摘要:

The mean electromagnetic fields are found in a layer of randomly oriented particles lying over a half space. A matrix‐dyadic formulation of Maxwell's equations is employed in conjunction with the Foldy‐Lax approximation to obtain equations for the mean fields. A two variable perturbation procedure, valid in the limit of small fractional volume, is then used to derive uncoupled equations for the slowly varying amplitudes of the mean wave. These equations are solved to obtain explicit expressions for the mean electromagnetic fields in the slab region in the general case of arbitrarily oriented particles and arbitrary polarization of the incident radiation. The results include special cases previously treated in the literature on propagation through the atmosphere. Numerical examples are given for the application to remote sensing of vegetat

ISSN:0048-6604    

DOI:10.1029/RS021i005p00771

年代:1986

数据来源: WILEY

摘要:

The effect of an intervening layer on a lateral wave which propagates along the interface between two different electrical media is considered. The lateral wave travels down from a time‐harmonic electric dipole source in the upper region, through the middle region, and parallel to the interface between the middle and lower regions. It is assumed that the magnitude of the wavenumber in the upper medium is much greater than that of the middle, which in turn is much greater than that of the lower. The middle layer affects the lateral wave in two ways. It multiplies the usual lateral wave results by an overall factor which depends on the thickness of the slab and the electrical properties of the three media. It also changes at what distance the transition from intermediate to far field behavior occurs. Typically, the presence of the slab increases the magnitude of the fields near the transmitter, but leads to smaller field strengths in the far field region. The formulas are derived in two ways. The first utilizes an iterative procedure based on impedance boundary conditions and boundary layer theory. The second uses the more traditional steepest descent evaluation of the exact integrals available for the proble

ISSN:0048-6604    

DOI:10.1029/RS021i005p00787

年代:1986

数据来源: WILEY

摘要:

A theoretical analysis of the radiation characteristics of the transverse electromagnetic mode linearly tapered slot antenna is presented. The theory presented is valid for antennas with air dielectric and forms the basis for analysis of the more popular dielectric‐supported antennas. The method of analysis involves two steps. In the first step, the aperture distribution in the flared slot is determined. In the second step, the equivalent magnetic current in the slot is treated as radiating in the presence of a conducting half‐plane, and the far‐field components are obtained. Detailed comparison with experiment is made and excellent agreement is obtained. Design curves for the variation of the 3‐dB and 10‐dB beamwidths as a function of the antenna length, with the flare angle as a parameter, are

ISSN:0048-6604    

DOI:10.1029/RS021i005p00797

年代:1986

数据来源: WILEY

摘要:

The intensity cross‐spectrum (spatial Fourier transform of the two‐frequency intensity correlation) for scintillations caused by a plane wave passing through a random phase screen is considered. Two series solutions (one valid for low and the other for high spatial frequencies) are obtained which are the generalizations of previous results for the monochromatic intensity spectrum. We show that the Gaussian‐field approximation (modeling the cross‐spectrum as the transform of the square of the second moment) breaks down when the outer scale is large compared with the diameter of the scatteri

ISSN:0048-6604    

DOI:10.1029/RS021i005p00805

年代:1986

数据来源: WILEY

摘要:

The low‐contrast or (first‐order) Born approximation is applied to the time domain scattering of a plane electromagnetic wave by a penetrable object of bounded extent, embedded in an isotropic and homogeneous medium. Closed‐form analytic expressions are obtained for the spherical wave far‐field scattering amplitude related to homogeneous objects of the following shapes: an ellipsoid, an elliptic cone of finite height, an elliptic cylinder of finite height, and a tetrahedron. Relaxation effects and anisotropy of the scattering object are included. The results are, among others, useful as test cases for time domain inverse scattering alg

ISSN:0048-6604    

DOI:10.1029/RS021i005p00815

年代:1986

数据来源: WILEY

摘要:

Integral equations are derived for the coherent field and for the field autocorrelation in the very general case of electromagnetic wave propagation in a medium of densely packed nontenuous particle scatterers. All orders of Ntuple particle correlations are included. The resulting equations are a generalization of those derived recently by Tsolakis et al. (1985); the four lowest‐order terms of each equation include those of the earlier work which only incorporate two‐particle correlati

ISSN:0048-6604    

DOI:10.1029/RS021i005p00823

年代:1986

数据来源: WILEY

摘要:

A specific physical interpretation of the effect of relative permittivities εrand conductivities σ upon the amplitude and phase of propagating electromagnetic surface waves is given, where ϵr and σ characterize the layered material regions of a planetary lithosphere. The interpretation is made possible by the availability of simple formulas for the fields of vertical and horizontal unit electric dipoles near interfaces between regions of matter; the earth's lithosphere at its interface with salt water is used as an example. The ranges of εr, σ, frequency ƒ, and radial distance ρ over which the formulas apply are shown to be quite broad. The E1ρcomponent (the radial electric field in region 1, characterized by complex wave number K1and adjoined at a planar interface to region 2, characterized by k2, where |k1|2» |k1|2) is discussed in detail. The attenuation of 20 log10|E1ρ| as a function of ρ and ρ/δ2, Where δ is the skin depth, is illustrated for conductivity ratios σ2/σ1= 10−1to 10−3, over a range of ƒ from 1 Hz to 105Hz. |E1ρ| is shown to be significant for determining permittivities ε2at the higher frequencies in this range. The use of |E1ρ| to infer conductivities σ2at lower frequencies in shallow sounding of the earth's sea floor is discussed in terms of specific lithological and sediment‐related parameters. The technology required to transmit and receive 20 log10|E1ρ| at freshwater and saltwater interfaces with the earth's crust is addressed. A specific experiment is proposed for testing a specialized insulated antenna for seafloor use in sha

ISSN:0048-6604    

DOI:10.1029/RS021i005p00831

年代:1986

数据来源: WILEY

摘要:

Measurements of the normalized radar cross section (NRCS) at 5.3 GHz (C band) of the sea surface as a function of wind speed and direction are presented. The data were obtained by a coherent scatterometer mounted on a small two‐engine airplane performing circle flights over the Atlantic. Our data show that the wind speed exponent at 5.3 GHz is typically 20% smaller than at 13.9 GHz (Kuband). Furthermore, the upwind/crosswind ratio of the NRCSs at C band is typically 20% smaller, and the upwind/downwind ratio typically 30% smaller than atKuban

ISSN:0048-6604    

DOI:10.1029/RS021i005p00845

年代:1986

数据来源: WILEY

摘要:

Errors in direction finding due to nonvertical channel sections over finitely conducting ground have been investigated. The results show that if the direction of the lightning flash is estimated from the initial peak of the magnetic radiation field then, for the conductivity of the ground in the range of 0.01 mho/m to 0.001 mho/m, the propergation errors caused by the inclination of the channel at distances of about 10 km or more would be less than about 1°

ISSN:0048-6604    

DOI:10.1029/RS021i005p00857

年代:1986

数据来源: WILEY

摘要:

The quality of radio astronomical images made with an antenna array depends upon atmospheric behavior. As baselines and frequencies increase, phase variations become increasingly erratic. The phase fluctuations are time dependent and we found them to be correlated in time order in each baseline. We can represent these correlations by stochastic models. Models obtained by the Box‐Jenkins method are referred to as autoregressive integrated moving average processes (ARIMA). ARIMA models of VLA phase provide good short‐term predictions that may be useful for improving present calibration techniques. ARIMA models of VLA phase are data dependent and can be used in a variety of situations. A technique that works in all cases can be programmed into a software package such that modeling can be accomplished with no operator interactions. Another important application of ARIMA models involves the use of Kalman filtering to reduce the atmospheric effects when self‐calibration does not work well. The performance of the Kalman filter critically depends upon the models of the processes. An ARIMA model of the phase fluctuation can be represented in a state space form as noise in the Kalman filter equa

ISSN:0048-6604    

DOI:10.1029/RS021i005p00863

年代:1986

数据来源: WILEY