摘要:

The mean speeds of short wavelength wind‐generated waves (wavelengths less than 4 cm) have been obtained from Doppler spectra measured at very short fetch in a wave tank for wind speeds up to 15 m sec−1. These speeds are compared with phase speeds calculated from a first‐order perturbation of the wind drift and reasonable agreement is obtained. The measurements show that the difference between mean wave speed and the mean surface drift becomes quite small for wind speeds exceeding 12 m

ISSN:0048-6604    

DOI:10.1029/RS009i012p01091

年代:1974

数据来源: WILEY

摘要:

The average behavior of the MFA1absorption data at night and sunrise times at Calcutta has been described with a view to understanding the maintenance of the nighttime absorbing region. The nighttime variation of absorption which attains a minimum around one hour after local midnight could easily be accounted for in terms of the scattered UV fluxes.A small decrease in absorption before sunrise is evidenced. The analysis using the partially reflectingEsecho suggests this is caused by a decrease in deviative loss atF‐region heights. The onset time for a further increase in absorption agrees very well with that observed from other technique

ISSN:0048-6604    

DOI:10.1029/RS009i012p01101

年代:1974

数据来源: WILEY

摘要:

Measurements of very low frequency (VLF) atmospherics were made simultaneously at a station close to the lightning sources (Norman, Oklahoma) and at stations 1787 km (La Posta, California) and 5912 km (Kamuela, Hawaii) from Norman. Timing synchronization was maintained between stations to better than 10 μsec which, coupled with the source bearing from Norman, allowed accurate fixing of source locations. Using the numerical techniques of Pappert et al. for propagation parameter calculations, an appropriate exponential ionospheric conductivity model was chosen which best fit the modal interference structure near 10 kHz as a function of source distance as measured at La Posta. From source current moment spectra measured at Norman, the electric field strengths at La Posta and Kamuela were predicted for a wide frequency band (2 to 30 kHz) using the selected conductivity profile. For β = 0.6 km−1andh′= 84 km (in the notation of Wait and Spies) good agreement between the numerical calculations and the average measured field strengths was obt

ISSN:0048-6604    

DOI:10.1029/RS009i012p01109

年代:1974

数据来源: WILEY

摘要:

A multipulse correlator system for the Chatanika, Alaska, incoherent scatter radar is described. The system utilizes a hardware correlator unit that can deliver as many as 40 8‐bit by 8‐bit lagged products every 20 μsec. The particular lags at which products are computed are patch‐wire programmable, and the range gates at which data are taken are set arbitrarily under computer control. The system operates with a fixed bandwidth of 50 kHz, so that the maximum range resolution is 6 km. To obtain sufficient lag resolution for operation at 1290 MHz, we compute lagged products at other than the nominal subpulse spacing. An example of the correlator operation is

ISSN:0048-6604    

DOI:10.1029/RS009i012p01117

年代:1974

数据来源: WILEY

摘要:

Analytical expressions are derived for the electromagnetic field associated with a vertical electric dipole (VED) above a dissipative earth. The scattered field is shown to consist of a direct contribution from a perfect image source, and a correction due to the finite conductivity of earth which is expressible in terms of an incomplete Hankel function. The resultant expression readily reduces to the well‐known asymptotic solutions in both the space‐wave and ground‐wave regions. Validity of the space‐wave expression in the far zone is found to be dependent upon the observation angle as well as the refractive index of earth. In the near field, alternative approximate formulas in closed form are derived from the incomplete Hankel function expression for different elevation angles. These formulas are shown to yield accurate results whenever the distance from the image source is greater than about 0.2λcwhere λcis the effective wavelength (or skin depth) of earth. For distance smaller than 0.2λc, however, an analytical expression based upon a quasistatic approximation is generally applicable and has been discussed

ISSN:0048-6604    

DOI:10.1029/RS009i012p01129

年代:1974

数据来源: WILEY

摘要:

The integral equations describing electromagnetic scattering from cylindrical, perfectly conducting surfaces are formulated and numerical results are presented. The results are compared with those obtained using approximate methods such as physical optics, geometrical optics, and perturbation theory. The integral equation solutions show that the surface radius of curvature must be greater than 2.5 wavelengths for either the physical optics or geometrical optics to give satisfactory results. It has also been shown that perturbation theory agrees with the exact fields as long as the root‐mean‐square surface roughness is less than one tenth of a wavelen

ISSN:0048-6604    

DOI:10.1029/RS009i012p01139

年代:1974

数据来源: WILEY

摘要:

Electromagnetic wave propagation inside an empty rectangular mine tunnel with imperfect walls is considered. The modal expansion of the fields is complicated by the coupling of the basic modes by the imperfect walls. To avoid this difficulty, and in view of the large guide dimensions relative to the free space wavelength, a geometrical ray approach is proposed. To provide a theoretical foundation for the method, we first consider an idealized waveguide model with two perfectly reflecting side walls. The modal field expansion for this prototype model is fully analyzed to provide a satisfactory comparison between the modal and the geometrical ray sums. The proposed general ray method is then applied to the rectangular waveguide when all four walls are imperfectly conducting. Finally, the influence of wall roughness is considered by a relatively simple method.

ISSN:0048-6604    

DOI:10.1029/RS009i012p01147

年代:1974

数据来源: WILEY

摘要:

A new diagnostic tool for space plasmas is presented. The oblique resonance excited by an antenna in a magnetoplasma has been detected in the ionosphere with a rocket experiment. The instrument is simple and consists of a fixed frequency transmitter and a receiver. The resonance cone and its fine structure are used to deduce the plasma density and the electron temperature. The possibility of measuring field‐aligned currents is briefly discusse

ISSN:0048-6604    

DOI:10.1029/RS009i012p01159

年代:1974

数据来源: WILEY

ISSN:0048-6604    

DOI:10.1029/RS009i012p01165

年代:1974

数据来源: WILEY