ALBERT

Description: Provides a listing of current staff, committee members and society officers.

Description: With the ever-increasing demand in the analysis and understanding of aerial images in order to remotely recognize targets, this paper introduces a robust system for the detection and localization of cars in images captured by air vehicles and satellites. The system adopts a sliding-window approach. It compromises a window-evaluation and a window-classification subsystems. The performance of the proposed framework was evaluated on the Vaihingen dataset. Results demonstrate its superiority to the state of the art.

Description: This paper investigates X-ray pulsar navigation for earth–moon libration-point mission. A comprehensive analysis shows that abnormal measurements are inevitable and bring quite adverse effects for navigation results. To approach this problem, a new algorithm called robust square-root cubature Kalman filter is proposed. An innovation-based adaptive scale factor is introduced to adjust measurement noise covariance so that the adverse effects of abnormal measurements can be suppressed. Effectiveness of the proposed method is demonstrated in simulation results.

Description: Multiple-input multiple-output (MIMO) radar enjoys the advantage of increased degrees-of-freedom and spatial diversity gain, but it cannot effectively resolves the targets closely spaced in the same angle cell (but different range cells). Frequency diverse array (FDA)-MIMO radar can handle this problem by exploiting its range-dependent beampattern. FDA-MIMO radar was, thus, suggested for range–angle estimation of targets. Nevertheless, it is necessary to provide theoretical performance analysis for such a relatively new radar technique. Since multiple signal classification (MUSIC) algorithm is widely adopted in most of the FDA-MIMO literature, this paper derives the Cramér–Rao lower bound and mean square error expressions in MUSIC-based range–angle estimation algorithms for a general FDA-MIMO radar. Furthermore, the corresponding range and angle resolution thresholds in target detection and localization are also derived. Numerical results verify that the FDA-MIMO indeed outperforms conventional MIMO radar in both range–angle estimation and resolution threshold performance.

Description: This paper considers the problem of multipath ghosts elimination for the through-wall radar imaging. We formulate a discrete signal model in the presence of first-order multipath, and propose an imaging dictionary based algorithm to suppress the multipath ghosts. Specifically, first, several estimated images are obtained via two different kinds of imaging dictionaries for the focus delays related to the direct propagation path and the multipaths, respectively. We find that all the estimated images possess large values around the genuine target positions and the multipath ghosts of them do not overlap with each other. Then, based on this feature, these images are fused via incoherent multiplication image fusion method to yield a multipath ghosts free image. Finally, the simulation and real data are used to prove the validity of the proposed approach.

Description: We consider the data-driven motion compensation problem in inverse synthetic aperture radar (ISAR) imaging. We present optimization-based ISAR techniques and propose improvements to the range alignment, time-window selection, autofocus, time–frequency-based image reconstruction, and cross-range scaling procedures. In experiments, the improvements reduced the computational burden and increased the image contrast by 50% at best and 28% on average in several test cases, including changing translational and rotational motion.

Description: The paper presents a new method of searching for a fixed solution in precise positioning based on carrier phase data. The main idea is to search for a fixed solution in the coordinate domain instead of in an ambiguity domain. The dimension of the ambiguity domain depends on the number of satellites. The dimension of the coordinate domain is always three, and it does not depend on the number of satellites. It considerably reduces computational load.

Description: This paper proposes a unified optimal control framework that can be used to formulate and solve aircraft performance problems, such as maximum endurance and maximum range, for both propeller-driven airplanes and jet-propelled aircraft. It is proved in this paper that such problems have a common mathematical formulation and, under strict convexity assumptions, they have a unique feedback solution for the speed as a function of weight. The feedback solution yields an analytic expression for the optimal speed. For maximum endurance, the solution corresponds to the minimization of the rate of fuel consumption per unit time. For maximum range, the rate of fuel consumption per unit distance is minimized. Moreover, the optimal solution for maximum range will be interpreted geometrically using the concept of convex conjugate function and Legendre transformation. Although the optimal control framework is illustrated for maximum range and maximum endurance, it is a general approach that can be used for other aircraft performance problems.

Description: The capture of a free-floating tumbling object using an autonomous vehicle is a key technology for many future orbital missions. Spacecraft proximity operations will play an important role in guaranteeing the success of such missions. In this paper, we technically propose a tracking control scheme for proximity operations between a target and a pursuer spacecraft that ensures accurate relative position tracking as well as attitude synchronization. Specifically, an integrated six degrees of freedom dynamics model is first established to describe the relative motion of the pursuer with respect to the target. Then, a robust fault-tolerant controller is derived by combining the sliding mode control and the adaptive technique. The designed controller is proved to be not only robust against unexpected disturbances and adaptive to unknown and uncertain mass/inertia properties of the pursuer, but also able to accommodate a large class of actuator faults. In particular, by incorporating a novel time-varying forcing function into the sliding dynamics, the proposed control algorithm is able to guarantee the finite-time convergence of the translational and rotational tracking errors, and the convergence time as an explicit parameter can be assigned a priori by the designers. Furthermore, a theoretical analysis is also presented to assess the fault tolerance ability of the designed controller. Finally, numerous examples are carried out to evaluate the effectiveness and demonstrate the benefits of the overall control approach.

Description: When a monopulse radar is subjected to main-lobe barrage interference, the target and the interference source are both located within the 3 dB beamwidth of the radar; the target returns are subsumed by the interference, which results in incorrect detection, erroneous angle measurements, and tracking error. Based on a hybrid polarimetric monopulse radar with six channels, a new approach is presented for estimating the target angle from a single snapshot in the presence of main-lobe barrage interference. By means of polarization filtering and polarization synthesis of signals from multiple channels with two orthogonal polarizations, a new pair of sum and difference signals is formed that represents the angle difference between the target and the interference source. After standard monopulse processing of these new signals and additional compensation, the estimate of the target angle is derived with low computational complexity.

Description: This paper deals with target classification by using both feature data and kinematic measurements. The problem is tackled by multihypothesis sequential testing with embedded target tracking. We implement an Armitage sequential test for nonmaneuvering and maneuvering targets. Both (centralized and distributed) fusion architectures are used for the embedded tracking. The contributions of the kinematic measurements to classification are analyzed, and classification performance improvement is shown analytically for a special case. Numerical results are provided to demonstrate the performance of our algorithms.

Description: If a nominally L-shaped sensor-array's two legs are not exactly perpendicular, its azimuth-polar direction-of-arrival estimation would be degraded. This paper quantifies this degradation via a deterministic Cramér–Rao bound analysis of the direction-finding error variance.

Description: Multiple-input multiple-output (MIMO) radar is an enabling technique for high-resolution imaging, which is especially useful for near-field electromagnetic scattering diagnosis of complex targets. Among others, high sidelobes and radar cross section (RCS) calibration uncertainty are the major challenges for such applications, due to array nonuniformity, imperfect channels, and antenna pattern tapering. These shortcomings prevent a MIMO radar from obtaining high-quality images with enough dynamic range and RCS accuracy. In this paper, we develop a complete solution for these problems. A novel adaptive weighting technique is proposed, where the complex weights are optimized for exact amplitude and phase error calibration of a MIMO array and for azimuth sidelobe reduction. A MIMO filtered backprojection algorithm is developed for image formation with improved RCS calibration accuracy, where propagation path-loss, antenna pattern tapering, and phase distortion due to the near-field spherical wave front are compensated. Both indoor and outdoor field test results are presented to show the high-quality images obtained using the proposed techniques, demonstrating the applicability of a MIMO radar for diagnostic RCS imaging of complex targets.

Description: Presents the front cover for this issue of the publication.

Description: Discusses the specific of the the cover for this issue of the publication.

Description: Presents the AESS president message for this issue of the publication.

Description: Presents the outgoing Editor-in-Chief message for this issue of the publication.

Description: Thirty-four participants from seventeen countries participated in the Planetary Defense Team Project at the International Space University's 2015 Space Studies Program (ISU-SSP15) to find solutions for short-term warning cosmic threats. The team spent nine weeks working intensively on departmental and lecture activities alongside this project. Space agencies and institutions around the world have discussed cosmic threats, including planetary defense. However, not enough attention has been given to a potentially catastrophic event; what has been done is limited to possible long-term cosmic threats. Having no specific pathway on how to tackle this global challenging task at the beginning of the project, the Integrated Product and Process Development (IPPD) methodology was used to enable the team to identify main elements of the project, starting from developing the mission statement, needs and requirements, and to proposing solutions to planetary defense. These elements include detection and tracking, deflection, collaboration, outreach and education, evacuation and recovery.

Description: The radio frequency (RF)spectrum is finite, yet the demand for its use is growing, largely driven by the needs of commercial cellular, albeit with equally important requirements for enhanced performance by other spectral users, most notably radar and navigation. In total, the "RF triad" of radar, communications, and navigation represents a myriad of different ways in which the EF spectrum is accessed and utilized. As such, sharing of spectrum between these fundamentally different modes realizes a vast systems engineering problem space that is currently being investigated. At a high level, examples of topics being explored include coexistence between radar/aeronautical/satellite links and terrestrial systems such as cellular and WiFi, cognitive systems for spectral avoidance and adaptive interference mitigation, and the co-design of simultaneous multi-function systems.

Description: Presents the back cover for this issue of the publication.

Description: Professor Yakov S. Shifrin from Kharkiv, Ukraine, was selected by the IEEE AES Society to receive the 2015 Pioneer Award (Figure 1). The citation reads “For fundamental contributions to modern radio physics and statistical antenna theory.”

Description: Advertisement.

Description: Presents the incoming Editor-in-Chief message for this issue of the publication.

Description: The cross ambiguity function (CAF) has been commonly used to find time difference of arrival (TDOA) and frequency difference of arrival (FDOA). In most cases, direct computation of the CAF by using a conventional method such as fast Fourier transform is too computationally intensive. Thus, a two-stage approach consisting of a coarse mode to find rough TDOA/FDOA estimates and a fine mode for precise estimation was introduced. However, there has been no methodology for selecting an interpolation factor determined by the sampling frequency and target precision which significantly affects the computational complexity. In addition, even if the computational complexity can be reduced by using the optimal interpolation factor, the huge transmission data through the datalink between sensors and the central station still remains to be an obstacle for an electronic warfare (EW) system. In this respect, we derive an optimal interpolation factor and then propose a new two-stage TDOA/FDOA estimation algorithm using a resampling block to reduce the computational complexity and the data size simultaneously in EW systems. In the proposed method, the optimal interpolation factor can be used irrespective of the sampling frequency and the target precision. Simulation results show that the optimal interpolation factor efficiently reduces the computational burden without the loss of estimation performance.

Description: Traditional passive radar detectors compute cross correlation of the raw data in the reference and surveillance channels. However, there is no optimality guarantee for this detector in the presence of a noisy reference. Here, we develop a new detector that utilizes a test statistic based on the cross correlation of the principal left singular vectors of the reference and surveillance signal-plus-noise matrices. This detector offers better performance by exploiting the inherent low-rank structure when the transmitted signals are a weighted periodic summation of several identical waveforms (amplitude and phase modulation), as is the case with commercial digital illuminators as well as noncooperative radar. We consider a scintillating target. We provide analytical detection performance guarantees establishing signal-to-noise ratio thresholds above which the proposed detection statistic reliably discriminates, in an asymptotic sense, the signal versus no-signal hypothesis. We validate these results using extensive numerical simulations. We demonstrate the “near constant false alarm rate (CFAR)” behavior of the proposed detector with respect to a fixed, SNR-independent threshold and contrast that with the need to adjust the detection threshold in an SNR-dependent manner to maintain CFAR for other detectors found in the literature. Extensions of the proposed detector for settings applicable to orthogonal frequency division multiplexing (OFDM), adaptive radar are discussed.

Description: Human pilot models are tightly dependent on the specific flight tasks. For a carrier landing task, the human pilot controls the aircraft glide path by the guidance information from the Fresnel lens optical landing system (FLOLS) during the aircraft approach to the carrier. This paper focuses on the modeling of the human pilot behavior of sensing and recognizing the guidance information from the Fresnel lens of the FLOLS in longitudinal motion. A fuzzy human pilot model is built based on a fuzzy logic control theory to simulate the human pilot behavior. The simulations of carrier landing are conducted to illustrate the advantages and effectiveness of the proposed fuzzy human pilot model.

Description: Coarse attitude initialization procedure is used to determine the initial attitude of the inertial navigation system. To improve the accuracy of the attitude to a desired value, fine alignment (FA) process is employed. In stationary conditions, zero velocity updates are usually used to achieve such goal. In this paper, an analytic evaluation of the steady-state properties of the FA process is presented. The contribution of this paper is twofold: 1) closed-form analytic solutions to the error-state covariance of the FA process are derived and 2) semianalytic solutions to the convergence time of the error-state covariance are shown. With such closed-form solutions at hand, insight can be gained into the parameters involved in the FA process in preliminary design process. Simulation and field experiments are given to support the analytical expressions.

Description: This paper addresses the issue of beampattern synthesis with flexible magnitude response and low sidelobe in a frequency diverse array radar. It is formulated as an optimization problem in terms of $ell _1$ -norm minimization, which encourages the sparsity of array pattern. An $ell _1$ iterative phase compensation (IPC) technique is employed to transform the nonconvex constraint to phase compensation form. Then, to further reduce the sidelobe level, a reweighted $ell _1$ -IPC algorithm is devised, in which a sparsity-enhanced scheme is utilized to convert the $ell _1$ -norm to a new cost function that more closely resembles $ell _0$ -norm. Numerical results are presented to demonstrate the effectiveness of the proposed approach in different scenarios.

Description: Boost-phase trajectory inference is one of the major objectives of the space-borne missile early-warning system. Traditional methods can be classified as either profile-based or profile-free methods. The profile-based methods are accurate but inadaptable to the types of missiles, whereas the profile-free methods are adaptable but inaccurate. To integrate the strengths of the profile-based and profile-free methods, a multimodel trajectory inference approach is proposed. First, a general net acceleration model (GNAM) containing only type-free prior information is constructed by the method of sieves. Then, a new kind of net acceleration profile is proposed by incorporating type-dependent prior information into the GNAM. After that, the multimodel approach is proposed following the Bayesian framework. Simulations indicate that the approach is accurate in estimation and capable for type identification.

Description: This paper investigates the statistical performance of three adaptive detectors in the presence of subspace interference and Gaussian noise. The interference is deterministic and lies in a known subspace but with unknown coordinates, while the noise is Gaussian distributed with unknown covariance matrix. For performance evaluation, we consider a more general case, namely, the case of subspace signal mismatch, where the actual signal does not completely lie in the presumed signal subspace. We derive the exact statistical distributions of the detectors, and then obtain analytical expressions for probabilities of detection and false alarm. The theoretical study reveals that the interference and signal mismatch affects the detection performance through two angles, which are the angle between the interference subspace and actual signal, and the angle between the actual signal and presumed signal subspace after they are both projected onto the interference-orthogonalized subspace. Numerical examples are provided to verify the theoretical results.

Description: The monopulse angle-estimation technique used in digital beamforming radars is investigated from the perspective of optimizing the angle accuracy. Specifically, a digital difference beamforming taper is proposed in this paper to optimize the monopulse angle accuracy. For a fully digitized array radar with an amplitude-tapered antenna aperture for sum beampattern with low sidelobes, the monopulse angle accuracy obtained using the proposed difference taper coincides with the Cramer–Rao lower bound. The derivation of the monopulse angle accuracy with the proposed difference taper is presented and an improvement of the accuracy over the conventional monopulse accuracy is proved theoretically. The results of computer simulations using a uniform linear array is included to highlight the accuracy improvement by a factor of 1.16 (over the conventional monopulse), which is equivalent to a 1.3 dB reduction in the signal-to-noise ratio for the requisite angle accuracy.

Description: To solve the problem of unknown noise covariance matrices inherent in the cooperative localization of autonomous underwater vehicles, a new adaptive extended Kalman filter is proposed. The predicted error covariance matrix and measurement noise covariance matrix are adaptively estimated based on an online expectation-maximization approach. Experimental results illustrate that, under the circumstances that are detailed in the paper, the proposed algorithm has better localization accuracy than existing state-of-the-art algorithms.

Description: This paper presents the detailed design, construction, and validation of a three-axis square Helmholtz coil. It also describes the methodology used to drive each pair of coils as well as the setup to operate it in a closed-loop system using a digital PID controller. The coil will be mainly used for aerospace applications, especially to aid the development and testing of attitude determination and control systems that use the earth's magnetic field as a reference vector. Most of the system was built using commercial components, reducing cost, and complexity compared to similar commercial systems. The assembled Helmholtz coil has approximately one cubic meter and can generate magnetic fields up to 2 G/ axis, keeping a uniformity of 0.04% around 11 cm of the center, in each axis. A custom-designed voltage-controlled current source, based on the Howland current pump, was employed, requiring no complex electronic circuits. The coil was designed to be part of a hardware-in-the-loop (HiL) system, which is controlled by a dSPACE modular simulation hardware and uses a commercial fluxgate magnetometer as the reference. This setup reduces the complexity of the proposed system when compared to similar ones. This paper presents two distinct results: first, there is the validation and results of the uniformity regarding the generated field around the system's center; second, results of the setup with the closed-loop HiL simulation are shown, which includes tests of the coil when generating a dynamic magnetic field.

Description: Provides instructions and guidelines to prospective authors who wish to submit manuscripts.

Description: This paper proposes a novel method to cope with local measurement ambiguity problem in particle filtering. The ambiguity of the measurement has been attributed as a crucial cause of filter degradation and divergence. Given the observation that the ambiguous measurement update is contributed by not only the shape of the measurement model but also the prior distribution of the filter estimate, we adopt a solution to the out-of-sequence measurement problem on the framework of the particle filter with sequential importance resampling. Once an ambiguous measurement update is detected, the proposed method skips the measurement update at the time step and utilizes the measurement later when the particle distribution becomes adequate for the measurement update. This strategy provides a remedy to the ambiguity problem to obtain accurate current position estimate with lower covariance. Numerical simulation is presented to demonstrate effectiveness and performance of the proposed method. Compared to other methods, such as the standard particle filter, the auxiliary particle filter, the mixture particle filter, and the receding-horizon Kalman filter, the proposed method shows better performance in terms of root-mean-square error and estimated covariance.

Description: Presents the AESS calendar of events.

Description: Presents the table of contents for this issue of the publication.

Description: The primary objective of the project was to acquaint ourselves with software defined radio (SDR) techniques to put into action some of the concepts covered during digital communications courses. SDR offers an easy way to design and implement flexible radiofrequency (RF) transceiver architectures using mainly software developments [1]. Thus, it allows to get promptly familiar with classic issues to overcome when designing receivers (RF electronics impairments, asynchronously-sampled signals...) without getting restricted by material constraints traditionally brought by full-hardware implementations (i.e., cost of hardware components to be soldered together, need of various development and testing instruments...).

Description: The use of autonomous vehicles is currently a growing trend, particularly in applications such as manufacturing, hazardous material handling, and surveillance [1]. A quadcopter is an emerging rotorcraft concept for an unmanned aerial vehicle (UAV) that is equipped with four rotors, two pairs of counter-rotating, and fixedpitch blades located at the four corners of the vehicle [2]. In a quadcopter system, yaw is controlled by increasing the angular velocity of rotors that spin in the same direction to a level higher than the velocity of other rotor pairs, and pitch or roll is controlled by increasing the angular velocity of a rotor to a level greater than the velocity of a diametrically opposite rotor (Figure 1) [3].

Description: Presents the table of contents for this issue of this publication.

Description: This paper deals with the problem of coherent radar detection of fast-moving targets in a high-range resolution mode. In particular, we are focusing on the spiky clutter modeled as a compound Gaussian process with rapidly varying power along range. Additionally, a fast-moving target of interest has a few range cells migration within the coherent processing interval. Two coherent CFAR detectors are proposed taking into account target migration and highly inhomogeneous clutter. Both detectors involve solution of a transcendental equation, carried out numerically in a few iterations. The performance evaluation is addressed by numerical simulations and it shows a significant improvement in detection of fast-moving targets in inhomogeneous heavy tailed radar clutter.

Description: In this paper, we propose an approach that uses deep learning to detect a human fall. The proposed approach automatically captures the intricate properties of the radar returns. In order to minimize false alarms, we fuse information from both the time-frequency and range domains. Experimental data is used to demonstrate the superiority of the deep learning based approach in comparison with the principal component analysis method and those methods incorporating predefined physically interpreted features.

Description: Access to the electromagnetic spectrum is an ever-growing challenge for radar. Future radar will be required to mitigate RF interference from other RF sources, relocate to new frequency bands while maintaining quality of service, and share frequency bands with other RF systems. The spectrum sensing, multioptimization (SS-MO) technique was recently investigated as a possible solution to these challenges. Prior results have indicated significant improvement in the signal-to-interference plus noise ratio at the cost of a high computational complexity. However, the optimization computational cost must be manageable in real time to address the dynamically changing spectral environment. In this paper, a bioinspired filtering technique is investigated to reduce the computational complexity of SS-MO. The proposed technique is analogous to the processing of the thalamus in the human brain in that the number of samples input to SS-MO is significantly decreased, thus, resulting in a reduction in computational complexity. The performance and computational complexity of SS-MO and the proposed technique are investigated. Both techniques are used to process a variety of measured spectral data. The results indicate a significant decrease in computational complexity for the proposed approach while maintaining performance of the SS-MO technique.

Description: Studies have demonstrated the usefulness of micro-Doppler signatures for classifying dynamic radar targets such as humans, helicopters, and wind turbines. However, these classification works are based on the assumption that the propagation channel consists of only a single moving target. When multiple targets move simultaneously in the channel, the micro-Dopplers, in their radar backscatter, superimpose thereby distorting the signatures. In this paper, we propose a method to detect multiple targets that move simultaneously in the propagation channel. We first model the micro-Doppler radar signatures of different movers using dictionary learning techniques. Then, we use a sparse coding algorithm to separate the aggregate radar backscatter signal from multiple targets into their individual components. We demonstrate that the disaggregated signals are useful for accurately detecting multiple targets.

Description: A novel “blind and evade” guidance concept for an aerial target, which is exposed to a threat of two homing missiles, is presented. Each missile is assumed to measure solely its own line-of-sight (LOS) angle and share it with the other missile. Such information sharing enables the missiles to form a triangular measuring baseline relative to the target and to improve their estimation accuracy. However, if the separation angle between the two LOS vectors is small enough, the observability of such double-LOS measuring approach becomes weak. Motivated by this observation, the idea of the proposed concept is to bring the missiles on the same LOS with the target, i.e., blinding them, and then perform an appropriately timed target evasive maneuver. The target's guidance law is derived under the assumption of perfect information and formulated as an optimal control problem. Simulation results demonstrate the potential of the proposed defense concept.

Description: In this paper, a path planning algorithm for a multi-arm space robot is proposed. The robot is capable of maneuvering on the exterior of a large space station. Based on the maneuver strategy, continuous and smooth trajectories of the manipulator end effectors are first determined via the polynomial interpolation method. Then, the kinematics describing the relation between the end effector and the joint angles as well as the platform are formulated. A Moore–Penrose pseudoinverse solution of the joint trajectories is calculated to describe the motion of the manipulators, particularly, considering the singularity avoidance. In addition, a collision detection algorithm is developed to estimate the security during operation. Constraints are formulated by considering collision avoidance, based on which a collision-free trajectory is optimized through the multiplier-penalty method. The numerical results of a triple-arm space robotic system are given to demonstrate the effectiveness of the proposed algorithms.

Description: Multiframe track-before-detect (MF-TBD) usually uses sliding-window-based batch processing, where a number $N$ of the latest data frames are jointly processed at each measurement time. The sliding window mechanism compromises the operating efficiency of MF-TBD by increasing both computational costs and memory requirements, thus, heavily restricting its application in practical problems. In this paper, an improved recursive implementation for MF-TBD is proposed. Unlike the sliding-window-based implementation, the proposed method calculates the merit function, a measure of the possibility that a state is target originated, of the current batch based on an approximated recursive relationship between the merit functions of consecutive batches. As a result, instead having to process the whole batch, at any given time only the latest frame needs to be processed. The recursive relationship is first derived for any arbitrary merit function, and then explored further with several typical merit functions that are used in MF-TBD. Both the theoretical analysis and simulation results demonstrate that the proposed method can achieve almost $N$ times reduction in computational complexity and memory requirements with negligible performance loss.

Description: In this paper, we describe and evaluate a new monitor that uses inertial navigation system (INS) measurements to detect spoofing attacks on global navigation satellite system (GNSS) receivers. Spoofing detection is accomplished by monitoring the Kalman filter innovations in a tightly coupled INS/GNSS mechanization. Monitor performance is evaluated against worst case spoofing attacks, including spoofers capable of tracking vehicle position. There are two main contributions of this paper. The first is a mathematical framework to quantify postmonitor spoofing integrity risk. The second is an analytical expression of the worst case sequence of spoofed GNSS signals. We then apply these to an example spoofing attack on a Boeing 747 on final approach. The results show that GNSS spoofing is easily detected, with high integrity, unless the spoofer's position-tracking devices have unrealistic, near-perfect accuracy, and no delays.

Description: The maintenance of the nominal multirevolution elliptic halo orbit, whose special features can benefit mercurial explorations, is first investigated through Monte–Carlo simulations in the elliptic Sun–Mercury model, and then validated in the high-fidelity ephemeris model. The receding horizon control strategy solved by the indirect Radau pseudospectral method demonstrates that the orbit can be maintained robustly with respect to very large initial deviations. Moreover, the result proves that the elliptic Sun–Mercury model is an accurate approximation.

Description: Complex motions of targets cause migration through resolution cells which leads to the inverse synthetic aperture radar (ISAR) image blurred and makes difficulties to follow-up work such as identification, recognition, and classification. In this paper, a novel ISAR imaging algorithm based on the fractional tap length keystone transform (FTLKT) is proposed for multiple targets with complex motions. In noncooperation case, different targets behave variously. For phase coupling of different orders, the proposed algorithm first employs FTLKT to achieve decoupling of the frequency and slow time variable, then detection of Doppler peaks is applied for ambiguity resolution of different targets. According to this, focused ISAR images of different targets are obtained. Simulation results demonstrate the validity of the proposed algorithm.

Description: This paper is a first introduction to the concept of using global navigation satellite systems (GNSS) as illuminators of opportunity in a passive bistatic real-time radar system for maritime target indication applications. An overview of the system concept and the signal processing algorithms for moving target indication is provided. To verify the feasibility of the system implementation as well as test the developed signal processing algorithms, an experimental test bed was developed and the appropriate experimental campaign with the new Galileo satellites and a ferry as the target was carried out. The results confirm the system concept and its potential for multistatic operation, with the ferry being detected simultaneously by two satellites.

Description: This paper presents a robust fuzzy tracking controller for position and attitude control, and for vibration suppression in a flexible spacecraft. The robust fuzzy controller guarantees $H_{infty }$ tracking control performance while satisfying the actuators’ amplitude constraints. The design problem of the fuzzy tracking controller is formulated in terms of linear matrix inequalities. The stability, performance, and robustness of the proposed fuzzy controller are examined and compared with a baseline nonlinear controller such as the model-reference adaptive controller with $sigma$ -modification via numerical simulations.

Description: Aeronautical ground lighting (AGL) systems provide a visual reference for aircraft during airport operations. Fast detection and location of failed luminaires is an important safety concern in AGL systems. In the event of luminaire failure, AGL transformers introduce harmonic currents. Resonances can increase harmonics, worsening the problem. This paper presents analytical expressions for determining resonance frequencies in AGL systems, as well as a simple procedure based on these expressions for locating failed luminaires from measurements.

Description: To accurately test aircraft models, the flow field featured by the stagnation pressure and the Mach number must be kept constant at the predefined state during wind tunnel tests. The objective of this study is to design a multivariable controller to quickly reject various disturbances for the varying angle of attack (AoA) tests in a large-scale Intermittent Transonic Wind Tunnel (ITWT). First, the flow field control structure is specially designed to simplify the controller design. Next, a novel AoA model (i.e., Hammerstein model) with corresponding modeling approach is developed to characterize the influence of varying AoA on the static pressure. Finally, the flow field controller is designed in the offset-free model predictive control (MPC) framework, which uses the feedforward strategy to compensate for the varying AoA disturbance and copes with other unknown disturbances and model mismatch using the augmented model method. Simulation results and practical wind tunnel tests prove the effectiveness of the proposed modeling and control methods.

Description: A method is derived for forming composite measurements when the line-of-sight measurements from multiple sensors are asynchronous and the position(s) of one or more passive sensors is (are) unknown. Using the composite measurement, the target position, velocity, and unknown sensor location are estimated. Additionally, general analytical observability conditions are derived.

Description: This paper devises a new constant false alarm rate (CFAR) detection scheme to deal with the problem of radar target detection in heterogeneous environment. The proposed scheme, called “clustering-CFAR detector,” is data dependent and composed of three stages: an adaptive clustering procedure that, exploiting the recorded measurements of the clutter environment, divides the detection area into different classes to provide auxiliary information, a dynamic reference cell selector that chooses appropriate secondary data according to the classes, and a conventional CFAR processor to make the final decision about the target presence. The performance of “clustering-CFAR detector” is analyzed by computer simulation and public radar measured data (IPIX data and MSTAR data), and compared with existing CFAR detectors. The results show that the new detector achieves a better performance in the aspects of terrain classification, control of false alarm points, and probability of detection.

Description: This paper presents a precorrelation interference detection method based on statistical analysis in the time-frequency (TF) domain for global navigation satellite system signals. In particular, the short-time Fourier transform (STFT) is considered as the TF tool due to its linear property and low computational complexity. A goodness-of-fit (GoF) test is applied to each frequency slice in the spectrogram of the received signal, which approximately follows a chi-square distribution in the absence of interference. The expected probability density function (PDF) of the observed TF-domain samples can be computed based on an interference-free signal or the noise power estimate. Two versions of the proposed technique are presented: one based on the canonical STFT with the maximum overlap size, and the other based on the block-wise STFT using nonoverlapped samples. The canonical STFT-based method shows better detection capability at the expense of degraded false alarm performance caused by the PDF distortion in the canonical STFT samples. The block-wise STFT-based method alleviates the false alarm issue but slightly weakens the detection capability. Simulations show that the proposed canonical and block-wise STFT-based methods improve the detection performance for both narrow- and wideband interference in low jammer-to-noise ratio environments when compared with the existing GoF test applied to the time-domain samples.

Description: In many practical scenarios with multipath propagation, one target may generate multiple detections in one scan. Proper use of multipath-induced measurements can improve the detection of very low observable (VLO) targets. In this paper, a true multitarget tracker, the joint multipath maximum likelihood probabilistic multihypothesis tracker (JMP-ML-PMHT) is proposed to address this problem. The standard ML-PMHT is extended to incorporate multipath detections and jointly track multiple VLO targets. The Cramer–Rao lower bound with multipath detections is derived. Simulation results with an over-the-horizon-radar scenario show that the JMP-ML-PMHT can detect and track multiple VLO targets by effectively utilizing the information in multipath measurements.

Description: Provides a listing of current committee members and society officers.

Description: Provides an overview of the technical articles and features presented in this issue.

Description: Advertisement.

Description: The history of rockets starts in antiquity, and has continued through to modern times. The modern rocket era started before World War II (WWII), when amateur rocket engineers were building and launching their rockets. During WWII rocket technology was closely associated with weapon development, with the famous V2 rocket as the most notable example. After the war, rockets were of major importance to space exploration programs [1]. Interest in rocket technology is still high, including among students and amateur engineers.

Description: Due to high-speed, highly maneuvering, and weak targets as well as strong clutter and jamming, it is known that the environment of modern radar becomes increasingly challenging [1–7]. To deal with the challenges, focus-before-detection (FBD) [8–15] has been introduced in the first article [1] of this two-article series. As some of the typical FBD methods, Radon-Fourier transform (RFT) and generalized RFT (GRFT) originally proposed in [8, 9] have briefly introduced in [1] for coherent integration of a long time on target (TOT) to focus the energy of a target in parameter space with arbitrary parametric motion. That is, the motion is modeled with a finite number of translational and rotational motion parameters, such as velocity, acceleration, and also jerk. The FBD methods can overcome the effects of across range cells (ARC), across Doppler cells (ADC), and even across beamwidths (ABW) in a long TOT. As a result, by combining accurate environment sensing from echoes and effective resource management for optimization, the proposed FBD-based methods can effectively improve target detection and parameter estimation without changing system parameters in a complicated environment.

Description: Advertisement.

Description: Presents the front cover for this issue of the publication.

Description: Presents the AESS calendar of events.

Description: Presents the table of contents for this issue of the publication.

Description: The idea for this Special Issue on HF Radar was conceived in early 2016 and refined at the 2016 IEEE Radar Conference in Philadelphia where the four Guest Editors-to-be were all present. Lamenting the rather fragmented nature of the literature on HF radar and, indeed, of the HF radar community itself, we decided that a special issue of a popular and authoritative journal would serve to expose the state-of-the-art of our discipline to the wider engineering community and, simultaneously, reinvigorate links between the various active research groups. The choice of the IEEE Aerospace and Electronic Systems Magazine as our medium was a no-brainer.

Description: Implicitly or explicitly, the extraction of information from radar echoes is based on a physical model of the interaction between the radar system and the target, the study of which is sometimes referred to as radar phenomenology [1]. It follows that the detail and fidelity of the physical model determine the prospective observables, the accuracy of measurement, and the fidelity of interpretation. Of course, there is little to be gained from employing a highly sophisticated model if the radar measurements have neither the dimensionality nor the dynamic range to support estimation of the parameters invoked. Contrariwise, there is much to be lost if valuable information encoded in the target echoes is overlooked because the signal analysis and interpretation procedures fail to undertake the corresponding decoding processes.

Description: Provides an overview of the technical articles and features presented in this issue.

Description: Skywave over-the-horizon radar (OTHR) is long-range beyond horizon radar technology that is presently employed by several nations for wide-area surveillance of aircraft and maritime vessels [1]. This radar class uses propagation via the ionosphere [2] to achieve radar energy propagation to and from the target region. The ionosphere is driven by varying solar interaction with the Earth, and this variability significantly influences the operational performance of a skywave OTHR. Considerable care in selecting radar-operating parameters is required to achieve the best performance.

Description: The Earth's geomagnetic poles represent the axis of a dipole field of best fit to the Earth's true magnetic field. Canada currently hosts the Geomagnetic North Pole on Ellesmere Island, near 80 N 75 W. In the vicinity of the geomagnetic pole, the magnetic field lines of the Earth extend many Earth radii into space and interact with the solar wind, leading to particle precipitation and horizontal ionospheric plasma drifts. Particle precipitation produces the visible Aurora Borealis in the area shown as green in Figure 1, which we denote the auroral oval. North of the auroral oval is the region of the polar cap, where the solar wind drives horizontal plasma drifts, shown by the red contours in Figure 1. Previous over-thehorizon radar (OTHR) experiments have looked at operation in both the auroral oval and the polar cap.

Description: Discusses the specific of the the cover for this issue of the publication.

Description: Presents the back cover for this issue of the publication.

Description: The articles in this special section address HF (high frequency) skywave radar technology and address a diverse range of issues that confront designers and users of HF radars.

Description: The high frequency surface wave radar (HFSWR) with detection capability of hundreds of kilometers plays an important role in marine surveillance [1]–[8]. Nevertheless, HFSWR has low azimuth measurement accuracy, which causes great deviation of target location and tracking [9]. Meanwhile, the miniaturization of radar arrays leads to the limitation of antenna length, which further causes severe decline of azimuth accuracy. Moreover, the interference from external environment also decreases the azimuth accuracy, making the accurate tracking of vessels difficult. In recent years, the 2-HFSWR multisensor surveillance system has become a hot spot, because it only requires parameters of distance and velocity without using the azimuth measurement when tracking vessels. The 2-HFSWR multisensor surveillance system consists of two independent radars implementing the target location and tracking task by detecting the radial distance and velocity, respectively. The 2-HFSWR multisensor surveillance system can ensure the detection accuracy without azimuth measurement, which is advantageous to the miniaturization of HFSWR. However, there are still certain complicated cases to be solved for continuous tracking of vessels, for example sudden change in motion state, an inaccurate model, and unknown priori statistical properties of noise.

Description: The objective of this article is to outline the sense-and-adapt capabilities of Canada's Third-Generation High Frequency Surface Wave Radar (3rd Gen HFSWR). This system is an evolution of Raytheon's pioneering SWR503 radar.

Description: A desirable goal for an over-the-horizon radar (OTHR) receiver chain is to avoid degradation of available signal to noise ratio over unused channels within a nominated band of interest. If there is a design requirement for the receiver to perform instantaneously wideband, this can present a significant challenge as the dynamic range of signals within the high frequency (HF) band in the form of large broadcast signals, by way of contrast to the very low spectral densities characterizing cosmic noise, can easily exceed the linear range of components in a typical receiver chain. In narrowband systems, this has been handled in various ways by constraining the bandwidth impinging on sensitive downstream components, with a highly linear bandpass filter, or custom mixer and filter. Even in narrowband systems care must be taken to ensure that the receive chain internal noise and nonlinear products do not significantly impact at operational frequencies of interest. More recently, with the advent of direct digital receivers (DDRx) based around high speed high dynamic range analogue to digital converters (ADCs), a desire to operate OTHR with wide open front ends (WOFE) has emerged. In a WOFE DDRx there is no bandpass filtering within the operational range of the receiver. The principle is to enable multiple simultaneous functions using the large radar receive array, e.g. the usual narrowband radar with a complementary wideband frequency management support (FMS) system [1]. This goal demands simultaneous access across the full spectrum and therefore constrains the filtering solution and increases the technical demand on the receiver components. As discussed in Barnes et. al. [2] the general application of Commercial-Off-The-Shelf (COTS) DDRx to attempt WOFE at HF will generally result in some level of system imposed performance limiting. The use of customized, dynamically adaptive front-end gain stages, including the use of equalization, where the gain is a tailored function o- frequency, can allow the receiver to approach a satisfactory WOFE solution in some applications, e.g. the spectral environment evaluation and recording [2] receiver.

Description: Multiple-Input Multiple-Output (MIMO) radar has been an active topic in the radar research community for more than a decade [1]–[3]. MIMO based approaches have been investigated for improving target detectability, improving target localization, achieving higher spatial resolution, and clutter reduction using transmit or joint transmit-receive beamforming. This paper describes two series of experiments undertaken by the author and coworkers in learning how we might apply MIMO radar techniques to challenges in skywave Over-the-Horizon Radar (OTHR).

Description: This paper investigates the effectiveness of multipath-decorrelating antenna motion in reducing the initialization time of global navigation satellite system (GNSS) receivers employing low-cost single-frequency antennas for carrier-phase differential GNSS (CDGNSS) positioning. Fast initialization times with low-cost antennas will encourage the expansion of CDGNSS into the mass market, bringing the benefits of globally referenced centimeter-accurate positioning to many consumer applications, such as augmented reality and autonomous vehicles, that have so far been hampered by the several-meter-level errors of traditional GNSS positioning. Poor multipath suppression common to low-cost antennas results in large and strongly time-correlated phase errors when a receiver is static. Such errors can result in the CDGNSS initialization time, the so-called time to ambiguity resolution (TAR), extending to hundreds of seconds—many times longer than for higher cost survey-grade antennas, which have substantially better multipath suppression. This paper demonstrates that TAR can be significantly reduced through antenna motion, particularly gentle wavelength-scale random antenna motion. Such motion acts to decrease the correlation time of the multipath-induced phase errors. A priori knowledge of the motion profile is shown to further reduce TAR, with the reduction shown to be more pronounced as the initialization scenario is more challenging.

Description: The optical orbit determination is one of the most important ways for noncooperative object tracking. One of the main problems with noncooperative object tracking is its recognition through different nights. In this study, the conditions that ensure the recognition of a geostationary satellite inside a cluster were assessed through a hard real case study. This study was developed through a three-phase approach. The first phase was the observation campaign for the images acquisition. The second phase was the image's astrometric reduction for the data collection and the third phase was the orbit determination and data analyses. To evaluate the recognition ability, the residuals between the celestial coordinates obtained from the propagated orbit, which was carried out from the fitting between first night data and the environment gravity model through a least squares approach, and the measures collected during the second night were assessed. This approach, which is totally independent from the satellite cooperation actions, can be extended to the space debris recognition during different nights.

Description: In this paper, a weighted least squares (WLS) method is presented to find the location of a single target by the use of bistatic range (BR) measurements in multistatic passive radar. The proposed method is based on the idea of eliminating the nuisance parameter. Then, the method employs several WLS minimizations to obtain the target location estimate. The weighting matrix producing a significant improvement in the performance of the method is derived in two different conditions—one of them results in the maximum likelihood estimator (MLE) and the other one leads to the best linear unbiased estimator (BLUE). The accuracy properties of the method are analyzed, and the Cramer-Rao lower bound (CRLB) for target localization accuracy is also derived. In addition, in a two-dimensional space and in the case of localizing with one transmitter and the minimal number of receivers, the different placements of receivers are analytically determined, in each of which the location solution is not unique. Furthermore, from different aspects, the BR-based localization is compared to the hyperbolic localization derived from range difference (RD) measurements.

Description: A novel modeling method, based on computational fluid dynamics (CFD) to simulate a parafoil flying in rain and wind environments, is proposed. Then, the dynamic model of the powered parafoil in the complex environment is established on the basis of revised aerodynamic equations. By introducing path-following controllers based on active disturbance rejection control (ADRC), horizontal and longitude trajectory tracking of the powered parafoil in realistic environments are simulated. Results verify the effectiveness of the model and control methods.

Description: This paper describes the use of Alamouti-encoded-shaped offset QPSK version TG (SOQPSK-TG) to solve the two-antenna problem in aeronautical telemetry. The Alamouti space-time block code is used to encode the phase states in the complex exponential representation of SOQPSK-TG. Because SOQPSK-TG possesses memory, the Alamouti decoder is a sequence estimator. Maximum likelihood and least squares sequence decoders are derived. To reduce the number of states, the eight-waveform cross-correlated trellis-coded quadrature modulation (XTCQM) approximate representation of SOQPSK-TG is used. A prototype decoder based on the least squares decoder and the estimators described in Part I and operating at a data rate of 10 Mb/s was tested in the laboratory in test flights at the Air Force Test Center, Edwards AFB. The test flights demonstrate that Alamouti-encoded SOQPSK-TG, as described in this paper, using the least squares decoder based on the estimators described in Part I solves the two antenna problem in aeronautical telemetry.

Description: This paper presents methods and results in modeling wind turbine dynamic radar signatures in the near field. The theoretical analysis begins with the simpler case of modeling wind turbine blades as rectangular plates. The theoretical radar signature for the wind turbine in the near field is formulated and its main peculiarities are investigated. Subsequently, the complex shape of the blades is considered and the corresponding radar signatures are modeled. Theoretical modeling is confirmed for both cases via experimental testing in laboratory conditions. It is shown that the experimental results are in good accordance with the theoretically predicted signatures.

Description: In this paper, we present a decentralized multitarget tracking system for cooperative unmanned aerial vehicles (UAVs) with limited sensing capabilities. The proposed system distributively incorporates a clustering algorithm, an optimal sensor manager, and an optimal path planner to track multiple mobile targets. A set of extended Kalman filters is used by each UAV to estimate the locations of mobile targets. The UAVs are equipped with gimbaled cameras with a limited field of view and sensing range. To make the system scalable, the density-based spatial clustering of applications with noise algorithm is used to group targets, sensor managers determine optimal gimbal poses and path planners collectively coordinate UAVs’ movements. The effective performance of the proposed system is shown through simulation results.

Description: Wireless machine-to-machine (M2M) communication with synchronized traffic patterns plays an important role in many aircraft systems. Recent research has separately examined collision avoidance mechanisms, such as presmoothing and access barring, as well as collision resolution mechanisms, such as tree resolution, for M2M random access. In contrast, we examine the combination of collision avoidance and tree collision resolution into hybrid M2M random access protocols in the context of the popular Long-Term Evolution wireless system.

Description: The authors report the simulation and actual implementation of chaotic oscillator synchronization for a pair of three-state variable Lorenz systems. The first oscillator performs as a driver (transmitter), while the second system is made to respond the received waveform. Specifically, one of the state variables of the driver circuit is judiciously selected to generate an RF waveform. This waveform is transmitted through a noisy channel and is used to drive the response system until both the systems of all three state variables achieve complete replacement synchronization. It is known that this synchronization is sensitive to changes in received power. To overcome this, a technique hereon called generalized projective synchronization is employed to accept an attenuated version of the transmitted waveform. A sensitivity analysis reveals that generalized projective synchronization is robust with respect to deviations in the control parameter values of the response system due to tolerances of electronic components. The potential of the generalized projective synchronization is illustrated for a bistatic radar system case, where synchronization is necessary to obtain the range-Doppler information of a moving target. In this instance, the cross correlation, short-time cross-correlogram and cross ambiguity surface of the transmitted and synchronized waveforms are of high quality as indicated by their entropy measures.

Description: The sensitivity of the initial guess in terms of optimizer based on an hp-adaptive pseudospectral method for solving a space maneuver vehicle's (SMV) trajectory optimization problem has long been recognized as a difficult problem. Because of the sensitivity with regard to the initial guess, it may cost the solver a large amount of time to do the Newton iteration and get the optimal solution or even the local optimal solution. In this paper, to provide the optimizer a better initial guess and solve the SMV trajectory optimization problem, an initial guess generator using a violation learning differential evolution algorithm is introduced. A new constraint-handling strategy without using penalty function is presented to modify the fitness values so that the performance of each candidate can be generalized. In addition, a learning strategy is designed to add diversity for the population in order to improve the convergency speed and avoid local optima. Several simulation results are conducted by using the combination algorithm; simulation results indicated that using limited computational efforts, the method proposed to generate initial guess can have better performance in terms of convergence ability and convergence speed compared with other approaches. By using the initial guess, the combinational method can also enhance the quality of the solution and reduce the number of Newton iteration and computational time. Therefore, the method is potentially feasible for solving the SMV trajectory optimization problem.

Description: This paper presents a generalized theoretical framework for carrier tracking of global navigation satellite systems signals by constructing a state space representation for the carrier tracking loop and applying control system design techniques to derive state feedback and state estimator gain matrices. Both phase-locked loop and frequency-locked loop are studied using this approach. Their performances are evaluated using the closed-form expressions in the presence of thermal noise, oscillator noise, and receiver platform dynamics. The proposed approach unified the phase tracking and frequency tracking within the same theoretical framework, thereby facilitating a systematic analysis of the effects of tracking loop design parameters under weak signal and highly dynamic signal environments.

Description: The use of satellite signals for passive radar detection has become quite attractive in the recent years. This paper focuses on the detection and the shadow inverse forward scatter radar (SISAR) imaging of aircrafts in the passive forward scatter radar (FSR) system using global navigation satellite system (GNSS) satellites as illuminators of opportunity. The signal model derived from GNSS tracking loop is given and its Doppler character is analyzed. Then, by comparing GNSS FSR and ground-based FSR, the SISAR signal model and the imaging method for GNSS FSR are constructed. Experiments using airliners as targets were carried out, in which forward scattering signals of both GPS satellites and BeiDou satellites were captured. The experimental results verified the correctness of the given model as well as the effectiveness of the novel imaging method.

Description: A complementary set of $K$ binary $\pm 1$ codes of length $N$ has the useful property that the sum of the autocorrelation sequences of the codes has only one nonvanishing element, its size- $KN$ peak. The $N\times K$ matrix whose columns are the codes of a binary complementary set, arranged in order, is the code set's complementary code matrix (CCM). One might ask for which $K$ and $N$ such matrices exist. A simple necessary condition for the existence of an $N\times K$ CCM is introduced, involving the sum of the squares of the imbalance values of the codes in the set (the imbalance of a binary $\pm 1$ code being the difference between the number of 1 and number of $-1$ s in the code). The one-to-one relationship between binary CCMs and binary complementary code sets allows the necessary condition for the $N\times K$ CCM existence to extend to a necessary condition for sets of $K$ complementary code sets of length $N$ . We examine the sum-of-squares condition for the separate cases of $N$ even and $N$ odd. The odd case is especially interesting, since representations in terms of sums of squares of odd integers are equivalent to representations as sums of triangular numbers, a subject of recent research in Number Theory. Furthermore, we exhibit a refinement of the existence condition in terms of the imbalance values of pairs of interlaced subcodes. This refinement is new, to the best of our knowledge. Finally, we investigate whether odd-length complementary code sets exist for $K>2$ , unlike the Golay case of $K=2$ where odd-length sets cannot exist. We easily find, by computer search, a four-code set of length 15, suggesting that these are likely not uncommon.

Description: A multimodel approach for constant false alarm ratio (CFAR) detection of vehicles through foliage in foliage penetrating synthetic aperture radar images is presented. Extreme value distributions and location scale properties are exploited to derive an adaptive CFAR approach that is able to cope with different forest densities. Performance analysis on real data is carried out to estimate the detection and false alarm probabilities in the presence of a ground truth.

Description: This paper presents the performance analysis and the optimizations of the generalized phase locked loop (PLL) and the generalized frequency locked loop (FLL). Using the minimum mean square error (MMSE) criterion as a performance measure, the optimal solutions for the generalized PLL and FLL designs under various scenarios: strong and weak signal strength, low and high dynamic, and good and poor oscillator quality are investigated. An adaptive PLL based on automatically adjustment of the integration time and loop parameters in an optimized manner is proposed. An adaptive FLL that operates with the optimal loop parameters is also presented. Simulation results demonstrate the effectiveness of the proposed generalized closed-loop tracking architecture and validate the proposed adaptive tracking schemes.

Description: Quad-phase codes of a given length can be grouped into equivalence classes based on operations preserving autocorrelation peak sidelobe level, or “ ${\rm PSL}$ -preserving operators.” The task of enumerating these equivalence classes is facilitated by establishing a relationship with the problem of enumerating equivalence classes of $2\times N$ binary grids with respect to a pair of binary grid symmetries. We show this connection by a one-to-one mapping between even-length quad-phase codes and $2\times N$ binary grids. When $N$ is even, this mapping allows the known enumeration of $2\times N$ binary grids to be applied to the enumeration of even-length quad-phase code PSL equivalence classes. Furthermore, this equivalence instructs the development of a simpler algorithm for visiting single representatives of quad-phase-code equivalence classes relative to the operations that preserve PSL. Lastly, we conduct exhaustive searches to determine the optimal ${\rm PSL}$ for quad-phase codes of lengths 25 and 26 (for the smaller of these lengths, the search space contains $4^{25}=2^{50}$ , or roughly 1 quadrillion codes). One of the devices used to narrow the search space while achieving an exhaustive search is to seed the search with the equivalence class representatives of length $N=6$ . The optimal ${\rm PSL}$ for length-25 quad-phase codes is determined to be 2, achieved by the codes in a single size-32 equivalence class. For length 26, the optimal ${\rm PSL}$ is found to be $\sqrt{5}$ , achieved by $604\,480$ codes belonging to 9445 equivalence classes of size 64.

Description: Estimation of the modulation frequency of a source is important in various sonar signal processing applications. The conventional estimator of modulating frequency has been formulated under the assumption that the source and noise are Gaussian distributed. This is often inaccurate in several applications such as underwater acoustics where the signal or noise can be impulsive. We formulate novel modulation frequency estimators that are robust to impulses in the data, and outperform the conventional estimator in environments where the observed data are contaminated by impulses. We demonstrate their performance using recorded data. We characterize the performance of the methods in terms of their accuracy, harmonic distortion, and robustness to knowledge of noise statistics. We also derive the Cramer–Rao lower bound for the modulation frequency estimation problem in impulsive data.

Description: In this paper, we introduce a bistatic inverse synthetic aperture radar (Bi-ISAR) cross-range scaling (CRS) method to more effectively use Bi-ISAR images in their applications. For this, we propose a method to estimate the effective rotation velocity of a target in a Bi-ISAR imaging system, and restore a linear-geometry distortion that yields a sheared shape of Bi-ISAR images. In the simulations, we observed that our proposed method is capable of performing robust and precise Bi-ISAR CRS.