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111.
An experimental program is described that had the objective of measuring the effects of the time-dependent structure of downlink (air craft to ground) interference generated by the Air Traffic Control Radar Beacon System (ATCRBS) in an active air traffic terminal area that are relevant to system and ground controller response time. The results of this program indicate a number of interesting details concerning the correlation of the level of the downlink interference with changes in the arrival and departure rates of aircraft at the local terminal sites. 相似文献
112.
113.
Adaptive cancellation method for geometry-induced nonstationary bistatic clutter environments 总被引:4,自引:0,他引:4
This paper describes and characterizes a new bistatic space-time adaptive processing (STAP) clutter mitigation method. The approach involves estimating and compensating aspects of the spatially varying bistatic clutter response in both angle and Doppler prior to adaptive clutter suppression. An important feature of the proposed method is its ability to extract requisite implementation information from the data itself, rather than rely on ancillary - and possibly erroneous or missing - system measurements. We justify the essence of the proposed method by showing its ability to align the dominant clutter subspaces of each range realization relative to a suitably chosen reference point as a means of homogenizing the space-time data set. Moreover, we numerically characterize performance using synthetic bistatic clutter data. For the examples considered herein, the proposed bistatic STAP method leads to maximum performance improvements between 17.25 dB and 20.75 dB relative to traditional STAP application, with average improvements of 6 dB to 10 dB. 相似文献
114.
Carlson B.D. Evans E.D. Wilson S.L. 《IEEE transactions on aerospace and electronic systems》1994,30(1):109-115
For pt.I see ibid., vol.30, no.1, (Jan.1994). This paper describes the calculation of PF and PD for the Hough transform technique when the primary threshold crossings are weighted by their power before transforming (i.e., noncoherent integration). After expressions for PF and PD are derived, we examine the question of optimal granularity of the Hough accumulator space. We also investigate the relationship between primary and secondary thresholds and its effect on detectability 相似文献
115.
The continued development of the symmetric measurement equation (SME) filter for track maintenance in multiple target tracking (MTT) is considered, focusing on the case in which the SMEs are generated by forming sums of products of the original position measurements. The SME filter is developed for the case of N targets whose motions consist of random perturbations about constant-velocity trajectories. It is assumed that measurements of x -coordinate positions are available, and that the number of measurements is equal to the number of targets. Various analytical properties of the SME filter are studied. It is shown that under a very weak condition, the estimation error equation is locally exponentially stable. The performance of the SME filter is investigated by comparing it with an optimal (minimum-variance) estimator and by generating a computer simulation in the six-target case 相似文献
116.
Light scattering in planetary atmospheres 总被引:45,自引:0,他引:45
This paper reviews scattering theory required for analysis of light reflected by planetary atmospheres. Section 1 defines the radiative quantities which are observed. Section 2 demonstrates the dependence of single-scattered radiation on the physical properties of the scatterers. Section 3 describes several methods to compute the effects of multiple scattering on the reflected light. 相似文献
117.
This paper deals with the application of modern estimation techniques to the problem of speech data rate reduction. It is desirable to adaptively identify and quantitize the parameters of the speech model. These paramaters cannot be identified and quantized exactly; the performance of the predictor is thereby degraded and this could prevent data reduction. In many cases it is desirable to emply a suboptimal predictor in order to simplify the algorithms, and predictor performance is again degraded. This paper develops sensitivity and error analysis as a potential method for determining quantitatively how speech data reduction system performance is degraded by imprecise parameter knowledge or suboptimal filtering. An intended use of the sensitivity and error analysis algorithms is to determine parameter identification and model structure requirements of configuration concepts for adaptive speech digitizers. First, sensitivity and error analysis algorithms are presented that form the basis for the remainder of the work. The algorithms are then used to determine how imprecise knowledge of vocal tract parameters degrades predictor performance in speech. Transversal filters have previously been proposed for this application. The sensitivity analysis algorithms are then used to determine when and by how much the transverse filter is suboptimal to the Kalman filter. In particular, the question of how effectively a higher order of all-pole model approximates a system with zeros is answered, as this question is of considerable importance in speech. Finally, the physical significance of the innovations process in speech data rate reduction is studied. 相似文献
118.
119.
The modulation of galactic cosmic rays in the heliosphere seems to be dominated by four major mechanisms: convection, diffusion,
drifts (gradient, curvature and current sheet), and adiabatic energy losses. In this regard the global structure of the solar
wind, the heliospheric magnetic field (HMF), the current sheet (HCS), and that of the heliosphere itself play major roles.
Individually, the four mechanisms are well understood, but in combination, the complexity increases significantly especially
their evolvement with time - as a function of solar activity. The Ulysses observations contributed significantly during the past solar minimum modulation period to establish the relative importance
of these major mechanisms, leading to renewed interest in developing more sophisticated numerical models, and in the underlying
physics, e.g., what determines the diffusion tensor. With increased solar activity, the relative contributions of the mentioned
mechanisms change, but how they change and what causes these changes over an 11-year solar cycle is not well understood. It
can therefore be expected that present and forthcoming observations during solar maximum activity will again produce very
important insights into the causes of long-term modulation. In this paper the basic theory of solar modulation is reviewed
for galactic cosmic rays. The influence of the Ulysses observations on the development of the basic theory and numerical models are discussed, especially those that have challenged
the theory and models. Model-based predictions are shown for what might be encountered during the next solar minimum. Lastly,
modulation theory and modelling are discussed for periods of maximum solar activity when a global reorganization of the HMF,
and the HCS, occurs.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
120.
F.B. Rizzato A.C.-L. Chian M.V. Alves R. Erichsen S.R. Lopes G.I. de Oliveira R. Pakter E.L. Rempel 《Space Science Reviews》2003,107(1-2):507-514
Langmuir waves and turbulence resulting from an electron beam-plasma instability play a fundamental role in the generation
of solar radio bursts. We report recent theoretical advances in nonlinear dynamics of Langmuir waves. First, starting from
the generalized Zakharov equations, we study the parametric excitation of solar radio bursts at the fundamental plasma frequency
driven by a pair of oppositely propagating Langmuir waves with different wave amplitudes. Next, we briefly discuss the emergence
of chaos in the Zakharov equations. We point out that chaos can lead to turbulence in the source regions of solar radio emissions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献