Spurious Targets Research Articles

Exact analysis of OS modified versions with noncoherent integration

This paper deals with the exact detection analysis of the Ordered-Statistic(OS) processor along with OS Greatest Of(OSGO) and OS Smallest Of(OSSO) modified versions, for M postdetection integrated pulses when the operating environment is nonhomogeneous. Analytical results are presented in multiple-target case as well as in regions of clutter power transitions. The primary and the secondary interfering targets are assumed to be fluctuating in accordance with the SWII target fluctuation model. As the number of noncoherently integrated pulses increases, lower threshold values and consequently better detection performances are obtained in both homogeneous and multiple target background models. However, the false alarm rate performance of OSSO-CFAR(Constant False Alarm Rate) scheme at clutter edges is worsen with increasing the postdetection integrated pulses. As predicted, the OSGO-CFAR detector accommodates the presence of spurious targets in the reference window, given that their number is within its allowable range in each local window, and controls the rate of false alarm when the contents of the reference cells have clutter boundaries.

Detection of linear objects in GPR data

In this paper, we propose a semi-automatic approach to the detection of linear scattering objects in geo-radar data sets, based on the 3D radon transform. The method that we propose is iterative, as each detected object is removed from the data set before the next iteration, in order to avoid mutual interference or masking. In addition, the algorithm is able to further analyze the data set in a local fashion in order to eliminate spurious targets from the set of lines of maximum consensus. Our algorithm proved robust and reliable even in the presence of data affected by heavy noise, artifacts and other undesired scattering objects. Although the application scenario of the proposed algorithm is that of the analysis of data sets generated by a ground penetrating radar, the method is general enough to apply to any problems where linear objects needs to be identified and localized in volumetric data.

Bank-to-Turn 유도탄의 호밍유도를 위한 2축 김발형 탐색기 동체운동 상관 보상

In a bank-to-turn(BTT) missile, if a 2-gimbaled seeker was stabilized using a 2-axis rate gyro mounted along its primary axis, the change of line of sight(LOS) measured by the seeker would be induced by rolling effects due to bank-to-turn(BTT) steering as well as an actual change. It is observed that the body-coupled effects in a homing loop of BTT missile are mainly concerned with the spurious target maneuver and the coupling due to the rate gyro misalignments. In this paper, we formulate a simple linear BTT homing loop model with seeker model including each body-coupling. With the model, we analyze the effects of the couplings on the homing loop stability, and propose a direct linear compensator for the coupling to recover the stability.

Matrix CRLB scaling due to measurements of uncertain origin

In many estimation situations, measurements are of uncertain origin. This is best exemplified by the target-tracking situation in which at each scan (of a radar, sonar, or electro-optical sensor), a number of measurements are obtained, and it is not known which, if any, of these is target originated. The source of extraneous measurements can be false alarms-especially in low-SNR situations that force the detector at the end of the signal processing chain to operate with a reduced threshold-or spurious targets. In several earlier papers, the surprising observation was made that the Cramer-Rao lower bound (CRLB) for the estimation of a fixed parameter vector (e.g., initial position and velocity) that characterizes the target motion, for the special case of multidimensional measurements in the presence of additive white Gaussian noise, is simply a multiple of that for the case with no uncertainty. That is, there is a scalar information-reduction factor; this is particularly useful as it allows comparison in terms of a scalar. In this paper, we explore this result to determine how wide the class of such problems is. It turns out to include many non-Gaussian situations. Simulations corroborate the analysis.

Analysis of adaptive radar systems processing M-sweeps in target multiplicity and clutter boundary environments

The problem of multipulse performance evaluation of radar detection systems in nonhomogeneous environments is addressed. The order-statistic (OS)-based algorithms, which set thresholds by processing magnitude-ordered observations within finite moving windows, give a marginal improvement compared with the cell-averaging (CA) procedure in false alarm rate performance in clutter power transitions and due to their immunity to the presence of spurious target returns among the reference cells. Three types of these CFAR detectors are analyzed in this paper. These systems are of the two-window type where they can be used to reduce the large processing time by half against the one-window scheme in ordering the contents of the estimation cells. The considered detectors are: the mean-level (ML) the maximum (MX) and the minimum (MN)-ordered statistics as well as the conventional OS scheme. The performance prediction of these systems employing noncoherent integration for chi-square family of fluctuating targets both in the absence and presence of clutter edges or interfering targets is calculated theoretically. Curves for the detectability loss required thresholds, false alarm rate performance in clutter boundaries and detection performance in multiple target situations are presented with special emphasis on the important Swerling II target fluctuation model. The results show that the ML-OS scheme has the best detection performance and the MX-OS scheme is the preferable one that behaves robust against clutter edges. While the MN-OS scheme does not appear to offer any advantage over others, except in the case where a cluster of radar targets exists among the contents of the reference windows.

Clutter-map CFAR detection for range-spread targets in non-Gaussian clutter. II. Performance assessment

The performance assessment of the clutter-map constant false-alarm rate (CFAR) procedure presented in Part I [1] is introduced. At first, the performance in the presence of point targets is investigated, subject to both Weibull and lognormal clutter, so as to elicit the influence of the system parameters. The study essentially relies on Monte-Carlo simulations, but approximations for the detection rate are also developed. Admittedly, a global figure of performance, the Average Threshold Deviation (ATD), is introduced and its worth as a design tool is validated. Next, the effect of extended as well as multiple targets is considered, showing that the system can be designed so as to avoid self-masking from either range-spread targets persisting on the same map cell, or spurious targets in close spatial proximity to the cell under test. Finally, the system robustness is demonstrated through a sensitivity study, aimed at investigating the effect of a possible mismatch between the design and the actual clutter distribution, that of the clutter correlation and of a thermal noise component in the overall disturbance.

The effects of spatiotemporal integration on maximum displacement thresholds for the detection of coherent motion

In a series of nine experiments, observers were required to identify the shapes of moving targets, and to discriminate regions of motion from regions of uncorrelated noise. Maximum displacement thresholds ( D max) for performing these tasks were obtained under a wide variety of conditions. The stimulus parameters manipulated included the number of distinct frames in the motion sequences, the stimulus onset asynchrony between each frame, the size of the moving dots, and the shape, area and eccentricity of the target regions. For two-frame displays presented in alternation, the area of the target region was the only one of these variables to have any significant effect on D max. For longer length sequences, in contrast, D max varied dramatically among the the different conditions over a range of 10 min arc to 10 deg. In an effort to isolate the specific processes of spatiotemporal integration, we also examined how performance is affected by having overlapping transparent motions in opposite directions, or by the presence of dynamic noise or limited dot lifetimes within the moving target regions. The overall pattern of results suggest that D max is primarily determined by the ability of the visual system to isolate motion signals from the noise produced by spurious false target correlations. As a general rule, D max will increase as a result of any stimulus manipulation that increases the number of local signal correlations detected relative to those arising from noise, and vice versa.

Ll-CFAR: a flexible and robust alternative

A new family of constant false alarm rate (CFAR) processors is introduced. An Ll-CFAR forms its noise power estimate by linearly filtering ranked samples from the reference set; the weights of this combination, however, depend not only on the rank, but also on the relative proximity of the sample to the cell under test. From the class of Ll-CFARs may be chosen members which effectively censor spurious targets; members which exhibit impressive control of false alarm in the presence of a clutter edge; and members which are robust against both such inhomogeneities. While the design of such schemes is involved, their implementation is not significantly more burdensome than that of plain ordered statistic CFAR (OS-CFAR). After a discussion of the stochastic training of Ll-CFAR, the performance is thoroughly assessed under the most commonly encountered instances of environmental conditions, and compared with those of classical CFAR techniques. >

Biparametric CFAR procedures for lognormal clutter

The authors consider procedures for constant false alarm rate in lognormal clutter, accounting for variations of both the scale and a shape parameter of the clutter. Adaptivity to both parameters is obtained through biparametric estimation based on a sliding window surrounding the radar cell under test. Some procedures exploiting best linear unbiased estimation (BLUE) are presented and compared to a previous procedure called Log-t, which uses maximum likelihood estimation (MLE). The comparison is carried on for both a homogeneous clutter environment and for instances of inhomogeneous environment (clutter edges and spurious targets). In the latter instances, some advantages of BLUE procedures which stem from the opportunity of censoring are highlighted. >

Effects of nearby soft screens on idealized array reception

Arrays of sensors must often function in the neighborhood of diffracting and reflecting surfaces; these, in turn, represent effective passive sources that add to the incoming signal. The result is a computed wave‐number spectrum contaminated by the presence of spurious targets in which the true sea source may appear shifted off its actual azimuth. Here, such effects are demonstrated for the fully analyzable situation of an unshaded array near a thin semi‐infinite soft screen, taken either as a colinear aft baffle or a perpendicular backstop to the incident wave. Exact and asymptotic expressions have been derived to predict perceived strengths of virtual targets and associated azimuthal distorsions; their reported numerical evaluations could serve as benchmark results against which one might gauge the effectiveness of sophisticated processing methods under similar array installation conditions.

Summary of the Status of Lasers for Inertial Confinement Fusion

Laser systems designed for plasma research are operating in many laboratories throughout the world. The laser performance itself has become reasonably consistant from laboratory to laboratory and the focusing properties of the laser beams are understood. The plasma physics data, obtained with these systems, also appears to be reasonably self-consistant and is of great interest for inertial fusion applications. These lasers are commonly providing output powers of 0.5 > 2 TW, and power densities on target of 10/sup 13/-10-/sup 16/ W/cm/sup 2/, pulse durations on the order of 100 psec to 3 nsec, wavelengths between 0.5 ..mu.. and 10 ..mu.., and focal spot sizes of 100 ..mu.. or larger where focal spot edge effects are becoming less dominant. In addition, spurious target responses due to such behavior as pre-pulses, self-focusing, or imprecise focal spot measurement are being observed less often. The technical problems of large multi-beam systems, performing at the 10 TW level, have been overcome and these systems (e.g. the Shiva and Helios lasers) are providing high density compression data with ablative targets. The next step in laser design, the 100 to 300 kJ systems, are under construction and 1 MJ lasers are being contemplated.

Feasibility of national population growth targets in LDC's

This study employs a simulation model and data on desired family size to evaluate feasibility of national population growth targets. A basic claim is that neglect to consider desired family size in population planning has resulted in spurious target setting by a number of governments. It is proposed that if presently attainable family size is below desired family size in any society i, then low utilization of family planning services can be expected to continue as a function of absence of demand. Policy implications of this claim for allocation of scarce international family planning funds are discussed.

Spurious Target Generation Due to Hard Limiting in Pulse Compression Radars

A method is presented to calculate the output of a hard limiter if the input consists of a superposition of three phase-coded signals. A detailed investigation is made of the case where the limiter input signals are phase reversal modulated according to a maximum length linear code. It is shown in this case that a false target signal is generated at the limiter output. The amplitude distribution of the false target signal is investigated along with the distribution of the captured true target signals. A digital computer simulation confirms the theoretically predicted effects.

Second-order beams of two-dimensional slot arrays

Second-order beams in the space patterns of two-dimensional slot array antennas may far exceed the sidelobe level and therefore increase the susceptibility of a search radar to jamming or to spurious target echoes. These beams arise from the nonuniform orientation of successive slots; i.e., alternating inclination or displacement with respect to the waveguide axis. In this paper, expressions are derived for the positions of the second-order beams and for their amplitudes relative to the main beam. Experimental verification of these expressions is presented for two-dimensional arrays of edge, series, and shunt slots. Methods for suppressing the second-order beams are discussed.

Some Comments on the Beta-Excited X-Ray Source

AbstractThe potential of the beta-ray excited X-ray source was evaluated in the search for a small, low energy, planar source for gross apposition studies. Such a. source utilizes the familiar phenomena wherein target impingement by particulate radiation from certain pure beta emitters is utilized for the production o£ useful bremsstrahlung and characteristic X-radiation. Some of the favorable attributes of such a source are; simplicity of design and fabrication, diminutive size, stability, low cost, zero power consutnption and the gamut of synthetic radioisotopes with which they may be powered. This paper deals with the preliminary development of such a beta-excited source for application to apposition radiography as well as with the small, compound source-target.The design of such a source type is concerned with certain stimulating problems, some of which are; development of adequate photon intensity, reduction of excessive white radiation production, shielding for scattered and spurious radiation, target and source s elf-absorption, Simple illustrations of source-target geometries are reviewed both for compound and separate source-target design. Some resolution studies for the gross apposition source are shown, plus some exposures made with compound sources. The available synthetic isotopes are described and preliminary applications with P32 , Sr90, Y90 and Pm147 sources are outlined. The paper is divided into two portions; one, a brief review of theory and design; two, construction and results for the apposition and compound source.

Detection of Birds by Radar

IN view of Lack and Varley's recent letter on this subject1, it may be of interest to quote some passages from a German document prepared this year. Under the heading "Spurious Echoes" (Scheinziele), it is stated that under special weather conditions up to 120 spurious echoes may be observed in an hour. Spurious targets occur especially near the mouths of rivers. Water temperatures which are higher than the temperature of the air seem to favour their appearance. There seems to be a definite connexion between wind direction and the direction of movement of the spurious echoes. Velocities up to 600 km./hr. The ratio of amplitudes between horizontal and vertical polarization is 3:1."