Leading Edge Estimation Errors

The leading edge estimator (LEE) of a pulse signal is defined as the instant at which a filtered version of the received noisy signal passes a preset threshold. A rigorous analysis for a rectangular pulse model of the signal results in an exact probability density function for the LEE, valid within the time interval of the leading edge of the filtered pulse. Possible occurrence of the threshold crossing outside of this interval is considered to be an anomalous estimate, since it leads to a gross error in comparison with the regular cases. It is found that the density function of the LEE error is asymmetrical and therefore biased, that the probability PA of anomalous estimation increases with the filter bandwidth, thus setting a well definable limit to the latter and that, for prespecified PA, the minimum bias and variance are proportional, respectively, to R-1 and R-2, minima being obtained by allowing for the largest bandwidth compatible with PA. On the other hand, for given bandwidth the variance decreases only as R-1. Here R is the signal-to-noise energy ratio. Results are presented in form of parameterized graphs.     

Cross Sections and Radar Equation for Nonlinear Scatterers

The nonlinear system concepts of nonlinear transfer functions are extended to nonlinear cross sections which may be used to quantitatively describe the characteristics of a nonlinear scatter. The concept of nonlinear cross sections is used to generalize the radar equation for nonlinear scattering objects.     

Radar Performance Review in Clear and Jamming Environments

The performance of electronically scanned radar systems is evaluated for clear and barrage jamming environments. Radar figures of merit in jamming are derived for search and track modes and are directly related to antenna pattern relative sidelobe levels. A random sidelobe model is analyzed with various numbers of independent jammers. Probability distributions of detection probability are derived to determine detection performance versus average jamming level and number of jammers.     

The transient highly excited solar flare plasma

Recent observations of the energetic particles produced in solar flares indicate that the production of electrons, with energies up to about 100 keV, is a fairly common feature of small flares. In those flares the acceleration of protons and other nuclei does not extend beyond about 1 MeV.The X-ray emission often exhibits two distinct components of which the first one is produced by non-thermal, the second by thermal electrons through bremsstrahlung collisions with the ambient ions. Along with these X rays, radio emission, in the microwave region, is observed. This radio emission is usually interpreted as due to gyrosynchrotron radiation from the same electrons.In this review a discussion is presented of the processes occurring in solar flares with special reference to the acceleration and radiation processes.     

Effect of Observation Errors on Satellite Attitude Estimation

A study of the effect of observation errors on the best least squares estimate of satellite attitude based on two sets of direction measurements, where one set contains two independent measurements which are corrupted by zero-mean normally distributed additive errors, is summarized. Using Monte-Carlo techniques, the statistics of the estimated rotation of the satellite, from a known reference, were obtained. It was found that one of the parameterizations of the rotation, namely, the vector z, is best suited for estimation, since ?z is normally distributed with zero mean and its standard deviation is independent of the two direction measurements.     

A Test of the Effect of Satellite Spin on Two-Way Doppler Range-Rate Measurements

Analysis indicates that the rotation of a satellite can cause an error in the range-rate measurements of a two-way Doppler tracking system. The error is proportional to the rotation rate, and the constant of proportionality depends on the polarization of the satellite transponder antennas. Measurements made by ground-based simulation confirmed the analytical prediction.     

Tracking of DABS-Equipped Aircraft

The Discrete Address Beacon System (DABS) is scheduled to replace the Air Traffic Control Beacon System (ATCRBS) as the prime sensing tool for air traffic control in the 1980's. The design of DABS requires knowledge of the tracking accuracy obtainable as a function of various system parameters. In particular, the potential value of air-to-ground telemetry of turn-rate data and its effect on intermittent positive control (IPC) must be assessed. The design of DABS tracking algorithms is discussed, and the results obtained with a Kalman tracker simulation are given. The major finding is that turn-rate telemetry of moderate accuracy can improve tracking by a factor of 6 to 10.     

Landmark Navigation Rule, a New Navigation Device

Two new methods of landmark navigation were recently presented. The landmarks are assumed to be within sight of the navigator but with unknown positions. Both methods require computations which are time consuming when a computer is not available. This correspondence presents the concept of a new navigation device called ?landmark navigation rule? which eliminates all the computation effort required in both new methods. The device is simple in construction, lightweight, and consumes no power.     

National and Regional Grids

The title of this paper provides a point of departure for the broadest possible discussion of electric power transmission and presents an opportunity to comment on some misconceptions regarding power systems. The subject of transmission is discussed in terms of 1) the grid concept, 2) its system function, and 3) its probable future development and some of the problems facing such development.