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261.
262.
The performance of an adaptive moving target indicator (MTI), which employs a Wiener predictor by means of a transversal filter, is discussed, taking into consideration the effect of the form of the clutter covariance matrix on the MTI performance. It is emphasized that the main tap position in the transversal filter is an important factor which provides degrees of freedom in the clutter covariance matrix to improve the MTI performance. Calculation results show that by exploiting these degrees of freedom, excellent performance is feasible, in particular shorter transient response. 相似文献
263.
A Fast Beamforming Algorithm for Large Arrays 总被引:3,自引:0,他引:3
This beamforming algorithm is written specifically for array radars in which the number of array elements K is very large compared with the number of jammers L the radar is designed to suppress. It uses a set of M noise vectors to construct a basis for the jammer component of the antenna output vectors. The component of the quiescent weight vector orthogonal to each basis vector is calculated, renormalized to unit length, and identified as the adapted weight vector. This algorithm is effective in the suppression of many types of jammers. The number of noise samples M required in the construction of the adapted weight vector is approximately equal to L. In the special case of L narrowband noise jammers, for example, a choice of M = L usually reduces the receiver output jammer power to a few dBs above the white noise background. It is permissible to have M相似文献
264.
A brief analysis is made of the interrelation of the intensity of cosmic-ray particles, the column density of gas and the intensity of cosmic γ-rays. It is shown that, locally, γ-ray data enable the calibration of H2 densities to be inferred from CO data and elsewhere the variation of cosmic-ray intensity with position to be assessed. Finally, the importance of cosmic-ray irradiated molecular clouds in simulating γ-ray ‘sources’ is reiterated. 相似文献
265.
A new modeling procedure is presented in which a mathematical model for random gyro drift rate is obtained directly from the original observations without requiring any theoretical conjectures or preprocessing of the data. The adequate model so obtained confirms the presence of a random walk component causing the "steady state" drift and a stochastic component of the nature of correlated noise. It also provides a quantitative measure of the relative contribution of each component, useful in determining the quality of the gyro in guidance over extended periods. 相似文献
266.
A new methodology to scan automated radar terminal system (ARTS-III) data for aircraft tracks exhibiting probable mode-C encoder/transponder faults is described. The tracks of more than 8000 climbing or descending aircraft, recorded at the Seattle-Tacoma terminal area, were analyzed using this method. Based on this sample, the probability of the previously recognized "stuck C-bit" error is estimated to be 0.44 percent (0.31-0.61 percent, 95 percent confidence). In addition, a new, more subtle error, here termed the "deficient response," was discovered which is estimated to occur with a probability of 0.77 percent (0.59-0.98 percent, 95 percent confidence). Subsequent tests found this new error to have much less impact on traffic alert and collision avoidance system (TCAS) performance than does the stuck C-bit error. 相似文献
267.
Expressions for moving target indicator (MTI) improvement factor limitation due to pulse repetition frequency (PRF) staggering and loss of target detectability for various values of Doppler frequency in the passband are presented. It is also shown that the product of variance of stagger periods and clutter variance is an important parameter determining the performance of a staggered PRF MTI radar. 相似文献
268.
We present results derived from the analysis of an equatorial streamer structure as observed by the UVCS instrument aboard
SOHO. From observations of the H I Lyα and Lyβ lines we infer the density and temperature of the plasma. We develop a preliminary
axisymmetric, magnetostatic model of the corona which includes the effects of gas pressure gradients on the magnetic structure.
We infer a coronal plasma β > 1 in the closed field regions and near the cusp of the streamer. We add to the model a parallel
velocity field assuming mass flux conservation along magnetic flux tubes. We then compute the Lyα emissivity and the line-of-sight
integrals to obtain images of Lyα intensity, taking into account projection effects and Doppler dimming. The images we obtain
from this preliminary model are in good general agreement with the UVCS observations, both qualitatively and quantitatively.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
269.
A five-phase Power Management and Distribution System for a More-Electric Aircraft (MADMEL) program was awarded by the Air Force to Northrop/Grumman Military Aircraft Division in September 1991. The objective of the program is to design, develop, and demonstrate an advanced electrical power generation and distribution system for a More-Electric Aircraft (MEA). The MEA emphasizes the use of electrical power in place of hydraulics, pneumatic, and mechanical power to optimize the performance and life cycle cost of the aircraft. This paper presents an overview of the MADMEL program and a top-level summary of the program results, development and test of major components to date. In Phase I and Phase II studies, the electrical load requirements were established and the electrical power system architecture was defined for both near-term (NT-year 1996) and far-term (FT-year 2003) MEA application. The detailed design and specification for the Electrical Power System (EPS), its interface with the Vehicle Management System, and the test set-up were developed under Phase III. Phase IV, fabrication and testing of the subsystem level hardware, has been completed. Overall system level integration and testing, Phase V, is scheduled to be completed by September 1999 相似文献
270.
L. Ofman M. Romoli G. Noci G. Poletto J. L. Kohl R. A. Howard C. St. Cyr C. E. Deforest 《Space Science Reviews》1999,87(1-2):287-290
In recent UVCS/SOHO White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness
(pB) in the polar coronal holes at heliocentric distances of 1.9 to 2.45 solar radii. The motivation for the observation is
the 2.5D MHD model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes.
In February 1998 we performed new observations using the UVCS/WLC in the coronal hole and obtained additional data. The new
data corroborate our earlier findings with higher statistical significance. The new longer observations show that the power
spectrum peaks in the 10–12 minute range. These timescales agree with EIT observations of brightness fluctuations in polar
plumes. We performed preliminary LASCO/C2 observations in an effort to further establish the coronal origin of the fluctuations.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献