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141.
A general method of continually restructuring an optimum Bayes-Kalman tracking filter is proposed by conceptualizing a growing tree of filters to maintain optimality on a target exhibiting maneuver variables. This tree concept is then constrained from growth by quantizing the continuously sensed maneuver variables and restricting these to a small value from which an average maneuver is calculated. Kalman filters are calculated and carried in parallel for each quantized variable. This constrained tree of several parallel Kalman filters demands only modest om; puter time, yet provides very good performance. This concept is implemented for a Doppler tracking system and the performance is compared to an extended Kalman filter. Simulation results are presented which show dramatic tracking improvement when using the adaptive tracking filter. 相似文献
142.
A model of a distributed target as a collection of independent, Poisson distributed point scatterers or scattering centers in a range-velocity target space is introduced and is characterized by a deterministic function called the ?scatterer density function.? This function is the density of the point scatterers in the range-velocity space and can be estimated in a relatively straightforward manner by any radar having adequate resolution in both range and velocity and no ambiguities in the region occupied by the distributed target. The use of the random signal radar with a correlator receiver is considered here and the statistical properties of the correlator output, when the return signal is from a distributed target, are derived. It is shown that the spectral density is simply related to the scatterer density function. The technique is illustrated by an example in which the target is a tornado modeled as a cylinder with constant angular velocity. The example suggests that is a possible to remotely estimate the radar cross section per unit volume as a function of distance from the center of the tornado. 相似文献
143.
Hopper D.J. Andryczyk R.W. 《IEEE transactions on aerospace and electronic systems》1971,(6):1147-1150
The design concept for the traveling wave tube amplifier converter for possible use in the Thermoelectric Outer Planet Spacecraft (TOPS) is presented. An unusual combination of semiconductors and magnetics were utilized to achieve very stable voltage regulation on a number of separate outputs to satisfy the requirements of a high-power traveling wave tube (TWT), and at the same time operate at an efficiency of better than 90 percent from a 30-volt source. The circuitry consists of an output filter, an auxiliary Jensen oscillator driving a high-reactance transformer to provide current limiting to the heater, a variable time delay, a main Jensen oscillator driving the power transformer with a maximum step-up ratio of 120 to 1, and series transistorized post regulators to provide precise voltage adjustment and low output impedance. This paper discusses the design of the high-reactance transformer and the high step-up ratio transformer, as well as the high-voltage series regulators that are limited in range and operate at the top of the unregulated output voltage. Test data is presented, and details of current transients caused by charging the filter circuits, input current ripple, and output voltage ripples are considered. The circuit provides better than 0.5 percent regulation against load change, input voltage change, and over-operating temperature range of from -20 to + 80°C, with output ripple voltage of less than 2 volts peak-to-peak on top of the 3600-Vdc output. The measured efficiency was typically 87 percent. and recommendations are included to improve this to in excess of 90 percent. 相似文献
144.
145.
Moyer L.R. Morgan C.J. Rugger D.A. 《IEEE transactions on aerospace and electronic systems》1989,25(4):584-587
An exact expression for the bistatic resolution-cell area (A B) is developed for the special case in which either the transmit or receive antenna has a broad azimuth beamwidth or is omnidirectional. Quantitative examples are presented to illustrate the variation of A B with location. A comparison is made with the performance of a commonly used approximation formula 相似文献
146.
A brief summary of the main results of magnetospheric ion composition measurements in general is first presented. PROGNOZ-7 measurements in the nightside plasma mantle are then described and analyzed. Some of the results are the following: In the nightside mantle not too far from midnight the properties of the mantle are sometimes consistent with the open magnetosphere model. However during most magnetic storm situations O+ ions appear in the mantle in large proportions and with high energies. The acceleration process affecting the ions has been found in several cases to give equal amounts of energy to all ions independent of mass. Along the flanks of the magnetosphere the flow of the plasma is often low or absent. The O+ content is high (up to 20%) and the energy spectrum of both ions and electrons may be very hot, even up to the level of the ring current plasma in the keV range.The O+ content in the plasma mantle is positively correlated with the magnetospheric activity level. The mantle, however, does not appear to be the dominating source for the storm time ring current. Direct acceleration of ionospheric ions onto the closed field lines of the plasma sheet and ring current is most likely the main source. The magnetopause on the nightside and along the flanks of the magnetosphere appears to be a fairly solid boundary for mantle ions of ionospheric origin. This is especially evident during periods with high geomagnetic activity, when the mantle is associated with fairly strong fluxes of O+ ions.An interesting observation in most of the mantle passages during geomagnetically disturbed periods is the occurrence of intense, magnetosheath like, regions deep inside the mantle. In some cases these regions with strong antisunward flow and with predominant magnetosheath ion composition was observed in the innermost part of the mantle, i.e. marking a boundary region between the lobe and the mantle. These magnetosheath penetration events are usually associated with strong fluxes of accelerated ionospheric ions in nearby parts of the mantle. Evanescent penetration regions with much reduced flow properties are frequently observed in the flank mantle. 相似文献
147.
An improved moving target detector (MTD) (a digital signal processor) has been designed, constructed, and tested which successfully rejects all forms of radar clutter while providing reliable detection of all aircraft within the coverage of the radar. The MTD is being tested on both terminal and enroute surveillance radars for the FAA. This processor has been integrated with automatic tracking algorithms to give complete rejection of ground clutter, heavy precipitation, and angels (birds). 相似文献
148.
Magnetic Position and Orientation Tracking System 总被引:3,自引:0,他引:3
Raab F.H. Blood E.B. Steiner T.O. Jones H.R. 《IEEE transactions on aerospace and electronic systems》1979,(5):709-718
Three-axis generation and sensing of quasi-static magneticdipole fields provide information sufficient to determine both the position and orientation of the sensor relative to the source. Linear rotation transformations based upon the previous measurements are applied to both the source excitation and sensor output vectors, yielding quantities that are linearly propotional to small changes in the position and orientation. Changes are separated using linear combinations of sensor output vectors, transformed to the desired coordinate frame, and used to update the previous measurements. Practical considerations for a head-tracking application are discussed. 相似文献
149.
The archiitecture and justification for an approach to built-in testing (BIT) in electronic circuits and systems is presented. The proposed system is capable of on-line fault detection and prediction up to the shop replaceable assembly (SRA) level and is designed to interface with external automatic test equipment (ATE) for off-line fault diagnosis within the SRA. The constituent parts of the BIT system have been extensively simulated and the approach appears to be suitable for hardware implementation both with respect to computational and economic considerations. 相似文献
150.
George R. Carruthers 《Space Science Reviews》1970,10(4):459-482
This paper reviews the present state of knowledge of the abundances and physical state of interstellar atomic and molecular hydrogen. Much new data in this area have been obtained in recent rocket observations. There have also been new developments as a result of ground-based infrared and 21-cm observations, and theoretical research.Rocket observations of the Lyman- interstellar absorption line of atomic hydrogen indicate that, in many directions in the sky, atomic hydrogen is up to a factor of 10 less abundant than previously indicated by 21-cm emission measurements. In the direction of the Orion Nebula, most of the absorbing gas appears to be concentrated in the near vicinity of the nebula and to have a temperature considerably lower than the average of 100 K obtained from 21-cm emission measurements. Molecular hydrogen appears essentially absent from the general interstellar medium, as confirmed by theoretical studies of photodissociation processes. However, ground-based infrared and 21-cm studies indicate that the hydrogen in dark dust clouds is mostly molecular. 相似文献