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101.
102.
Thomas Hobiger Jun Amagai Masanori Aida Hideki Narita 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
Reflected signals of the Global Navigation Satellite System (GNSS) from the sea or land surface can be utilized to deduce and monitor physical and geophysical parameters of the reflecting area. Unlike most other remote sensing techniques, GNSS-Reflectometry (GNSS-R) operates as a passive radar that takes advantage from the increasing number of navigation satellites that broadcast their L-band signals. Thereby, most of the GNSS-R receiver architectures are based on dedicated hardware solutions. Software-defined radio (SDR) technology has advanced in the recent years and enabled signal processing in real-time, which makes it an ideal candidate for the realization of a flexible GNSS-R system. Additionally, modern commodity graphic cards, which offer massive parallel computing performances, allow to handle the whole signal processing chain without interfering with the PC’s CPU. Thus, this paper describes a GNSS-R system which has been developed on the principles of software-defined radio supported by General Purpose Graphics Processing Units (GPGPUs), and presents results from initial field tests which confirm the anticipated capability of the system. 相似文献
103.
Thomas I. Gray Byron D. Tapley 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(6):371-377
Observational data to effectively evaluate weather effects, which accumulate into current climate status, are available for affluent nations but often are inadequate elsewhere. Data acquired by satellite sensors in the visible-near infrared portion of the reflected solar energy spectrum have been accumulated daily since 1965 and for the earth's emitted radiance in the 11000 nm window since 1972. With the advent of the TIROS-N satellite in 1978, the solar reflected energy has been sensed in two separate channels and beginning with NOAA-6, the second vehicle of the TIROS-N family, these two channels became complementary rather than overlapping. This feature makes vegetative monitoring possible and now is being exploited to provide daily experimental products. These global vegetative index (GVI) arrays have been used to observe and map the effects of droughts, floods, adverse winds and thermal stresses on the global arable lands. These data and the related sea surface temperatures, both derived from satellite data, provide realistic measures of the global climate and can assist climatic forecasting. 相似文献
104.
This summarizes the authors' research into the state-of-the-practice of software quality assurance (SQA) in software organizations throughout the Department of Defense (DoD). Information was obtained through personal visits to a limited number of software facilities and by utilizing a SQA questionnaire that was mailed to 27 DoD software organizations. Twenty questionnaires were returned from Army, Navy, Marine Corps, and Air Force organizations involved in the Life Cycle Software Support (LCSS) process. The survey developed information regarding such topics as: staffing; personnel qualifications; quality standards used; SQA responsibilities; error data collection; adequacy of existing documentation; staff composition; distribution of SQA effort; and workforce mix. In addition, a list of SQA ``Lessons Learned' was developed from comments made by DoD quality managers. The results of this study indicate a wide variance in the application of SQA within the DoD. 相似文献
105.
Thomas W. Becker 《Space Policy》1991,7(1)
The discoveries and knowledge gained from space exploration and technology development are valuable scientific education tools which are not being adequately used in the classroom. Moreover, the increasing application of space technology to everyday life and industry requires a work force educated to be able to work productively in this field and to take advantage of all it has to offer. This article provides a survey of what is presently being done in the field of space education in Europe and the USA. Although encouraging, it is not nearly enough to meet the needs of 21st century society, principally because current efforts lack government or industry support. The author argues that this state of affairs must change, and proposed an international symposium as a first step towards this goal. 相似文献
106.
R.W.L. Thomas 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(5):157-166
A Monte Carlo simulation program has been used to compute the signal contribution of surface elements outside the field of view of a satellite borne sensor in both the visible and infrared spectra for realistic atmospheric models. For azimuthally symmetric reflection the effect of an arbitrary surface albedo pattern can be represented by two spread functions, namely, 1) the ground-satellite spread function, and 2) the ground-ground spread function. Examples of computed spread functions are shown together with their Fourier correspondents, the modulation transfer functions. It has been shown that the central portions of the line spread functions behave as the inverse distance while the point spread functions always possess a region behaving as the inverse square of the radial distance. The median distance is shown to relate to the weighted molecular and aerosol scale height, and for large distances the spread functions become independent of the aerosol loading. 相似文献
107.
Clarence A. Wingate Jr. Thomas B. Coughlin Ralph M. Sullivan 《Acta Astronautica》1980,7(12):1389-1401
An optical bench has been designed and built that must hold the alignment of five optical elements to deflections of 1–2 arc s during orbital operation. In addition, it must suffer no alignment changes during the launch and prestabilization phase of the mission. Severe weight constraints, in conjunction with the thermal and structural requirements, led to the choice of graphite fiber reinforced epoxy egg crate core and face sheets for the bench construction. Active temperature control was necessary to meet thermal deflection objectives, and novel kinematic mountings were required to prevent spacecraft bending from deflecting the bench. The structural and thermal analyses both show that the mission objectives can be met with margin by the present design. No adverse effects from launch are expected, and the maximum thermal bending is expected to be less than 2 arc s. 相似文献
108.
Thomas H. Zurbuchen 《Space Science Reviews》2006,124(1-4):77-90
Research into the heliospheric structure and its relation to the solar boundary is at an impasse. After successful predictions
by Parker about the zeroth-order behavior of the heliospheric magnetic field and the solar wind, the heliospheric community
struggles to make substantive progress toward a predictive model describing the connections between the Sun and its space
environment, between the closed corona and the open corona extending to the planets. This is caused by our lack of understanding
of the basic processes heating the corona and transporting open magnetic field. We detail the models used to describe this
connectivity, from potential field source surface models to full MHD techniques. We discuss the current limitations of both
approaches. Finally, we address a recent attempt to advance our understanding beyond these limitations. At this point in time
the proposed theory remains controversial in the community, but it addresses important shortcomings of current approaches
outlined above. 相似文献
109.
Cyanobacteria and similar organisms produced most of the oxygen found in Earth's atmosphere, which implies that early photosynthetic organisms would have lived in an atmosphere that was rich in CO2 and poor in O2. We investigated the tolerance of several cyanobacteria to very high (>20 kPa) concentrations of atmospheric CO2. Cultures of Synechococcus PCC7942, Synechocystis PCC7942, Plectonema boryanum, and Anabaena sp. were grown in liquid culture sparged with CO2-enriched air. All four strains grew when transferred from ambient CO2 to 20 kPa partial pressure of CO2 (pCO2), but none of them tolerated direct transfer to 40 kPa pCO2. Synechococcus and Anabaena survived 101 kPa (100%) pCO2 when pressure was gradually increased by 15 kPa per day, and Plectonema actively grew under these conditions. All four strains grew in an anoxic atmosphere of 5 kPa pCO2 in N2. Strains that were sensitive to high CO2 were also sensitive to low initial pH (pH 5-6). However, low pH in itself was not sufficient to prevent growth. Although mechanisms of damage and survival are still under investigation, we have shown that modern cyanobacteria can survive under Earth's primordial conditions and that cyanobacteria-like organisms could have flourished under conditions on early Mars, which probably had an atmosphere similar to early Earth's. 相似文献
110.
Jones TD 《Aerospace America》2005,43(8):14-16
A former astronaut justifies human space exploration and provides a rebuttal to criticism of continued exploration. The discussion includes examples of skeptics' arguments and examples of NASA achievements that have had direct economic and social impacts on the United States. 相似文献