ISSN:0048-6604    

DOI:10.1029/RS023i003p00209

年代:1988

数据来源: WILEY

摘要:

This paper presents information on two new models: an ionospheric specification model and a magnetospheric specification model. The goal of these models is to provide operational information based on real‐time satellite and ground‐based measurements. The ionospheric model will be described in detail and the magnetospheric model, which is in an earlier state of development, will be outlined.

ISSN:0048-6604    

DOI:10.1029/RS023i003p00211

年代:1988

数据来源: WILEY

摘要:

A study of empirical ionospheric models was undertaken to improve the accuracy of the ionospheric correction that is needed in satellite orbit determination. Our evaluation concerns the two most widely used empirical ionospheric models(Bent and international reference ionosphere(IRI)) and suggests improvements based on comparisons with satellite and ground‐based data. In both models, the topside electron density profiles decrease too sharply with increasing altitude. Our improved IRI topside formula compares well with AEROS satellite data and incoherent scatter measurements of the Jicamarca, Peru, radar facility. For the bottomside, a model for the effective parabolic thickness is introduced, based on the detailed IRI predictions. Recent progress in modeling the F2peak altitude and electron density is reviewed. The increase in prediction accuracy compared to older F2models is evaluated with Ionosphere Sounding Satellite b results(for density) and incoherent scatter measurements from Millstone Hill, Massachusetts(for altitude). The plasmaspheric electron content is also taken into account. Finally, results of a METEOSAT tracking exercise are used to check the ionospheric delays calculated with the different models. The changes indicated above were found to be helpful and resulted in an overall improvement.

ISSN:0048-6604    

DOI:10.1029/RS023i003p00223

年代:1988

数据来源: WILEY

摘要:

In preparation for the second session of the High‐Frequency Broadcasting Conference the Institute for Telecommunication Sciences developed a computer program to assess the impact of planning the frequency bands allocated to the high‐frequency broadcasting service on U.S. broadcasting objectives. The program provides a powerful tool to numerically simulate the performance of high‐frequency sky wave systems operating in both noise‐limited and interference‐limited environments. This paper describes the philosophy behind the design of the program and its various components, such as propagation model, antenna routines, and interference assessment. Examples are given of the application of the program for frequency planning and frequency assignment. Areas in which the program can be expanded to include other services(fixed, mobile, amateur, etc.) operating in the frequency range 3–30 MHz are also discussed.

ISSN:0048-6604    

DOI:10.1029/RS023i003p00233

年代:1988

数据来源: WILEY

摘要:

During 1985 a flight expedition for signal and noise measurements of long‐wavelength radio waves was undertaken to the Arctic. Ground‐based measurements have been made in Greenland and Norway. The data suggest the revision of long‐wave coverage prediction programs to satisfy the special requirements of the Arctic. Polar cap absorption events and the structure of the Greenland ice cap must be taken into account.

ISSN:0048-6604    

DOI:10.1029/RS023i003p00240

年代:1988

数据来源: WILEY

摘要:

An algorithm for accurate three‐dimensional ray tracing is presented for realistic, nonspherical ionospheric electron density distributions, ignoring effects of the magnetic field. At the start of each ray path increment a truncated Taylor series expansion of the electron density results in a computationally efficient, closed‐form solution of the Euler‐Lagrange equations for the increment. The technique is applied to computations of ray paths in a nonspherical ionosphere which is specified by a climatological model used for HF over‐the‐horizon(OTH) radar studies. The effects of tilts in a sunrise transition region on signal losses and ray path deviations are found to be substantial. Results of various ionospheric approximations used for single‐site transmitter location are calculated.

ISSN:0048-6604    

DOI:10.1029/RS023i003p00247

年代:1988

数据来源: WILEY

摘要:

Between 1981 and 1985, absolute time of arrival(TOA) measurements were made on HF sky wave time standard signals at different frequencies. A total of 113 path months of TOA data were collected over a one‐hop path between Fort Collins, Colorado and San Diego, California. In addition, 15 path months of data were collected between Fort Collins and Oahu, Hawaii, and 12 path months were gathered on signals between Tokyo, Japan and Oahu. The data show a higher degree of ionospheric movement than had been expected by the experimenters. They also show a higher degree of stratification within layers than can normally be explained with simple models based on a single‐layer ionosphere.

ISSN:0048-6604    

DOI:10.1029/RS023i003p00257

年代:1988

数据来源: WILEY

摘要:

The Jindalee HF sky wave radar has been developed to carry out surveillance and remote sensing missions over Australia's northern Exclusive Economic Zone. Offering an unequaled combination of versatility, resolution, and signal processing capability, Jindalee is also a powerful instrument for observing the structure and dynamics of the ionosphere, as illustrated by the examples shown here. The interpretation of HF sky wave backscatter in terms of ionospheric phenomena is more complicated than for conventional ionosondes, but this is compensated for by the vast spatial coverage and the use of clutter analysis techniques which enable the relationship between group range and ground range to be estimated.

ISSN:0048-6604    

DOI:10.1029/RS023i003p00265

年代:1988

数据来源: WILEY

摘要:

The low‐frequency radio telescope at the Clark Lake Radio Observatory (CLRO) near Borrego Springs, California, provides a unique and powerful method for studying ionospheric structure at mid‐latitudes. By observing the refractive offsets that ionospheric gradients impose upon the signals from natural radio sources, we are able to measure these gradients simultaneously at many points in the ionosphere. The telescope is a highly sophisticated system which operates in the 10‐ to 125‐MHz frequency range—a range in which ionospheric refraction completely dominates tropospheric refraction. It is sensitive enough to detect many thousands of natural radio sources and, because it is electronically steered, it can be pointed anywhere in the sky in less than a millisecond. The telescope can be programmed to rapidly cycle over a grid of sources whose astronomical coordinates are well known and can be used to determine the refractive displacements of the apparent positions of these sources. Thus the ionosphere can be “punctured” at separations of a few kilometers to a few hundreds of kilometers by the lines of sight to these sources and ionospheric gradients can be measured at each of these puncture points. Ionospheric waves are observed; their amplitude, wavelength, direction of propagation, and speed of propagation can be measured. The two‐dimensional shapes and sizes of ionospheric irregularities are determined as well as large‐scale iono

ISSN:0048-6604    

DOI:10.1029/RS023i003p00273

年代:1988

数据来源: WILEY

摘要:

Faraday observations of total electron content (TEC) at Haifa, Israel (32.87°N, 35.09°E), during periods near the maximum (1980) and minimum (1984) phases of the current solar cycle have yielded information about the structure and variability of the ionosphere during both epochs in general, and about traveling ionospheric disturbances (TIDs) in particular. The TEC is characterized by the large differences in the seasonally dependent absolute values, by the generally occurring spatially confined postsunset secondary maxima during solar maximum which are absent during solar minimum, and by the regularly appearing modulations of the structure due to TIDs. There is a definite seasonal and solar phase dependence in the characteristics of the TIDs. This is expressed in terms of their frequency of occurrence, likely phase of the diurnal variation during which the occurrences take place, their absolute magnitudes, and the time rate of change of these magnitude

ISSN:0048-6604    

DOI:10.1029/RS023i003p00283

年代:1988

数据来源: WILEY