The Generation of Correlated Weibull Clutter for Signal Detection Problems

A method is discussed for generating Weibull vectors with a desired correlation matrix and specified parameters. Such vectors may represent samples of a correlated clutter signal. The presented method makes use of a suitable nonlinear transformation of random Gaussian vectors with correlated components. Computational aspects of the method are also discussed.     

Some Comments on the Dynamics of Urban Structural Development

The suggestion is made that the aerospace industry examine the dynamics of urban structural development, that it identify the forces which act on the elements comprising the structure of the city, and that it describe the relationship between and the relative movements of those elements. By formulating such a general theory of urban structural development, urban political, social, and economic leadership may be given the means by which permanent remedies?including technological?may be devised and applied. This paper presents examples of such means and explains their application and effects.     

One-kVA, Three-Phase dc-ac Inverter with Digital Control

This paper describes a method of applying digital techniques to the control of a 1-kVA three-phase dc-ac inverter to generate a sinusoidal 400-Hz output, using high-frequency bridge-chopper techniques. The model which was constructed used predominantly off-theshelf digital microcircuits and resulted in a device with an overall efficiency of 85 percent, in a 0.52 cubic-foot package which weighed 19.5 lbs. Sinusoidal output with less than 2 percent harmonic distortion at 115 volts line to neutral was obtained with 28 volts dc input.     

A Performance Measure for Evaluating Aircraft Landing Trajectories

A general performance index is developed for evaluating aircraft landing trajectories. The primary term in the index is the effect of noise on people residing near the air terminal. Other terms included are passenger comfort, fuel consumed, and the time spent in the near-terminal area. Models are developed for aircraft engine noise, passenger comfort, the population distribution about a specific airport, and the aircraft flight behavior. While this performance index may be used in computing optimal trajectories, it is also useful for comparing nonoptimal trajectories which, for one reason or another, may be worthy of consideration. Some examples of such comparisons are included through simulations of landing. The aircraft considered is a Boeing 737.     

The Electric Antennas for the STEREO/WAVES Experiment

The STEREO/WAVES experiment is designed to measure the electric component of radio emission from interplanetary radio bursts and in situ plasma waves and fluctuations in the solar wind. Interplanetary radio bursts are generated from electron beams at interplanetary shocks and solar flares and are observed from near the Sun to 1 AU, corresponding to frequencies of approximately 16 MHz to 10 kHz. In situ plasma waves occur in a range of wavelengths larger than the Debye length in the solar wind plasma λ _D ≈10 m and appear Doppler-shifted into the frequency regime down to a fraction of a Hertz. These phenomena are measured by STEREO/WAVES with a set of three orthogonal electric monopole antennas. This paper describes the electrical and mechanical design of the antenna system and discusses efforts to model the antenna pattern and response and methods for in-flight calibration.     

Influence of fuel hydrogen additives on the characteristics of a gas-piston engine under changes of an ignition advance angle

We present the results of experimental studies of the fuel hydrogen additive influence on the characteristics of a gas-piston engine converted for operation by natural gas under changes of an ignition advance angle (IAA). The results of investigations were used to determine the influence of the hydrogen additive on the effective engine efficiency and fuel consumption under IAA changes.     

Solar Sources of Heliospheric Energetic Electron Events—Shocks or Flares?

Electrons with near-relativistic (E≳30 keV, NrR) and relativistic (E≳0.3 MeV) energies are often observed as discrete events in the inner heliosphere following solar transient activity. Several acceleration mechanisms have been proposed for the production of those electrons. One candidate is acceleration at MHD shocks driven by coronal mass ejections (CMEs) with speeds ≳1000 km s⁻¹. Many NrR electron events are temporally associated only with flares while others are associated with flares as well as with CMEs or with radio type II shock waves. Since CME onsets and associated flares are roughly simultaneous, distinguishing the sources of electron events is a serious challenge. On a phenomenological basis two classes of solar electron events were known several decades ago, but recent observations have presented a more complex picture. We review early and recent observational results to deduce different electron event classes and their viable acceleration mechanisms, defined broadly as shocks versus flares. The NrR and relativistic electrons are treated separately. Topics covered are: solar electron injection delays from flare impulsive phases; comparisons of electron intensities and spectra with flares, CMEs and accompanying solar energetic proton (SEP) events; multiple spacecraft observations; two-phase electron events; coronal flares; shock-associated (SA) events; electron spectral invariance; and solar electron intensity size distributions. This evidence suggests that CME-driven shocks are statistically the dominant acceleration mechanism of relativistic events, but most NrR electron events result from flares. Determining the solar origin of a given NrR or relativistic electron event remains a difficult proposition, and suggestions for future work are given.     

Cross-correlation properties of algebraically constructed Costasarrays

The problem of determining the cross-correlation properties of signals based on algebraically constructed Costas arrays is addressed by examining the discrete cross-correlation of the algebraically constructed Costas arrays for a given construction and dimension. Finding two arrays that minimally correlate implies that the signals based on these arrays also minimally correlate. The properties of finite fields are reviewed, and the major algebraic constructions for Costas arrays are presented, i.e. the Welch construction and the Golomb construction. The discrete cross-correlation properties of the Costas arrays are derived for arrays of the same dimension derived from the same construction. The use of Costas arrays in the signal design problem is discussed, and examples are given to show the cross-correlation of the signals based on the algebraically constructed arrays     

Optimum gain control for A/D conversion using digitized I/Q data inquadrature sampling

Calculation of optimum gain for minimum distortion due to A/D (analog-to-digital) conversion requires the estimation of the input signal strength. To use a common AGC (automatic gain control) for both the I/Q (in-phase and quadrature) signals, it is efficient to estimate the input signal strength using the quantized A/D output from both channels. Assuming a Gaussian input, the relationship between σ of the input of the A/D converter and E(|x|+|y|) and E(max(|x|,|y|)+1/2 min (|x|,|y|)) for t quantized I/Q output x and y is derived. Numerical results obtained using the derived expression and the statistical data obtained through simulation show excellent agreement. It is concluded that, because of its simplicity, the cubic equation obtained by fitting the numerical results should be useful     

Beamspace ML bearing estimation incorporating low-angle geometry

A problem in low-angle radar tracking, namely, bearing estimation in the presence of a strong specular multipath component that arrives within the beamwidth of the direct path signal, is studied. Three-dimensional beamspace domain maximum likelihood (3D-BDML) is a computationally simple ML bearing estimation algorithm applicable in this scenario which operates in a 3-D beamspace. A variation of 3D-BDML incorporating the multipath geometry as a priori information is presented. In symmetric 3D-BDML the pointing angle of the center beam is equal to the bisector angle between the direct path ray and the image ray, which may be estimated a priori given only the radar height and the target range. The effect of the inclusion of a priori information on the performance of 3D-BDML is analyzed in terms of the dependence on the relative phase difference between the direct and specular path signals, the sensitivity to error in the bisector angle estimate, and the results of operation when no specular multipath component is present in the data. In addition, computationally simple schemes for coherently incorporating multifrequency data into 3D-BDML are investigated