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671.
L. Vigroux J. A. Paul P. Delache G. F. Bignami P. A. Caraveo L. Salotti 《Space Science Reviews》1985,40(1-2):91-97
Einstein and EXOSAT data on the soft X-ray source IE 0630+178, the proposed counterpart of the -ray source GEMINGA, are analyzed for variability on the time scale of one to three hours. The EXOSAT September 1983 data, with an uninterrupted strech of over 10 hours offer the most interesting case. In parallel, a similar analysis is presented for the first time, for the optical data of the mV21 proposed counterpart. About 30 CCD exposures, of 15 min. each, taken over two consecutive nights at the 3.6 m CFH telescope, yield evidence of variability, when compared to the data of similar nearby objects in the field.Visiting astronomer at the Canada-France-Hawaii Telescope, operated by the National Concil of Research, Canada, the Centre National de la Recherche Scientifique, France, and the University of Hawaii. 相似文献
672.
"Integral relay" is a relay concept in which all the aircraft in a control sector that are under the control of an Army flight operations center (FOC) are electronically capable of functioning as relays for communication with aircraft out of direct contact with the FOC. This paper deals with the effectiveness of integral relay operations based on the assumption of random spatial distribution of aircraft. It describes the development of a control sector line-of-sight (LOS) model and of a methodology for effectiveness analysis, and the application of the methodology to one numerical example. It is shown that the LOS conditions in the control sector may be represented by two LOS characteristics which are functions of both aircraft clearance and the terrain and FOC characteristics. Probabilities of direct and indirect (via relay) LOS between the FOC and randomly located aircraft are derived for operations without and with integral relay. The effectiveness, expressed as an increase in LOS probability, is a function of aircraft density and the above two LOS characteristics and is representative of the control sector as a whole. Numerical results are obtained by probability analysis and statistical sampling. 相似文献
673.
E. Hilsenrath M. R. Schoeberl A. R. Douglass P. K. Bhartia J. Barnett R. Beer J. Waters M. Gunson L. Froidevaux J. Gille P. F. Levelt 《Space Science Reviews》2006,125(1-4):417-430
Aura, the last of the large EOS observatories, was launched on July~15, 2004. Aura is designed to make comprehensive stratospheric
and tropospheric composition measurements from its four instruments, HIRDLS, MLS, OMI and TES. These four instruments work
in synergy to provide data on ozone trends, air quality and climate change. The instruments observe in the nadir and limb
and provide the best horizontal and vertical resolution ever achieved from space. After over one year in orbit the instruments
are nearly operational and providing data to the scientific community. We summarize the mission, instruments, and initial
results and give examples of how Aura will provide continuity to earlier chemistry missions. 相似文献
674.
R. F. Wimmer-Schweingruber N. U. Crooker A. Balogh V. Bothmer R. J. Forsyth P. Gazis J. T. Gosling T. Horbury A. Kilchenmann I. G. Richardson J. D. Richardson P. Riley L. Rodriguez R. von Steiger P. Wurz T. H. Zurbuchen 《Space Science Reviews》2006,123(1-3):177-216
While interplanetary coronal mass ejections (ICMEs) are understood to be the heliospheric counterparts of CMEs, with signatures
undeniably linked to the CME process, the variability of these signatures and questions about mapping to observed CME features
raise issues that remain on the cutting edge of ICME research. These issues are discussed in the context of traditional understanding,
and recent results using innovative analysis techniques are reviewed. 相似文献
675.
Radar: The Cassini Titan Radar Mapper 总被引:1,自引:0,他引:1
C. Elachi M. D. Allison L. Borgarelli P. Encrenaz E. Im M. A. Janssen W. T. K. Johnson R. L. Kirk R. D. Lorenz J. I. Lunine D. O. Muhleman S. J. Ostro G. Picardi F. Posa C. G. Rapley L. E. Roth R. Seu L. A. Soderblom S. Vetrella S. D. Wall C. A. Wood H. A. Zebker 《Space Science Reviews》2004,115(1-4):71-110
The Cassini RADAR instrument is a multimode 13.8 GHz multiple-beam sensor that can operate as a synthetic-aperture radar (SAR) imager, altimeter, scatterometer, and radiometer. The principal objective of the RADAR is to map the surface of Titan. This will be done in the imaging, scatterometer, and radiometer modes. The RADAR altimeter data will provide information on relative elevations in selected areas. Surfaces of the Saturn’s icy satellites will be explored utilizing the RADAR radiometer and scatterometer modes. Saturn’s atmosphere and rings will be probed in the radiometer mode only. The instrument is a joint development by JPL/NASA and ASI. The RADAR design features significant autonomy and data compression capabilities. It is expected that the instrument will detect surfaces with backscatter coefficient as low as −40 dB.RADAR Team LeaderThis revised version was published online in July 2005 with a corrected cover date. 相似文献
676.
677.
MIMO radar: snake oil or good idea? 总被引:2,自引:0,他引:2
MIMO communication is theoretically superior to conventional communication under certain conditions, and MIMO communication also appears to be practical and cost-effective in the real world for some applications. It is natural to suppose that the same is true for MIMO radar, but the situation is not so clear. Researchers claim many advantages of MIMO radar relative to phased array radars (e.g., better detection performance, better angular resolution, better angular measurement accuracy, improved robustness against RFI, ECM, multipath, etc.). We will evaluate such assertions from a system engineering viewpoint. In particular, there are serious trade-offs of MIMO vs. phased array radars relative to cost, system complexity, and risk considering numerous real world effects that are not included in most theoretical analyses. Moreover, in many cases one can achieve essentially the same radar system improvement with phased array radars using simpler, less expensive, and less risky algorithms. We evaluate roughly a dozen asserted advantages of MIMO radar relative to phased arrays. 相似文献
678.
S. A. Stern D. C. Slater J. Scherrer J. Stone M. Versteeg M. F. A’hearn J. L. Bertaux P. D. Feldman M. C. Festou Joel Wm. Parker O. H. W. Siegmund 《Space Science Reviews》2007,128(1-4):507-527
We describe the design, performance and scientific objectives of the NASA-funded ALICE instrument aboard the ESA Rosetta asteroid flyby/comet rendezvous mission. ALICE is a lightweight, low-power, and low-cost imaging spectrograph optimized for cometary far-ultraviolet (FUV) spectroscopy. It will be the first UV spectrograph to study a comet at close range. It is designed to obtain spatially-resolved spectra of Rosetta mission targets in the 700–2050 Å spectral band with a spectral resolution between 8 Å and 12 Å for extended sources that fill its ~0.05^ × 6.0^ field-of-view. ALICE employs an off-axis telescope feeding a 0.15-m normal incidence Rowland circle spectrograph with a toroidal concave holographic reflection grating. The microchannel plate detector utilizes dual solar-blind opaque photocathodes (KBr and CsI) and employs a two-dimensional delay-line readout array. The instrument is controlled by an internal microprocessor. During the prime Rosetta mission, ALICE will characterize comet 67P/Churyumov-Gerasimenko's coma, its nucleus, and nucleus/coma coupling; during cruise to the comet, ALICE will make observations of the mission's two asteroid flyby targets and of Mars, its moons, and of Earth's moon. ALICE has already successfully completed the in-flight commissioning phase and is operating well in flight. It has been characterized in flight with stellar flux calibrations, observations of the Moon during the first Earth fly-by, and observations of comet C/2002 T7 (LINEAR) in 2004 and comet 9P/Tempel 1 during the 2005 Deep Impact comet-collision observing campaign. 相似文献
679.
C. Giammanco P. Bochsler R. Karrer F. M. Ipavich J. A. Paquette P. Wurz 《Space Science Reviews》2007,130(1-4):329-333
Solar chemical abundances are determined by comparing solar photospheric spectra with synthetic ones obtained for different
sets of abundances and physical conditions. Although such inferred results are reliable, they are model dependent. Therefore,
one compares them with the values for the local interstellar medium (LISM). The argument is that they must be similar, but
even for LISM abundance determinations models play a fundamental role (i.e., temperature fluctuations, clumpiness, photon
leaks). There are still two possible comparisons—one with the meteoritic values and the second with solar wind abundances.
In this work we derive a first estimation of the solar wind element ratios of sulfur relative to calcium and magnesium, two
neighboring low-FIP elements, using 10 years of CELIAS/MTOF data. We compare the sulfur abundance with the abundance determined
from spectroscopic observations and from solar energetic particles. Sulfur is a moderately volatile element, hence, meteoritic
sulfur may be depleted relative to non-volatile elements, if compared to its original solar system value. 相似文献
680.
Tracking of a Ballistic Missile with A-Priori Information 总被引:2,自引:0,他引:2
Benavoij A. Chisci L. Farina A. 《IEEE transactions on aerospace and electronic systems》2007,43(3):1000-1016
The paper addresses the problem of estimating the launch and impact points of a ballistic target from radar measurements. The problem has been faced under different hypotheses on the available prior knowledge. The proposed approach combines a nonlinear batch estimator with a recursive MM (multiple model) particle filter in order to attain the estimation goal. Extensive simulations assess the achievable estimation performance. 相似文献