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Aerospace and Electronic Systems, IEEE Transactions on

Issue 2 • Date Apr 2001

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Displaying Results 1 - 25 of 34
  • Flight path estimation using frequency measurements from a wide aperture acoustic array

    Page(s): 685 - 694
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (676 KB) |  | HTML iconHTML  

    A narrowband technique based on the acoustical Doppler effect is proposed for estimating the trajectory of a turbo-prop aircraft in level flight with constant velocity as it transits over a ground-based passive acoustic sensor array. The basic principle is to measure the temporal variation of the instantaneous frequency (IF) of the acoustic signal received by each sensor and then to minimize the sum of the squared deviations of the IF estimates from their predicted values over a sufficiently long period of time for all sensors. The technique provides estimates of the propeller blade rate and the five source motion parameters that describe the aircraft trajectory. The six dimensional minimization problem is reduced to a five dimensional maximization problem, which is solved numerically using the quasi-Newton method. A simple method is described that provides the initial parameter estimates required for the numerical maximization. The effectiveness of the motion parameter estimation technique is verified using real acoustic data recorded from a wide aperture microphone array during various transits of a turbo-prop aircraft View full abstract»

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  • Airborne GMTI radar position bias estimation using static-rotator targets of opportunity

    Page(s): 695 - 699
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB) |  | HTML iconHTML  

    In target tracking systems: using GMTI (ground moving target indicator) radars on airborne platforms, the locations of these platforms are available from GPS-based estimates. However, these estimated locations are subject to errors that are, typically, stationary autocorrelated random processes, i.e., slowly varying biases. In situations where there are no known-location targets to estimate these biases, the next best recourse is to use targets of opportunity at fixed but unknown locations. Such targets can be, e.g., static rotators (ground-based radars with rotating antenna), which yield detections in moving target indicator (MTI) radars. It is shown that these biases can be estimated in such a scenario, i.e., they meet the complete observability condition. Following this, the achievable accuracy for a generic scenario is evaluated. It is shown that accurate georegistration can be obtained even with a small number of measurements View full abstract»

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  • FPGA-based adaptive tracking estimation computer

    Page(s): 699 - 706
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (604 KB) |  | HTML iconHTML  

    We describe an FPGA-based adaptive tracking estimation computer (FATEC) for a multiple target tracking (MTT) radar system. Its design is centered around a small processor core customized according to the requirements of tracking application, to run the main control program and provide software flexibility, with a number of tracking algorithms (models) implemented in hardware-type functional units, in order to meet the timing requirements of the application. The FATEC approach provides combination of software flexibility, hardware efficiency, and functional adaptivity of implementation of application-specific computers for the other applications of a similar type, enabling various partitioning options between the software and the hardware parts of the solution View full abstract»

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  • Identification of large aircraft

    Page(s): 706 - 710
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (412 KB) |  | HTML iconHTML  

    Large commercial aircraft are much more easily identified by radar than are fighter aircraft, because the former's two-dimensional images have sufficient details to let one recognize the aircraft's shape. The usual problem with identification based on shape is lack of knowledge of the aspect angle. As an indication of the relative ease with which commercial aircraft can be identified, this note describes a shape-based identification method that does not require knowledge of the aspect angle View full abstract»

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  • Analysis of single-platform passive emitter location with terrain data

    Page(s): 495 - 507
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1228 KB) |  | HTML iconHTML  

    Frequency measurements made at a moving platform can be used to locate an emitter. An error ellipsoid analysis is used to compare the performance under three levels of a priori information on the emitter's altitude: (1) no knowledge, (2) terrain data, and (3) complete knowledge of the emitter's altitude. The analysis is performed for two simple platform paths that provide frequency measurements that are approximately time reversed versions of one another. When no a priori knowledge is available there is little difference between the performance when the platform maneuvers on a concave circular path or on a convex circular path and the performance depends very Little on the platform altitude. However, when some a priori altitude information is available the performance is markedly different on the two paths and is highly dependent on the platform altitude. Thus, this analysis provides the unexpected result that for seemingly similar platform paths, the performance can vary markedly when the emitter altitude is assumed known. Also, an interesting result is that for some cases it is possible to achieve better x-y accuracy when using terrain data than when the emitter's z location is known, because the terrain data provides terrain slope information. These cases are characterized in terms of the terrain slope at the emitter View full abstract»

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  • Improved SAR target detection via extended fractal features

    Page(s): 436 - 451
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2112 KB) |  | HTML iconHTML  

    The utility of the extended fractal (EF) feature is evaluated for the enhancement of the focus of attention (FOA) stage of a synthetic aperture radar (SAR) automatic target recognition (ATR) system. Unlike more traditional SAR detection features that distinguish target pixels from the background only on the basis of contrast, the EF feature is sensitive to both the contrast and size of objects. Furthermore, the structure for the EF feature computational algorithm lends itself to very fast implementation, and it can be shown that the new feature has a CFAR-like (constant false alarm rate) property. We demonstrate the improved performance using the new feature by testing a number of different detection approaches over two databases of SAR imagery View full abstract»

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  • Cascaded adaptive canceller using loaded SMI

    Page(s): 710 - 719
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (724 KB) |  | HTML iconHTML  

    A fast-converging, highly parallel/pipeline cascaded canceler which uses the 2-input loaded sample matrix inversion (SMI) algorithm as the fundamental building block is developed which has convergence performance almost identical to one of the standards of a fast-converging adaptive canceler, the fast maximum likelihood (FML) canceler. Furthermore, the new algorithm, denoted as the cascaded loaded SMI (CLSMI), does not require the numerically intensive singular value decomposition (SVD) of the input data matrix as does the FML algorithm. For both the FML and CLSMI developments it is assumed that the unknown interference covariance matrix has the structure of an identity matrix plus an unknown positive semi-definite Hermitian (PSDH) matrix. The identity matrix component is associated with the known covariance matrix of the system noise and the unknown PSDH matrix is associated with the external noise environment. For narrowband (NB) jamming scenarios with J jammers it was shown via simulation that the CLSMI and FML converge on the average -3 dB below the optimum in about U independent sample vectors per sensor input. Both the CLSMI and FML converge much faster than the standard canceler technique, the SMI algorithm View full abstract»

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  • ISAR imaging of targets at low elevation angles

    Page(s): 419 - 435
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1604 KB) |  | HTML iconHTML  

    The problem of inverse synthetic aperture radar (ISAR) image reconstruction of targets at low elevation angle is considered. In this geometric condition the main causes affecting the reconstructed ISAR image are the multipath effect due to the reflection of the Earth's surface and the angular motions of the target produced by external action like wind, fast maneuvering, and sea waves as in the case of ships. The aim of this work is to analyze the effects that the multipath and the target angular motions jointly produce on the ISAR image. The results show that multipath generates some artifacts in the image whereas the target oscillations undergo a spatial-dependent blurring of the point spread function of the ISAR system. These theoretical results are validated by presenting some numerical examples relevant to aircrafts and ships in rectilinear or circular motion. A wide discussion on possible solutions of this problem is made in the conclusion View full abstract»

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  • Adaptive digital beamforming for angle estimation in jamming

    Page(s): 508 - 523
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1636 KB) |  | HTML iconHTML  

    A radar digital beamforming (DBF) architecture and processing algorithm is described for nulling the signal from a mainlobe electronic jammer and multiple sidelobe electronic jammers while maintaining monopulse angle estimation accuracy on the target. The architecture consists of a sidelobe jamming (SLJ) cancelling adaptive array (AA) followed by a mainlobe jamming (MLJ) canceller. A mainlobe maintenance (MLM) technique or constrained adaptation during the sidelobe cancellation process is imposed so that the results of the SLJ cancellation process do not distort the subsequent mainlobe cancellation process. The SLJ signals and the MLJ signals are thus cancelled sequentially in separate processes. This technique was developed for improving radar processing in determining the angular location of a target, and specifically for improving the monopulse technique by maintaining the accuracy of the target echo monopulse ratio in the presence of electronic jamming by adaptive suppression of the jamming signals before forming the monopulse sum and difference beams View full abstract»

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  • Passive ranging of a low observable ballistic missile in a gravitational field

    Page(s): 481 - 494
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1292 KB) |  | HTML iconHTML  

    In this paper we present an estimation algorithm for tracking the motion of a low-observable target in a gravitational field, for example, an incoming ballistic missile (BM), using angle-only measurements. The measurements, which are obtained from a single stationary sensor, are available only for a short time. Also, the low target detection probability and high false alarm density present a difficult low-observable environment. The algorithm uses the probabilistic data association (PDA) algorithm in conjunction with maximum likelihood (ML) estimation to handle the false alarms and the less-than-unity target detection probability. The Cramer-Rao lower bound (CRLB) in clutter, which quantifies the best achievable estimator accuracy for this problem in the presence of false alarms and nonunity detection probability, is also presented. The proposed estimator is shown to be efficient, that is, it meets the CRLB, even for low-observable fluctuating targets with 6 dB average signal-to-noise ratio (SNR). For a BM in free flight with 0.6 single-scan detection probability, one can achieve a track detection probability of 0.99 with a negligible probability of false track acceptance View full abstract»

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  • Support vector machines for SAR automatic target recognition

    Page(s): 643 - 654
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1140 KB) |  | HTML iconHTML  

    Algorithms that produce classifiers with large margins, such as support vector machines (SVMs), AdaBoost, etc, are receiving more and more attention in the literature. A real application of SVMs for synthetic aperture radar automatic target recognition (SAR/ATR) is presented and the result is compared with conventional classifiers. The SVMs are tested for classification both in closed and open sets (recognition). Experimental results showed that SVMs outperform conventional classifiers in target classification. Moreover, SVMs with the Gaussian kernels are able to form a local “bounded” decision region around each class that presents better rejection to confusers View full abstract»

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  • Efficient multisensor fusion using multidimensional data association

    Page(s): 386 - 400
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1324 KB) |  | HTML iconHTML  

    We present the development of a multisensor fusion algorithm using multidimensional data association for multitarget tracking. The work is motivated by a large scale surveillance problem, where observations from multiple asynchronous sensors with time-varying sampling intervals (electronically scanned array (ESA) radars) are used for centralized fusion. The combination of multisensor fusion with multidimensional assignment is done so as to maximize the “time-depth” in addition to “sensor-width” for the number S of lists handled by the assignment algorithm. The standard procedure, which associates measurements from the most recently arrived S-1 frames to established tracks, can have, in the case of S sensors, a time-depth of zero. A new technique, which guarantees maximum effectiveness for an S-dimensional data association (S⩾3), i.e., maximum time-depth (S-1) for each sensor without sacrificing the fusion across sensors, is presented. Using a sliding window technique (of length S), the estimates are updated after each frame of measurements. The algorithm provides a systematic approach to automatic track formation, maintenance, and termination for multitarget tracking using multisensor fusion with multidimensional assignment for data association. Estimation results are presented for simulated data for a large scale air-to-ground target tracking problem View full abstract»

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  • Output voltage bounds of a three-phase boost rectifier

    Page(s): 671 - 678
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB) |  | HTML iconHTML  

    A general closed-form duty cycle control law is derived based on the linear combination of two sets of continuous duty cycle control laws. From this general solution one can generate infinitely many pulsewidth modulation (PWM) control strategies to achieve the same ideal performance. Then, from the resulting closed-form solution, a general explicit lower bound and a general explicit upper bound of the output dc voltage are derived. Besides the academic interests, these bounds are very useful practically as a convenient guideline for helping quickly design the three-phase boost rectifier. Finally, some illustrative examples are given and some experimental results provided for verifying the derived bounds View full abstract»

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  • Radar power multiplier for acquisition of low observables using an ESA radar

    Page(s): 401 - 418
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1396 KB) |  | HTML iconHTML  

    In this paper the acquisition of a low observable (LO) incoming tactical ballistic missile using the measurements from a surface based electronically scanned array (ESA) radar is presented. We present a batch maximum likelihood (ML) estimator to acquire the missile while it is exo-atmospheric. The proposed estimator, which combines ML estimation with the probabilistic data association (PDA) approach resulting in the ML-PDA algorithm to handle false alarms, also uses target features. The use of features facilitates target acquisition under low signal-to-noise ratio (SNR) conditions. Typically, ESA radars operate at 13-20 dB, whereas the new estimator is shown to be effective even at 4 dB SNR (in a resolution cell, at the end of the signal processing chain) for a Swerling III fluctuating target, which represents a significant counter-stealth capability. That is, this algorithm acts as an effective “power multiplier” for the radar by about an order of magnitude. An approximate Cramer-Rao lower bound (CRLB), quantifying the attainable estimation accuracies and shown to be met by the proposed estimator, is derived as well View full abstract»

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  • Validation of windblown radar ground clutter spectral shape

    Page(s): 538 - 548
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1292 KB) |  | HTML iconHTML  

    We investigate the robustness of the linear matched filter (MF) operating in a Gaussian environment in the presence of a mismatch between the design clutter-power spectral density (PSD) shape and the actual one. The Gaussian, the power-law (PL), and the double-exponential spectral models have been considered with the goal of investigating which one fits best for windblown foliage. We analyze the MF performance in terms of improvement factor, probability of false alarm, and probability of detection by making use of the theoretical models and measured X-band ground clutter data. The numerical results validate the double-exponential spectral model for windblown foliage by showing that the differences in performance prediction between using measured clutter data and modeled clutter data of various spectral shapes (viz., Gaussian, FL, and double-exponential) are minimized when the spectral model employed is of double-exponential shape View full abstract»

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  • Monopulse DOA estimation of two unresolved Rayleigh targets

    Page(s): 452 - 469
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1476 KB) |  | HTML iconHTML  

    This paper provides for new approaches to the processing of unresolved measurements as two direction-of-arrival (DOA) measurements for tracking closely spaced targets rather than the conventional single DOA measurement of the centroid. The measurements of the two-closely spaced targets are merged when the target echoes are not resolved in angle, range, or radial velocity (i.e., Doppler processing). The conditional Cramer Rao lower bound (CRLB) is developed for the DOA estimation of two unresolved Rayleigh targets using a standard monopulse radar. Then the modified CRLB is used to give insight into the boresight pointing for monopulse DOA estimation of two unresolved targets. Monopulse processing is considered for DOA estimation of two unresolved Rayleigh targets with known or estimated relative radar cross section (RCS). The performance of the DOA estimator is studied via Monte Carlo simulations and compared with the modified CRLB View full abstract»

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  • Fuzzy-logic-based CLOS guidance law design

    Page(s): 719 - 727
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (604 KB) |  | HTML iconHTML  

    A fuzzy-logic-based command to line-of-sight (CLOS) guidance law is proposed. In this design, the guidance problem is converted to the tracking problem. Then the fuzzy controller is designed to achieve satisfactory tracking performance. Meanwhile, an on-line tuning factor is introduced to speed up the convergence of tracking error and to reduce the miss distance. Besides, a CLOS compensator is designed to eliminate the pseudo-CLOS effect. Simulation results for different engagement scenarios illustrate the validity of the proposed guidance law View full abstract»

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  • Random hysteresis PWM inverter with robust spectrum shaping

    Page(s): 619 - 629
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (940 KB) |  | HTML iconHTML  

    A hysteresis current-controlled pulsewidth modulation (PWM) scheme is simple and robust in switching control, but it is subject to not constant switching frequency. However, since its harmonic spectrum is not randomly distributed like those yielded by the random PWM (RPWM) scheme, the annoying harmonic effects still exist. A random switching control strategy is proposed here to let the harmonic spectrum of the hysteresis current-controlled PWM inverter be randomly distributed. First, the effect of varying band on the harmonic distribution characteristic of a hysteresis current-controlled PWM scheme is analyzed. Then a random hysteresis PWM scheme and its quantitative design procedure are proposed. Finally, a robust spectrum shaping technique is devised such that the desired harmonic distribution pattern can be achieved. In the resulting frequency spectrum, the magnitudes of lower frequency harmonics are shaped and reduced. Hence the inverter output with a better harmonic attribute is obtained. Validity of the proposed random hysteresis PWM scheme is verified by some simulated and measured results View full abstract»

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  • MTI data clustering and formation recognition

    Page(s): 524 - 537
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1464 KB) |  | HTML iconHTML  

    Image exploitation technology approaches have generally focused on the detection and spatial analysis of stationary groups of objects on the ground using various sensors. While spatial arrangement is clearly necessary in analyzing military formations, it is usually not sufficient. Typically the arrangement must be examined within some context in order to interpret a pattern of deployment. For moving objects the spatial arrangement of the group relative to the direction of motion is key to recognizing the formation. By examining ground moving target indicator (MTI) radar data over time, motion can be inferred and used to establish a context for interpreting the spatial arrangement of the data. New techniques that exploit the multitemporal nature of MTI data are described. The first is a space-time clustering technique that locates compact groups of objects that persist in time. The technique Is an application of Marr and Hildreth's edge detection methodology to the dual problem of region segmentation, or more accurately, volumetric segmentation of space-time. The second technique is based on the use of the Hough transform for recognizing moving formations such as columns, wedges, and lines abreast by analyzing the shape of clustered MTI detections (specifically the orientation of linear arrangements within the group) with respect to their direction of motion. Preliminary results from simulated MTI data sets are presented View full abstract»

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  • Central limit theorem: Use with caution

    Page(s): 739 - 740
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB) |  | HTML iconHTML  

    The validity of the Central Limit Theorem for the sum of N, K distributed random phasors is investigated. It is demonstrated that the number of phasors that must be summed to obtain an amplitude distribution that can be approximated by a Rayleigh depends strongly on the underlying K-distribution, and is of order 200 for Weibull statistics View full abstract»

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  • On-line gain-tuning IP controller using RFNN

    Page(s): 655 - 670
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1236 KB) |  | HTML iconHTML  

    In this study an integral-proportional (IP) controller with on-line gain-tuning using a recurrent fuzzy neural network (RFNN) is proposed to control the mover position of a permanent magnet linear synchronous motor (PMLSM) servo drive system. The structure and operating principle of the PMLSM are first described in detail. A field-oriented control PMLSM servo drive is then introduced. After that, an IP controller with on-line gain tuning using an RFNN is proposed to control the mover of the PMLSM for achieving high-precision position control with robustness. The backpropagation algorithm is used to train the RFNN on line. Moreover to guarantee the convergence of tracking error for the periodic step-command tracking, analytical methods based on a discrete-type Lyapunov function are proposed to determine the varied learning rates of the RFNN. Furthermore, the proposed control system is implemented in a PC-based computer control system, Finally, the effectiveness of the proposed PMLSM servo drive system is demonstrated by some simulated and experimental results. Accurate tracking response and superior dynamic performance can be obtained due to the powerful on-line learning capability of the RFNN. In addition, the proposed on-line gain-tuning servo drive system is robust with regard to parameter variations and external disturbances View full abstract»

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  • Direction finding/polarization estimation-dipole and/or loop triad(s)

    Page(s): 679 - 684
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB) |  | HTML iconHTML  

    This paper shows (1) how measurement of the three Cartesian components of the electrical-field or magnetic-field suffices for multisource azimuth/elevation direction finding and polarization estimation, and (2) how the vector cross-product direction-of-arrival estimator is fully applicable even when the dipole triad is arbitrarily displaced from the loop triad View full abstract»

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  • High resolution 3D “snapshot” ISAR imaging and feature extraction

    Page(s): 630 - 642
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1004 KB) |  | HTML iconHTML  

    We have developed a new formulation for three dimensional (3D) radar imaging of inverse synthetic aperture radar (ISAR) data based on recent developments in high resolution spectral estimation theory. Typically for non real-time applications, image formation is a two step process consisting of motion determination and image generation. The technique presented focuses on this latter process, and assumes the motion of the target is known. The new technique offers several advantages over conventional techniques which are based on the correlation imaging function. In particular, the technique provides for a direct 3D estimate (versus back projection to a 3D target grid matrix) of the locations of the dominant scattering centers using only a minimum set of independent 2D range-Doppler ISAR “snapshots” of the target. Because of the snapshot nature of the technique, it is particularly applicable to 3D imaging of sectors of sparse-angle data, for which the sidelobes of the correlation imaging integral become high. Furthermore, the technique provides for an estimate of amplitude and phase of each scattering center as a function of aspect angle to the target, for those aspect angles which encompass the set of 2D range-Doppler snapshots. Results illustrating the technique developed are presented for both simulated and static range data View full abstract»

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  • Improved Kalman filter design for three-dimensional radar tracking

    Page(s): 727 - 739
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (932 KB) |  | HTML iconHTML  

    The problem of three-dimensional (3D) radar tracking is considered. The usual tracking filter design relying on first-order (or linear) approximations leads to poor convergence and erratic filter behavior in highly nonlinear situations. Simple filter algorithms that can overcome these ill effects are developed for two different types of 3D radar measurement. For each type of radar measurement, an accurate expression for the measurement covariance is obtained by evaluating inherent nonlinearities of radar measurements via coordinate transformation. Then algebraic manipulations and reasonable approximations are employed to yield a simple filter formulation based on the expression. The resulting filter equations are similar to the extended Kalman filter (EKF) and provide some useful insights into the behavior of linearized Kalman filters designed with radar measurements. Finally, simulation results show that the proposed approach is very effective in accounting for the measurement nonlinearities View full abstract»

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  • Multiaspect classification of airborne targets via physics-based HMMs and matching pursuits

    Page(s): 595 - 606
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1172 KB) |  | HTML iconHTML  

    Wideband electromagnetic fields scattered from N distinct target-sensor orientations are employed for classification of airborne targets. Each of the scattered waveforms is parsed via physics-based matching pursuits, yielding N feature vectors. The feature vectors are submitted to a hidden Markov model (HMM), each state of which is characterized by a set of target-sensor orientations over which the associated feature vectors are relatively stationary. The N feature vectors extracted from the multiaspect scattering data implicitly sample N states of the target (some states may be sampled more than once), with the state sequence modeled statistically as a Markov process, resulting in an HMM due to the “hidden” or unknown target orientation. In the work presented here, the state-dependent probability of observing a given feature vector is modeled via physics-motivated linear distributions, in lieu of the traditional Gaussian mixtures applied in classical HMMs. Further, we develop a scheme that yields autonomous definitions for the aspect-dependent HMM states. The paradigm is applied to synthetic scattering data for two simple targets 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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Editor-in-Chief
Lance Kaplan
Army Research Laboratory