effectiveness of our proposed approach is verified by simulation and real data experimental results. [ABSTRACT FROM AUTHOR]

The automotive synthetic aperture radar (SAR) can obtain two-dimensional (2-D) high-resolution images and has good robustness compared with the other sensors. Generally, the 2-D high-resolution always conflicts with the real-time requirement in conventional SAR imaging. This article suggests an automotive video SAR (ViSAR) imaging technique based on sub-aperture spectrum fusion to address this issue. Firstly, the scene space variation problem caused by close observation distance in automotive SAR is analyzed. Moreover, the sub-aperture implementation method, frame rate and resolution of automotive ViSAR are also introduced. Then, the improved Range Doppler algorithm (RDA) is used to focus the sub-aperture data. Finally, a sub-aperture stitching strategy is proposed to obtain a high-resolution frame image. Compared with the available ViSAR imaging method, the proposed method is more efficient, performs better, and is more appropriate for automotive ViSAR. The simulation results and actual data of the automotive SAR validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

With the rapid development of high-resolution synthetic aperture radar (SAR) systems, the technique that utilizes multiple two-dimensional (2-D) SAR images with different view angles to extract three-dimensional (3-D) coordinates of targets has gained wide concern in recent years. Unlike the traditional multi-channel SAR utilized for 3-D coordinate extraction, the single-channel curvilinear SAR (CLSAR) has the advantages of large variation of view angle, requiring fewer acquisition data, and lower device cost. However, due to the complex aerodynamic configuration and flight characteristics, important issues should be considered, including the mathematical model establishment, imaging geometry analysis, and high-precision extraction model design. In this paper, to address these challenges, a 3-D vector model of CLSAR was presented and the imaging geometries under different view angles were analyzed. Then, a novel 3-D coordinate extraction approach based on radargrammetry was proposed, in which the unique property of the SAR system, called cylindrical symmetry, was utilized to establish a novel extraction model. Compared with the conventional approach, the proposed one has fewer constraints on the trajectory of radar platform, requires fewer model parameters, and can obtain higher extraction accuracy without the assistance of extra ground control points (GCPs). Numerical results using simulated data demonstrated the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

A large time-bandwidth product bistatic radar offers several advantages in high-resolution target detection and motion parameter estimation, but the scale factor and inner-pulse Doppler will also be introduced in the radar echoes when detecting high-speed targets. Under this condition, the conventional matched filter will cause a certain energy loss and a nonnegligible shift of the range center, which is called mismatch effect. Considering the special geometries of the bistatic radar, we first establish the precise echo signal (PES) model to describe the radar echoes for high-speed targets in a space–air-based bistatic radar system. By analyzing the mismatch effect within the pulse and the migration between pulses, we have obtained the mathematic relationship between the scale factor, inner-pulse Doppler shift, range, equivalent velocity, and acceleration. Following that, we perceive that the parameters of the matched filter are related to the target motion parameters, i.e., a priori unknown, which inspires us to propose an iterative coherent integration method to achieve the intrapulse and interpulse integration. A PES model matched filter with initial parameters is defined and a roughly motion parameter estimation is acquired by the PES model-based Keystone transform (PES-KT) and inner-pulse chirp Fourier transform (CFT). The estimated parameters are used for matched filter construction and coherent integration. This process is performed over multiple iterations to provide an accurate motion parameter result. In the end, a target detection experiment is given to show the effectiveness of the proposed method using space–air-based bistatic radar. [ABSTRACT FROM AUTHOR]

The research into curvilinear flight synthetic aperture radar (CF-SAR) is the inevitable result of the comprehensive practicality of SAR. The flight path of the SAR platform in real applications, which is highly nonlinear or curvy due to three-dimensional velocity and acceleration, cannot be described by the traditional uniform linear motion model. New mathematical models, signal characteristics, imaging algorithms, and system design criteria must be proposed and investigated for CF-SAR. This paper provides a comprehensive overview of CF-SAR. Firstly, the basic concept, unified model, and general signal characteristics of CF-SAR are defined, derived, and analyzed, respectively. Additionally, the advantages and drawbacks of current methodologies are reviewed. Discussions on the CF-SAR's applications are presented from the perspective of typical platforms, new configurations, and advanced technologies, which are suitable means to fulfill the increasing user requirements. Finally, the challenges faced by CF-SAR are summarized, and some future trends for the study of CF-SAR are explored. Hopefully, this paper will serve as a reference for SAR researchers/engineers and stimulate the future development and actual application of CF-SAR. [ABSTRACT FROM AUTHOR]

In this paper, a diverse-region hyperspectral image classification (DRHy) method is proposed by considering both irregularly local pixels and globally contextual connections between pixels. Specifically, the proposed method is operated on non-Euclidean graphs, which are constructed by superpixel segmentation methods for diverse regions to cluster irregularly local-region pixels. In addition, the dimensionality reduction method is employed to alleviate the curse of dimensionality problem with a lower computational burden, generating more representative data with the input graph features. In this context, it then constructs a superpixelwise Chebyshev polynomial graph convolution network (ChebyNet) to aggregate global-region superpixels. Benefiting from different superpixel numbers of segmentations, we construct different graph structures, and multiple classification results are obtained, which brings more opportunities to represent the hyperspectral data correctly. Then, all the diverse-region results are further fused by a majority voting technique to improve the final performance. Finally, numerical experiments on two benchmark datasets are provided to demonstrate the superiority of the proposed DRHy-ChebyNet method to the other state-of-the-art methods. [ABSTRACT FROM AUTHOR]

For unmanned aerial vehicle (UAV) synthetic aperture radar (SAR) imaging, motion errors cannot be obtained accurately when high precision motion sensors are not equipped on the platform. This means that traditional data-based motion compensation (MOCO) cannot be directly implemented due to large measurement errors. In addition, classic autofocusing techniques, such as phase gradient autofocus (PGA) or map-drift algorithm (MDA), do not perform well with spatially variant errors, greatly affecting the imaging qualities, especially for high-resolution and large-swath cases. In this study, an improved spatially variant MOCO approach based on an MDA is developed to effectively eliminate the spatially variant errors. Based on the coarse and precise MDA chirp rate error estimation, motion errors are optimally acquired by the random sample consensus (RANSAC) iteration. Two-dimensional (2D) mapping is used to decouple the spatially variant residual errors into two linear independent dimensions so that the chirp-z transform (CZT) can be performed for echo data correction. Unlike traditional approaches, the spatially variant components can be compensated without any measured motion information, which indicates that the proposed approach can be applied to the common UAV SAR system with significant measurement errors. Simulations and real data experiments were used to evaluate the performance of the proposed method. The simulation results show that the proposed algorithm is able to effectively minimize spatially variant errors and generate much better imaging results. [ABSTRACT FROM AUTHOR]

Synthetic aperture radar (SAR) image similarity metric is at the core of SAR image interpretation techniques, however, it is still a challenging task due to complex nonlinear intensity, scale, and rotation differences between SAR images and other remote sensing images. This letter addresses this problem by proposing a novel similarity metric method for SAR images using structure and shape properties. The magnitude and orientation representation of the phase congruency model is first built based on the local phase of images. Then a new scale and rotation‐invariant local binary pattern (SRI‐LBP) descriptor is proposed using local structure and shape information. Finally, a similarity metric is defined using the symmetry Kullback Leibler divergence (SKLD) of the SRI‐LBP descriptors. Numerical experiment results verify its robustness in terms of nonlinear intensity, scale, and rotation differences. [ABSTRACT FROM AUTHOR]

The mainlobe jamming suppression technique is one of the key techniques of radar electronic counter-countermeasure (ECCM). In the view of multistatic radar, the interference signals received with different view angles would be highly coherent, on the contrary, the target echoes would be independent due to the radar cross section (RCS) of target would randomly fluctuate as the variation of view angle. As a consequence, After the interference signals have been aligned, a steering vector can be found of interference signals, the energy of the interference signals will be concentrated in a single-rank subspace whereas the energy of the target echo signals will be scattered throughout the whole signal space of the multistatic radar. By exploiting this phenomenon, a new mainlobe interference suppression method for multistatic radar is proposed. In this method, the projection matrix is trained based on the time domain sampling data. The interference signals received by multiple node radars with different view angles can be effectively suppressed through the noise subspace projection operation. Then, a general likelihood ratio test detector used for the residual signals after projection operation is derived. The results of simulations indicate that the proposed method can effectively suppress various kinds of mainlobe jamming and improve the detection performance. Furthermore, this method is adaptive to the variation of the interference pattern and the geometric configuration of the node array. [ABSTRACT FROM AUTHOR]

As an emerging multifunctional material, Gallium-based room temperature liquid metal has attracted a lot of attention for a variety of applications due to its mobility and deformability. However, controlling the motion of a liquid metal droplet accurately still remains unrevealed, which restricts its application in many fields. In this article, we propose a hybrid framework that would control the motion of a liquid metal droplet in a one-dimensional (1-D) fluidic channel. A dynamic model of a liquid metal droplet immersed in the electrolyte when an electrical field is applied to each end of the channel is discussed first, followed by a setpoint controller designed to calculate the current input needed to drive the liquid metal droplet to its destination with vision feedback. To obtain the desired high-resolution current output, a fast and high-resolution current output power supply will be established by integrating a fast PID controller and a simple programmable dc power supply. The effectiveness of this proposed approach will be verified by controlling a liquid metal droplet so that it reaches its destination inside the polymethyl methacrylate channel. In this article, the proposed approach may lead to the development of tiny soft robots, or microfluidic systems that can be driven accurately by the liquid metal droplets. [ABSTRACT FROM AUTHOR]

As a transition platform between aircraft and satellite, hypersonic vehicle-borne (HSV) synthetic aperture radar (SAR) could offer many advantages such as strong survival ability, fast response, and wide detection range. However, due to the complex aerodynamic configuration and flight characteristics of the hypersonic platform, the HSV SAR faces new challenges including serious cross-couplings and spatial variations. In order to deal with these issues, a radius/angle algorithm (RAA) is devised, which has a similar processing flow as that of the conventional polar format algorithm (PFA). In the RAA, a novel 2-D interpolation function, similar to that of the PFA which is performed in the Cartesian coordinates, is derived in the curvilinear coordinate system. Due to the high accuracy of the multi-decomposition by using the polar radius and polar angle, the RAA has a much larger depth-of-focus than that of the PFA. Moreover, the RAA approach is insensitive to the height variations for the HSV SAR with curved trajectory flight, whereas the PFA is not because of the out-of-plane projection effect. Simulation results verify the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

A non‐adaptive space‐time clutter canceller (NSCC) for multi‐channel (MC) synthetic aperture radar (SAR) was proposed. First, a new three‐part range equation was derived on the basis of the two‐dimensional Taylor series expansion. Then, each part of the model was analysed. By compensating of the high‐order coupling part and the compression of the Doppler extension part of the derived equation, the interlaced signal of a moving target and a clutter patch was easily separated in a space‐time domain. The clutter signal in different pulses only contained a constant phase difference. Using radar parameters, the authors constructed a non‐adaptive clutter canceller that prevented traditional space time adaptive processing (STAP) issues, such as secondary sample support, computational complexity burden, and unknown moving target information. Compared with the representative non‐adaptive method, that is displaced phase centre antenna (DPCA), NSCC is robust to a small degree of parameter error. It can be applied when DPCA condition is not satisfied. The effectiveness of the proposed method was validations through simulation. [ABSTRACT FROM AUTHOR]

Rescue is a tough and time-consuming task in huge disaster. After stricken by a catastrophic natural disaster, the rescue force is typically deployed under the circumstance of traffic paralysis and lack of supplies. To cope with this situation, plenty of human resource and professional equipment are required. However, both the human resource and equipment are insufficient in most situations. The rescue force needs an efficient technology for searching the survivals, such as the life detection, which can be a key factor in disaster relief. Fast and accurate locating of the survivals will guide the limited rescue resource to save more survivors. However, current life detection technology cannot meet the demand of rescue in huge disaster. A novel life detection system based on fake base station is proposed. The detection system can scan the whole disaster area and find the cell phones, which leads to the surviving owners. As the system works in different way with other traditional human localization technology, a novel RSS/AOA hybrid positioning algorithm was proposed in this paper to increase the accuracy of localization. To verify the accuracy, two simulation tests were designed. The result of the two tests illustrates that the novel algorithm is more suitable to work with the novel life detection system. [ABSTRACT FROM AUTHOR]

In disaster relief, especially in the rescue of serious disaster like great earthquake or tsunami, detecting the exact location of survivors via portable devices can greatly improve the efficiency of search and rescue work. A novel infrastructure-free cell phone positioning system based on software-defined radio, virtual base transceiver station software and its running scheme is proposed in this paper. The identification information of cell phones, receive signal strength and signal transceiver power data can be collected by this system. By using customized antennas with new positioning method, the proposed system can indicate the location of survivals trapped under debris without any operation on cell phones by survivors. With the new hybrid algorithm, search radius of the system can reach more than 1.2 km. And it is also able to implement accurate positioning by this system at the same time. Experimental results demonstrated that the system has significantly improved performance over the traditional methods. [ABSTRACT FROM AUTHOR]

This paper investigates the enhancement of convective heat transfer within a sub-millimetre diameter copper tube using AlO, CoO and CuO microparticle suspensions. Experiments are conducted at different particle concentrations of 1.0, 2.0 and 5.0 wt% and at various flow rates ranging from 250 to 1000 µl/min. Both experimental measurements and numerical analyses are employed to obtain the convective heat transfer coefficient. The results indicate a significant enhancement in convective heat transfer coefficient due to the implementation of microparticle suspensions. For the case of AlO microparticle suspension with 5.0 wt% concentration, a 20.3 % enhancement in convective heat transfer coefficient is obtained over deionised water. This is comparable to the case of AlO nanofluid at the same concentration. Hence, there is a potential for the microparticle suspensions to be used for cooling of compact integrated systems. [ABSTRACT FROM AUTHOR]

In the traditional model of monostatic synthetic aperture radar (SAR), the flying platform should have a uniform linear trajectory. In practice, the flight path of the SAR platform, which is highly nonlinear or curvy caused by 3-D velocity and acceleration, cannot be used in the traditional model. In this paper, a geometrical model of the monostatic SAR with general configurations is graphically illustrated by vector notation. Moreover, the gradient method is utilized to point out the effects of the motion parameters, namely, velocity vector and acceleration vector, on total bandwidth and image resolution. Based on the accurate model, a general frequency-domain algorithm, with the incorporations of pre- and postprocessing, is proposed to focus the raw data. Applicability is studied through theoretical analysis and numerical experiments. All these general analyses can be applied to different realizations of monostatic SAR mode, including spotlight SAR, sliding spotlight SAR, and Terrain Observation by Progressive Scans (TOPS) SAR. [ABSTRACT FROM PUBLISHER]

Synthetic aperture radar (SAR) imaging is usually performed along a straight path. In practice, variations from the ideal caused by maneuvers with acceleration are inevitable. The main problem is the complex signal processing, particularly in the highly squinted spotlight mode. In this paper, acceleration model is analyzed in more details. Impacts are obtained how the acceleration influences the Doppler parameters and space-variant terms, including the SAR resolution and azimuth bandwidth. According to the special signal properties of the acceleration case, an approximation of the range history is made to avoid using the method of series reversion (MSR) to obtain an accurate spectrum. Based on the high-accurate spectrum, a spotlight algorithm with a modified two-step approach is given. Simulation results show the effectiveness of the modified algorithm. [ABSTRACT FROM PUBLISHER]

This letter proposes an omega-K algorithm for missile-borne synthetic aperture radar (SAR) diving with constant acceleration. The essence of the novel method is to derive a reference function multiplication from the equivalent range history. The true range history is divided into two parts: range independent and range dependent. After compensating the range-independent part with considering all the terms, we can regard the range-dependent part as an equivalent range history with a form similar to that of conventional SAR. Then, an analytical 2-D spectrum can be used for the omega-K algorithm. The proposed algorithm can handle general missile configurations with wide swaths and high squint angles. Simulation results are presented to validate the proposed method. [ABSTRACT FROM PUBLISHER]

In high‐resolution spaceborne synthetic aperture radar (SAR), the hyperbolic range equation assumption fails to precisely describe the range history; thus, the traditional resolution analysis used for a spaceborne SAR design is imprecise. A curved orbit geometrical model based on the modified equivalent squint range model is graphically presented by vector notation. According to the model, the vectorial calculation of resolution is analytically presented, based on the gradient method. Additionally, a physical model is introduced to derive the effective integration time, which is quite difficult to derive due to the three‐dimensional curved orbit. Simulation results are presented to validate the proposed method. [ABSTRACT FROM AUTHOR]

The problem of target detection in impulsive non-Gaussian sea clutter has attracted a lot of attention in recent years. The positive alpha-stable (PαS) distribution has been validated as a suitable model for the impulsive non-Gaussian sea clutter. Since the probability density function (PDF) of the PαS variable cannot be expressed as a closed-form expression, the research into constant false alarm rate (CFAR) detectors in PαS distributed sea clutter is limited. This paper formulates and evaluates some CFAR detectors, such as Greatest Of-CFAR (GO-CFAR), Smallest Of-CFAR (SO-CFAR), Order Statistic-CFAR (OS-CFAR) and censored mean level (CML) detectors, in PαS distributed sea clutter. Firstly, the Fox's H-function is adopted to express the PDF of the PαS variable, and the cumulative density function based on Fox's H-function is derived in this paper. Then, by use of the properties of the H-function and PαS distribution, exact expressions of the probabilities of false alarm and detection for CFAR detectors in the PαS background are derived. Some CFAR properties of these detectors in the PαS background are also explored. Numerical results based on derived expressions are given and verified by Monte Carlo simulation. Some analyses of detection performance from a practical perspective are also given. [ABSTRACT FROM AUTHOR]

This work investigates particle focusing under Dean-flow-coupled elasto-inertial effects in symmetric serpentine microchannels. A small amount of polymers were added to the sample solution to tune the fluid elasticity, and allow particles to migrate laterally and reach their equilibriums at the centerline of a symmetric serpentine channel under the synthesis effect of elastic, inertial and Dean-flow forces. First, the effects of the flow rates on particle focusing in viscoelastic fluid in serpentine channels were investigated. Then, comparisons with particle focusing in the Newtonian fluid in the serpentine channel and in the viscoelastic fluid in the straight channel were conducted. The elastic effect and the serpentine channel structure could accelerate the particle focusing as well as reduce the channel length. This focusing technique has the potential as a pre-ordering unit in flow cytometry for cell counting, sorting, and analysis. Moreover, focusing behaviour of Jurkat cells in the viscoelastic fluid in this serpentine channel was studied. Finally, the cell viability in the culture medium containing a dissolved polymer and after processing through the serpentine channel was tested. The polymer within this viscoelastic fluid has a negligible effect on cell viability. [ABSTRACT FROM AUTHOR]

The spaceborne transmitter/missile-borne receiver (ST/MR) synthetic aperture radar (SAR) could provide several unique advantages, such as wide coverage, unrestricted geography, a small detection probability of the missile, and forward-looking imaging. However, it is also accompanied by problems in imaging, including geometric model establishment and focusing algorithm design. In this paper, an ST/MR SAR model is first presented and then the flight-path constraint, characterized by geometric configurations, is derived. Considering the impacts brought about by the maneuvers of the missile, a non-'Stop-Go' mathematical model is devised and it can avoid the large errors introduced by the acceleration, which is neglected in the traditional model. Finally, a two-dimensional (2-D) scaling algorithm is developed to focus the ST/MR data. Without introducing any extra operations, it can greatly remove the spatial variations of the range, azimuth, and cross-coupling phases simultaneously and entirely in the 2-D hybrid domain. Simulation results verify the effectiveness of the proposed model and focusing approach. [ABSTRACT FROM AUTHOR]

Near space is the key to integrating "sky" and "space" into the future. A synthetic aperture radar (SAR) that works in this area would initiate a technological revolution for remote sensing applications. This study mainly focused on ground moving target imaging (GMTIm) for a near-space hypersonic vehicle-borne SAR (NS-HSV-SAR) with squint angle. The range history, parameter coupling, and Doppler ambiguity of the squint-looking NS-HSV-SAR are more complicated than traditional side-looking airborne or space-borne SARs. Thus, a precise range model is presented on the basis of phase error analyses. Then, all potential distributions of echo's azimuth spectrum are derived, and a GMTIm method is proposed on the basis of a detailed analysis of the echo characteristics. The proposed method consists of three steps. Firstly, a prior information-based pre-processing function was created to decrease the Doppler ambiguity and range migration effects. Secondly, a blur matched keystone transform was developed to correct the residual range walk migration. Thirdly, a time-saving chirp Fourier transform was investigated for azimuth focusing. Implementation considerations, including the curvilinear trajectory of the NS-HSV-SAR, multiple moving target imaging, and applicability and limitation of the method, are discussed. Finally, simulation results are presented to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

With the increasing requirement for resolution, the negligence of topography variations causes serious phase errors, which leads to the degradation of the focusing quality of the synthetic aperture (SAR) imagery, and geometric distortion. Hence, a precise and fast algorithm is necessary for high-resolution airborne SAR. In this paper, an extended back-projection (EBP) algorithm is proposed to compensate the phase errors caused by topography variations. Three-dimensional (3D) variation will be processed in the time-domain for high-resolution airborne SAR. Firstly, the quadratic phase error (QPE) brought by topography variations is analyzed in detail for high-resolution airborne SAR. Then, the key operation, a time-frequency rotation operation, is applied to decrease the samplings in the azimuth time-domain. Just like the time-frequency rotation of the conventional two-step approach, this key operation can compress data in an azimuth time-domain and it reduces the computational burden of the conventional back-projection algorithm, which is applied lastly in the time-domain processing. The results of the simulations validate that the proposed algorithm, including frequency-domain processing and time-domain processing can obtain good focusing performance. At the same time, it has strong practicability with a small amount of computation, compared with the conventional algorithm. [ABSTRACT FROM AUTHOR]

Maneuvers provide flexibility for high-resolution highly-squinted (HRHS) airborne synthetic aperture radar (SAR) imaging and also mean complex signal properties in the echoes. In this paper, considering the curved path described by the fifth-order motion parameter model, effects of the third- and higher-order motion parameters on imaging are analyzed. The results indicate that the spatial variations distributed in range, azimuth, and height directions, have great impacts on imaging qualities, and they should be eliminated when designing the focusing approach. In order to deal with this problem, the spatial variations are decomposed into three main parts: range, azimuth, and cross-coupling terms. The cross-coupling variations are corrected by polynomial phase filter, whereas the range and azimuth terms are removed via Stolt mapping. Different from the traditional focusing methods, the cross-coupling variations can be removed greatly by the proposed approach. Implementation considerations are also included. Simulation results prove the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]