A technique for selecting a rational variant of a multifunctional aircraft system

A technique for selecting a rational variant of a multifunctional aircraft system using the analytic hierarchy process is proposed and a solution of a practical problem is presented.     

Refractive Errors in Angle-of-Elevation Measurements

It is shown that the errors associated with radio elevation measurements may be investigated systematically using a variational technique. The error occurring when spaced antennas are used is compared with that for a single directional antenna. Integral expressions are obtained for the refractive errors.     

Small-Scale Solar Magnetic Fields

As we resolve ever smaller structures in the solar atmosphere, it has become clear that magnetism is an important component of those small structures. Small-scale magnetism holds the key to many poorly understood facets of solar magnetism on all scales, such as the existence of a local dynamo, chromospheric heating, and flux emergence, to name a few. Here, we review our knowledge of small-scale photospheric fields, with particular emphasis on quiet-sun field, and discuss the implications of several results obtained recently using new instruments, as well as future prospects in this field of research.     

Computation of the circular error probability integral

The author describes a simplified derivation of the representation of the circular error probability (CEP) integral, which is the integral over a disk centered at the origin of a zero mean two-dimensional Gaussian random variable, as a one-dimensional integral. In addition, two series are presented which can be used to compute efficiently the CEP integral. The domain of applicability of the series and methods for acceleration of the convergence of these series are discussed. The integral occurs in the evaluation of communication and radar signals, and in other statistical applications.<>     

Near-surface stratigraphy in comets inferred from observation,laboratory studies,and modeling

A brief discussion is given of the physical processes that may lead to a differentiation of the nucleus of short period comets. It is concluded that samples from the near-surface layers of such comets may give us important information on the initial state of cometary organics and refractories. Cometary ices are more likely to be indicators of the recent evolution of the comet.     

Comparison of two theories of angle glint: polarization considerations

Angle glint can be explained as distortions in the radar echo signal phase front, or alternatively, deviations of the direction of power flow from the radial direction. Here we show that these two theories yield identical results when the polarization of the scattered waves and the receiving antenna are considered.     

Covariance matrix estimation for adaptive CFAR detection incompound-Gaussian clutter

We address the estimation of the structure of the covariance matrix and its application to adaptive radar detection of coherent pulse trains in clutter-dominated disturbance modeled as a compound-Gaussian process. For estimation purposes we resort to range cells in spatial proximity with that under test and assume that these cells, free of signal components, can be clustered into groups of data with one and the same value of the texture. We prove that, plugging the proposed estimator of the structure of the covariance matrix into a previously derived detector, based upon the generalized likelihood ratio test (GLRT), leads to an adaptive detector which ensures the constant false alarm rate (CFAR) property with respect to the clutter covariance matrix as well as the statistics of the texture. Finally, we show that this adaptive receiver has an acceptable loss with respect to its nonadaptive counterpart in cases of relevant interest for radar applications     

Autonomous fault-tolerant attitude reference system using DTGs insymmetrically skewed configuration

A novel symmetrically skewed configuration for an attitude reference system (ARS) using three dynamically tuned gyros (DTGs) is developed. Simple schemes for autonomous detection and identification of a faulty DTG in real time and subsequent reconfiguration of the attitude estimation algorithm are proposed. The performance of the present configuration is shown to be better than that of configurations proposed earlier, and it is shown to have better features. It tolerates all types of failures of DTG failures, requires very simple computations, and gives less error in attitude estimate than the other configurations     

Forward error correction for radiobeacon broadcast of differentialGPS data

Marine radiobeacon networks are being used to broadcast differential Global Positioning System (DGPS) corrections to marine users. The correction data digitally modulate signals from some of the existing marine radiobeacons, which operate in the 285 to 325 kHz band, creating DGPS/radiobeacons. The corrections improve the accuracy of the GPS fix from 100 m to 5-10 m, and provide position fixing service for many marine applications which are too demanding for the normal GPS service. Forward error correction can be used to improve the reliability or range of the DGPS/radiobeacon signal. The improvements made possible by channel coding are analyzed, and a code for DGPS/radiobeacons is recommended     

Multiparametric importance sampling for simulation of radar systems

The performances of the importance sampling (IS) techniques are improved by using multiparametric distortions of the input random processes. The analysis of different constant false-alarm rate (CFAR) algorithms confirms the usefulness of this method. The potential of this new approach is fully exploited if optimization techniques are used to obtain the optimum distortions and to avoid bias in the estimates