摘要:

The electric and magnetic currents induced by an incoming electromagnetic wave on a rough surface which separates free space from a lossy dielectric medium are calculated as expansions to first‐order in Wiener‐Hermite functionals. The diffuse scattered intensity resulting from this approach is compared with the classical results following from the use of perturbation theory or the Kirchhoff approximat

ISSN:0048-6604    

DOI:10.1029/RS025i001p00001

年代:1990

数据来源: WILEY

摘要:

At millimeter wave frequencies a typical leaf is a significant fraction of a wavelength in thickness, and its nonuniform dielectric profile now affects the scattering. To provide a simple and efficient method for predicting the scattering, two types of physical optics approximations are examined. The first approximates the volume polarization current by the current which would exist in an infinite dielectric slab with the same profile, while the second (and simpler) one employs the surface current which, on the infinite slab, produces the known reflected field. It is shown that the first method is superior, and, provided the actual dielectric profile is used, it predicts the scattered field to an accuracy which is adequate for most practical purposes.

ISSN:0048-6604    

DOI:10.1029/RS025i001p00009

年代:1990

数据来源: WILEY

摘要:

A theoretical study was made of the surface impedanceZfor an electromagnetic transverse magnetic wave from free space on a magnetized ferrite surface moving normal to the plane of incidence. It was found convenient to decompose the surface impedance into two transfer impedances,Z1andZ2, which relate the hybrid reflected amplitudes to the amplitude of the incident wave. The surface impedance does not vary much with respect to the angle of incidence, so only the case of normal incidence (θi= 0°) was evaluated. Resonant poles at ƒc, [ƒc(ƒc+ ƒm)]1/2, and ƒc+ ƒmdominate the frequency characteristics ofZ1andZ2. The frequencies ƒcandƒmare the precessional frequency and magnetization frequency, res

ISSN:0048-6604    

DOI:10.1029/RS025i001p00019

年代:1990

数据来源: WILEY

摘要:

Calculations of the input admittance of a thin cylindrical horizontal dipole antenna over a two‐layered lossy half‐space have been carried out. This has allowed an evaluation to be made of the sensitivity of admittance measurements to variations in the electrical characteristics of the Earth below a conducting overburden and hence to determine the potential of such measurements in geophysical surveying. The results show that maximum sensitivity to changes in the complex permittivity of the lower half‐space is obtained by the use of a band of frequencies about the first antenna resonance. The maximum depth of sensitivity of the observations was found to be approximately one quarter of the resonance wavelength or 8 m for an antenna of length 15 m, indicating that admittance measurements provide a potentially useful and simple geological surveying tech

ISSN:0048-6604    

DOI:10.1029/RS025i001p00027

年代:1990

数据来源: WILEY

摘要:

Available laboratory and field data on fine structures of the wind‐disturbed water surface are reviewed and analyzed to deduce the quantitative variation of directional mean square slopes with the wind condition. The mean square slope is associated with the wind‐friction velocity, with its maximum component in the upwind‐downwind direction and minimum component in the crosswind direction. Its angular distribution is suggested to follow an elliptical function. Spectral compositions of fine surface structures are estimated; in the field, gravity wave components contribute the most at low winds (U10<7 m s−1oru*<20 cm s−1) and capillary components at high winds; in laboratory tanks, gravity components are relatively much more important. These along with the other features are used to explain discrepancies between laboratory and field results as well as those within e

ISSN:0048-6604    

DOI:10.1029/RS025i001p00037

年代:1990

数据来源: WILEY

摘要:

The analysis of digital ionograms taken in short‐time intervals shows rapid changes of sporadicEparameters. This is directly visible in the variation of the top frequency or maximum electron density of such layers. Angle of arrival data which were available with those ionograms also showed fast changes of the apparent direction and often large deviations from vertical propagatio

ISSN:0048-6604    

DOI:10.1029/RS025i001p00049

年代:1990

数据来源: WILEY

摘要:

The interaction of electromagnetic radiation with a time‐switched magnetoplasma is considered. It is shown that for the case of the incident electric field normal to the static magnetic field, the original wave splits into four new extraordinary waves whose frequencies are different from the incident wave frequency. Two of these new waves are transmitted waves, and two are reflected waves. The characteristics of these waves (frequencies, power carried by them, and their damping rates) are discusse

ISSN:0048-6604    

DOI:10.1029/RS025i001p00061

年代:1990

数据来源: WILEY

摘要:

Daytime traveling ionospheric disturbances (TIDs) are studied with a close‐spaced triangulation network of rapid‐run ionosondes. Observations in November and March (1985–1986) found disturbances traveling only southward, with a clockwise progression during the day from southeastward to southwestward. Further observations in May and August (1987) found travel in all directions with no apparent order or progression. These observations are contrary to earlier results in May (1982), using a wider‐spaced network in northern New England together with a chain of single stations extending northward, in which source locations appeared to be bracketed between the northern stations with waves traveling northward as well as southward from those sources. These results suggest possible seasonal control but, at present, still leave as a quandary the question of what and where the sources are. With new digital equipment it is planned to obtain longer time series of observations and the vertical component of the propagation vector. With the latter and the horizontal component the vertical inclination of the phase fronts can be obtained and they in turn can be tracked backward to source regions at any given

ISSN:0048-6604    

DOI:10.1029/RS025i001p00073

年代:1990

数据来源: WILEY

ISSN:0048-6604    

DOI:10.1029/RS025i001p00085

年代:1990

数据来源: WILEY

ISSN:0048-6604    

DOI:10.1029/RS025i001p00089

年代:1990

数据来源: WILEY