Comments on `Existence and uniqueness of GPS solutions' by J.S.Abel and J.W. Chaffee

The commenter points out that a direct Global Positioning System (GPS) algorithm together with discussions on the existence and uniqueness of the solution appeared in his paper (J. Guidance, Control, and Dynamics, vol.9, p.715-17, Nov./Dec. 1986). Since the GPS solution is reduced to solving a quadratic equation, the existence and uniqueness can be easily tested. J.S. Abel and J.W. Chaffee, in the above-titled paper (ibid., vol.26, no.6, p.748-53, Sept. 1990), show that the GPS solution problem is similar to the hyperbolic-fix problem. The commenter notes that it can be inferred from his later work (ibid., vol.26. no.5, p.748-53, Sept. 1990) that the two solutions exist if and only if the four GPS satellites are coplanar, in which case the two solutions are mirror-symmetric with respect to the GPS plane     

Comments on `SCR 584 radar and Mk.56 gunfire control' by I. Getting

Some errors in the above-titled article (see ibid., vol.5, no.10, p.3-15, Oct. 1990) are pointed out. Although the material is peripheral to the principal subject, the commenter feels that they are significant to the article if taken as historical     

Comments on `Tracking a maneuvering target using input estimation''

P.L. Boglar (see ibid., vol.AES-23, no.3, p.298-310, May 1987) developed a recursive formulation of the Chan, Hu, and Plant (CHP) algorithm, and the results of the simulation verified the performance improvements. The commenter claims that Bogler obtained an incorrect recursive formulation of input estimation because he incorrectly used the formulation of the Kalman filter. The commenter presents calculations that aim to demonstrate this claim     

Comments on `SCR-20 Radar Development' and `The SCR-270 in Japan'by Viewager et al

To add to the history of the SCR-270 radar's development (see Viewager et al., vol.3, no.12, p.3-6, 1988 and F. Voltaggio, ibid., vol.3, no.12, p.7-14, 1988) the commenter presents personal recollections regarding the modifications made to several SCR-270 radar sets operating in Hawaii just before the start of World War II     

Comments on `Detector relative efficiencies in the presence ofLaplace noise' by M.I. Dadi and J.R. Marks II

In the above-titled paper (see ibid., vol.AES-23, p.568-82, July 1987) M.I. Dadi and J.R. Marks II studied the relative efficiencies of the Neyman-Pearson optimal detector with respect to the linear and sign detectors, for the detection of a constant signal in additive Laplace noise. By applying the central limit theorem, they derived expressions for three types of asymptotic relative efficiencies (AREs). However, as noted in the above paper, the Gaussian approximation to the sign detector fails to yield the correct asymptotic efficiency. The commenter derives the correct ARE of the optimal detector with respect to the sign detector for the Laplace noise     

Comments, with reply, on 'A new algorithm to optimize Barker code sidelobe suppression filters' by X.H. Chen and J. Oksman

In the above-titled paper (see ibid., vol.26, no.4, July 1990), the authors presented a simple approach to suppressing Barker code compression sidelobes. It consists of approximating an inverse filter in a finite series of terms with unknown coefficients. The coefficients are then determined by a simplex solution to an appropriate linear programming problem. The commenter indicates the results are correct, but the steps taken contain two errors which, however, compensate for each other. The corrections are given by the authors in their reply.<>     

Comments, with reply, on 'convergence properties of Gram-Schmidt and SMI adaptive algorithms' by K. Gerlach and F.F. Kretschmer, Jr

The commenter summarizes Q-R decomposition techniques for solving the least squares (LS) problem and comments on associated aspects of the work presented by K. Gerlach and F.F. Kretschmer, Jr. (ibid., vol.267, no.1, Jan.90). In response to the commenter's statement that the statistical properties of the LS that determine the convergence performance are well known. Gerlach and Kretschmer assert that this is true only under the assumptions that have been used in the past to analyze the convergence performance of the canceler and for only a limited number of convergence performance measures. Gerlach and Kretschmer also address the commenter's points on overmatching degrees of freedom.<>     

Comments, with reply, on `Optimal detection and performance ofdistributed sensor systems'

The commenter observes that the general solution proposed in the above paper (see ibid., vol.AES-23, no.1, p.24-30, Jan. 1988) for the global optimization of a distributed sensor detection system with fusion leads to coupled equations whose solution is a formidable computational task. This necessitated several simplifying assumptions that he comments on here. In response, the authors review the extent of the equal local threshold assumption throughout the work and make comments on the numerical performance comparison they gave there     

Comments on `Comparison of two-sensor tracking methods based onstate vector fusion and measurement fusion' by J. Roecker et al

As shown in the above named work (ibid., vol.24, p.447-9, July, 1988), the improvement in the centralized scheme over the decentralized one was shown to be about 6-8%. The reason is briefly described     

Sequence design for IIR inverse filter pulse compression

An infinite impulse response (IIR) inverse filter structure is presented, and compared with the performance of two finite impulse response (FIR) designs. The IIR design is shown to provide better performance and be able to improve further (e.g., -1.4 dB in sidelobe levels per unit delay increase for the length-13 Barker sequence) by increasing delay. The performance parameters of this IIR inverse filter suggest a design criterion for sequences on which the filter operates; that is related to the roots of the Z transform polynomial of the sequence. The sidelobe-optimal sequence derived according to this criterion is shown to provide sharper sidelobe reduction (-6 dB per unit delay increase for the sidelobe optimal length-13 sequence)     

Low sidelobe radar waveforms derived from orthogonal matrices

Novel waveforms are described that have low sidelobes when individual or multiple waveforms are approximately processed. They are related to orthogonal matrices that may be associated with complementary sequences and also with periodic waveforms having autocorrelation functions with constant zero-amplitude sidelobes. Also described are sets of sequences whose cross-correlation functions sum to zero everywhere. A potential application is the elimination of ambiguous range stationary clutter     

Adaptive Radar Detection with Asymptotically Regulated False-Alarm Rate

An adaptive detection procedure is described by which the detection threshold is so adjusted as to provide an asymptotic false-alarm probability PFA that is approximately invariant with changes in radar clutter return amplitude probability density functions (pdf's) in a broad class. The class includes Rayleigh, chi, Weibull, and lognormal pdf's. The receiver noise is also taken into account. The clutter-plus-noise pdf is approximated by a truncated generalized Laguerre series, the coefficients of which are estimated from the radar returns using "cell averaging" techniques. This estimation is assumed to be perfect. The results obtained indicate that the "bias" error, defined as the normalized difference between the design PFA and the asymptotic PFA corresponding to the computed threshold, lies within a fraction of an order of magnitude for 10-3?PFA ? 10-6. For PFA ?10-6 the bias error is more than an order of magnitude. These results are for the case when a single independent radar return is processed at a time. The bias error decreases as the number of postdetection integrations of independent returns increases.     

Comments with reply, on `A new look at nonseparable syntheticaperture radar processing' by A. Di Cenzo

The commenters point out that the idea using a two-dimensional digital correlation technique to perform synthetic-aperture-radar (SAR) processing, presented as new in the above-titled paper (see ibid., vol.24, p.218-23, May 1988), was described by them as early as 1978 and has since been described by other authors. They discuss some of these earlier studies. The author replies that he was unaware of the earlier work, and that he did not intend to convey the impression that the nonseparable transform domain processor that he presented was the first     

ATS-6 Spacecraft Attitude Precision Pointing & Slewing Adaptive Control Experiment

The primary objective of the Spacecraft Attitude Precision Pointing and Slewing Adaptive Control (SAPPSAC) Experiment is to establish feasibility and evaluate capabilities of a ground-based spacecraft attitude control system, wherein RF command and telemetry links, together with a ground station on-line minicomputer, perform closed loop attitude control of the Applications Technology Satellite -6 (ATS-6). The ground processor is described, including operational characteristics and the controller software. Attitude maneuvers include precision pointing to fixed targets, slewing between targets, and generation of prescribed ground tracks. Test results show high performance and reliability for over 30 h of on-line control with no serious anomalies. Attitude stabilization relative to a prescribed target has been achieved to better than 0.007° in pitch and roll and 0.020° in yaw for a period of 43 min. Ground tracks were generated which had maximum latitude/longitude deviations less than 0.150 from reference.     

单面螺纹抽钉干涉配合复合材料连接结构的疲劳性能研究

通过疲劳试验研究了单面螺纹抽钉干涉配合复合材料连接结构的疲劳性能,分别考虑了紧固件类型、干涉配合量、搭接板材料及铺层次序等影响因素。采用了拉压疲劳试验,拉压比R=-1,循环应力水平则根据静载极限挤压强度值选定。根据疲劳试验循环应力和疲劳寿命曲线(S-N曲线),得到了不同影响因素对疲劳寿命的影响规律。结果表明,选择适当的干涉配合量、紧固件类型及搭接板均能提高结构的疲劳寿命,4种不同主板铺层次序均对结构疲劳寿命影响不大。     

Maximum likelihood azimuth estimation applied to SSR/IFF systems

A conventional (nonmonopulse) secondary surveillance radar (SSR) is significantly cheaper than a monopulse SSR but exhibits much greater azimuthal error, especially when some of the replies are missing. Estimation techniques and their performance are discussed with special reference to SSR applications, and a novel estimator for conventional SSR is described. The proposed technique is a close approximation of the maximum-likelihood estimator (MLE), taking into account the receiver characteristics as well as the missed replies. Estimator performance obtained by analysis and computer simulation is compared with that of conventional estimators that are based on the leading and trailing edges of binary sequences and shows significantly improved accuracy     

发动机电调控制技术在直升机上的应用

本文介绍了 PT6B-67A 发动机电调控制系统的主要功能,根据 PT6B-67A 发动机电调控制系统的工作原理,简述发动机电调控制技术在直8F 型机上的具体应用。     

Comparison of motion and stereo methods in passive ranging systems

The authors compare the estimates in passive ranging systems using motion and stereo approaches. It is shown that an integrated approach is necessary to provide better range estimates over a field-of-view (FOV) of interest in helicopter flight. The recursive approach for processing a sequence of stereo images, described together with a recursive motion algorithm (RMA), provides the basis for an integrated method to provide more accurate range information. Results based on motion sequences of stereo images are presented     

NF-6风洞喷液氮降温系统研制

通过降低试验气体温度来进一步提高NF 6增压连续式跨声速风洞的雷诺数,采用喷液氮降温的方式成功实现了降温运行。结果表明:风洞气流总温达到-20℃,有效提高了试验雷诺数。所叙述的NF 6风洞喷液氮降温系统的设计指标、总体方案、系统组成、系统调试等,为国内连续式降温风洞的建设积累了经验。