摘要:

Lateral waves can propagate when an antenna is placed close to an interface between two different media. In this paper, a study is made of how the lateral wave is affected by a conducting plate placed parallel to the interface. This changes the type of decay of the wave along the interface from that of algebraic to exponential. A new method is used in developing the formulas. Impedance boundary conditions are used to decouple the two media at each step of an iterative procedure. Single medium techniques can then be used in each region. The formulas are seen to agree well with numerical results from the exact integral representations of the fields.

ISSN:0048-6604    

DOI:10.1029/RS021i002p00175

年代:1986

数据来源: WILEY

摘要:

A method is described for solving the problem of a plane electromagnetic wave at nonnormal (skew) incidence on a wedge with one face imperfectly conducting and the other metallic. The method is based on a modified statement of the impedance boundary condition used in conjunction with Maliuzhinets' technique, and is applicable to a wedge whose open angle ismπ/2 withm= 1, 2, 3 or 4. For each wedge angle the general form of the solution is developed, and detailed results are presented for a right‐ang

ISSN:0048-6604    

DOI:10.1029/RS021i002p00185

年代:1986

数据来源: WILEY

摘要:

Transient scattering, particulary the associated pole configuration, is nowadays intensively studied for target identification purposes. At least theoretically, it is interesting to understand the effects introduced by time dependence. However, these heretofore neglected phenomena might be even of practical importance for cases where the velocities are close to the wave velocity, e.g., acoustics, or where the distances between scatterer and source are small. Although the simple Doppler effect becomes ambiguous for short pulse scattering, the velocity effects are present, manifesting themselves in virtual migration of poles and virtual creation of poles of higher multiplicity. The new ideas are explored by using the spectral approach, i.e., the wealth of studies available on Doppler effects and harmonic scattering is exploited, and by complex integration the conclusions pertinent to pulse scattering can be drawn. Inasmuch as this is a theoretical study, focusing mainly on electromagnetic waves, the exact relatlvistic formalism is used. The first‐order velocity effects, which are of more practical interest, are emphasize

ISSN:0048-6604    

DOI:10.1029/RS021i002p00192

年代:1986

数据来源: WILEY

摘要:

Measurements of wideband medium frequency atmospheric noise have been made over the past several years in the southwestern United States. In part 1 of a two‐part paper the measurement and data transcription system and the statistical analysis software used to analyze the data are presented. Specific results given in part 1 include the temporal structure of the noise and the distribution and time variation of the measured average noise power. In part 2, representative first‐ and higher‐order statistics and the impact of the data on bandwidth and system performance are described. Specifically, bit error rate simulations of a coherent receiver operating in either modeled or measured atmospheric noise are pres

ISSN:0048-6604    

DOI:10.1029/RS021i002p00203

年代:1986

数据来源: WILEY

摘要:

An attempt has been made to derive the envelope amplitude probability distributions (APD) for atmospheric radio noise near thunderstorms. Formulas for APD's have been derived based upon the model for atmospheric radio noise near thunderstorms: First, elementary formulas for APD's are derived for the case when impulsive noise sources are continuously distributed over a limited range. Next, by taking into account the characteristics of the return stroke andKchange pulses, APD curves at VLF are calculated using these formulas for atmospheric radio noise near a thunderstorm. Good agreement is shown between the calculated and measured APD curves. Further calculations indicate that the changes of the measurement frequency, and of the shortest distance to a thunderstorm influence the characteristics of the APD's. At last, similar procedure in analysis is applied to derive APD's for automotive radio noise, and the resulting calculated APD curves are shown for (1) a single vehicle and (2) a large number of vehicles running on a roadway, respectively.

ISSN:0048-6604    

DOI:10.1029/RS021i002p00223

年代:1986

数据来源: WILEY

摘要:

This paper presents two methods for computing differential propagation phase shift (ϕDP) using time series data form a coherent radar with alternate switching between two linear but orthogonal polarizations. An analysis of the statistical error in ϕDPestimate shows that ϕDPcan be estimated with less than 0.5° standard error using time and range averaging. To evaluate the usefulness of ϕDPfor estimating rainfall rate (R) vis‐a‐vis the ZDRmethod, a discussion on the sensitivity ofRto standard errors in ϕDPas well asZHandZDRis presented. It is shown that the relation, differential propagation phase constant Δϕ versusR, is relatively insensitive to drop size distribution (DSD) variations and thus can yield more accurateRestimate, even when a direct relationship between Δϕ andRis assumed. However, standard error in Δϕ estimate causes large inaccuracies ofRat low values (R<50 mmh−1), thus limiting its usefulness to higher rainfall rates. It is also shown that Δϕ can be used as a third remote measurable in conjunction withZHandZDRto determine a three parameter gamma DSD. Another use of Δϕ is likely to be in hydrometeor type identification, especially

ISSN:0048-6604    

DOI:10.1029/RS021i002p00235

年代:1986

数据来源: WILEY

摘要:

Observations of electron density irregularities have been made with the Langmuir probe (LANG) on DE‐2. The DE‐2 LANG data were examined for irregularities with scale sizes of 30 to 170 km. Such irregularities were found at all longitudes in the polar cap and auroral oval with stronger fluctuations in the oval. Night time equatorial passes having local times near 1900 or 2400 LT and occurring in an 80 day wide band about equinox were examined for irregularity occurrence. A definite longitude pattern was found in the data from several hundred orbits which showed an eastward shift at later local times. The equatorial irregularity occurrence pattern found in the LANG data is consistent with earlier in situ and remote observations of irregularities and spread F. In fact, the combined data set was found to closely follow the season‐longitude pattern determined by the condition of solar terminator alignment with magnetic field lines. Tsunoda (1985) first showed this correlation with scintillation

ISSN:0048-6604    

DOI:10.1029/RS021i002p00248

年代:1986

数据来源: WILEY

摘要:

Atmospheric dynamics, such as turbulence or buoyancy waves, modulate the quiescent refractive index and cause radio‐wave scattering during occultations of spacecraft by planetary atmospheres. The resulting rapid signal fluctuations are a common feature observed during occultation experiments, especially in the outer solar system, and provide an opportunity for remote sensing of the underlying atmospheric dynamics. However, the absence of a theory that accounts for strong scattering during atmospheric occultations has obstructed progress in this area, and has restricted data interpretation to the weak‐scattering regime. We have removed this limitation of the theory by deriving a formula for the spatial spectrum of intensity fluctuations due to strong scattering in the occultation geometry. In obtaining this new result, we generalized an existing formula for strong scattering from an irregular thin screen to include the effect of a spatially varying average refractive index in the scattering region. In the model phase screen, the refractive irregularities are anisotropic with a size distribution that follows a power law. The strength, axial ratio, orientation, and power‐law exponent which characterize the irregularities, as well as the scale height and radius of curvature of the background refractive index, are included in the theoretical expression as free parameters. Unfortunately, the final result takes the form of an intractable double integral. To obtain specific results for the theoretical intensity spectrum, we developed an accurate algorithm for numerical integration. Representative results are given, showing the dependence of the spectrum on each of the free param

ISSN:0048-6604    

DOI:10.1029/RS021i002p00257

年代:1986

数据来源: WILEY

摘要:

A bistatic 50‐MHz CW radar was used to simultaneously observe the horizontal components of E region auroral drift motions and the underlying D region meteor trail drift motions over northern Saskatchewan (L ∼ 6.5). About 1800 meteor trail echoes were analyzed over 5 separate days, 3 of which were geomagnetically quiet and 2 of which were disturbed. For the quiet days, the observed meteor trail drifts were consistent with the normal D region motions observed at these latitudes. For the disturbed days, however, the meteor trail drifts near local midnight were much larger than normal, were predominantly southward and were well correlated with the E region auroral drifts measured at some 10 km higher altitude. This suggests that meteor trail drift motions may not be representative of the neutral medium motions at auroral latitudes during periods of geomagnetic disturba

ISSN:0048-6604    

DOI:10.1029/RS021i002p00271

年代:1986

数据来源: WILEY