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Aerospace and Electronic Systems, IEEE Transactions on

Issue 2 • Date APRIL 2012

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Displaying Results 1 - 25 of 76
  • Contents

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  • [Inside front cover]

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  • From the Editor

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  • Active CLEAN: A Modified CLEAN Algorithm for HRRPs of Contiguous Targets with Thinned Spectrum

    Page(s): 930 - 939
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1410 KB) |  | HTML iconHTML  

    High range resolution profiles (HRRPs) of contiguous targets often suffer from sidelobe artifacts. Deconvolution algorithms, such as coherent CLEAN, do not perform well in these scenarios because of spurious peaks and peak mislocations. The problem is more serious when only a portion of the frequency spectrum is used for generating the range profile (i.e., 1-D imaging with thinned spectrum) because of high sidelobes. We propose a modification to the coherent CLEAN technique in which we use a point spread function (PSF) best suited for 1-D imaging. Upper bounds on the average location error have been derived for the proposed technique and extensive simulations have been carried out to corroborate the theory. The proposed technique has been found to work well even in low signal-to-noise ratio (SNR) scenarios. View full abstract»

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  • Space-Variant Filtering for Wavefront Curvature Correction in Polar Formatted Bistatic SAR Image

    Page(s): 940 - 950
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1819 KB) |  | HTML iconHTML  

    An analytical expression of the phase error from wavefront curvature in bistatic spotlight-mode synthetic aperture radar (SAR) image reconstructed via polar format algorithm (PFA) is derived in this paper. The wavefront curvature effect, which arises from the unrealistic planar wavefront assumption in bistatic PFA, induces phase error terms resulting in space-variant geometry distortion and defocusing. Based on the analytical expression of the wavefront curvature error, a space-variant filtering approach is applied to compensate for it in the polar formatted bistatic SAR image. Analysis on the scene size limit after using the correction method indicates that the derived space-variant filter is capable of extending the focused scene size of bistatic PFA considerably. Point target (PT) simulation validates the approach. View full abstract»

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  • Autocorrelation Constraints in Radar Waveform Optimization for Detection

    Page(s): 951 - 968
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2980 KB) |  | HTML iconHTML  

    We consider the design of radar transmit waveforms that are optimal for the purposes of detecting multiple unknown targets in a known interference environment. Specifically, we introduce constraints on the waveform's autocorrelation function, which is of fundamental importance in practice. The incorporation of autocorrelation constraints leaves the problem analytically intractable, and numeric techniques must be employed. We introduce the concept of "waveform optimized performance" in order to provide a framework for suggesting and analyzing various approaches. We show that unlike the solutions to the more relaxed formulations found in the literature, eigenfunction solutions are no longer optimal, and the Neyman-Pearson receiver is no longer the most appropriate choice for many scenarios. Furthermore, for some scenarios, numeric solutions to the autocorrelation-constrained problems can provide signal-to-interference-plus-noise ratio improvements comparable to the solutions of the more relaxed formulations found in the literature. RDManuscript received March 7, 2009; revised September 7, 2010; released for publication February 21, 2011. View full abstract»

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  • Classification via the Shadow Region in SAR Imagery

    Page(s): 969 - 980
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1272 KB) |  | HTML iconHTML  

    The use of a target's shadow in synthetic aperture radar (SAR) imaging has garnered much attention for automated target recognition (ATR) applications. A technique of hidden Markov modeling (HMM) of the shadow profile is developed here. The basic HMM technique is refined using ensemble averaging, mission-based model selection criteria, multi-look scenarios, and data fusion. The algorithms are tested using DARPA's moving and stationary target acquisition and recognition (MSTAR) data. One of the drawbacks of using SAR shadows is that there exist certain, yet limited, target-radar configurations where the shadow simply does not robustly provide discriminatory target information. This limitation, however, can be easily overcome by imaging a target at multiple poses. With two orthogonal looks, the shadow-only classifier was seen to have an average classification performance of over 90% for a five target system. Additionally, the output of the shadow-only classifier is illustrated to be independent of a scattering center based classifier. All of the results indicate that the shadows provide useful discriminatory information that can be used to advance recognition capabilities in SAR ATR applications. View full abstract»

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  • Nonlinear Filter for Ionosphere Divergence Error Reduction in LAAS

    Page(s): 981 - 990
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1572 KB) |  | HTML iconHTML  

    The Hatch filter, the industry-standard method for smoothing GPS code measurements with carrier data in the local area augmented system (LAAS), is susceptible to divergence errors during severe ionospheric storms. The work presented here develops an alternate single-frequency filter called a nonlinear divergence elimination (NLDE) filter that mitigates divergence errors without increasing measurement noise. Application of the filter to GPS data indicates that the nonlinear filter not only zeroes steady-state divergence but also reduces maximum transient errors by 0-24% relative to the Hatch filter. View full abstract»

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  • Radon-Fourier Transform for Radar Target Detection (III): Optimality and Fast Implementations

    Page(s): 991 - 1004
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1714 KB) |  | HTML iconHTML  

    As a generalized Doppler filter bank processing, Radon-Fourier transform (RFT) has recently been proposed for long-time coherent integration detection of radar moving targets. The likelihood ratio test (LRT) detector is derived here for rectilinearly moving targets. It is found that the proposed LRT detector has the identical form as the existing RFT detector, which means that the RFT detector is an optimal detector for rectilinearly moving targets under the white Gaussian noise background. For the fast implementations of the RFT detector, instead of the joint 2-D trajectory searching and coherent integration in pulse-range domain, the 1-D fast Fourier transform (FFT)-based frequency bin RFT (FBRFT) method is proposed in the pulse-range frequency domain without loss of integration performance. Moreover, at the cost of a controllable performance loss, a suboptimal approach called subband RFT (SBRFT) is also proposed to reduce the storage memory. It is shown that not only the long-time coherent integration gain can be obtained via the proposed SBRFT, but also the computational complexity and memory cost can be reduced to the level of the conventional Doppler filter banks processing, e.g., moving target detection (MTD). Some numerical experiments are also provided to demonstrate the effectiveness of the proposed methods. View full abstract»

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  • Improved Target Tracking in the Presence of Wakes

    Page(s): 1005 - 1017
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (984 KB) |  | HTML iconHTML  

    Tracking methods attempt to follow the movement of a target of interest while suppressing irrelevant clutter. A particularly troublesome source of clutter is wakes that appear behind the target. This problem arises in sonar tracking of human divers, in the tracking of boats using surveillance radars, and also in radar tracking of ballistic missiles. Previous research has integrated a solution to this problem in the popular probabilistic data association filter (PDAF). A new solution to this problem in the same framework is proposed here. While previous research has used an approach described as probabilistic editing, the new solution solves the wake problem in a Bayesian framework by means of marginalization. Monte-Carlo simulations show that the new solution provides significantly increased robustness as compared with both the standard PDAF and the probabilistic editing approach. As the new solution has improved theoretical underpinnings, we hope that it can be useful for further research on tracking in the presence of wake clutter. View full abstract»

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  • New Insights on Flower Constellations Theory

    Page(s): 1018 - 1030
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2108 KB) |  | HTML iconHTML  

    The theory of Flower Constellations consists of a general methodology to design axial-symmetric satellite constellations whose satellites all move on the same trajectory with respect to a reference frame rotating at assigned constant angular velocity. Due to the complexity, the Flower Constellations theory as introduced by the authors, is incomplete, leaving open several problems, such as the equivalency and the similarity. In this article, the foundations of the Flower Constellations theory are revisited from a mathematical perspective, and three new important invariants of these constellations are found constituting fundamentals toward the complete theory. These are: the -space, the flower anomaly, and the configuration number. Using these elements, we provide a theorem giving the necessary and sufficient conditions for the equivalency problem in the -space and an algorithm allowing to generate all the similar Flower Constellations to a given one. View full abstract»

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  • Fault-Tolerant Flight Control System Design Against Control Surface Impairments

    Page(s): 1031 - 1051
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2393 KB) |  | HTML iconHTML  

    An active fault-tolerant flight control system design technique against control surface impairments is proposed here. The aircraft control surface impairments are modeled as a polytopic linear parameter varying (LPV) system. Relying on the existing control surface redundancy of the aircraft, both state feedback and static output feedback controllers are synthesized against various degrees of control surface impairments. Simulation examples of an aircraft subject to inner elevon impairments have been used to illustrate the design process and to demonstrate the effectiveness of the proposed method. View full abstract»

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  • Acceleration Constraints for Maneuvering Formation Flight Trajectories

    Page(s): 1052 - 1060
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2145 KB) |  | HTML iconHTML  

    Maneuver acceleration constraints for formation flight path planning based on the leader-follower concept are proposed. First, a minimum maneuver radius is derived to restrict the excessive required velocity over the minimum or maximum value. Second, in order to prevent an abrupt velocity reduction, which may cause large formation errors, a velocity reduction slope is derived to avoid a reverse-thrust command. Finally, we propose a scheme to put these constraints on the leader's maneuver to obtain a feasible path plan for formation flight based on the leader-follower concept. View full abstract»

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  • WiFi-Based Passive Bistatic Radar: Data Processing Schemes and Experimental Results

    Page(s): 1061 - 1079
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4925 KB) |  | HTML iconHTML  

    The practical feasibility of a WiFi transmissions based passive bistatic radar (PBR) is analyzed here. The required data processing steps are described including the adopted techniques for 1) the control of the signal autocorrelation function (ACF) usually yielding a high sidelobe level, and 2) the removal of the undesired signal contributions which strongly limit the useful dynamic range. The performance of the proposed techniques is firstly evaluated against simulated data generated according to the IEEE 802.11 Standards. Moreover the results are presented against a real data set collected by an experimental setup when using the conventional dual (reference and surveillance) channels PBR receiving scheme. This allows us to demonstrate the potentialities of a WiFi-based PBR for local area surveillance applications, where vehicles and people can be detected and tracked. Based on the digital nature of the exploited signals of opportunity, the attractive possibility is also investigated of avoiding the use of a dedicated receiving channel for the reference signal, by synthesizing it from the surveillance channel. This approach is shown to yield comparable performance with respect to the conventional PBR approach while yielding a remarkable saving in terms of system complexity. View full abstract»

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  • Prony Analysis of Flat-Spin Motion from Accelerometer Data

    Page(s): 1080 - 1099
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (9851 KB) |  | HTML iconHTML  

    The data from a flat-spin maneuver by a small spacecraft are used to investigate the performance of a motion measurement system constructed with nine linear accelerometers. A novel solution method yields only two values of the angular rate vector of the instrument, and subsequently the values for the linear and angular accelerations. The component values are approximated by complex exponential functions according to Prony's method. View full abstract»

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  • Noniterative Filter-Based Maximum Likelihood Estimators for GNSS Signal Tracking

    Page(s): 1100 - 1114
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2538 KB) |  | HTML iconHTML  

    This paper presents alternate forms of a signal tracking algorithm for Global Navigation Satellite System (GNSS) receivers that use a maximum likelihood estimation (MLE) technique. The cost function of the MLE for estimating signal parameters such as code delay, carrier phase, and Doppler frequency is used to derive discriminator functions to create error signals from incoming and reference signals. Assuming a code-free signal and an additive white Gaussian noise, we derive an efficient, practical form of general purpose signal tracking algorithms by using a noniterative MLE approach for arbitrary spreading codes and modulation schemes in accordance with computational efficiency. Two versions of an MLE algorithm are derived. The first is a coherent MLE algorithm derived from the gradient of the log-likelihood cost function for signal parameters. The second is a noncoherent MLE algorithm derived on the basis of complex domain signal that is insensitive to carrier phase error and data bits, thereby eliminating the coupling effect between the carrier phase and Doppler frequency. Analytical test results demonstrate the performance of the proposed algorithms in comparison with those from conventional approaches in terms of pull-in-range, coupling effect, and computational efficiency. View full abstract»

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  • Sensitivity Analysis of a Tightly-Coupled GPS/INS System for Autonomous Navigation

    Page(s): 1115 - 1135
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5202 KB) |  | HTML iconHTML  

    The work presented here empirically analyzes the design of the tightly-coupled position, velocity, and attitude estimator used as a feedback signal for autonomous navigation in a large scale robot driving in urban settings. The estimator fuses GNSS/INS signals in an extended square root information filter (ESRIF), a numerically-robust implementation of an extended Kalman filter (EKF), and was used as the basis for Cornell University's 2007 DARPA Urban Challenge robot, "Skynet." A statistical sensitivity analysis is conducted on Skynet's estimator by examining the changes in its behavior as critical design elements are removed. The effects of five design elements are considered: map aiding via computer vision algorithms, inclusion of differential corrections, filter integrity monitoring, Wide Area Augmentation System (WAAS) augmentation, and inclusion of carrier phases; the effects of extensive signal blackouts are also considered. Metrics of comparison include the statistical differences between the full solution and variant; the Kullback-Leibler divergence; and the average and standard deviation of the position errors, attitude errors, and filter update discontinuities. View full abstract»

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  • Design of a Middleware Interface for ARINC 429 Data Bus

    Page(s): 1136 - 1149
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5767 KB) |  | HTML iconHTML  

    This work is focused on the design and development of a middleware software layer which will enable real-time communication among different embedded avionics modules through an ARINC 429 bus. The implemented layer is based on a C++ object-oriented (OO)-based structure and it has been designed in accordance with middleware concepts. It makes each specific avionics application independent from the bus, from the manufacturers' hardware and finally, from the avionics hardware board model. View full abstract»

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  • UAV Path Planning for Passive Emitter Localization

    Page(s): 1150 - 1166
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2717 KB) |  | HTML iconHTML  

    A path planning algorithm is presented for uninhabited aerial vehicles (UAVs) trying to geolocate an emitter using passive payload sensors. The objective is to generate a sequence of waypoints for each vehicle that minimizes localization uncertainty. The path planning problem is cast as a nonlinear programming problem using an approximation of the Fisher information matrix (FIM) and solved at successive waypoints to generate vehicle trajectories. The effectiveness of the proposed algorithm is illustrated with simulation examples. View full abstract»

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  • MIMO Radar Waveforms and Cancellation Ratio

    Page(s): 1167 - 1178
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1596 KB) |  | HTML iconHTML  

    The performance of adaptive multiple-input multiple-output (MIMO) radar waveforms is examined. We begin by defining a metric, called "MISO cancellation ratio", for numerically screening MIMO waveforms so as to assess their clutter cancellation performance. Next, we evaluate the MISO cancellation ratio levels provided by a number of MIMO waveform classes. Finally, we describe a new MIMO waveform approach, called "dithered DDMA" (Doppler division multiple access), which enables high performance clutter cancellation over a large range-Doppler region without introducing ambiguous ranges or blind speeds, and without increasing the computational load on the MIMO processor. View full abstract»

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  • Track Quality Based Multitarget Tracking Approach for Global Nearest-Neighbor Association

    Page(s): 1179 - 1191
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5290 KB) |  | HTML iconHTML  

    In multitarget tracking, in addition to the problem of measurement-to-track association, there are decision problems related to track confirmation and termination. In general, such decisions are taken based on the total number of measurement associations, length of no association sequence, and total lifetime of the track in question. For a better utilization of available information, confidence of the tracker on a particular track can be used. This quantity can be computed using the measurement-to-track association likelihoods corresponding to the particular track, target detection probability for the sensor-target geometry, and false alarm density. A track quality measure is proposed here for assignment-based global nearest neighbor (GNN) trackers. It can be noted that to compute track quality measure for assignment-based data association one needs to consider different detection events than those considered for computation of the track quality measures available in the literature, which are designed for probabilistic data association (PDA) based trackers. In addition to the proposed track quality measure, a multitarget tracker based on it is developed, which is particularly suitable in scenarios with temporarily undetectable targets. In this work, tracks are divided into three sets based on their quality and measurement association history: initial tracks, confirmed tracks, and unobservable tracks. Details of the update procedures of the three track sets are provided. The results show that discriminating tracks on the basis of their track quality can lead to longer track life while decreasing the average false track length. View full abstract»

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  • New State and Measurement Models for Endo-Atmospheric Tracking of Ballistic Targets using Seeker Measurements

    Page(s): 1192 - 1209
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3767 KB) |  | HTML iconHTML  

    Two state models and a measurement model for estimation of relative kinematics using measurements from RF seekers are proposed. The state vector for the first state model includes the acceleration of the target along with target-interceptor relative position and velocity in the state vector. In the other state model, the jerk of the target is also included among the state variables. Both models also include the ratio of the air density and the ballistic coefficient and its time derivatives as elements of the state vector to account for the aerodynamic drag in the endo-atmospheric phase. Such formulations obviate the need for assuming empirical models of air density and drag coefficient. In the proposed measurement model, the line of sight (LOS) angle is derived from the seeker measurements of LOS rate and gimbal angle and used for measurement update of the state estimator. This reduces the dimension of the measurement vector and obviates the need for modeling the dynamics of the seeker tracking and the stabilization loop. Performance results of the proposed methods have been compared with a well- known model from the literature under closed-loop guidance employing the augmented proportional navigation (APN) law for endo-atmospheric ballistic target tracking. It is clearly seen that the proposed methods yield more accurate estimates of target acceleration in terms of reduced mean error and a more favourable cumulative distribution of miss distances that effectively increase the probability of hit for a given warhead lethality radius. View full abstract»

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  • Integrated Clutter Estimation and Target Tracking using Poisson Point Processes

    Page(s): 1210 - 1235
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5532 KB) |  | HTML iconHTML  

    In this paper, based on Poisson point processes, two new methods for joint nonhomogeneous clutter background estimation and multitarget tracking are presented. In many scenarios, after the signal detection process, measurement points provided by the sensor (e.g., sonar, infrared sensor, radar) are not distributed uniformly in the surveillance region as assumed by most tracking algorithms. On the other hand, in order to obtain accurate results, the target tracking filter requires information about clutter's spatial intensity. Thus, nonhomogeneous clutter spatial intensity has to be estimated from the measurement set and the tracking filter's output. Also, in order to take advantage of existing tracking algorithms, it is desirable for the clutter estimation method to be integrated into the tracker itself. Nonhomogeneous Poisson point processes, whose intensity function are assumed to be a mixture of Gaussian functions, are used to model clutter points here. Based on this model, a recursive maximum likelihood (ML) method and an approximated Bayesian method are proposed to estimate the nonhomogeneous clutter spatial intensity. Both clutter estimation methods are integrated into the probability hypothesis density (PHD) filter, which itself also uses the Poisson point process assumption. The mean and the covariance of each Gaussian function are estimated and used to calculate the clutter density in the update equation of the PHD filter. Simulation results show that both methods are able to improve the performance of the PHD filter in the presence of slowly time-varying nonhomogeneous clutter background. View full abstract»

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  • Optimal Linear Fusion of Smoothed State Estimates

    Page(s): 1236 - 1248
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1087 KB) |  | HTML iconHTML  

    The work presented here deals with estimation fusion of smoothed state estimates. Two problems of fusion for smoothing are considered: fixed point and fixed interval. Optimal linear fusion rules in the sense of the optimal weighted least squares (OWLS) and the linear minimum mean-square error (LMMSE) are obtained. These rules are in recursive forms convenient for implementation. We also propose a more practical method for real-time smoothing, which in essence is fusing smoothed and filtered estimates. Illustrative numerical results are provided to verify the performance and credibility of the fusion rules. View full abstract»

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  • Reliability-Oriented Design of Three-Phase Power Converters for Aircraft Applications

    Page(s): 1249 - 1263
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2484 KB) |  | HTML iconHTML  

    This paper presents a reliability-oriented design (ROD) procedure for three-phase power converters in aircraft applications. These require the highest reliability levels for all its components-as high as space applications; hence the need to maximize the reliability of three-phase power converters, which are in increasing demand and use in commercial and military aircrafts as a result of the more-electric aircraft (MEA) initiative. Specifically, the proposed procedure takes reliability up-front in the design process of power converters, carrying out the design in three steps. First, the identification of critical system components; second, the assessment of reliability factors such as risk analysis, failure mode analysis, and fishbone diagrams; and third, the actual design, which is carried out by minimizing system complexity and stress, and by the use of the most reliable components, materials, and structures. To this end, reliability models were developed for all critical components based on the military handbook MIL-HDBK-217F, and field and vendor data. For verification purposes, the paper includes the ROD of a 60 kW three-phase power converter for aircraft applications together with experimental results of the prototype constructed. View full abstract»

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Aims & Scope

IEEE Transactions on Aerospace and Electronic Systems focuses on the equipment, procedures, and techniques applicable to the organization, installation, and operation of functional systems designed to meet the high performance requirements of earth and space systems.

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Meet Our Editors

Editor-in-Chief
Lance Kaplan
Army Research Laboratory