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排序方式: 共有199条查询结果,搜索用时 31 毫秒
191.
Bipasha Paul Shukla V. Sathiyamoorthy P.K. Pal 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009,43(12):1931-1939
In this paper, the shortwave and longwave anisotropy for clear sky Indian desert scene has been estimated using long-term surface data, radiative transfer calculations and Helmholtz reciprocity for missing values. This study is important in the perspective of the low inclination satellites like Megha–Tropiques (MT) mission, carrying Scanner for Radiation Budget (ScaRaB) payload, which will provide broadband radiative fluxes at the top of the atmosphere (TOA). Due to low inclination angle, the angular models for clear sky land scenes for the MT-ScaRaB orbits will be dominated by desert points.The Angular Distribution Models (ADMs) determined in this study were compared with existing desert models. It is observed that for longwave radiation, the largest disagreement is observed for higher values of viewing zenith angle, especially for the summer season, where the difference in flux can reach up to 13 W/m2. For the shortwave radiation, higher values of both solar zenith angle and viewing zenith angle cause largest incongruity in the computed albedo from the different models, suggesting the need of caution in interpretation of the flux computations from these bins. In fact at the higher solar zenith angle bin, the disparity in albedo can go up to 6.4%. 相似文献
192.
This paper traces the way in which the European Commission has framed and reframed the issue of EU satellite navigation over 20 years. It investigates how the EU's agenda-setter has ‘talked about’ space policy, with a particular focus on Galileo, and how its own institutional discourse – as revealed in its communications throughout the agenda-setting stage of Galileo's ‘definition’ phase – evolved in the 1990s through the use of ‘frame sets’. In so doing, it illustrates the ways in which, over time, the EU's executive has ‘projected’ the issue of independent satellite navigation capabilities as being politically and economically desirable for Europe, and has sought to persuade decision makers of its cross-policy relevance and potential economic, social and security benefits. The article deconstructs official documents and engages in a close-up analysis of policy formulation, to identify nascent, evolving and mature frames in the definition of Galileo. 相似文献
193.
194.
The present state of knowledge as regards interstellar dust is reviewed in Section 1 (Introduction); Section 2 (Composition of Dust Grains: graphite, silicate, dirty-ice, diamond); Section 3 (Size of Grains: mainly r 10–6 cm); Section 4 (Charge and Temperature of Grains: charge varies from 1–10 electrons (H i clouds) to 500 electrons (H ii clouds); temperature of grain material is about 10–20 K); Section 5 (Distribution and Origin of Grains: confined mainly to discs and arms of spiral galaxies, having had a passive origin by efflux from late-type stars or carbon-stars); Section 6 (Cosmogonical and Cosmological Aspects of Interstellar Grains: accretion by electrical-image forces of one dust grain onto a similarly-charged grain links up the absence of dust and gas in elliptical galaxies with the absence of a magnetic field of the type found in spirals. The origin of the 3 K background radiation field could be produced by a population of rotating silicate grains of r 10–7 cm); Section 7 (Conclusion). 相似文献
195.
This paper describes a set of life cycle methods that were developed in 1980 and 1981 and used in the later phases of the 757/767 airplane programs. They have been used as a framework to establish and guide the introduction of a wide use of similar methods for the future avionics of Boeing's next airplane, the 7J7. The methods were designed to improve communication of the system's requirements, architecture and implementation to a wide group of interested parties ? not just the development engineers but also the users, maintainers, customers and support organizations. A major aspect of these methods is that they were designed to be used for systems in general not just software systems. This paper will describe the background and goals and objectives leading to the need for systems engineering methods, describe the methods and give an example of their use. It will conclude with remarks on steps taken to introduce methods of this type on a wide scale to support the next Boeing airplane. 相似文献
196.
Conclusions Passive observation of the naturally occurring γ-ray and X-ray from the planets is potentially an important technique for
determining their gross chemical composition and on the basis of natural γ-radiation determining if the planetary surface
is composed of differential material. If the planet is not covered by a thick atmosphere then it is possible to map the distribution
of the most abundant elements on a scale of spatial resolution that is of the order of the altitude at which the observations
are made. Initial observations carried out from lunar orbit have shown that the flux levels are approximately as expected
and that the lunar surface is not characterized by any widespread distribution of acidic rocks in the region observed by the
Luna 10 spacecraft. 相似文献
197.
198.
Adolf K. Paul 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(10):51-54
Deviations from horizontal stratification in the F-region can cause significant errors in electron density profile calculations from ionograms. Such situations exist every day during sunrise and sunset. Angle of arrival measurements and studies of the variation of other F-region parameters indicate that gravity waves are frequently strong enough to produce effects of comparable magnitudes. Ray tracing model studies permit a first order estimate of the resulting errors which are largest for the peak parameters. 相似文献
199.