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741.
Green J.L. Benson R.F. Fung S.F. Taylor W.W.L. Boardsen S.A. Reinisch B.W. Haines D.M. Bibl K. Cheney G. Galkin I.A. Huang X. Myers S.H. Sales G.S. Bougeret J.-L. Manning R. Meyer-Vernet N. Moncuquet M. Carpenter D.L. Gallagher D.L. Reiff P.H. 《Space Science Reviews》2000,91(1-2):361-389
The Radio Plasma Imager (RPI) will be the first-of-its kind instrument designed to use radio wave sounding techniques to perform repetitive remote sensing measurements of electron number density (N
e) structures and the dynamics of the magnetosphere and plasmasphere. RPI will fly on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission to be launched early in the year 2000. The design of the RPI is based on recent advances in radio transmitter and receiver design and modern digital processing techniques perfected for ground-based ionospheric sounding over the last two decades. Free-space electromagnetic waves transmitted by the RPI located in the low-density magnetospheric cavity will be reflected at distant plasma cutoffs. The location and characteristics of the plasma at those remote reflection points can then be derived from measurements of the echo amplitude, phase, delay time, frequency, polarization, Doppler shift, and echo direction. The 500 m tip-to-tip X and Y (spin plane) antennas and 20 m Z axis antenna on RPI will be used to measures echoes coming from distances of several R
E. RPI will operate at frequencies between 3 kHz to 3 MHz and will provide quantitative N
e values from 10–1 to 105 cm–3. Ray tracing calculations, combined with specific radio imager instrument characteristics, enables simulations of RPI measurements. These simulations have been performed throughout an IMAGE orbit and under different model magnetospheric conditions. They dramatically show that radio sounding can be used quite successfully to measure a wealth of magnetospheric phenomena such as magnetopause boundary motions and plasmapause dynamics. The radio imaging technique will provide a truly exciting opportunity to study global magnetospheric dynamics in a way that was never before possible. 相似文献
742.
The Radio Plasma Imager investigation on the IMAGE spacecraft 总被引:1,自引:0,他引:1
Reinisch B.W. Haines D.M. Bibl K. Cheney G. Galkin I.A. Huang X. Myers S.H. Sales G.S. Benson R.F. Fung S.F. Green J.L. Boardsen S. Taylor W.W.L. Bougeret J.-L. Manning R. Meyer-Vernet N. Moncuquet M. Carpenter D.L. Gallagher D.L. Reiff P. 《Space Science Reviews》2000,91(1-2):319-359
Radio plasma imaging uses total reflection of electromagnetic waves from plasmas whose plasma frequencies equal the radio sounding frequency and whose electron density gradients are parallel to the wave normals. The Radio Plasma Imager (RPI) has two orthogonal 500-m long dipole antennas in the spin plane for near omni-directional transmission. The third antenna is a 20-m dipole along the spin axis. Echoes from the magnetopause, plasmasphere and cusp will be received with the three orthogonal antennas, allowing the determination of their angle-of-arrival. Thus it will be possible to create image fragments of the reflecting density structures. The instrument can execute a large variety of programmable measuring options at frequencies between 3 kHz and 3 MHz. Tuning of the transmit antennas provides optimum power transfer from the 10 W transmitter to the antennas. The instrument can operate in three active sounding modes: (1) remote sounding to probe magnetospheric boundaries, (2) local (relaxation) sounding to probe the local plasma frequency and scalar magnetic field, and (3) whistler stimulation sounding. In addition, there is a passive mode to record natural emissions, and to determine the local electron density, the scalar magnetic field, and temperature by using a thermal noise spectroscopy technique. 相似文献
743.
This paper considers an air pressure probe, the head part of which is made in the form of a polyhedron inscribed into a sphere. Wind tunnel testing of the probe models is performed, a mathematical model and an algorithm are constructed to calculate all the altitude and airspeed parameters, and an error estimation is given. 相似文献
744.
Brigitte Knapmeyer-Endrun Naomi Murdoch Balthasar Kenda Matthew P. Golombek Martin Knapmeyer Lars Witte Nicolas Verdier Sharon Kedar Philippe Lognonné William B. Banerdt 《Space Science Reviews》2018,214(5):94
Based on an updated model of the regolith’s elastic properties, we simulate the ambient vibrations background wavefield recorded by InSight’s Seismic Experiment for Interior Structure (SEIS) on Mars to characterise the influence of the regolith and invert SEIS data for shallow subsurface structure. By approximately scaling the synthetics based on seismic signals of a terrestrial dust devil, we find that the high-frequency atmospheric background wavefield should be above the self-noise of SEIS’s SP sensors, even if the signals are not produced within 100–200 m of the station. We compare horizontal-to-vertical spectral ratios and Rayleigh wave ellipticity curves for a surface-wave based simulation on the one hand with synthetics explicitly considering body waves on the other hand and do not find any striking differences. Inverting the data, we find that the results are insensitive to assumptions on density. By contrast, assumptions on the velocity range in the upper-most layer have a strong influence on the results also at larger depth. Wrong assumptions can lead to results far from the true model in this case. Additional information on the general shape of the curve, i.e. single or dual peak, could help to mitigate this effect, even if it cannot directly be included into the inversion. We find that the ellipticity curves can provide stronger constraints on the minimum thickness and velocity of the second layer of the model than on the maximum values. We also consider the effect of instrumentation resonances caused by the lander flexible modes, solar panels, and the SEIS levelling system. Both the levelling system resonances and the lander flexible modes occur at significantly higher frequencies than the expected structural response, i.e. above 35 Hz and 20 Hz, respectively. While the lander and solar panel resonances might be too weak in amplitude to be recorded by SEIS, the levelling system resonances will show up clearly in horizontal spectra, the H/V and ellipticity curves. They are not removed by trying to extract only Rayleigh-wave dominated parts of the data. However, they can be distinguished from any subsurface response by their exceptionally low damping ratios of 1% or less as determined by random decrement analysis. The same applies to lander-generated signals observed in actual data from a Moon analogue experiment, so we expect this analysis will be useful in identifying instrumentation resonances in SEIS data. 相似文献
745.
V. P. Okhlopkov 《Cosmic Research》2018,56(2):101-107
The quasi-biennial variations in the flux of galactic cosmic rays (GCRs) have been studied based on the data of stratospheric sensing and measurements by neutron monitors, as well as in various manifestations of solar activity and interplanetary medium parameters. It has been shown that quasi-biennial GCR variations are caused by variations with the same period in the mean magnetic field of the Sun that coincide with them over time and have been identified in the anti-phase, which respond to the sign of this field. The variations in the quasi-biennial cosmic ray are caused by quasi-biennial variations in the mean magnetic field of the Sun via the quasi-biennial variations in the interplanetary magnetic field. 相似文献
746.
A. B. Agul’nik I. V. Kravchenko A. A. Gorbunov A. A. Novoselova A. P. Sklyarova 《Russian Aeronautics (Iz VUZ)》2018,61(3):441-444
This paper considers double bypass aircraft engine with controlled air bleed to the second bypass duct. Its performance is evaluated by mathematical modeling techniques. The second bypass air bleed amount is determined to provide the best engine efficiency at various operating modes. 相似文献
747.
The dynamics of a satellite-gyrostat moving in the central Newtonian force field along a circular orbit is studied. In the particular case when the vector of gyrostatic moment is parallel to one of the satellite’s principal central axes of inertia, all the equilibrium states are determined. For each equilibrium orientation, sufficient conditions of stability are obtained as a result of the analysis of the generalized energy integral, and necessary conditions of stability are determined as a result of analysis of the linearized equations of motion. The evolution of regions of validity for the conditions of stability of equilibrium positions are studied in detail depending on the parameters of the problem. All the bifurcation values of the parameters at which qualitative changes of the regions of stability take place are determined.__________Translated from Kosmicheskie Issledovaniya, Vol. 43, No. 4, 2005, pp. 283–294.Original Russian Text Copyright © 2005 by Sarychev, Mirer, Degtyarev. 相似文献
748.
N.V. Jorjio R.A. Kovrazhkin M.M. Mogilevsky J.M. Bosqued H. Rème J.A. Sauvaud C. Béghin J.L. Rauch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(4):141-144
The plasma diagnostic experiments on the AUREOL-3 satellite have revealed flows of low energy 0+ ions deep inside the night plasmasphere during a large substorm. Flux gradients of the 0+ ions were accompanied by enhancements of ELF electric field noise. The appearance of suprathermal ions at is interpreted within the framework of electrostatic ion-cyclotron acceleration of ionospheric ions in the diffuse auroral zone /12/ followed by a radial displacement of these ions inside the plasmasphere driven by azimuthal electric fields during substorm activity. Electrostatic oscillations observed inside the plasmasphere are apparently associated with gradient instability at the sharp boundaries of suprathermal ion flows. 相似文献
749.
K.H. Ohle G. Sonnemann B. Fichtelmann 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(6):69-72
Quartz-UV occultation measurements by the satellite Interkosmos-16 have been used to calculate ozone densities at altitudes between 50 and 90 km for the period August to October 1976. Below 65 km densities agree well with the Krueger-Minzner-model. Mesopause densities have been studied in some detail. A certain percentage of the profiles show close correlation with the model of Shimazaki and Laird (with a pronounced minimum below the mesopause) while others fit better to the Park and London model (no minimum). This variability of the ozone density may be caused by different processes in the photo-chemistry of ozone. Two possible causes, the temperature dependent rate coefficients and the odd hydrogen processes are discussed in greater detail. 相似文献
750.