摘要:

With the aid of a two‐dimensional integral equation formulation, the ground wave propagation of electromagnetic waves transmitted by a vertical electric dipole over an inhomogeneous flat earth is investigated. For the configuration in which a ground wave is propagating across an “island” on a flat earth, the modulus and argument of the attenuation function have been computed. The results for the two‐dimensional treatment are significantly more accurate in detail than the calculations using a one‐dimensional integral

ISSN:0048-6604    

DOI:10.1029/RS010i011p00925

年代:1975

数据来源: WILEY

摘要:

Tropospheric refraction introduces errors into radar and radio communication systems by causing radio waves to travel along a curved path and at a speed which changes with position. Common error correction techniques, such as making estimates of refractive effects from surface refractivity, rely implicitly on the assumption that the troposphere is horizontally stratified. This study demonstrates that such an assumption may be unwarranted especially at elevation angles below 10°, and that such reliance can lead to substantial errors. The end product of this research is a system which employs atmospheric emission measurements in addition to surface refractivity to estimate refractive bending and range error. This approach relies on the similar dependence of refraction and emission on atmospheric parameters to account for nonhorizontal stratification. Performance results establish that such a system need employ no more than one radiometer channel to provide potential error reduction of more than 40% over conventional approaches, along with a potentially automated, real‐time operational capabili

ISSN:0048-6604    

DOI:10.1029/RS010i011p00935

年代:1975

数据来源: WILEY

摘要:

Microwave data acquired over the Great Salt Lake Desert area by sensors aboard Skylab and Nimbus 5 indicate that the microwave emission and backscatter were strongly influenced by contributions from subsurface layers of sediment saturated with brine. This phenomenon was observedby Skylab's S‐194 radiometer operating at 1.4 GHz, S‐193 RADSCAT (Radiometer‐Scatterometer) operating at 13.9 GHz, and the Nimbus 5 ESMR (Electrically Scanning Microwave Radiometer) operating at 19.35 GHz. The availability of ESMR data over an 18‐month period allowed an investigation of temporal var

ISSN:0048-6604    

DOI:10.1029/RS010i011p00947

年代:1975

数据来源: WILEY

摘要:

Whistlers observed on records of the OGO‐4 satellite during the sunset/sunrise hours show evidence of both the proresonance (PR) and prolongitudinal (PL) mode of propagation. By tracingrays in a model magnetosphere suitable for these hours, the whistlers observed on these records are reproduced. The upper cutoff frequency presented in the walking trace whistlers appears naturally as a consequence of the inclusion of latitudinal gradients in the electron density model. A new whistler trace is predicted which appears as a consequence of the transition from the PR to the PL mode of propagatio

ISSN:0048-6604    

DOI:10.1029/RS010i011p00965

年代:1975

数据来源: WILEY

摘要:

Radio scintillation on satellite signals caused by small‐scale irregularities inF‐region ionospheric electron density can be an important limitation on earth‐satellite communication and navigation systems. Scintillation imposes distortion in both amplitude and phase on wideband signals. In the present work, the shallow‐modulated phase screen theory is developed in terms of coherence bandwidth including a model based on a turbulent‐like power‐law description of the irregularities. The model results usually show a greater coherence bandwidth in the signal phase than in the signal amplitude. Therefore, systems that require phase coherence over a large bandwidth should be less affected than those requiring amplitud

ISSN:0048-6604    

DOI:10.1029/RS010i011p00973

年代:1975

数据来源: WILEY

摘要:

Born's method is applied to the time‐dependent wave equation. Exact solutions, valid for all wavelengths, are obtained for the first‐order perturbation terms for monochromatic plane and spherical waves propagating in random media with stationary temporal fluctuations. It is shown that the temporal fluctuations of the medium can be neglected if the temporal frequencies of the fluctuations are much less than the frequency of the propagating wave and if the propagation time from the transmitter to receiver is much less than the coherence time of the medium. In the atmosphere for the case where (λ30/l40)L≪ 1, wherel0is the inner scale of turbulence, log‐amplitude and phase covariance functions were calculated for the polarized and depolarized fluctuations of plane waves propagating in slightly different directions. Numerical evaluation revealed that the polarized log‐amplitude fluctuations decorrelate for angular separations on the order of tan−1[(λ0/L)1/2] while phase fluctuations decorrelate for angular separations on the order of tan−l(L0/L), where L0is the outer scal

ISSN:0048-6604    

DOI:10.1029/RS010i011p00979

年代:1975

数据来源: WILEY

摘要:

The properties of an electric field probe that consists of two mutually perpendicular conductors attached to the end of a long coaxial line are investigated with a view to minimizing the pickup by the cable. The structure is treated as a junction‐loaded crossed‐wire antenna. Coupled integral equations for the currents are derived and solved approximately. It is shown that the contribution to the voltage across the load can be kept relatively small compared with the contributions by the active elements of the probe if a correct design is maintained. The analysis is carried out specifically for a normally incident plane wave with components of the electric field parallel to both the cable and the elements of the pr

ISSN:0048-6604    

DOI:10.1029/RS010i011p00989

年代:1975

数据来源: WILEY

摘要:

Using a perturbation method, we consider the effect of a simple two‐dimensional model on the electromagnetic fields at the surface of the Earth for a postulated downcoming plane wave. We examine the calculated change in the surface impedance and wave tilt due to lateral inhomogeneities. It is found that the magnetic wave tilt (Hz/Hx) is most seriously affected by such anomalies. This may have important consequences on electromagnetic probing of nonuniform portions of the Earth's crus

ISSN:0048-6604    

DOI:10.1029/RS010i011p01001

年代:1975

数据来源: WILEY