排序方式: 共有14条查询结果,搜索用时 187 毫秒
1.
John C. Raymond Raid Suleiman John L. Kohl Giancarlo Noci 《Space Science Reviews》1998,85(1-2):283-289
A great deal of evidence for elemental abundance variations among different structures in the solar corona has accumulated
over the years. Many of the observations show changes in the relative abundances of high- and low-First Ionization Potential
elements, but relatively few show the absolute elemental abundances. Recent observations from the SOHO satellite give absolute
abundances in coronal streamers. Along the streamer edges, and at low heights in the streamer, they show roughly photospheric
abundances for the low-FIP elements, and a factor of 3 depletion of high-FIP elements. In the streamer core at 1.5 R·, both
high- and low-FIP elements are depleted by an additional factor of 3, which appears to result from gravitational settling.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
Spaceborne along-track SAR interferometry: performance analysis andmission scenarios 总被引:1,自引:0,他引:1
A system study of a spaceborne along-track synthetic aperture radar (SAR) interferometer is presented. This sensor has been successfully experienced for detecting moving targets by using only airborne installations. Several key issues must be addressed when spaceborne configurations are envisaged. To this end, a quantitative evaluation of system performance and measurement accuracy has been conducted. First, the identification of possible space configurations has been accomplished. In particular, the two antennas can operate on a single satellite or they can be carried along appropriate trajectories by two spacecrafts. Then, an error budget of radial velocity measurement accuracy has been performed. Finally, two possible mission scenarios are dealt in details, and numerical results are reported 相似文献
3.
This paper presents an application for modern star trackers aimed at the estimation of the spacecraft angular velocity vector on the basis of the star field images acquired during fast rotations, when star identification and tracking are not possible. Angular rates in the range 2–8°/s are considered, which strongly affect the characteristics of the acquirable images, in particular for shape and brightness. The procedure consists in the exploitation of the rigid motion equations to identify the rotation that best fits the observed star trajectories in the sensor field of view. Its coverage capability is analysed with reference to the sensitivity of state-of-the-art photodetectors. The probability of an adequate acquisition is shown to be 0.80 with random pointing and rotation axis over the celestial sphere. Firstly, the accuracy of the procedure is discussed in numerical tests. Then, end-to-end tests are reported, which have been operated by implementing the procedure in a hardware sensor model that acquires simulated star field scenes in a laboratory facility. Both the validations point out that the accuracy of 1°/s, suggested by the European Space Agency for this kind of application, has been achieved. Moreover, the rate of rotation about axes perpendicular to the boresight can be computed with accuracy one order of magnitude better. 相似文献
4.
5.
Mauro Messerotti Francesca Zuccarello Salvatore L. Guglielmino Volker Bothmer Jean Lilensten Giancarlo Noci Marisa Storini Henrik Lundstedt 《Space Science Reviews》2009,147(3-4):121-185
Key drivers of solar weather and mid-term solar weather are reviewed by considering a selection of relevant physics- and statistics-based scientific models as well as a selection of related prediction models, in order to provide an updated operational scenario for space weather applications. The characteristics and outcomes of the considered scientific and prediction models indicate that they only partially cope with the complex nature of solar activity for the lack of a detailed knowledge of the underlying physics. This is indicated by the fact that, on one hand, scientific models based on chaos theory and non-linear dynamics reproduce better the observed features, and, on the other hand, that prediction models based on statistics and artificial neural networks perform better. To date, the solar weather prediction success at most time and spatial scales is far from being satisfactory, but the forthcoming ground- and space-based high-resolution observations can add fundamental tiles to the modelling and predicting frameworks as well as the application of advanced mathematical approaches in the analysis of diachronic solar observations, that are a must to provide comprehensive and homogeneous data sets. 相似文献
6.
Giancarlo Setti 《Space Science Reviews》1999,89(3-4):691-691
This volume contains the proceedings of the NATO Advanced Study Institute on Polar Cap Boundary Phenomena held at Longyearbyen,
Svalbard, Norway on June 4–13, 1997, which was the third NATO Workshop on magnetospheric boundary phenomena observable at
high latitudes. Svalbard has a uniquely interesting location from observational point of view in that the dayside aurora can
be observed there in the noon local time sector during the midwinter. The Norwegian groups working at Svalbard were the organisers
of this third workshop as well as of the two earlier ones, but only this third one was held at Svalbard. It was attended by
86 space physicists from all over the world. The book contains 36 papers, of which the majority were presented as invited
papers at the workshop, a few were contributed papers and the last paper in the volume gives a summary of the content of the
workshop.
As emphasized in both the Foreword and the Summary chapter of the book, the research field of the polar cap and its boundaries
to other magnetospheric regions at high latitudes is one that has seen a fast development in the last ten years. This is to
a great deal due to the research work done at Svalbard in combination with satellite measurements and theory development.
The review in these proceedings provide also the non-specialist reader with good summaries of where different research questions
stand at present.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
Deep and Shallow Solid-Earth Structures Reconstructed with Sequential Integrated Inversion (SII) of Seismic and Gravity Data 总被引:3,自引:0,他引:3
In this paper, the possibility of using simultaneously seismic and gravity data, for the reconstruction of solid-Earth structures,
has been investigated through the use of an algorithm which allows joint efficient and reliable optimisation of compressional
velocity and mass density parameters. We view the measured data as a realisation of a stochastic process generated by the
physical parameters to be sought and we construct a “probability density function” which includes three kinds of information:
information derived from gravity measurements; information derived from seismic travel time inversion and information on the
physical correlation among density and velocity parameters. We show that combining data has a beneficial effect on the inversion
since: it makes the problem more stable and as a consequence, providing that the quality of data is sufficiently high, enables
more accurate and reliable reconstruction of the unknown parameters. In this context, we look forward the GOCE mission, which
promises high spatial resolution (100–200 km) and accurate (1–2 mGals) gravity data.
We show results obtained from data sets calculated for a lateral inhomogeneous earth synthetic model and from seismic and
gravity field data analysed:
— in the framework of TOMOVES (TOMOgraphy of Mt. VESuvius) experiment, an European project aiming at reconstructing the 3-D
image of Mt. Vesuvius volcano and the crust underneath. using high resolution seismic tomography techniques and other geophysical
methods;
— for a profile inserted in a project aiming at reconstructing the crustal structure between Corsica and the Northern Appennines
which crosses the Ligurian Sea and cuts the Ligurian Appennines W of La Spezia, extending up to Parma.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
Roberta Paradiso Roberta Buonomo Mike A. Dixon Giancarlo Barbieri Stefania De Pascale 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Soybean [Glycine max (L.) Merr.] is one of the plant species selected within the European Space Agency (ESA) Micro-Ecological Life Support System Alternative (MELiSSA) project for hydroponic cultivation in Biological Life Support Systems (BLSSs), because of the high nutritional value of seeds. Root symbiosis of soybean with Bradirhizobium japonicum contributes to plant nutrition in soil, providing ammonium through the bacterial fixation of atmospheric nitrogen. The aim of this study was to evaluate the effects of two hydroponic systems, Nutrient Film Technique (NFT) and cultivation on rockwool, and two nitrogen sources in the nutrient solution, nitrate (as Ca(NO3)2 and KNO3) and urea (CO(NH2)2), on root symbiosis, plant growth and seeds production of soybean. Plants of cultivar ‘OT8914’, inoculated with B. japonicum strain BUS-2, were grown in a growth chamber, under controlled environmental conditions. 相似文献
9.
Initial attitude acquisition by a modern star tracker is investigated here. Criteria for efficient organization of the on-board database are discussed with reference to a brightness-independent initial acquisition algorithm. Star catalog generation preprocessing is described, with emphasis on the identification of minimum star brightness for detection by a sensor based on a charge coupled device (CCD) photodetector. This is a crucial step for proper evaluation of the attainable sky coverage when selecting the stars to be included in the on-board catalog. Test results are also reported, both for reliability and accuracy, even if the former is considered to be the primary target. Probability of erroneous solution is 0.2% in the case of single runs of the procedure, while attitude determination accuracy is in the order of 0.02/spl deg/ in the average for the computation of the inertial pointing of the boresight axis. 相似文献
10.
Performance of spaceborne bistatic synthetic aperture radar 总被引:2,自引:0,他引:2
Moccia A. Salzillo G. D'Errico M. Rufino G. Alberti G. 《IEEE transactions on aerospace and electronic systems》2005,41(4):1383-1395
This paper reports on a model developed for evaluating major system performance of a spaceborne bistatic synthetic aperture radar (SAR) for remote sensing applications. The procedure accounts for formation flying aspects. It is particularly aimed at comparison of monostatic and bistatic cases, and, as a test case, it is applied to study a novel configuration, based on a small satellite equipped with a receiving-only antenna orbiting in tandem with a large, noncooperative transmitting spacecraft, the Italian COSMO-SkyMed mission. Numerical results and plots show the effectiveness of the procedure as a mission design tool and put in evidence key issues and characteristics of the proposed spaceborne bistatic formation. 相似文献