摘要:

From 14 March through 9 April 1971, the New London Laboratory of the Naval Underwater Systems Center conducted a far‐field, extremely‐low‐frequency (ELF) attenuation‐constant measurement test. Two sites located along the same great‐circle path were utilized. One site (3.9 Mm) was in St. John Island, Virgin Islands; the other (1.7 Mm) was near Swansboro, North Carolina. The horizontal magnetic‐field strengths were measured at a band of frequencies centered at 45 Hz and at 75 Hz to determine the attenuation rates for daytime and nighttime propagation conditions. The EW antenna of the US Navy ELF Wisconsin Test Facility, Clam Lake, Wisconsin, was the transmission source. The principal results obtained from these measurements were that (a) the daytime attenuation rate is higher than the nighttime rate at both 45 and 75 Hz and (b) the ionospheric excitation factors are quite different for daytime and nighttime propagation conditions. A comparison of these results with the data taken previously and concurrently shows excellen

ISSN:0048-6604    

DOI:10.1029/RS008i007p00623

年代:1973

数据来源: WILEY

摘要:

Previous studies of range and angular errors caused by variation of atmospheric refractivity with altitude generally have used functional expressions, averaged data, or data from a small number of radiosonde ascents. In this investigation a large data base was employed consisting of radiosonde measurements made at intervals of about 2 hr for a period of 1 week. In the analysis it was assumed that the refractivity varied only as a function of altitude and that there was no ducting. Curves showing the deterioration of range correction with time for selected terminal points were developed by tracing rays at a succession of elevation angles. Thus, for a ground range of 416.7 km and an aircraft at 15.24 km, the standard deviation of the ground‐to‐plane radio distance 4 hr after a radiosonde ascent is .9 m, increasing to 1.3 m after 8 hr, and 1.6 m after 12

ISSN:0048-6604    

DOI:10.1029/RS008i007p00633

年代:1973

数据来源: WILEY

摘要:

The determination of theD‐region electron‐density profile may be obtained by the solution of an integral equation when the absorption at several frequencies is known. A new method based upon an iterative process is derived and is found to be more reliable than the previous meth

ISSN:0048-6604    

DOI:10.1029/RS008i007p00641

年代:1973

数据来源: WILEY

摘要:

Resonance conditions concerning the nonlinear interaction of acoustic gravity waves are considered. It is shown that a resonant trio of waves with nonzero frequencies can be found in situations in which viscous damping has to be taken into account.

ISSN:0048-6604    

DOI:10.1029/RS008i007p00651

年代:1973

数据来源: WILEY

摘要:

The interaction of an electromagnetic wave with a plane interface between a stationary isotropic medium (dielectric or vacuum) and a homogeneous cold magnetized plasma moving uniformly parallel to the interface is considered for arbitrary angles of incidence. Calculations are presented for the case in which the static magnetic field lies in the interface and is oriented normal to both the plane of incidence and the direction of the streaming motion. It is found that the reflection and the transmission characteristics for an incidentEwave are unaffected by the anisotropy and the velocity of the moving medium. Numerical results for the reflection and the transmission coefficients for an obliquely incidentHwave have been obtained for several values of the magnetic field and the electron density of the moving plasma half‐space. It is found that the moving magnetized plasma medium allows certain stop and pass bands under suitable physical condition

ISSN:0048-6604    

DOI:10.1029/RS008i007p00653

年代:1973

数据来源: WILEY

摘要:

The input admittance or impedance and the effective height of small metal antennas, with a finite gap, located in a dispersive environment, is obtained in an analytical form by properly renormalizing a modal series. The equivalent network of the antenna turns out to be composed of physically realizable elements, thus allowing the computation of the transient response by using Laplace transform techniques. The extension to the case of an inhomogeneous or a uniaxial anisotropic environment is also suggested.

ISSN:0048-6604    

DOI:10.1029/RS008i007p00667

年代:1973

数据来源: WILEY

摘要:

For tapered circular aperture with illumination of the form [b+ (1 —ξ)v]/(b+ 1) expressions for the on‐axis electric‐field intensity, power density, and directivity reduction are developed. Those expressions are presented in terms of the degenerate hypergeometric function. Whenvis an integer, the use of recurrence relationship permits simple expressions in closed form to be obtained. For special values ofvandb,a set of curves is presented. Also, the application of the expressions developed for any other nonuniform illumination involving circular symmetry are briefly pre

ISSN:0048-6604    

DOI:10.1029/RS008i007p00677

年代:1973

数据来源: WILEY

摘要:

Small‐angle multiple‐scattering is considered from randomly spaced cylindrical plasma striations. It is shown that multiple scattering from several underdense plasma clouds can cause considerable backscatter even though a single undense cloud is capable only of deflecting the ray through fairly small angles. In a case in which the deflection angles are small and many deflections occur before a ray passes through the scattering region, the ray density can be shown to satisfy a Fokker‐Planck transport equation. A diffusion coefficient is obtained for this equation for the case of cylindrical Gaussian striations by means of a numerical ray‐tracing program. The transport equation is solved by a finite‐difference method to obtain scattering patterns and waveform distortion. The methods of solving the transport equation can be applied to the scattering of radio waves, laser pulses, and other radiation propagating in ran

ISSN:0048-6604    

DOI:10.1029/RS008i007p00681

年代:1973

数据来源: WILEY

摘要:

The properties of an insulated dipole antenna are derived when the wavenumber of the surrounding infinite, homogeneous, and isotropic medium is large compared with that of the insulation. It is shown that even when the surrounding medium is a perfect dielectric, the distributions of current and charge along the antenna and its driving‐point admittance are substantially like those of a section of transmission line with a distributed radiation loss appearing as a part of the series impedance per unit lengt

ISSN:0048-6604    

DOI:10.1029/RS008i007p00699

年代:1973

数据来源: WILEY

摘要:

The performance of a bare antenna as a radiator in a dissipative medium can be significantly altered by placing a dielectric coating around the antenna. For certain antenna types and specific properties of the dissipative medium, the dielectric insulation has been shown to improve the performance of the antenna. In this paper the thin‐wire circular‐loop antenna centered in an insulating spherical cavity and immersed in an infinite homogeneous isotropic dissipative medium is analyzed. A Fourier series solution for the antenna current distribution is derived. The coefficients of the series are a combination of the coefficients for the loop in an infinite dielectric medium, which were determined previously byWu[1962], and a second term, which is an infinite sum. The properties of the sum are examined, and expressions for the antenna input admittance, impedance, and electromagnetic field in the dissipative medium are obtained. Numerical results are presented for specific antenna sizes and dissipative media. For the special case of a loop with a uniform current distribution in an electrically small sphere the expression for the input impedance is shown to reduce to a solution previously given byWait and Spies[1964]. The construction of an experimental model for the antenna is discussed, and antenna input impedances and current distributions measured with the model immersed in various salt‐water solutions are compared with theoretical calcula

ISSN:0048-6604    

DOI:10.1029/RS008i007p00711

年代:1973

数据来源: WILEY