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1.
Samuel N. Goward 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(5):41-50
Shortwave infrared sensors were included on Thematic Mapper to observe vegetation reflected radiance patterns that are related to leaf water content. However, there was some uncertainty whether these measurements would increase the information content of multispectral measurements beyond that provided by visible and near infrared measurements. Analysis of field measurements for corn and soybeans observed throughout the growing season shows that shortwave infrared measurements enhance discrimination between these species, particularly in mid-season. Modeling the canopy reflectances shows that differential leaf absorptance can produce the observed pattern. Analysis of coincident aerial photography suggests that within canopy shadowing is also important. Too few studies of leaf optical properties have been conducted to permit generalization of the results to other vegetation species but the results do show that shortwave infrared measurements contribute new information about vegetation not previously available in visible and near infrared measurements. 相似文献
2.
We revisit the validity of the presence of O(2) or O(3) in the atmosphere of a rocky planet as being a biosignature. Up to now, the false positive that has been identified applies to a planet during a hot greenhouse runaway, which is restricted to planets outside the habitable zone (HZ) of the star that are closer to the star. In this paper, we explore a new possibility based on abiotic photogeneration of O(2) at the surface of a planet that could occur inside the HZ. The search for such a process is an active field of laboratory investigation that has resulted from an ongoing interest in finding efficient systems with the capacity to harvest solar energy on Earth. Although such a process is energetically viable, we find it to be a very unlikely explanation for the observation of O(2) or O(3) in the atmosphere of a telluric exoplanet in the HZ. It requires an efficient photocatalyst to be present and abundant under natural planetary conditions, which appears unlikely according to our discussion of known mineral photochemical processes. In contrast, a biological system that synthesizes its constituents from abundant raw materials and energy has the inherent adaptation advantage to become widespread and dominant (Darwinist argument). Thus, O(2) appears to continue to be a good biosignature. 相似文献
3.
Another derivation of a continuous-time optimal linear filter is presented. Using this result as a point of departure, a feedback version of this continuous filter is postulated and shown to be optimal in the limit as the ``feedback gain' becomes infinite. It is then demonstrated that the need for this infinite feedback gain can frequently be eliminated. This feedback realization of the continuous optimal filter has application to the problem of optimally mixing two or more redundant signals, each contaminated by random noise. The feedback configuration has the advantages of simplicity and the bounding of otherwise troublesome very large errors. A simple example is given of the mixing of two (velocity) references each having exponentially correlated error. 相似文献
4.
Laminar dust flames in a reduced-gravity environment 总被引:1,自引:0,他引:1
Samuel Goroshin Francois-David Tang Andrew J. Higgins John H.S Lee 《Acta Astronautica》2011,68(7-8):656-666
The propagation of laminar dust flames in suspensions of iron in gaseous oxidizers was studied in a low-gravity environment onboard a parabolic flight aircraft. The reduction of buoyancy-induced convective flows and particle settling permitted the measurement of fundamental combustion parameters, such as the burning velocity and the flame quenching distance over a wide range of particle sizes and in different gaseous mixtures. Experimentally measured flame speeds and quenching distances were found in good agreement with theoretical predictions of a simplified analytical model that assumes particles burning in a diffusive mode. However, the comparison of flame speeds in oxygen–argon and oxygen–helium iron suspensions indicates the possibility that fine micron-sized particles burn in the kinetic mode. Furthermore, when the particle spacing is large compared to the scale of the reaction zone, a theoretical analysis suggests the existence of a new so-called discrete flame propagation regime. Discrete flames are strongly dependent on particle density fluctuations and demonstrate directed percolation behavior near flame propagation limits. The experimental observation of discrete flames in particle suspensions will require low levels of gravity over extended periods available only on orbital platforms. 相似文献
5.
Committee on Space Policy H.Guyford Stever Laurence J. Adams Consultant Retired President William A. Anders Senior Executive Vice President Arden L. Bement Jr Vice President Joseph V. Charyk Chairman of the Board Retired Chairman CEO Richard N. Cooper Robert S. Cooper President Edward E. David Jr President John M. Logsdon Director Jeremiah P. Ostriker Director Samuel C. Phillips Retired General Elmer B. Staats Edward C. Stone Jr Vice President 《Space Policy》1989,5(3)
6.
The response of the lower and middle atmosphere to variations in solar irradiance typical of those observed to take place over the 11-year activity cycle has been investigated. The effects on radiative heating rates of changing total solar irradiance, solar spectral irradiance and two different assumptions concerning stratospheric ozone have been studied with a radiative transfer code. The response in the stratosphere depends on the changes specified in the ozone distribution which is not well known. A general circulation model (GCM) of the atmosphere up to 0.1 mbar (about 65 km) has been used to study the impacts of these changes on the thermodynamical structure. The results in the troposphere are very similar to those reported by Haigh99 using a quite different GCM. In the middle atmosphere the model is able to reproduce quite well the observed seasonal evolution of temperature and wind anomalies. Calculations of radiative forcing due to solar variation are presented. These show that the thermal infrared component of the forcing, due to warming of the stratosphere, is important but suggest a near balance between the longwave and shortwave effects of the increased ozone so that ozone change may not be important for net radiative forcing. However, the structure of the ozone change does affect the detailed temperature response and the spectral composition of the radiation entering the troposphere. 相似文献
7.
Coffman Samuel W. Nussberger Arthur A. 《IEEE transactions on aerospace and electronic systems》1966,(5):511-525
Solid explosive detonation in direct contact with a metal body is examined to determine the energy transfer from latent chemical energy of an explosive into kinetic energy of the neighboring body structural members and spacecraft. Much of this is of an empirical nature since the time-dependent, three-dimensional problem involves extremely difficult analysis. Acoustic experiments were performed on a partially constructed spacecraft. A complete set of sound intensity maps was obtained. 相似文献
8.
Daniel S. Goldin Administrator Samuel L. Venneri Chief Technologist Ahmed K. Noor 《Acta Astronautica》1999,44(7-12):407-418
The Intelligent Synthesis Environment (ISE), which is one of the major strategic technologies under development at NASA centers and the University of Virginia, is described. One of the major objectives of ISE is to significantly enhance the rapid creation of innovative affordable products and missions. ISE uses a synergistic combination of leading-edge technologies, including high performance computing, high capacity communications and networking, human-centered computing, knowledge-based engineering, computational intelligence, virtual product development, and product information management. The environment will link scientists, design teams, manufacturers, suppliers, and consultants who participate in the mission synthesis as well as in the creation and operation of the aerospace system. It will radically advance the process by which complex science missions are synthesized, and high-tech engineering systems are designed, manufactured and operated. The five major components critical to ISE are human-centered computing, infrastructure for distributed collaboration, rapid synthesis and simulation tools, life cycle integration and validation, and cultural change in both the engineering and science creative process. The five components and their subelements are described. Related U.S. government programs are outlined and the future impact of ISE on engineering research and education is discussed. 相似文献
9.
Merged series of normalized water leaving radiances obtained from multiple satellite missions for the Mediterranean Sea 总被引:1,自引:0,他引:1
Frédéric Mélin Giuseppe Zibordi Samuel Djavidnia 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
Merging time series of ocean color-derived products provided by independent satellite missions supports related biogeochemical and environmental applications by combining temporally overlapping data sets and by increasing data coverage. The creation of a merged series of normalized water leaving radiances LWN, the primary ocean color product, is presented for the Mediterranean Sea using the SeaWiFS and MODIS data records. The merging relies on an optically-based technique that combines the available LWN signal in a spectrally consistent way. Validation statistics indicate uncertainties associated with the merged LWN decreasing from 23% at 412 nm to 12% in the 500- to 555-nm spectral range. The inter-comparison of the sensor-specific products, conducted at the scale of the basin for daily-to-monthly time scales, indicates an overall consistency. The level of differences varies with the wavelength considered and shows a marked seasonal cycle, with differences that tend to be higher in winter. The merged series is remarkably consistent with the sensor-specific data, with average absolute percent differences lower than 10% for all wavelengths below 555 nm. The benefit of merging in terms of sampling frequency over the basin is also illustrated. A merged series of LWN data based on the two considered missions provides valid data over 36% of the basin area on a daily basis. 相似文献
10.
James C. Leary Richard F. Conde George Dakermanji Carl S. Engelbrecht Carl J. Ercol Karl B. Fielhauer David G. Grant Theodore J. Hartka Tracy A. Hill Stephen E. Jaskulek Mary A. Mirantes Larry E. Mosher Michael V. Paul David F. Persons Elliot H. Rodberg Dipak K. Srinivasan Robin M. Vaughan Samuel R. Wiley 《Space Science Reviews》2007,131(1-4):187-217
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft was designed and constructed to withstand the harsh environments associated with achieving and operating in Mercury
orbit. The system can be divided into eight subsystems: structures and mechanisms (e.g., the composite core structure, aluminum
launch vehicle adapter, and deployables), propulsion (e.g., the state-of-the-art titanium fuel tanks, thruster modules, and
associated plumbing), thermal (e.g., the ceramic-cloth sunshade, heaters, and radiators), power (e.g., solar arrays, battery,
and controlling electronics), avionics (e.g., the processors, solid-state recorder, and data handling electronics), software
(e.g., processor-supported code that performs commanding, data handling, and spacecraft control), guidance and control (e.g.,
attitude sensors including star cameras and Sun sensors integrated with controllers including reaction wheels), radio frequency
telecommunications (e.g., the spacecraft antenna suites and supporting electronics), and payload (e.g., the science instruments
and supporting processors). This system architecture went through an extensive (nearly four-year) development and testing
effort that provided the team with confidence that all mission goals will be achieved.
Larry E. Mosher passed away during the preparation of this paper. 相似文献