摘要:

A novel approach to wind profiling is presented which is based on the hybrid use of spatial interferometry (SI) and frequency domain interferometry (FDI). Many algorithms exist that can be used to determine the wind field using SI. However, the imaging Doppler interferometry (IDI) technique is somewhat unique in that the wind field within the radar beam is angularly “imaged” using the Doppler sorting effect. The spatial locations of scatterers are determined by assuming a wind field across the beam and Fourier analyzing signals to sort Doppler velocities. Pulsed radar systems are limited in range resolution by the length of the transmitted pulse, and wind estimates are obtained for a discrete set of altitudes determined by sampling the continuous stream of signals. Frequency domain interferometry (FDI) can be used to determine the radial location of scattering layers within the resolution volume. Thus the combined use of FDI and IDI can provide the radial and angular location of particular scattering points. Using the Doppler sorting idea, a new wind profiling technique is presented which uses FDI to increase the altitude resolution of wind estimates obtained from IDI. Experimental data that illustrate the implementation of the algorithm are presented from the Middle and Upper (MU) Atmosphere ra

ISSN:0048-6604    

DOI:10.1029/95RS02594

年代:1995

数据来源: WILEY

摘要:

Transient response from a cylinder with longitudinal slots is more complicated than that from a perfect cylinder because the electromagnetic waves are reflected from various parts of the slotted cylinder: exterior surfaces, interior surfaces, and edges. We gave the numerical analysis forE‐polarized andH‐polarized cases by combining the modified point matching method (MPMM) with the fast inversion of Laplace transform method (FILT). Numerical results for the inner field are presented and discussed. The physical meaning of the transient waveform is discussed in detail. Also, the precision of the analysis is checked carefu

ISSN:0048-6604    

DOI:10.1029/95RS02440

年代:1995

数据来源: WILEY

摘要:

The one‐dimensional transient problem of a wave incidence on a layer of inhomogeneous medium is considered. It is shown that a measurement of the internal fields allows one to reconstruct the permittivity profile in certain parts of the slab. Combining the embedding and differential run equations, we obtain the closed equations for the internal fields and construct the solution procedure for the inverse scattering problem. The generalization of the analytical solution of the inverse problem, for the case in which the time dependence of scattering field is exponential, is presente

ISSN:0048-6604    

DOI:10.1029/94RS03170

年代:1995

数据来源: WILEY

摘要:

By using two rotating noncollinear antennas or three spatially fixed noncoplanar antennas on a spacecraft, full information on the polarization and the direction of arrival of an electromagnetic wave can be obtained by measuring the voltages created by the electric field of the incident wave. The physical parameters (polarization and direction of arrival) of the incoming wave are related to the received voltages on the antenna system by the so‐called direction‐finding equations. Since the used antennas are generally of small directivity (electrically short monopoles or dipoles), the resulting system of equations is numerically close to singular, and generally no unique solution can be obtained for the physical parameters of the wave throughout the inversion process. However, there exists a very powerful tool for dealing with sets of equations that are singular or close to singular, known as singular‐value decomposition (SVD), which precisely focuses the problem. For illustration, this paper analyzes the direction‐finding equations for the Radio and Plasma Wave Science (RPWS) experiment on the Cassini spacecraft by using SVD techniques. It also compares the expected performances of RPWS with those of the Ulysses Unified Radio and Plasma Wave (URAP) experiment achieved at Jupiter for the kilometer and hectometer emissions. The RPWS experiment on Cassini, which will be launched in 1997, is supposed to observe wave phenomena between a few hundred Hertz and 16 MHz in the Saturnian magnet

ISSN:0048-6604    

DOI:10.1029/95RS02479

年代:1995

数据来源: WILEY

摘要:

Most electromagnetic problems can be reduced to either integrating oscillatory integrals or summing up complex series. However, limits of the integrals and the series usually extend to infinity, and, in addition, they may be slowly convergent. Therefore numerically efficient techniques for evaluating the integrals or for calculating the sum of an infinite series have to be used to make the numerical solution feasible and attractive. In the literature there are a wide range of applications of such methods to various EM problems. In this paper our main aim is to critically examine the popular series transformation (acceleration) methods which are used in electromagnetic problems and to introduce a new acceleration technique for integrals involving Bessel functions and sinusoidal functions.

ISSN:0048-6604    

DOI:10.1029/95RS02060

年代:1995

数据来源: WILEY

摘要:

The transient excitation of a straight thin wire segment parallel to a plane interface between two homogeneous dielectric half spaces is analyzed by the continuous‐time, discretized‐space approach. The analysis is carried out in three steps. First, the subproblem of a single wire embedded in a homogeneous dielectric medium, excited by a voltage source and an incident electric field, is studied with the aid of a time domain integral equation. This equation is discretized in space and transformed to the frequency domain. This procedure results in a system of linear equations of a fixed dimension which is solved by marching on in frequency. Second, the subproblem of a horizontal, pulsed dipole over the interface between two homogeneous dielectric half spaces is considered. The reflected field in the upper medium is computed by spectral techniques. With the aid of a time domain Weyl representation, a fixed, composite Gaussian quadrature rule is derived for the semi‐infinite integral involved. The angular integral is evaluated in closed form. Third, for the complete problem, the reflected field in the upper medium is expressed as a superposition of contributions from dipole sources on the wire axis, and subsequently treated as a secondary incident field in the integral equation for the current on the wire. This integral equation is then solved by combining the techniques developed for the two subproblems. Representative numerical results are presented and disc

ISSN:0048-6604    

DOI:10.1029/95RS02334

年代:1995

数据来源: WILEY

摘要:

In the model of a perfectly reflecting surface the inverse problem of restoring dynamic and statistical parameters of traveling ionospheric disturbances (TIDs) from variations of angles of arrival and Doppler frequency shift of HF radio signals on one‐hop oblique radio paths is solved. The technique for determining dispersion law, fluctuation spectrum, geometry, direction, and velocity of TID motion is describe

ISSN:0048-6604    

DOI:10.1029/95RS01992

年代:1995

数据来源: WILEY

摘要:

The resonant absorption of a short pulse of electromagnetic radiation in a plasma slab is considered in order to examine the effectiveness of using short pulses for information transfer through the plasma sheaths surrounding reentry vehicles. The amplitudes of the Raman scattering (RS) on the Langmuir oscillations associated with resonant absorption and the amplitude of the Brillouin scattering (BS) on the nonlinear modifications of the plasma profile are calculated. On‐board detection of the RS and BS signals are proposed as parallel and independent channels for reading the message encoded on the electromagnetic pulse sequence. The information transfer capacity of two other nonlinear effects, the generation of the fast electrons in the wave breaking process, and the excitation of the ion‐sound waves by the radiative pressure of the Langmuir oscillations are also conside

ISSN:0048-6604    

DOI:10.1029/95RS02190

年代:1995

数据来源: WILEY

摘要:

Temperature sensitivity is an important measure in the evaluation of radiometers. However, it is not directly determined by traditional methods of radiometer performance evaluation. Instead, beam efficiency is commonly evaluated to determine the accuracy of a radiometer antenna. This paper introduces a new parameter, the residue beam efficiency ratio, which relates directly to the relative error of temperature measurement and overcomes the inaccuracies and difficulties associated with beam efficiency. Also discussed is an optimization method which uses the minimum residue beam efficiency ratio to improve the temperature resolution and to reduce the antenna aperture diameter. Although the concept may be extended, the scope of this paper is limited to large‐reflector antennas for space‐based remote sensing of the Ea

ISSN:0048-6604    

DOI:10.1029/95RS01759

年代:1995

数据来源: WILEY

摘要:

The presence of derivatives of high order in generalized impedance boundary conditions (GIBCs) makes possible the simulation of point defects or point conductors placed on a surface. In case of the second‐order GIBC, the model of a point conductor is formulated via appropriate contact condition. For a plane boundary the problem of diffraction by a point defect is accurately solvable. A scattering diagram for an arbitrary point conductor is computed. The resulting formula depends on relative Wiener capacity, which is an integral characteristic of a two‐dimensional scatterer. The problem of diffraction by a periodic set of point conductors on a plane surface is solved in a closed f

ISSN:0048-6604    

DOI:10.1029/95RS01991

年代:1995

数据来源: WILEY