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101.
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   
102.
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   
103.
Tobias  S.M.  Weiss  N.O. 《Space Science Reviews》2000,94(1-2):153-160
The 11–year solar activity cycle is magnetic in origin and is responsible for small changes in solar luminosity and the modulation of the solar wind. The terrestrial climate exhibits much internal variability supporting oscillations with many frequencies. The direct effect of changing solar irradiance in driving climatic change is believed to be small, and amplification mechanisms are needed to enhance the role of solar variability. In this paper we demonstrate that resonance may play a crucial role in the dynamics of the climate system, by using the output from a nonlinear solar dynamo model as a weak input to a simplified climate model. The climate is modelled as oscillating about two fixed points (corresponding to a warm and cold state) with the weak chaotically modulated solar forcing on average pushing the solution towards the warm state. When a typical frequency of the input is similar to that of the chaotic climate system then a dramatic increase in the role of the solar forcing is apparent and complicated intermittent behaviour is observed. The nonlinear effects are subtle however, and forcing that on average pushes the solution towards the warm state may lead to increased intervals of oscillation about either state. Owing to the intermittent nature of the timeseries, analysis of the relevant timeseries is shown to be non-trivial.  相似文献   
104.
This paper reviews the progress achieved in planetary atmospheric electricity, with focus on lightning observations by present operational spacecraft, aiming to fill the hiatus from the latest review published by Desch et al. (Rep. Prog. Phys. 65:955–997, 2002). The information is organized according to solid surface bodies (Earth, Venus, Mars and Titan) and gaseous planets (Jupiter, Saturn, Uranus and Neptune), and each section presents the latest results from space-based and ground-based observations as well as laboratory experiments. Finally, we review planned future space missions to Earth and other planets that will address some of the existing gaps in our knowledge.  相似文献   
105.
With major emphasis on simulation, a university laboratory telerobotics facility permits problems to be approached by groups of graduate students. Helmet-mounded displays provide realism; the slaving of the display to the human operator's viewpoint gives a sense of `telepresence' that may be useful for prolonged tasks. Using top-down 3-D model control of distant images allows distant images to be reduced to a few parameters to update the model used for display to the human operator in a preview model to circumvent, in part, the communication delay. Also, the model can be used as a format for supervisory control and permit short-term local autonomous operations. Image processing algorithms can be made simpler and faster without trying to construct sensible images from the bottom. Control studies of telerobots lead to preferential manual control modes and, in this university environment, to basic paradigms for human motion and thence, perhaps, to redesign of robotic control, trajectory path planning, and rehabilitation prosthetics. Speculation as to future industrial drives for this telerobotic field suggests efficient roles for government agencies such as NASA  相似文献   
106.
The ordered-statistics (OS) constant false-alarm rate (CFAR) is relatively immune to the presence of interfering targets among the reference cells used to determine the average background. OS CFAR performance in a multitarget environment was previously studied by simulation. The author obtains analytic expressions for the added detection loss, assuming strong interfering targets. The real target is assumed to be a Rayleigh fluctuating target. Numerical examples are included  相似文献   
107.
The Cassini visual and infrared mapping spectrometer (VIMS) investigation is a multidisciplinary study of the Saturnian system. Visual and near-infrared imaging spectroscopy and high-speed spectrophotometry are the observational techniques. The scope of the investigation includes the rings, the surfaces of the icy satellites and Titan, and the atmospheres of Saturn and Titan. In this paper, we will elucidate the major scientific and measurement goals of the investigation, the major characteristics of the Cassini VIMS instrument, the instrument calibration, and operation, and the results of the recent Cassini flybys of Venus and the Earth–Moon system.This revised version was published online in July 2005 with a corrected cover date.  相似文献   
108.
The Cassini-Huygens Cosmic Dust Analyzer (CDA) is intended to provide direct observations of dust grains with masses between 10−19 and 10−9 kg in interplanetary space and in the jovian and saturnian systems, to investigate their physical, chemical and dynamical properties as functions of the distances to the Sun, to Jupiter and to Saturn and its satellites and rings, to study their interaction with the saturnian rings, satellites and magnetosphere. Chemical composition of interplanetary meteoroids will be compared with asteroidal and cometary dust, as well as with Saturn dust, ejecta from rings and satellites. Ring and satellites phenomena which might be effects of meteoroid impacts will be compared with the interplanetary dust environment. Electrical charges of particulate matter in the magnetosphere and its consequences will be studied, e.g. the effects of the ambient plasma and the magnetic field on the trajectories of dust particles as well as fragmentation of particles due to electrostatic disruption.The investigation will be performed with an instrument that measures the mass, composition, electric charge, speed, and flight direction of individual dust particles. It is a highly reliable and versatile instrument with a mass sensitivity 106 times higher than that of the Pioneer 10 and 11 dust detectors which measured dust in the saturnian system. The Cosmic Dust Analyzer has significant inheritance from former space instrumentation developed for the VEGA, Giotto, Galileo, and Ulysses missions. It will reliably measure impacts from as low as 1 impact per month up to 104 impacts per second. The instrument weighs 17 kg and consumes 12 W, the integrated time-of-flight mass spectrometer has a mass resolution of up to 50. The nominal data transmission rate is 524 bits/s and varies between 50 and 4192 bps.This revised version was published online in July 2005 with a corrected cover date.  相似文献   
109.
Role of BIT in support system maintenance and availability   总被引:1,自引:0,他引:1  
The role of built in test (BIT) in electronic systems has grown in prominence with the advances in system complexity and concern over maintenance lifecycle costs of large systems. In an environment where standards drive system designs (and provide an avenue for focused advancement in technology), standards for BIT are very much in an evolutionary state. The reasons for advancing the effectiveness of BIT include reduced support overhead, greater, confidence in operation, and increased system availability. The cost of supporting military electronic systems (avionics, communications, and weapons systems) has driven much of the development in BIT technology. But what about the systems that support these end items that contain test and measurement instrumentation - such as automatic test equipment (ATE), simulators and avionics development suites? There has also been a beneficial effect on the maintenance and availability of these systems due to the infusion of BIT into their component assemblies. But the effect has been much more sporadic and fragmented. This paper looks at the state of BIT in test and measurement instruments, explain its affect on system readiness, and present ideas on how to improve BIT technologies and standards. This will not provide definitive answers to BIT development questions, since the factors that affect it are specific to the instrument itself. The topics covered in this paper are: definitions of built-in test, instrument BIT history, importance of BIT fault coverage and isolation in support systems, overview of BIT development process issues that limit the effectiveness of BIT Standards related to instrument BIT, making BIT more effective in support system maintenance and availability and conclusions.  相似文献   
110.
The purpose was to combine bicycle exercise and LBNP as a model to investigate the mechanisms regulating circulation during gravitatiobal stresses. METHODS: Cardiac Output (CO) by acetylene-, argon-, oxygen rebreathing; Heart Rate (HR) from ECG; Mean Arterial Pressure (MAP) by arm cuff; Plasma Nor-Epinephrine (NE), Epinephrine (E), and Lactate (HLa) by isotope and enzymatic techniques respectively. Total Peripheral Resistance (TPR)=MAP/CO and stroke volume (SV)=CO/HR. Six subjects exercised at 180–200 Watts in the upright position on a mechanically braked computer controlled small bicycle ergometer placed in a LBNP box. The above parameters were measured at rest and at 5 and 9 min of exercise without and with LBNP at −30 or −40 mmHg (depending on LBNP tolerance). RESULTS AND CONCLUSIONS: In the face of an increased sympathetic nervous activity (Ne+E, TPR, and HR increased) during exercise in LBNP, there was a decrease in CO and SV indicating that the venous return was insufficient. However, HLa was unchanged demonstrating that the blood flow to the working muscles did not suffer.  相似文献   
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