摘要:

The material in this document has been prepared by various members of Commissions to the U.S. National Committee of URSI. It represents a highly condensed account of progress within the general field of each Commission during the past three years.Every three years URSI holds a General Assembly in which the member countries report to each other the advances that have been made. The material contained here represents the report of the United States to this international body. The subject matter is arranged in accordance with the commission structure of URSI. These Commissions, eight in number, are 1, Radio Standards and Measurements; 2, Radio and Non‐ionized Media; 3, On the Ionosphere; 4, On the Magnetosphere; 5, Radio Astronomy; 6, Radio Waves and Circuits; 7, Radio Electronics; and 8, Radio Noise of Terrestrial Origi

ISSN:0048-6604    

DOI:10.1029/RS004i007p00577

年代:1969

数据来源: WILEY

摘要:

On Friday, October 13, 1967, the General Conference of Weights and Measures adopted the atomic definition of the unit of time, the second. The development of atomic frequency standards is still most heavily weighted toward cesium beam devices, with considerable work also on hydrogen masers [Vessot et al., 1966;McCoubrey, 1967]. Probably because of budget problems, there has been little work on thallium beams. There has been significant interest in optical frequency standards with a notable development of a methane‐stabilized laser by John Hall [Barger and Hall, 1969

ISSN:0048-6604    

DOI:10.1029/RS004i007p00579

年代:1969

数据来源: WILEY

摘要:

The past three years evidence vigorous activity in the areas of interest to Commission 2, especially those concerned with planetary atmospheres, rough surfaces, effects of turbulence, and the general applicability of millimeter waves for scientific study and for communications. If any particular study were to be designated outstanding, it might be the investigation of clear‐air structure by microwave radar, but meaningful advances have been made in all of the areas discusse

ISSN:0048-6604    

DOI:10.1029/RS004i007p00591

年代:1969

数据来源: WILEY

摘要:

The major advances in our understanding of the morphology of theDregion in the last three years have come about through the application of rocket techniques. A series of rocket measurements carried out at Wallops Island [Mechtly and Smith, 1968a] at different seasons but at roughly the same solar zenith angle have shown the principal features of the seasonal variation in the electron density profile between 50 and 100 km. It appears that electron densities are lower by a factor of about 3 below 82 km on ‘normal’ winter days as compared with summer days for a solar zenith angle of 60°. The anomalous winter days of high absorption have been the subject of a separate rocket investigation [Sechrist et al., 1969], which has shown that the electron density profile is remarkably similar to that of a normal summer day and that in at least one case was associated with a pronounced temperature inversion near 7

ISSN:0048-6604    

DOI:10.1029/RS004i007p00603

年代:1969

数据来源: WILEY

摘要:

Since the last report was written (in the spring of 1966), there has been a remarkable advance in our knowledge and understanding of the structure and behavior of the magnetosphere, especially with regard to the fundamental problems of the aurora and geomagnetic storms.The average structure of the quiet magnetosphere has been studied in considerable detail [Ness et al., 1966;Spieser and Ness, 1967;Behannon, 1968;Fairfield, 1968;Mihalov et al., 1968], and it has been shown that the tail and ‘neutral’ sheet extend well past the moon, and possibly to much greater distances [Ness et al., 1967]. The nature of the changes that occur in the geomagnetic field during disturbed periods has been observed, especially by magnetometers on the geostationary satellite ATS 1 [Brown et al., 1968;Cummings et al., 1968;Cummings and Coleman, 1968]. It has been found that the ring current, which is usually situated between 3 and about 10REdepending on the degree of geomagnetic activity, commonly has a pronounced asymmetric component, with the maximum inflation of the geomagnetic field occurring in the evening sec

ISSN:0048-6604    

DOI:10.1029/RS004i007p00623

年代:1969

数据来源: WILEY

摘要:

The institutions that contributed material for this report are:1. Arecibo Ionospheric Observatory.2. NASA‐Goddard Space Flight Center.3. Bell Telephone Laboratories.4. University of Texas.5. University of Maryland.6. University of Virginia.7. Florida State University.8. Air Force Cambridge Research Laboratories.9. Stanford University.10. MIT Lincoln Laboratory.11. Ohio State University.12. University of Colorado.13. National Radio Astronomy Observatory.14. Jet Propulsion Laboratory.15. Owens Valley Radio Observatory.Only a minor attempt has been made to mention work performed at other observatories in the U.S.

ISSN:0048-6604    

DOI:10.1029/RS004i007p00635

年代:1969

数据来源: WILEY

摘要:

In this area, by far the greatest effort has been focused on arrays, particularly phased arrays; the results have been summarized in three books [Hansen, 1966;King et al., 1968] and two special journal issues [Radio Science, 1968;IEEE, 1968]. Complete design formulas for scannable Baklanov‐Chebyshev arrays [Tseng and Cheng, 1968] and new approximations for long Dolph‐Chebyshev arrays [Drane, 1968] were developed. Infinite array models dominated in numerous studies of large phased arrays. Grating lobe effects were investigated by the induced emf method [Stark, 1966] and by use of impedance craters [Wheeler, 1966] Important and unexpected element pattern nulls not attributable to grating lobes have been observed and explained as coupling accumulation [Lechtreck, 1968] and as external resonances in dielectric sheets [Knittel et al., 1968;Wu and Galindo, 1968]. They have also been observed as mismatches in array simulators [Hannan, 1967a]. Proof of the possibility of impedance matching for all scan angles has been offered [Hannan, 1967b] and contested [Varon and Zysman, 1968] Limited control of coupling for wide angle impedance matching has been achieved by means of dielectric sheets [Magill and Wheeler, 1966], hole coupling of waveguides [Amitay, 1966], multiple modes in waveguides [Tang and Wong, 1968], and parasitic chokes [Dufort, 1968], and the form of asymptotic decay of coupling with distance has been established [Galindo and Wu, 1968]. Systematic procedures for the design of phased array elements have appeared [Wheeler, 1968;Amitay et al., 1968], as have methods of analysis of waveguide phased arrays without [Farrell and Kuhn, 1968], and/or with [Borgiotti, 1968a] dielectric sheets. Finally, there was developed an important geometrical description of phased array behavior, based on the fundamental principle of planar apertures, that unifies much of the existing knowledge of infinite arrays [Diamond, 1968]. A thorough application of this development to arrays of rectangular waveguides shows clearly the individual roles of the lattice and the elements [Ehlenberger et al., 1968]. The same principle was used to compute mutual admittances between slots [Borgiotti, 1968b], and formulas for observable stored energies of planar apertures have been derived from it [Rhodes, 1966] and contested [Borgiotti, 1967;Collin, 19

ISSN:0048-6604    

DOI:10.1029/RS004i007p00641

年代:1969

数据来源: WILEY

摘要:

As in previous summaries, the words ‘information theory’ are used in the wide sense to include such areas as (1) statistical communication theory, (2) detection theory, (3) pattern recognition and adaptive systems, (4) coding theory, and similar examples of the interaction of random processes and communication systems. For classification purposes, progress in information theory will be described under the four headings just lis

ISSN:0048-6604    

DOI:10.1029/RS004i007p00651

年代:1969

数据来源: WILEY

摘要:

The advances of the past 3 years in the science and technology of quantum electronics are well summarized by the technical programs of the May 1968 International Conference on Quantum Electronics, held in Miami [IEEE, 1968a], and of the May 1969 Conference on Laser Engineering and Applications, held in Washington, D. C. [IEEE, 1969a]. The pace of development of new laser devices, new techniques, and new basic quantum electronic phenomena does not seem to be slowing, even though the maser concept has been with us for two decades, and working laser devices for one decade. On the technological side, the development of practical laser applications has obviously reached and passed the take‐off point, with new and different practical applications of lasers emerging at a rapid rate in an almost uncountable number of applications area

ISSN:0048-6604    

DOI:10.1029/RS004i007p00657

年代:1969

数据来源: WILEY

摘要:

Since Commission 8 was only created on a provisional basis at the Munich General Assembly of URSI in 1966, and since also the U.S. National Committee does not maintain an organization for Commission 8 within the U.S.A., it seems appropriate for informative reasons to start this survey by listing the fields of scientific activity covered by the Commission. These are:1. Atmospherics, their source characteristics and location.2. Propagational influences on radio noise (with Commission 3).3. ELF noise from lightning (with Commission 4).4. Types of lightning flashes generating whistlers. Propagational effects, other than those in the whistler mode, influencing whistler characteristics (with Commission 4).5. Statistical properties of noise, noise interference with radio communications.6. Man‐made noise.This review will discuss work falling within the above fields of study carried out under U.S. auspices and described in 1966, 1967, and 1968. The survey will be confined to papers appearing in recognized journals and other sources of ready availability to which my attention has been drawn; reports of limited circulation and private information will not be considere

ISSN:0048-6604    

DOI:10.1029/RS004i007p00661

年代:1969

数据来源: WILEY