摘要:

By using a quasi‐static integral equation technique a transcendental equation for the propagation constants of an axially slotted, dielectric‐filled coaxial waveguide is obtained. The equation is solved on the computer, and curves of the propagation constants versus various line parameters are presented. Also calculated are expressions for the transfer impedance and field quantit

ISSN:0048-6604    

DOI:10.1029/RS014i005p00741

年代:1979

数据来源: WILEY

摘要:

With the aid of graphs a detailed description is given of the experimentally determined distributions of the currents and charges induced by a normally incident plane electromagnetic wave on all of the surfaces of a metal cross formed by a vertical tubular cylinder and a horizontal flat plate. The cylinder is a wavelength in circumference and 1.75λ high over a large ground plane. The horizontal plate consists of two equal arms that extend 0.75λ from the surface of the cylinder; it is 0.2125λ wide and 0.0255λ thick. It is centered at a height of 1.25λ from the ground plane. The distributions are compared with the corresponding ones on crossed tubular cylinders and on isolated cylin

ISSN:0048-6604    

DOI:10.1029/RS014i005p00753

年代:1979

数据来源: WILEY

摘要:

The concept of a natural slot antenna for very low frequency is discussed. It is suggested that a viable system needs to have an insulated cavity backing the slot aperture.

ISSN:0048-6604    

DOI:10.1029/RS014i005p00765

年代:1979

数据来源: WILEY

摘要:

Using a spherical earth model, we develop a normal mode analysis for the excitation by an azimuthally symmetric source region. We then specialize the general formulation to deal with a vertical antenna with a prescribed current distribution. In particular, we consider the current distribution that would excite a pure Zenneck wave on the corresponding planar earth model. But we also consider excitation by vertical electric dipole and a uniform current distribution. Finally, we examine a horizontal antenna that is excited by a traveling current wave. Our general conclusion is that the Zenneck wave aperture illumination (i.e., current distribution) is a poor choice for enhancing the ground wave over a spherical earth. This point is illustrated for specific calculations at a frequency of 1 and 10 MHz over both land and sea.

ISSN:0048-6604    

DOI:10.1029/RS014i005p00767

年代:1979

数据来源: WILEY

摘要:

A rigorous treatment is given to a spatial filtering method for remotely determining the transverse wind velocity and the atmospheric structure constant along a line‐of‐sight path, assuming a Kolmogorov spectrum of refractivity and weak scattering. The results are applicable from the millimeter‐wave range to the optical range for linear array configurations at either one end or both ends of the path. Various methods of signal detection are considered, such as coherent, quasi‐coherent (knowledge of relative phases), and incoherent. In order to determine the two parameters the integral for the time covariance or the spectrum of the wave fluctuations must be inverted. For simple arrangements of single elements or pairs of elements at the transmitting and receiving locations the inversion is ill conditioned and yields only three or four resolution cells along the path. A statement of the problem in spectral form for line apertures representing narrow bandpass‐type spatial filters leads to optimal orthogonality of the inversion problem. In the limiting case of ideally sharp spatial filters, the inversion is shown to degenerate into a simple one‐to‐one relationship between spectral measurements of the spatially filtered wave fluctuations and the values of the parameters at a specified location along the path. A subsequent paper will be devoted to an experimental application of the principle in the m

ISSN:0048-6604    

DOI:10.1029/RS014i005p00781

年代:1979

数据来源: WILEY

摘要:

The microwave brightness temperature measurements for Nimbus 5 electrically scanned microwave radiometer (ESMR) and Nimbus‐E microwave spectrometer (NEMS) are used to retrieve the atmospheric water vapor, liquid water, and wind speed by a quasi‐statistical retrieval technique. It is shown that the brightness temperature can be utilized to yield these parameters under various weather conditions. Observations at 19.35, 22.235, and 31.4 GHz were input to the regression equations. The retrieved values of these parameters for portions of two Nimbus 5 orbits are presented. Then comparison between the retrieved parameters and the available observations on the total water vapor content and the surface wind speed are made. The estimated errors for retrieval are approximately ±0.15 g/cm2for water vapor content, ±6.5 mg/cm2for liquid water content, and ±6.6 m/s for surface wind

ISSN:0048-6604    

DOI:10.1029/RS014i005p00793

年代:1979

数据来源: WILEY

摘要:

In this paper, path loss calculations for frequencies between 4 and 32 MHz are compared with Hansen's recent measurements on a 235‐km over‐ocean southern California path. The calculations involve standard waveguide theory along with available radiosonde data and show convincingly that signal enhancement, relative to that expected on the basis of ground wave theory, observed on frequencies greater than 20 MHz was due to superrefractive environme

ISSN:0048-6604    

DOI:10.1029/RS014i005p00803

年代:1979

数据来源: WILEY

摘要:

Dynasonde software for data acquisition in three modes is described. The ‘I’ mode corresponds to an ionogram format but includes complete echo polarization and angle‐of‐arrival information.Kmode provides time series and high time resolution at freely selected sounding frequencies.Bmode combines features of the other two modes. All share a real‐time noise rejection method which is described statistically. The system includes a digitally driven CRT (cathode ray tube) display and a variety of display formats for real time or deferred examination of data; in particular, dynamic time‐lapse displays of ionospheric activity can be maintained by th

ISSN:0048-6604    

DOI:10.1029/RS014i005p00815

年代:1979

数据来源: WILEY

摘要:

Phase measurements by the Dynasonde are obtained for each echo from four spaced receiving antennas in a square array. The antennas are oriented along the array diagonals, and the phase values thus contain contributions identified with echo polarization and arrival angle. A unified procedure for separating these contributions is described. Ionograms with discriminated ordinary and extraordinary polarizations are displayed. ‘Skymap’ and ‘Gonionogram’ formats are also illu

ISSN:0048-6604    

DOI:10.1029/RS014i005p00827

年代:1979

数据来源: WILEY

摘要:

It is well known that various diurnal and morphological features of the ionosphere reveal substantial departures from the normally simplified assumption of spherical symmetry at certain times of the day or at certain geographic locations. A radio ray passing through such an ionosphere must bear information about its horizontal gradients. The leading edge of a backscatter ionogram is formed by obliquely propagated radio rays of minimum time delay and hence is useful in deducing information about the ionospheric horizontal gradients. In this regard, the ionospheric electron density distribution is modeled by a locally quasi‐parabolic layer with six parameters. This six‐parameter space is known as the ‘ionostate.’ Our object is to seek the ‘best’ ionostate in the sense that the corresponding mean square error in group delay is a minimum. A computer program has been written to carry out the specified procedure. A number of sample calculations are presented an

ISSN:0048-6604    

DOI:10.1029/RS014i005p00837

年代:1979

数据来源: WILEY