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911.
Flight path estimation using frequency measurements from a wideaperture acoustic array 总被引:1,自引:0,他引:1
A narrowband technique based on the acoustical Doppler effect is proposed for estimating the trajectory of a turbo-prop aircraft in level flight with constant velocity as it transits over a ground-based passive acoustic sensor array. The basic principle is to measure the temporal variation of the instantaneous frequency (IF) of the acoustic signal received by each sensor and then to minimize the sum of the squared deviations of the IF estimates from their predicted values over a sufficiently long period of time for all sensors. The technique provides estimates of the propeller blade rate and the five source motion parameters that describe the aircraft trajectory. The six dimensional minimization problem is reduced to a five dimensional maximization problem, which is solved numerically using the quasi-Newton method. A simple method is described that provides the initial parameter estimates required for the numerical maximization. The effectiveness of the motion parameter estimation technique is verified using real acoustic data recorded from a wide aperture microphone array during various transits of a turbo-prop aircraft 相似文献
912.
R. W. Schunk T. -Z. Ma 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(12):107-110
The field-aligned expansion of plasma clouds in the ionosphere was studied with different mathematical models and for a wide range of conditions. In all cases, the expanding plasma cloud acted as an electrostatic snowplow, creating an O+ hole in the ionosphere coincident with the cloud and O+ bumps on the two sides of the cloud that are aligned with the geomagnetic field. 相似文献
913.
It is argued that human factors professionals in large R&D organizations should have a centralized human factors group (or department) with a manager sensitive to human factors organizational issues. This arrangement permits these professionals to maximize their contributions to the design, development, and testing of a product or service. Managers of human factors groups and departments can help educated project managers about the value of human factors. Human factors groups, departments, and managers provide benefits to the company by resolving project conflicts concerning user-oriented designs. They help foster a sense of a behavioral sciences community within the R&D organization and aid in recruiting job candidates. They are good for the product or service, the company, and the human factors profession 相似文献
914.
McCormick W.S. Miller D.E. Tsui J.B.Y. 《IEEE transactions on aerospace and electronic systems》1995,31(1):2-8
An algorithm is proposed to resolve a fundamental 2π ambiguity problem occurring in multiple frequency spectral estimation. Given M frequencies fm, and I separate frequency estimators with unambiguous bandwidths Fi, the ambiguity problem can be stated as solving for the fm, given the estimator outputs, αmi, (1⩽m⩽M;1⩽i⩽I) where fm=αmi+KmiFi and Kmi is some integer. The proposed algorithm exhaustively resolves all possible αmi groupings into single frequency values using a noise insensitive technique that exchanges system bandwidth for noise protection. The correct multiple frequencies are then defined as the single frequencies that repeat a specified number of times. A complete analysis is included 相似文献
915.
Thompson M.W. Ho-Shin Chang 《IEEE transactions on aerospace and electronic systems》1994,30(2):452-461
The discrete-time detection of a time-varying, additive signal in independent Laplace noise is considered. Previous efforts in this area have been restricted to the constant signal, and identically distributed noise case. Theoretical (closed form) expressions for the false alarm and detection probabilities are developed for both the Neyman-Pearson optimal detector and the classical matched filter detector. Comparisons between the two detectors are made which illustrate the effects of signal-to-noise power ratio and sample size for certain false alarm and detection probability constraints. In view of the fact that the optimal Laplace detector is not UMP, we also investigate the effect of signal amplitude mismatch 相似文献
916.
S. W. Falk 《Space Science Reviews》1980,27(3-4):545-553
917.
R.A. West C.W. Hord K.E. Simmons H. Hart L.W. Esposito A.L. Lane R.B. Pomphrey R.B. Morris M. Sato D. Coffeen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(3):45-48
The Voyager 2 photopolarimeter experiment observed the intensity and polarization of scattered sunlight from the atmospheres of Saturn and Titan in the near-UV at 2640 Å and in the near-IR at 7500 Å. Measurements of Saturn's limb brightening and polarization at several phase angles up to 70° indicate that a significant optical depth of UV absorbers are present in the top 100 mbar of Saturn's atmosphere in the Equatorial Zone and north polar region, and possibly at other latitudes as well. UV absorbers are prominent in polar regions, suggesting that charged particle precipitation from the magnetosphere may be important in their formation.The whole-body polarization of Titan is strongly positive in both the UV and near IR. If spherical particles are responsible for the polarization, no single size distribution or refractive index can account for the polarization at both wavelengths. The model atmosphere proposed by Tomasko and Smith [1], characterized by a gradient in particle size with altitude, seems capable of explaining the Voyager observations. If non-spherical particles predominate, the Voyager observations place important constraints on their scattering properties. 相似文献
918.
A.W. Wolfendale 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(4):23-29
An examination of the evidence favouring the detection of gamma rays from the irradiation of giant molecular clouds by cosmic rays is given. Data relevant to specific nearby clouds are studied in some detail and the evidence favouring some of the so-called gamma ray sources being due to the irradiation of these and more distant clouds is critically assessed. The need for enhancement of cosmic ray intensity in some clouds is discussed. The relevance of this work to interpretation of current and planned X-ray measurements as well as future gamma-ray space missions is discussed. 相似文献
919.
Resolution limits and corresponding optimum linear apertures are determined in the presence of phase errors. Let ?(t) be the phase aberration at position t across the aperture; it is assumed that the random process ? has a power law structure function, E{[(?(t)-?(?)]2}= c|t-?|n. Beam tilting caused by the phase error is "removed" (for each sample of ?), then resolution formulas are developed. An approximate analysis is obtained in closed form and yields an optimum resolution proportional to c1/n for O < n < 2. The exact analysis is given for Gaussian ?, and again the optimum resolution is proportional to c1/n. In applications n= 5/3 is of interest, and in the Gaussian case the best obtainable equivalent rectangle resolution is ? ?)/2? (0.975)c3/5 radians with a corresponding optimum linear aperture of 14c-3/5. When long exposures are considered, imaging without removing beam tilting is of interest, and resolution is degraded by a factor of about 2.5 for a linear aperture. Alternatively, in some applications optimum focus as well as beam tilt should be considered, in this case resolution is improved by a factor of about 1.4 (again for n= 5/3). Finally, joint (tilt corrected) optimization over aperture length and taper is treated; however, as one might expect, the use of taper offers negligible resolution improvement. 相似文献
920.
Albersheim's detection formula is extremely accurate over the usual range of parameters. It is much more convenient to use than lengthy computer programs, and it provides direct insight into tradeoffs in design. Quantitative information on the accuracy bounds of Albersheim's formula is given here. Other contributions made by Albersheim are discussed and some biographical information is provided. 相似文献