Showing papers in "Radio Science in 1970"
TL;DR: Long term effects model evaluation of meteoritic impact against lunar surface compared with analyses of Lunar Orbiter photographs was presented in this paper, where the authors used a long-term effects model.
Abstract: Long term effects model evaluation of meteoritic impact against lunar surface compared with analyses of Lunar Orbiter photographs
210 citations
TL;DR: The degree of delay-measurement precision that is achievable by very long baseline interferometry depends on the effective recorded bandwidth of the recorded signals as mentioned in this paper, which is a function analogous to the beam-pattern function of a one-dimensional antenna array.
Abstract: The degree of delay-measurement precision that is achievable by very long baseline interferometry depends on the effective bandwidth of the recorded signals. Methods of extending the effective recorded bandwidth for a fixed tape-recorder bandwidth are examined in theory. Two major schemes (simultaneous recording of many widely separated frequency channels and recording sequentially different frequency channels) are examined in detail. Other techniques which involve rapid sampling and temporary ‘buffering’ of data bits are discussed. Methods of processing the data to achieve the maximum-likelihood estimates of phase delay, fringe phase, and fringe rate are derived. Factors that determine the optimum choice of frequency channels are discussed by using a delay ‘resolution or ambiguity’ function. This function is analogous to the beam-pattern function of a one-dimensional antenna array. Theoretical signal-to-noise ratios for the delay and fringe phase measurements are derived by using a simple vector representation of the signal and noise.
170 citations
TL;DR: The results of the remote probing of the moon by means of infrared and microwave emissions and by radar are reviewed in this paper, where the authors discuss how the various observational results can help to explain physical parameters of the lunar surface, such as thermal and electrical conductivities, dielectric constant, density, particle sizes in the lunar regolith, depth of the surface layer.
Abstract: The results of the remote probing of the moon by means of infrared and microwave emissions and by radar are reviewed. Also, we discuss how the various observational results can help to explain physical parameters of the lunar surface, such as thermal and electrical conductivities, dielectric constant, density, particle sizes in the lunar regolith, depth of the surface layer, roughness of the surface, variation of these parameters from point to point on the surface, and amount of heat generated in the lunar interior.
145 citations
TL;DR: In this paper, the boundary value problem of multiple scattering by two equal, parallel, but non-overlapping, circular cylinders is considered, and numerical results are presented only for the extinction and backscattering cross sections, both of which are treated as functions of the separation distance between the two cylinders.
Abstract: The boundary-value problem of multiple scattering by two equal, parallel, but non-overlapping, circular cylinders is considered. Solutions are derived in the form of infinite sums for the scattering intensities and cross sections, but numerical results are presented only for the extinction and back-scattering cross sections, both of which are treated as functions of the separation distance between the two cylinders. Endfire and broadside illumination are distinguished from each other.
99 citations
TL;DR: In this article, exact equations for calculating the brightness temperature of a medium that is bounded by a plane surface and whose properties (dielectric constant and thermometric temperature) vary only with depth are derived.
Abstract: Exact equations are derived for calculating the brightness temperature of a medium that is bounded by a plane surface and whose properties (dielectric constant and thermometric temperature) vary only with depth. Although no approximations are made in the development of the principal results, the final equations are presented in a form most convenient for use in the area of microwave radiometry (that is, in the limit where the Rayleigh-Jeans approximation to the Planck blackbody radiation law is valid). Some special cases in which the differential equations arising in the theory can be solved analytically are presented as examples. A practical numerical method for evaluating the exact equations by use of a digital computer is also discussed.
84 citations
TL;DR: Mars upper atmosphere refractivity, free electron number density and plasma temperature altitude profiles from Mariner 1969 radio occultation measurements were extracted from NASA's Mars Exploration Vehicle (MESV).
Abstract: Mars upper atmosphere refractivity, free electron number density and plasma temperature altitude profiles from Mariner 1969 radio occultation measurements
75 citations
TL;DR: In this article, an integral equation for cauculating the attenuation of radio waves propagating over irregular terrain is derived and applied to three terrain profiles, and the solutions are compared with solutions obtained by using classical methods such as residue series and diffraction theory.
Abstract: An integral equation for cauculating the attenuation of radio waves propagating over irregular terrain is rederived. The integral equation is applied to three terrain profiles, and the solutions are compared with solutions obtained by using classical methods such as the residue series and diffraction theory.
74 citations
TL;DR: In this paper, the authors used the waveguide computer program developed at the Naval Electronics Laboratory Center to obtain waveguide mode constants, each 2° of arc or 222 km along each path, where an exponential electron density profile defined by β = 0.5 km−1 and h′ = 85.5 was assumed.
Abstract: Computations of nighttime field intensity versus distance are made for a 23.4-kHz signal radiated from Hawaii and for propagation paths to Seattle, Ontario (California), Samoa, and Wake Island. The computations were made by using the waveguide computer program developed at the Naval Electronics Laboratory Center to obtain waveguide mode constants, each 2° of arc or 222 km along each path. An exponential electron-density profile defined by β = 0.5 km−1 and h′ = 85.5 was assumed, where β and h′ are defined by Wait [1964]. The resultant field was computed by using a WKB approximation to allow for the variation of mode constants along the paths. Experimental measurements of 23.4-kHz signals from NPM were made aboard an airplane as it flew along these propagation paths. (NPM are the call letters for the Lualualei Navy Radio Station in Hawaii.) Good agreement was obtained, between the theoretical calculations and experimental measurements, strongly supporting the validity of the theoretical approach used (the β = 0.5, h′ = 85.5 km profile assumed) and the conclusion that the increased attenuation observed for propagation to the south is an effect of the geomagnetic field.
66 citations
TL;DR: In this article, it was shown that the increase in electron content of the ionosphere often responds in a dramatic way to increases in geomagnetic activity by monitoring the VHF signals from the geostationary satellite ATS 3, which has been able to study in detail the very pronounced increases in total content often found during the afternoon hours on the day of the commencement of a magnetic storm.
Abstract: The total electron content of the ionosphere often responds in a dramatic way to increases in geomagnetic activity By monitoring the VHF signals from the geostationary satellite ATS 3, it has been possible to study in detail the very pronounced increases in total content often found during the afternoon hours on the day of the commencement of a magnetic storm Comparisons with magnetic field data show that the enhancements in electron content coincide with increases in the total magnetic field This simultaneity suggests that, when the magnetosphere is compressed during the initial phase of a storm, the ionization stored in the magnetic tubes of force may be dumped into the topside of the F region Such a depletion of the protonosphere is in agreement with whistler measurements, which indicate that a contraction of the plasmasphere occurs during periods of increased magnetic activity
54 citations
TL;DR: Lunar near surface gravity estimation by mass density model for agreement between Doppler tracking data from Lunar Orbiter and trajectory predictions as mentioned in this paper, which is based on the mass density models.
Abstract: Lunar near surface gravity estimation by mass density model for agreement between Doppler tracking data from Lunar Orbiter and trajectory predictions
52 citations
TL;DR: In this article, the continuity equation of ionization and the equation of motion of the neutral atmosphere are solved simultaneously in the ionospheric F2 region for different seasons in different epochs of solar activity.
Abstract: The continuity equation of ionization and the equation of motion of the neutral atmosphere are solved simultaneously in the ionospheric F2 region for different seasons in different epochs of solar activity. The model atmosphere used is that given by L. G. Jacchia (1965). Epstein functions are used to simulate the electron and ion temperature profiles. An ionization production function in a Jacchia model atmosphere is derived and used. The computed wind velocity and f0F2 behavior are presented and compared with other theoretical results as well as the existing experimental data. The meridional wind is found to agree reasonably well with the incoherent scatter data. It is found that the declination effect resulting from neutral winds can be used to explain certain experimental observations in a semi-quantitative manner.
TL;DR: In this article, an extension of Fermat's principle, in which the complex phase refractive index is used instead of only the real part, expresses both of these criteria and leads to a corresponding extension of Snell's law or of Haselgrove's equations to calculate the ray path.
Abstract: Standard ray-tracing programs do not calculate satisfactorily the reflection of LF radio waves from the ionosphere because they do not take losses into account. In lossy media, requiring the ray path to have a minimum attenuation in addition to a minimum wave interference gives a more accurate approximation to the full-wave solution. An extension of Fermat's principle, in which the complex phase refractive index is used instead of only the real part, expresses both of these criteria and leads to a corresponding extension of Snell's law or of Haselgrove's equations to calculate the ray path. Although such a path can have complex coordinates, only those with end points in real space are physically significant. An approximation, in which plane waves in the neighborhood of the receiver are assumed, solves the common ray-tracing problem of homing in on the receiver, a problem that is worse for ray tracing in complex space. Applying ray tracing in complex space to a plane wave incident on a plane stratified medium gives a result that agrees exactly with the result obtained by the phase integral method and that agrees satisfactorily with full-wave solutions above 30 kHz for all results shown.
TL;DR: In this paper, the bulk vertical velocity of the ambient electrons can be determined from Thomson scatter observations of the F region at altitudes between 450 and 900 km using a new spectrum analyzer.
Abstract: Thomson scatter observations of the F region at altitudes between 450 and 900 km are described; from them the bulk vertical velocity of the ambient electrons can be determined. These measurements were made possible by the construction of a new spectrum analyzer; they supplement earlier established programs to measure F-region densities and temperatures at Millstone Hill. The uncertainty in the results varies both with time of day and with altitude but is of the order of ±5 m/sec. Sample results are presented which show evidence of (1) thermal expansion and contraction of the layer and (2) oscillatory fluctuations attributed to traveling ionospheric disturbances.
TL;DR: In this article, the zero-order term of the residue series has been employed to calculate the variation of field strength with distance over the earth's surface in the frequency band 78 Hz to 1 kHz.
Abstract: The zero-order term of the residue series has been employed to calculate the variation of field strength with distance over the earth's surface in the frequency band 78 Hz to 1 kHz Spherical symmetry is assumed for the earth and ionosphere The ionosphere is taken to be isotropic, but radial inhomogeneity is allowed A vertical electric dipole source and a realistic propagation-constant model were assumed The computations indicate the accuracy of the usual approximations to the residue series and enable the magnitude of the standing wave effects in the earth-ionosphere cavity to be assessed
TL;DR: The University of Illinois and the GCA Corporation launched a series of four Nike Apache rockets from Wallops Island, Virginia, on July 24, 1968, for the study of changes of lower ionosphere electron densities with solar zenith angle on the same day as mentioned in this paper.
Abstract: The University of Illinois and the GCA Corporation launched a series of four Nike Apache rockets from Wallops Island, Virginia, on July 24, 1968, for the study of changes of lower ionosphere electron densities with solar zenith angle on the same day. An improved method of data analysis is outlined. Profiles of electron density for each of the four rockets are presented and compared with two profiles from years of quiet sun, 1964 and 1965. Evidence is found for an initial increase of free electrons followed by a decrease and then an increase in electron number density as the solar zenith angle changes from 94° to 18°. This pattern suggests a sequence of processes; i.e., electron detachment, recombination, and photo-ionization.
TL;DR: Polarized and depolarized radar maps of moon, attributing anomalies and average diffuse component of echoes to scattering behavior of surface and subsurface rocks are presented in this article.
Abstract: Polarized and depolarized radar maps of moon, attributing anomalies and average diffuse component of echoes to scattering behavior of surface and subsurface rocks
TL;DR: In this article, the radiation resistance of short filamentary electric dipole at arbitrary angle to magnetic field in cold uniform plasma, using full wave theory, was investigated using VLF radiation resistance.
Abstract: VLF radiation resistance of short filamentary electric dipole at arbitrary angle to magnetic field in cold uniform plasma, using full wave theory
TL;DR: In this article, the Haystack radar was used to determine the topography in a belt near the equator of the planet Mars during the 1969 opposition, and the results showed that the variation of surface height with longitude between latitudes 3°N and 12°N is similar to that measured for latitudes near 22°N during the 1967 opposition.
Abstract: During the period surrounding the 1969 opposition, the planet Mars was observed with the Haystack radar to determine the topography in a belt near the equator. Elevation values obtained for the same surface location on Mars on different days of observation agree, for high signal-to-noise ratio cases, to within about 100 meters. Preliminary results show that the variation of surface height with longitude between latitudes 3°N and 12°N is similar to that measured for latitudes near 22°N during the 1967 opposition. The most notable difference is found near 215° longitude, where at 22°N there is a highland at Elysium, although at 5°N a lowland is found. Optically dark regions often have a high radar cross section. However, the topography shows no significant correlation with either the visual or the radar brightness.
TL;DR: In this article, a Monte Carlo technique is used to simulate photoelectron diffusion through the atmosphere; one such method to deduce photo-electron distributions is described. But it is difficult to study the energy, pitch-angle and spatial distributions of photoelectrons with a continuity equation approach because of the large variety and nature of the physical processes that must be considered.
Abstract: Photoelectrons in the ionosphere result from the action of solar ultraviolet radiation on atmospheric gases. It is extremely difficult to study the energy, pitch-angle and spatial distributions of photoelectrons with a continuity equation approach because of the large variety and nature of the physical processes that must be considered. A Monte Carlo technique is well suited to simulate photoelectron diffusion through the atmosphere; one such method to deduce photoelectron distributions is described. Elastic and inelastic collisions with the neutral gases and Coulomb losses to thermal electrons are included. Illustrative results are presented for the photoelectron escape fluxes that result from the release of 20-ev electrons from various ionospheric altitudes.
TL;DR: In this paper, the authors measured the difference in attenuation of horizontally and vertically polarized fields propagating along a 1.89-km path at 30.9 GHz for a rain-induced fade of 18.5 db/km.
Abstract: An experiment that measures the difference in attenuation of horizontally and vertically polarized fields propagating along a 1.89-km path at 30.9 GHz is discussed. For a rain-induced fade of 18.5 db/km, differences between attenuations in horizontal and vertical polarizations as large as 3 db/km have been observed. There is good agreement when these microwave measurements are compared with calculations based on raindrop shapes that were measured visually by an independent investigator. From the data, we conclude that there are significant differences between attenuations in these polarizations for rain-induced fades and that we should think in terms of an effective rain rate for vertical polarization that is less than that measured by rain gages.
TL;DR: In this paper, the authors describe experiments designed to measure the radiation patterns of a longitudinal wave excited in a warm plasma by both monopole and dipole antennas, and the longitudinal wave used in this experiment is the low-frequency ion acoustic wave that propagates with a phase velocity [γkTe/M/i]½.
Abstract: This paper describes experiments designed to measure the radiation patterns of a longitudinal wave excited in a warm plasma by both monopole and dipole antennas. The longitudinal wave used in this experiment is the low-frequency ion acoustic wave that propagates with a phase velocity [γkTe/M/i]½. Experimental results agree well with the theoretical predicted radiation pattern.
TL;DR: In this article, a procedure for determining ray trajectories in warm magnetoplasmas is presented; it is based on mathematical treatments of the wave dispersion relation and is used to interpret top-side resonance at the upper hybrid frequency as oblique echoes.
Abstract: A procedure for determining ray trajectories in warm magnetoplasmas is presented; it is based on mathematical treatments of the wave dispersion relation. This procedure is used to interpret topside resonance at the upper hybrid frequency as oblique echoes. The following results are obtained: when ƒτ 2ƒH.
TL;DR: In this paper, the authors used the full adiabatic theory to describe wave propagation in a warm magnetoplasma for frequencies around the plasma frequency and the upper hybrid resonance frequency.
Abstract: The full adiabatic theory is used to describe wave propagation in a warm magnetoplasma for frequencies around the plasma frequency and the upper hybrid resonance frequency. By comparison with the microscopic theory for directions perpendicular and parallel to the static magnetic field, we can well define the range of validity of the full adiabatic theory, which can then be used for computation of the group velocity. The variation of this group velocity as a function of frequency for several directions of propagation is shown for models corresponding to the ionosphere and the far magnetosphere. Three factors deserve attention: (1) the upper hybrid resonance and its neighborhood can be rigorously studied for far magnetospheric conditions by using the full adiabatic theory; (2) the computed modes present a mixed electrostatic-electromagnetic character; (3) The minima in group velocities for pseudoresonance frequencies progressively fill up as the temperature increases.
TL;DR: In this article, the eigenvalues of spheroidal wave functions are calculated as functions of complex propagation constants; they are displayed on a complex plane to form "eigenvalue charts".
Abstract: Eigenvalues of spheroidal wave functions are calculated as functions of complex propagation constants; they are displayed on a complex plane to form ‘eigenvalue charts.’ These charts show that the eigenvalues have many branch points in the complex planes of their arguments. The values of the branch points and the corresponding eigenvalues are then calculated exactly; a range of several points is shown in a table. These values are the universal constants; they are very important, because they are the basis for determining a complete set of spheroidal wave functions, they give the circle of convergence of the power-series expansions of the eigenvalues, and they also aid in the discovery of domains in which the eigenvalues are obtained by either prolate or oblate asymptotic expansions.
TL;DR: In this article, the D-region electron densities between 65 and 83 km were computed for full-sun conditions assuming this value of recombination coefficient, the [37+] profile of Narcisi and Bailey [1965], and the NO profiles of Barth [1966], Pearce [1969, and Hesstvedt and Jansson [1969].
Abstract: D-region electron densities measured by rockets during the November 12, 1966, solar eclipse are shown to imply an effective recombination coefficient at an altitude of about 80 km of the order of 10−5 cm3 sec−1. The D-region electron densities between 65 and 83 km are computed for full-sun conditions assuming this value of recombination coefficient, the [37+] profile of Narcisi and Bailey [1965], and the NO profiles of Barth [1966], Pearce [1969], and Hesstvedt and Jansson [1969]. Electron densities between 60 and 65 km are estimated on the basis of the above-mentioned NO profiles and the negative-ion model of LeLevler and Branscomb [1968]. Also, electron densities between 80 and 90 km are computed by assuming an effective electron-ion recombination coefficient for NO+ and O2+ of 10−6 cm3 sec−1. There is a reasonable agreement between the computed electron densities and those measured by rockets launched from Wallops Island near 60° solar zenith angle. These results suggest that variability of D-region electron densities may be caused by changes in H2O vapor concentration induced by atmospheric circulation or eddy transport effects.
TL;DR: In this article, a two-fold hypothesis is offered; the increase in TEC is attributed to an electron flux descending from the protonosphere, which is linked to lowering electron temperatures in the force tube after sunset in the conjugate hemisphere.
Abstract: Studies of total electron content (TEC) have been made by using data obtained during three winter solstices in Paris, France, and Kiruna, Sweden. A nocturnal winter maximum is clearly shown by these data, and an effort is made to hypothesize its cause. A two-fold hypothesis is offered; the increase in TEC is attributed to an electron flux descending from the protonosphere. This flux is linked to lowering electron temperatures in the force tube after sunset in the conjugate hemisphere. In addition to this production process, a regulatory process is invoked to reconcile the observed values with the maximum flux intensity compatible with the theory. The regulatory process is attributed to an interaction betweenthe neutral winds and the ionospheric plasma in the presence of the earth's magnetic field.
TL;DR: In this article, it was shown that the theoretical shape of the quasi-specular component for backscatter is not due to the nature of the correlation coefficient but to the form and behavior of the probability density function for the surface slopes evaluated for tilts near their mean values, the horizontal.
Abstract: The purpose of this note is to put to rest once and for all the use of an erroneous result derived from the linear (or exponential) height correlation coefficient in the physical optics formulation of rough surface scatter. The form of the correlation coefficient near the origin must be quadratic so that the physical optics integral can be evaluated asymptotically. Hence, the theoretical shape of the quasi-specular component for backscatter is not due to the nature of the correlation coefficient but to the form and behavior of the probability density function for the surface slopes evaluated for tilts near their mean values, the horizontal.
TL;DR: Nonlinear oscillations averaging method applied to resonant interactions of acoustic gravity waves is used in this paper for nonlinear oscillation averaging of gravity wave interactions with acoustic resonant interaction.
Abstract: Nonlinear oscillations averaging method applied to resonant interactions of acoustic gravity waves
TL;DR: In this article, the amplitude and phase spectra of forty pairs of selected atmospherics were computed, and propagation parameters for the zero-order wave-guide mode were calculated for nighttime conditions only.
Abstract: Slow-tail portions of atmospherics were recorded simultaneously in Japan and the United States from sources located in the Pacific Ocean area. The amplitude and phase spectra of forty pairs of selected atmospherics were computed, and propagation parameters for the zero-order wave-guide mode were calculated for nighttime conditions only. Attenuation rates for W-E propagation extended from about 0.5 db/Mm at 20 Hz to 2.0 db/Mm at 300 Hz and for E-W propagation from 0.8 db/Mm at 20 Hz to about 2.8 db/Mm at 300 Hz. The phase velocities extended from about 0.7 and 0.8 the velocity of light for W-E and E-W propagation, respectively, at 20 Hz to about 0.93 the velocity of light for either direction at 300 Hz.
TL;DR: In this article, the external impedance per unit length of a long elevated horizontal line source and the mutual impedance between elements of an array of parallel line sources are derived by employing finitely conducting earth image theory techniques.
Abstract: Suitable engineering expressions for the external impedance per unit length of a long elevated horizontal line source and the mutual impedance between elements of an array of parallel line sources are derived by employing finitely conducting earth image theory techniques. It is shown that the image theory and previously derived analytical results, which are rather complicated, are in excellent agreement.