摘要:

The Valley Forge‐Wallops Island bistatic radar has routinely identified high‐altitude clear‐air atmospheric targets. Bistatically detected target signatures are interpreted in terms of layer and diffuse distributions of scatterers. Simplified numerical models appear to explain well the layer signature characteristics. Locations of bistatically detected targets are compared with locations of meteorological features and monostatically detected atmospheric targets. Comparison shows the advantage gained when bistatic radars complement monostatic observations of clear‐air atmospheric

ISSN:0048-6604    

DOI:10.1029/RS007i011p00993

年代:1972

数据来源: WILEY

摘要:

This paper presents an investigation of the propagation of cylindrical waves (the field being independent of x) along the z direction inducts described bywhere c(y, z) is the wave velocity, C0and ϵ0are constants, ϵ2(z) is an arbitrary function of z, and ϵ corresponds to the dielectric constant for electromagnetic waves.It has been shown that the intensity A02of the wave is in general given bywhere E0is a constant, yois a constant,Fis an arbitrary function of [y/yoƒ(z)L], and ƒ(z) is a dimensionless beam‐width parameter given byin the geometrical optics approximation.The nature of the variations of ƒ with z has been discussed for some simple profiles of ϵz(z) in the geometrical optics approximation; diffraction has also been taken into account when the beam (F) is

ISSN:0048-6604    

DOI:10.1029/RS007i011p01005

年代:1972

数据来源: WILEY

摘要:

Atmospheric noise resulting from lightning discharges is modeled as a Poisson‐related process that depends on two major physical factors: (a) the world distribution of thunderstorms and (b) the prevailing propagation conditions. In this work theoretical models of atmospheric noise have been developed by postulating physically motivated combinations of source distributions and propagation conditions. Then the noise statistics at the output of a narrow‐band receiver for each combination are calculated. Particular noise statistics that are computed for several cases include the amplitude‐probability distribution, the average envelope‐level crossing rate, and the pulse‐spacing distribution. The models postulated are found to be consistent with both experimental and prior theoretica

ISSN:0048-6604    

DOI:10.1029/RS007i011p01011

年代:1972

数据来源: WILEY

摘要:

Higher‐order sine‐cosine azimuth patterns for Adcock direction finding are investigated to determine spacing errors, reradiation errors, and pickup factor. The higher modes achieve wider apertures and reduced wave interference error; they exhibit comparable pickup factors but require an increase in the minimum number of antennas and different sensing methods. The 1.220λ spacing limit is appropriate only to the dipole mode, the corresponding limit for the quadrupole mode being 1.684λ and correspondingly greater for the higher modes. Reduced spacing error for the minimum number of antennas occurs at increasingly wider apertures which also tend to more closely approach the theoretical limits with increasing mode. The higher modes exhibit reduced response in the vicinity of the zenith. The resolution of the additional bearing ambiguities involves the use of one or more lower‐order patterns. Predicted sense performance as a function of reradiated field amplitude is computed for a combination of quadrupole and dipol

ISSN:0048-6604    

DOI:10.1029/RS007i011p01025

年代:1972

数据来源: WILEY

摘要:

A method is described to accomplish automatic data selection and profile inversion to obtain ionospheric electron‐density profiles from digitized radio soundings. The profile inversion is based upon the well‐established formulation ofPaul[1960] by which the optimum radio‐frequency sounding intervals can be specified from an approximate knowledge of the profile. The expected virtual height coordinates (h') at these frequencies (ƒ) are likewise estimated, and procedures are then used to select h'(ƒ) observations nearest the predicted coordinates from a subsequent digital ionogram. From these the next profile is obtained. The process adaptively follows the changing shape and detail of the profile. The procedure requires an average of 20 sec per profile on a standard data‐processing computer and can be adapted, with benefit to on‐line real‐time use in our ‘dynasonde,’

ISSN:0048-6604    

DOI:10.1029/RS007i011p01033

年代:1972

数据来源: WILEY

摘要:

The advent of the phase ionosonde, which gives more precise experimental data than the conventional instrument, has made it necessary to seek improvement in the technique of true‐height reduction by reducing calculation errors. The method described here gives errors of approximately a few meters when the lowest observable frequency is 0.6 MHz and both magnetoionic modes are use

ISSN:0048-6604    

DOI:10.1029/RS007i011p01045

年代:1972

数据来源: WILEY

摘要:

The technique of measuring ionosphere motion from the shift in the incoherent‐scatter ion line has been known for some time. The underlying assumption in the adaptations of the technique applied so far is that there are no detectable current‐induced asymmetries in the spectrum. In the auroral zone this assumption can be violated during magnetospheric storms. To cope with this possibility we use an estimate of the first moment of the spectrum together with a matched‐filter‐like estimate.The first moment is the sum of the first moment of the unshifted spectrum plus the Doppler shift. The matched‐filter estimate, while not unaffected by asymmetries, tends to give an estimate closer to the Doppler shift. Hence, a difference between the two estimates is an indication of a current flowing in the range gate where the spectrum is measured. We assume that no other sources of asymmetry are present, although a large temperature gradient would have a similar effect. In principle the difference can be calibrated to give the magnitude of the current. This step is not yet completed owing to uncertainties in the composition of the ionosphere at low altitudes and a loss of frequency resolution due to the finite pulse length. The detectability of the currents by our method, however, is not affected by poor frequency resolution.Preliminary results from the Chatanika Auroral‐Zone Incoherent‐Scatter Radar are presented which show large velocities correlated in detail with simultaneous magnetometer data. Also an indication of a current flow has been observed in premidnight data taken on a very active night. An azimuth scan showed the sense of the current to be predomina

ISSN:0048-6604    

DOI:10.1029/RS007i011p01049

年代:1972

数据来源: WILEY

摘要:

A horizontal current‐carrying wire near the surface of the earth will maintain a tangential electric field in the ionosphere overhead. The questions of how large this field must be to produce a given local increase in electron temperature in the D region and the corresponding required current (dipole moment) in the wire are addressed here. To achieve a 20 K modulation (about 10% of ambient temperature) of the local electron temperature at an altitude of 70 km under daytime conditions would require an rms current of 2730 amp at 45 Hz over a length of at least 300 km where the ground conductivity is 1.4×10−4mho m−1. A parallel array of 23 wires spaced at 10‐km intervals will produce the same temperature modulation with only 139 amp in e

ISSN:0048-6604    

DOI:10.1029/RS007i011p01061

年代:1972

数据来源: WILEY

摘要:

This symposium is being held to commemorate the late Professor Sydney Chapman whose pioneering studies in geomagnetism contributed greatly to our present understanding of the magnetosphere. The subject emphasis will be the dynamic magnetosphere, the physics of its changing state, the detection and prediction of such changes, and the important influence of the magnetospheric motions upon the earth's environment. Topics for presentationare to include the magnetospheric interaction with the solar wind, the bow shock, magnetopause, cusps, tail formation, current sheets, plasma sheet, plasmasphere, and substorm dynamics. The meetings will be held at the NOAA Environmental Research Laboratory auditoriums, 325 Broadway, Boulder, Colorado.

ISSN:0048-6604    

DOI:10.1029/RS007i011p01067

年代:1972

数据来源: WILEY

摘要:

The 1973 Main Meeting sponsored by the U.S. National Committee of URSI and the 1973 IEEE International Antennas and Propagation Symposium will be held jointly at the Engineering Center of the University of Colorado. URSI and IEEE/G‐AP technical programs will be arranged separately, except for the appropriate coordinatio

ISSN:0048-6604    

DOI:10.1029/RS007i011p01068

年代:1972

数据来源: WILEY