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Aerospace and Electronic Systems, IEEE Transactions on

Issue 1 • Date Jan 1992

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Displaying Results 1 - 25 of 28
  • Calibration of complex polarimetric SAR imagery using backscatter correlations

    Publication Year: 1992 , Page(s): 183 - 194
    Cited by:  Papers (24)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    A technique for calibration of multipolarization synthetic-aperture radar (SAR) imagery is described. If scatterer reciprocity and lack of correlation between co- and cross-polarized radar echoes (for azimuthally symmetric distributed targets) are assumed, the effects of signal leakage between the radar data channels can be removed without the use of known ground targets. If known targets are available, all data channels can be calibrated relative to one another and radiometrically as well. The method is verified with simulation and application to airborne SAR data View full abstract»

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  • Design of a CLOS guidance law via feedback linearization

    Publication Year: 1992 , Page(s): 51 - 63
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (784 KB)  

    An application of the feedback linearization technique to the design of a new command to line-of-sight (CLOS) guidance law for short-range surface-to-air missiles is described. The key idea lies in converting the three-dimensional CLOS guidance problem to the tracking problem of a time-varying nonlinear system. The result may shed new light on the role of the feedforward acceleration terms used in the conventional CLOS guidance laws. Through computer simulation, the effect of the dynamics of the ground tracker and the autopilot on the guidance performance of the new CLOS guidance law is investigated View full abstract»

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  • Automatic censored CFAR detection for nonhomogeneous environments

    Publication Year: 1992 , Page(s): 286 - 304
    Cited by:  Papers (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1312 KB)  

    In constant false alarm rate (CFAR) detection, the clutter background in the cell under test is estimated by combining the outputs of the nearby resolution cells. In a nonhomogeneous background environment, the false alarm regulation capabilities and the detection performance of a CFAR detector depend on the robustness of the noise level estimator. The authors propose and study automatic censoring algorithms for nonhomogeneous clutter background environments. A cell-by-cell criterion for accepting or rejecting reference samples is introduced. The detection schemes that are considered do not require any a priori knowledge about the background environment. The case where a clutter edge is present in the reference window is considered, and the case of multiple target situations is studied. The case when both interfering targets and a clutter edge appear in the reference window of the cell under test is considered. The performances of the proposed schemes are compared with that of the trimmed-mean (TM) CFAR detector, in which the censoring points are preassigned View full abstract»

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  • Direction-of-arrival estimation using signal subspace modeling

    Publication Year: 1992 , Page(s): 64 - 79
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1220 KB)  

    A computationally viable algorithm for estimating the direction-of-arrival (DOA) of multiple wavefields that are incident on an array of sensors is developed. The geometry of the array is unrestricted and the incident wavefields may be generated by mixtures of incoherent and coherent emitting sources. In the approach taken, the sensor signals are modeled as a noise-contaminated linear combination of steering vectors which are functionally dependent on a set of DOA parameters. These parameters are to be chosen so that this sensor signal model is most compatible with empirically measured data (i.e., snapshot data). An iterative procedure is developed for selecting the most data compatible set of DOA parameters in both the snapshot domain and the array covariance matrix domain. Critical to the success of such iterative solution procedures is the generation of quality DOA parameters to initialize the algorithm. A sequential beamforming method for this initialization is presented. Numerical examples to illustrate the effectiveness of the proposed algorithmic approach are given View full abstract»

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  • Constant-speed target tracking via bearings-only measurements

    Publication Year: 1992 , Page(s): 174 - 182
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (588 KB)  

    The observability properties of the constant-speed target tracking problem via bearings-only measurements are investigated. It is shown that there exists a one-dimensional unobservable foliation which is computed. Explicit formulas are given to recover the observable part. It is shown that the direction of target trajectory is observable and that the whole state is observable if either the norm of the velocity or the distance is also known. A nonlinear observer which has a parallel structure and tolerates faults on distance measurements is presented. Finite-dimensional filters for the approximating models in the case of noisy measurements are given on the basis of output function polynomial approximations View full abstract»

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  • A noncoherent adaptive detection technique

    Publication Year: 1992 , Page(s): 115 - 124
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (772 KB)  

    An adaptive detection technique suitable for both stationary and nonstationary noise environments based upon a generalized likelihood ratio test (GLRT) formulation is presented. The detector, which is statistically equivalent to a special form of the Wilks's lambda test, noncoherently combines the information contained in a pulse train of arbitrary length for decision-making purposes. The probability density function of the test under the noise only hypothesis is shown to be central χ2. Under the signal plus noise hypothesis, an exact statistical characterization of the test cannot be obtained, and, therefore, a Chernoff bound is derived. Results in terms of the probability of detection versus signal-to-noise ratio (SNR) obtained from Monte Carlo simulation, the Chernoff bound, and the optimal matched filter case are examined. The performance of the noncoherent detector is shown to be a function of the covariance matrix estimate and the number of data samples View full abstract»

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  • MLS system error model identification and synthesis

    Publication Year: 1992 , Page(s): 164 - 173
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (708 KB)  

    Signal-in-space modeling of approach and landing guidance systems such as the microwave landing system (MLS), which is necessary for aircraft certification, is addressed. A technique which can, in principle, identify the error sources in navigation systems and can also perform the inverse operation of synthesizing an error generator whose output is statistically equivalent to the original error data is described. The technique can also be used to validate equipment error budget assumptions. The identification and synthesis technique applies not only to MLS but to all navigation systems View full abstract»

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  • Graceful degradation of an adaptive beamforming processor

    Publication Year: 1992 , Page(s): 305 - 315
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    The phase and amplitude weights of each element in an adaptive, digitally beamformed array antenna can be calculated by a systolic parallel processor. The authors propose that the entire weight calculation (both QR decomposition, previously discussed by W.M. Gentleman and H.T. Kung (1981), and the back-substitutions, which are presented for the first time) be performed in a triangular array of processors. This has the highly desirable property of graceful degradation: the loss of one or more component processors does not cause the computed weights to degrade catastrophically. The loss of a processor in the systolic array merely reduces the number of available degrees of freedom. Moreover, the processing array does not need to be globally reconfigured; the functions of all the remaining processors are unaffected and their interconnections are undisturbed. The authors describe the processing flow in the systolic array, show how its degradation is inherently graceful, and present a realistic example of graceful degradation View full abstract»

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  • Observability, ensemble averaging and GPS time

    Publication Year: 1992 , Page(s): 224 - 240
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1028 KB)  

    Obtaining time from an ensemble of clocks with a Kalman filter when the system is not observable is examined. Particular attention is given to the Global Positioning System (GPS) master control station (MCS) Kalman filter and the ramifications of estimating ensemble time under conditions of unobservability are explored. The effect of one proposed workaround to problems caused by unobservability is addressed View full abstract»

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  • Impulse radar evaluation of asphalt-covered bridge decks

    Publication Year: 1992 , Page(s): 125 - 137
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    The use of impulse radar to distinguish between areas of good bridge deck and areas which suffer from one or more different forms of deterioration, including delamination, scaling, and debonding, is reported. The radar signal is also used to measure the thickness of asphalt and concrete cover over reinforcement. These quantities are important in determining the amount of material to be removed when resurfacing a bridge deck. The calibration procedure and interpretation of radar waveforms are discussed in detail View full abstract»

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  • CFAR data fusion center with inhomogeneous receivers

    Publication Year: 1992 , Page(s): 276 - 285
    Cited by:  Papers (40)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    Detection systems with distributed sensors and data fusion are increasingly used by surveillance systems. A system formed by N inhomogeneous constant false alarm rate (CFAR) detectors (cell-averaging (CA) and ordered statistic (OS) CFAR detectors) is studied. A recursive formulation of an algorithm that permits a fixed level of false alarms in the data fusion center is presented, to set the optimum individual threshold levels in the CFAR receivers and the optimum `K out of N' decision rule in order to maximize the total probability of detection. The algorithm also considers receivers of different quality or with different communication channel qualities connecting them with the fusion center. This procedure has been applied to several hypothetical networks with distributed CA-CFAR and OS-CFAR receivers and for Rayleigh targets and interference, and it was seen that in general the fusion decision OR rule is not always the best View full abstract»

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  • Analysis and design of series-parallel resonant power supply

    Publication Year: 1992 , Page(s): 249 - 258
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    A modified series-parallel high-frequency resonant DC/DC converter configuration is proposed. A simplified steady-state analysis of the converter, including the effect of a high-frequency transformer using complex circuit analysis, is presented. Based on the analysis, a simple design procedure is given. The effect of magnetizing inductances of the high-frequency transformer on the performance of the converter is discussed. Detailed experimental results obtained from a MOSFET (metal-oxide-semiconductor field-effect-transistor)-based 1-kW converter are presented to verify the analysis. The converter presented has almost constant efficiency from full load to quarter load, and the converter has load short circuit capability View full abstract»

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  • General forms and properties of zero cross-correlation radar waveforms

    Publication Year: 1992 , Page(s): 98 - 104
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    General forms for both the complementary and noncomplementary zero cross-correlation waveform sets are developed. Various properties of these codes and their relationship to zero sidelobe periodic codes are stated and proved. Some radar applications and practical considerations of using these codes are briefly discussed View full abstract»

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  • Biparametric linear estimation for CFAR against Weibull clutter

    Publication Year: 1992 , Page(s): 138 - 151
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1092 KB)  

    The authors deal with constant false alarm rate (CFAR) procedures against nonstationary clutter, modeled as a Weibull distributed process whose scale parameter α and shape parameter β are both variable. It is shown that conventional CFAR procedures, which compensate only for α, degrade intolerably as β deviates from β=2, namely, as the Rayleigh distributional assumption is violated. A biparametric CFAR procedure is shown to be suited to such situations. The authors introduce a logarithmic transformation to reduce the Weibull probability density function (pdf) to a Gumbel pdf, i.e., to the location-scale type, and then exploit the best linear unbiased estimation (BLUE) of location-scale parameters to adjust the detection threshold. True CFAR is thus achieved when the clutter is locally homogeneous. Resilience against local inhomogeneities can also be conferred since BLUE lends itself to censoring. Through a performance analysis, the influence of various system and distributional parameters is elicited View full abstract»

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  • Analysis and design of parallel resonant convertor at high Q L

    Publication Year: 1992 , Page(s): 35 - 50
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (876 KB)  

    A parallel resonant convertor (PRC) operating in the continuous conduction mode (CCM) is analyzed, using a high loaded quality factor QL assumption (i.e., QL>2.5) and Fourier series techniques. Simple analytical expressions for performance characteristics are derived under steady-state conditions for use in designing and understanding the behavior of the PRC. Three Class-D voltage-driven rectifiers are analyzed, taking into account the diode threshold voltage and the diode forward resistance. Experimental results measured for a 50-W convertor above the resonance at different load resistances and input voltages show excellent agreement with the theoretical performance predicted by the equations View full abstract»

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  • Error estimation of INS ground alignment through observability analysis

    Publication Year: 1992 , Page(s): 92 - 97
    Cited by:  Papers (35)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    A systematic analysis of the observability of an inertial navigation system (INS) in ground alignment with Bar-Itzhack and Berman's error model is presented. It is shown that the unobservable states are separately contained in two decoupled subspaces. The constraints on the selection of unobservable states are discussed. An estimation algorithm which is derived fully from the horizontal velocity outputs for computing the misalignment angles is provided. It reveals that the azimuth error can be entirely estimated from the estimates of leveling error and leveling error rate, without using gyro output signals explicitly View full abstract»

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  • Detection probabilities for correlated Rayleigh fading signals

    Publication Year: 1992 , Page(s): 259 - 267
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    Both the method of saddlepoint integration and its associated saddlepoint approximation are applied to calculating the probability of detecting correlated Rayleigh-fading signals in Gaussian noise by means of a detector that integrates M samples of the output of a quadratic rectifier. The quadrature components of the signal samples are modeled as an autoregressive moving-average process, and specific results are exhibited for a first-order Markov process. By these methods the fluctuation loss can be computed for much larger values of M and for larger values of the detection probability than previously. Values calculated by the saddlepoint approximation prove to be close enough to the exact values to be useful over a broad range of signal parameters View full abstract»

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  • A new approach to automatic target recognition

    Publication Year: 1992 , Page(s): 105 - 114
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (900 KB)  

    The fundamental problems of automatic target recognition (ATR) are discussed. A new approach to ATR is suggested that includes: a new method of scoring ATR performance, a new concept of artificial images, a new method called probing for extracting target signature knowledge from image experts, and suggestions for coping with the problem of insufficient test data and algorithm obsolescence View full abstract»

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  • Narrowband interference suppression in impulsive channels

    Publication Year: 1992 , Page(s): 15 - 34
    Cited by:  Papers (33)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1352 KB)  

    Suppression algorithms are developed first for a channel containing only impulsive background noise and then for a channel containing a spread-spectrum signal as well. These algorithms are based on nonlinear filters that produce predictions of the interfering signals that are then subtracted from the received signal to suppress the interference. Several such filters, including both fixed and adaptive ones, are proposed and compared using extensive computer simulations. The independence of the filtering procedures from the noise distribution shape, given constant second-order statistics, is shown View full abstract»

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  • Low-altitude target detection by coastline operated marine radar

    Publication Year: 1992 , Page(s): 217 - 223
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    Relevant to a Richian family of fluctuating targets with a composite background of sea-plus-land clutter, the performance prediction of a radar operating in near-coastal regions is elucidated by assuming noncoherent integration of the pulses. Considering the dominance of land clutter, a modified K-distributed statistic is indicated for the overall clutter envelope; and the corresponding probability of false alarm and probability of detection are deduced for fixed threshold detection (s) based on N pulses integrated in the presence of the sea-plus-land clutter and the noise. Even when the target offers a dominant scattered echo, the worst situations of the land clutter affecting the detection performance are indicated View full abstract»

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  • Computation of aircraft geometric height under radar surveillance

    Publication Year: 1992 , Page(s): 241 - 248
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    A radar system for geometric height estimation of civil aircraft is described. The system consists of one standard or mode S secondary surveillance radar (SSR) and one omnidirectional antenna sited away from SSR under an airplane. The geometric height is derived by trilateration. Systematic errors are compensated for by deriving the profile of the effect on height measurements of the bias in range measurements. A curve-fitting technique is then used, which estimates both the geometric height and any non-zero systematic errors View full abstract»

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  • Detumbling and reorientation maneuvers and stabilization of NASA SCOLE system

    Publication Year: 1992 , Page(s): 80 - 91
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (744 KB)  

    The questions of rotational maneuver and vibration stabilization of the NASA Spacecraft Control Laboratory Experiment (SCOLE) system is considered. The mathematical model of the SCOLE system includes the rigid body dynamics as well as the elastic dynamics representing transverse and torsional deformations of the elastic beam connecting the orbiter and end body (reflector). For the rotational maneuver, a new control law (orbiter control law) is derived using an orbiter input torque vector. Detumbling and reorientation maneuvers of the SCOLE system are accomplished using this control law; however, this excites the elastic modes of the beam. The orbiter control law asymptotically linearizes the flexible dynamics. Using the linearized model, a linear feedback control law is designed for vibration suppression. An observer is designed for estimating the state variables using sensor outputs which are also used for the synthesis of the control law. Simulation results are presented to show that in the closed-loop system detumbling and reorientation maneuvers can be accomplished and the effect of control and observation spillover is insignificant View full abstract»

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  • A parallel square-root algorithm for modified extended Kalman filter

    Publication Year: 1992 , Page(s): 153 - 163
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    A parallel square-root algorithm and its systolic array implementation are proposed for performing modified extended Kalman filtering (MEKF). The proposed parallel square-root algorithm is designed based on the singular value decomposition (SVD) and the Faddeev algorithm, and a very large scale integration (VLSI) systolic array architecture is developed for its implementation. Compared to other square root Kalman filtering algorithms, the proposed method is more numerically stable. The VLSI architecture described has good parallel and pipelining characteristics in applying to the MEKF and achieves higher efficiency. For n-dimensional state vector estimations, the proposed architecture consists of O(2n2) processing elements and uses O ((s+17)n) time-steps for a complete iteration at each instant, in contrast to the complexity of O((s+6) n3) time-steps for a sequential implementation, where s≈log n View full abstract»

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  • New maximum entropy spectrum using uncertain eigenstructure constraints

    Publication Year: 1992 , Page(s): 2 - 14
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    A number of modern spectral estimators are shown to have a common generic formulation. These include minimum variance, MUSIC, and maximum entropy. A new maximum entropy spectral estimator is derived using constraints on the modal powers or the expected-square projections of the data onto the eigenvectors of the data covariance matrix. The formulation incorporates uncertainty in the modal power constraints and the signal-versus-noise subspace separation. The resulting estimators have forms which incorporate all other modern estimators, including maximum entropy and minimum norm. The new estimators allow further development when a priori information is used in the constraints. Comparison of one version of the estimator with the minimum norm verifies the greater probability of resolution of the minimum norm but indicates in some instances the value of the incorporated uncertainties. Another version uses complex constraints and reduces to conventional maximum entropy or minimum norm under certain conditions View full abstract»

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  • A CFAR adaptive matched filter detector

    Publication Year: 1992 , Page(s): 208 - 216
    Cited by:  Papers (345)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    An adaptive algorithm for radar target detection using an antenna array is proposed. The detector is derived in a manner similar to that of the generalized likelihood-ratio test (GLRT) but contains a simplified test statistic that is a limiting case of the GLRT detector. This simplified detector is analyzed for performance to signals on boresight, as well as when the signal direction is misaligned with the look direction View full abstract»

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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