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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1928

Experiments with a wing from which the boundary layer is removed by pressure or suction

With an unsymmetrical wing and a rotating Magnus cylinder, the lift is produced by the superposition of parallel and circulatory flows. An explanation of the circulatory flow is furnished by the boundary-layer theory of Prandtl and the consequent vortex formation. According to this explanation, it must evidently be possible to increase the circulation either by increasing the size of the stronger (lower) vortex or by decreasing the size of the weaker (upper) vortex. In this sense, according to Professor H. Zickendraht, we have a new type of wing from which the boundary layer is removed by forcing air out or sucking it in through openings in the upper surface of the wing near its trailing edge.

VORTICES - WINGS↗
NASA NTRS2014

Nanoscale Compositional Relations in Lunar Rock Patina: Deciphering Sources for Patina Components on an Apollo 17 Station 6 Boulder

Space weathering on the Moon and other airless bodies modifies the surfaces of regolith grains as well as the space-exposed surfaces of larger rocks and boulders. As space weathering witness plates, rocks and boulders are distinguished from regolith grains based on their ability to persist as physically intact substrates over longer time scales before being disaggregated by impact processes. Because lunar surfaces, including exposed rocks, quickly develop an optically thick layer of patina, it is important to understand the compositional relationship between patinas and their underlying rock substrates, particularly to support remote-sensing of rocky lunar terrains. Based on analytical TEM techniques, supported by focused ion beam (FIB) cross-sectioning, we have begun to systematize the multi-layer microstructural complexity of patinas on rock samples with a range of space exposure histories. Our on-going work has particularly focused on lunar rock 76015, both because it has a long (approx. 22 my) exposure history, and because its surface was exposed to patina development approximately 1 m off the regolith surface on a boulder in the Apollo 17 Station 6 boulder field. Potential sources for the 76015 patina therefore include impact-melted and vaporized material derived from the local rock substrate, as well as from the mix of large boulders and regolith in the Station 6 area. While similar, there are differences in the mineralogy and chemistry of the rocks and regolith at Station 6. We were interested to see if these, or other sources, could be distinguished in the average composition, as well as the compositional nanostratigraphy of the 76015 patina. To date we have acquired a total of 9 TEM FIB cross-sections from the 76015 patina, giving us reasonable confidence of being able to arrive at an integrated average for the patina major element composition based on analytical TEM methods.

Christoffersen, R.↗
NASA NTRS1988

Watching a disappearing shield

The remote-sensing techniques used to monitor atmospheric ozone levels are reviewed, and recent results are discussed. The importance of the ozone layer as a shield for UV radiation is stressed, and the impact of human activities generating ozone-destroying compounds is considered. Ground-based, airborne, balloon-borne, and satellite remote-sensing methods are shown to complement each other to provide both global coverage and detailed structural information. Data obtained with the Nimbus-7 TOMS and solar-backscatter UV instruments are presented in graphs and briefly characterized.

Stolarski, Richard S.↗
NASA NTRS1990

Direct and remote sensing observations of the effects of ships on clouds

Under certain conditions ships can affect the structure of shallow overlying layer clouds. It has been suggested that this is due to particles emitted from the ships, which increase the concentration of cloud condensation nuclei in the air, which, in turn, increases the concentrations of cloud droplets and reduces the average size of the droplets. Two ship track signatures in stratus clouds were observed simultaneously from a satellite and from an aircraft. The airborne measurements showed that in the ship tracks the droplet sizes and concentrations, as well as the total concentrations of particles, were substantially different from those in adjacent clouds. Furthermore, in-situ solar radiation measurements showed a significant enhancement in the upwelling radiance within the ship tracks at visible wavelengths and a significant reduction in radiance at 2.2 micrometers. Remote sensing measurements from the NOAA-10 satellite showed the effects of these differences in cloud structure as an enhancement in cloud reflectivity at 0.63 and 3.7 micrometers. These observations support the contention that ship track signatures in clouds are produced primarily by particles generated by ships.

Radke, Lawrence F.↗
NASA NTRS2004

Improved BN Coatings on SiC Fibers in SiC Matrices

Modifications of BN-based coatings that are used as interfacial layers between the fibers and matrices of SiCfiber/SiC-matrix composite materials have been investigated to improve the thermomechanical properties of these materials. Such interfacial coating layers, which are also known as interphases (not to be confused with interphase in the biological sense), contribute to strength and fracture toughness of a fiber/matrix composite material by providing for limited amounts of fiber/matrix debonding and sliding to absorb some of the energy that would otherwise contribute to the propagation of cracks. Heretofore, the debonding and sliding have been of a type called inside debonding because they have taken place predominantly on the inside surfaces of the BN layers that is, at the interfaces between the SiC fibers and the interphases. The modifications cause the debonding and sliding to include more of a type, called outside debonding, that takes place at the outside surfaces of the BN layers that is, at the interfaces between the interphases and the matrix (see figure). One of the expected advantages of outside debonding is that unlike in inside debonding, the interphases would remain on the crack-bridging fibers. The interphases thus remaining should afford additional protection against oxidation at high temperature and should delay undesired fiber/fiber fusion and embrittlement of the composite material. A secondary benefit of outside debonding is that the interphase/matrix interfaces could be made more compliant than are the fiber/interphase interfaces, which necessarily incorporate the roughness of the SiC fibers. By properly engineering BN interphase layers to favor outside debonding, it should be possible, not only to delay embrittlement at intermediate temperatures, but also to reduce the effective interfacial shear strength and increase the failure strain and toughness of the composite material. Two techniques have been proposed and partially experimentally verified as candidate means to promote outside debonding in state-of-the-art SiC/SiC composites.

Morscher, Gregory N.↗
NASA NTRS1982

Evapotranspiration and remote sensing

There are three things required for evapotranspiration to occur: (1) energy (580 cal/gm) for the change of phase of the water; (2) a source of the water, i.e., adequate soil moisture in the surface layer or in the root zone of the plant; and (3) a sink for the water, i.e., a moisture deficit in the air above the ground. Remote sensing can contribute information to the first two of these conditions by providing estimates of solar insolation, surface albedo, surface temperature, vegetation cover, and soil moisture content. In addition there have been attempts to estimate precipitation and shelter air temperature from remotely sensed data. The problem remains to develop methods for effectively using these sources of information to make large area estimates of evapotranspiration.

Schmugge, T. J.↗
NASA NTRS2003

Passive and Active Detection of Clouds: Comparisons between MODIS and GLAS Observations

The Geoscience Laser Altimeter System (GLAS), launched on board the Ice, Cloud and Land Elevation Satellite in January 2003 provides space-borne laser observations of atmospheric layers. GLAS provides opportunities to validate passive observations of the atmosphere for the first time from space with an active optical instrument. Data from the Moderate Resolution Imaging Spectrometer aboard the Aqua satellite is examined along with GLAS observations of cloud layers. In more than three-quarters of the cases, MODIS scene identification from spectral radiances agrees with GLAS. Disagreement between the two platforms is most significant over snow-covered surfaces in the northern hemisphere. Daytime clouds detected by GLAS are also more easily seen in the MODIS data as well, compared to observations made at night. These comparisons illustrate the capabilities of active remote sensing to validate and assess passive measurements, and also to complement them in studies of atmospheric layers.

Mahesh, Ashwin↗
NASA NTRS2010

Optical and Microphysical Retrievals of Marine Stratocumulus Clouds off the Coast of Namibia from Satellite and Aircraft

Though the emphasis of the Southern Africa Regional Science Initiative 2000 (SAFARI-2000) dry season campaign was largely on emission sources and transport, the assemblage of aircraft (including the high altitude NASA ER-2 remote sensing platform and the University of Washington CV-580, UK MRF C-130, and South African Weather Bureau JRA in situ aircrafts) provided a unique opportunity for cloud studies. Therefore, as part of the SAFARI initiative, investigations were undertaken to assess regional aerosol-cloud interactions and cloud remote sensing algorithms. In particular, the latter part of the experiment concentrated on marine boundary layer stratocumulus clouds off the southwest coast of Africa. Associated with cold water upwelling along the Benguela current, the Namibian stratocumulus regime has received limited attention but appears to be unique for several reasons. During the dry season, outflow of continental fires and industrial pollution over this area can be extreme. From below, upwelling provides a rich nutrient source for phytoplankton (a source of atmospheric sulfur through DMS production as well as from decay processes). The impact of these natural and anthropogenic sources on the microphysical and optical properties of the stratocumulus is unknown. Continental and Indian Ocean cloud systems of opportunity were also studied during the campaign. SAFARI 2000 aircraft flights off the coast of Namibia were coordinated with NASA Terra Satellite overpasses for synergy with the Moderate Resolution Imaging Spectroradiometer (MODIS) and other Terra instruments. MODIS was developed by NASA and launched onboard the Terra spacecraft on December 18, 1999 (and Aqua spacecraft on May 4, 2002). Among the remote sensing algorithms developed and applied to this sensor are cloud optical and microphysical properties that include cloud thermodynamic phase, optical thickness, and effective particle radius of both liquid water and ice clouds. The archived products from these algorithms have applications in climate change studies, climate modeling, numerical weather prediction, and fundamental atmospheric research. The archived MODIS Collection 5 cloud products processing stream will be used to analyze low water cloud scenes off the Namibian and Angolan coasts during SAFARI 2000 time period, as well as other years. Pixel-level Terra and Aqua MODIS retrievals (l. km spatial resolution at nadir) and gridded (1' uniform grid) statistics of cloud optical thickness and effective particle radius will be presented, including joint probability distributions between the two quantities. In addition, perspectives from the MODIS Airborne Simulator, which flew on the ER-2 during SAFARI 2000 providing high spatial resolution retrievals (50 m at nadir), will be presented as appropriate. The H-SAF Program requires an experimental operational European-centric Satellite Precipitation Algorithm System (E-SPAS) that produces medium spatial resolution and high temporal resolution surface rainfall and snowfall estimates over the Greater European Region including the Greater Mediterranean Basin. Currently, there are various types of experimental operational algorithm methods of differing spatiotemporal resolutions that generate global precipitation estimates. This address will first assess the current status of these methods and then recommend a methodology for the H-SAF Program that deviates somewhat from the current approach under development but one that takes advantage of existing techniques and existing software developed for the TRMM Project and available through the public domain.

Platnick, Steven E.↗
NASA NTRS1996

Construction of a Piezoresistive Neural Sensor Array

The construction of a piezoresistive - piezoelectric sensor (or actuator) array is proposed using 'neural' connectivity for signal recognition and possible actuation functions. A closer integration of the sensor and decision functions is necessary in order to achieve intrinsic identification within the sensor. A neural sensor is the next logical step in development of truly 'intelligent' arrays. This proposal will integrate 1-3 polymer piezoresistors and MLC electroceramic devices for applications involving acoustic identification. The 'intelligent' piezoresistor -piezoelectric system incorporates printed resistors, composite resistors, and a feedback for the resetting of resistances. A model of a design is proposed in order to simulate electromechanical resistor interactions. The goal of optimizing a sensor geometry for improving device reliability, training, & signal identification capabilities is the goal of this work. At present, studies predict performance of a 'smart' device with a significant control of 'effective' compliance over a narrow pressure range due to a piezoresistor percolation threshold. An interesting possibility may be to use an array of control elements to shift the threshold function in order to change the level of resistance in a neural sensor array for identification, or, actuation applications. The proposed design employs elements of: (1) conductor loaded polymers for a 'fast' RC time constant response; and (2) multilayer ceramics for actuation or sensing and shifting of resistance in the polymer. Other material possibilities also exist using magnetoresistive layered systems for shifting the resistance. It is proposed to use a neural net configuration to test and to help study the possible changes required in the materials design of these devices. Numerical design models utilize electromechanical elements, in conjunction with structural elements in order to simulate piezoresistively controlled actuators and changes in resistance of sensors. The construction of these devices may show significant improvement in ability to interrogate signals and in the control of effective compliance. This work focuses on the development a variety of series/parallel interconnected piezoresistive control elements for the neural sensing function.

Carlson, W. B.↗
NASA NTRS1984

Comparison of winds, waves, and turbulence as observed by airborne lidar, ground-based radars, and instrumented tower

On June 29, 1981, two ground-based Doppler radars, an airborne Doppler optical radar (lidar), an instrumented tower, and a rawinsonde were employed to collect wind data in the planetary boundary layer (PBL) in central Oklahoma. The main objectives of this experiment were related to a comparison of wind estimates and the visualization of the three-dimensional eddy structure in the convective atmospheric boundary layer. Discrepancies in the mean wind and wind profile detected by the different sensing systems were explained as being caused by a Schuler resonance of the aircraft's inertial navigation system, which caused an erroneous component of the aircraft's ground-relative velocity vector to be subtracted from the lidar-measured radial velocities. It is concluded that NASA's airborne Doppler optical radar system is capable of measuring wind fields in clear air on a smaller scale than was previously available with fixed remote sensors.

Eilts, M. D.↗
NASA NTRS1991

Titan's surface and troposphere, investigated with ground-based, near-infrared observations

Characterizations are presently made of Titan's haze, cloud, surface albedo, and atmospheric H2 abundance on the bases of 4000-5000/cm near-IR spectrum and points from the Fink and Larson (1979) 4000-12,500/cm spectrum. The strength of solar radiation absorption varies significantly with wavelength, facilitating a probing of the various atmospheric levels down to the surface. The present observations suggest the existence of an optically thin CH4 cloud layer, as well as haze and cloud optical depths sufficiently small for surface sensing at 4900, 6250, and 7700/cm. The albedos at these wavenumbers indicate the dominant surface material to be 'dirty' water ice.

Griffith, Caitlin A.↗
NASA NTRS1993

Possible near-IR channels for remote sensing precipitable water vapor from geostationary satellite platforms

Remote sensing of troposheric water vapor profiles from current geostationary weather satellites is made using a few broadband infrared (IR) channels in the 6-13 micron region. Uncertainties greater than 20% exist in derived water vapor values just above the surface from the IR emission measurements. In this paper, we propose three near-IR channels, one within the 0.94-micron water vapor band absorption region, and the other two in nearby atmospheric windows, for remote sensing of precipitable water vapor over land areas, excluding lakes and rivers, during daytime from future geostationary satellite platforms. The physical principles are as follows. The reflectance of most surface targets varies approximately linearly with wavelength near 1 micron. The solar radiation on the sun-surface-sensor ray path is attenuated by atmospheric water vapor. The ratio of the radiance from the absorption channel with the radiances from the two window channels removes the surface reflectance effects and yields approximately the mean atmospheric water vapor transmittance of the absorption channel. The integrated water vapor amount from ground to space can be obtained with a precision of better than 5% from the mean transmittance. Because surface reflectances vary slowly with time, temporal variation of precipitable water vapor can be determined reliably. High spatial resolution, precipitable water vapor images are derived from spectral data collected by the Airborne Visable-Infrared Imaging Spectrometer, which measures solar radiation reflected by the surface in the 0.4-2.5 micron region in 10-nm channels and has a ground instantaneous field of view of 20 m from its platform on an ER-2 aircraft at 20 km. The proposed near-IR reflectance technique would complement the IR emission techniques for remote sensing of water vapor profiles from geostationary satellite platforms, especially in the boundary layer where most of the water vapor is located.

Gao, B.-C.↗
NASA NTRS1996

Global Single and Multiple Cloud Classification with a Fuzzy Logic Expert System

An unresolved problem in remote sensing concerns the analysis of satellite imagery containing both single and multiple cloud layers. While cloud parameterizations are very important both in global climate models and in studies of the Earth's radiation budget, most cloud retrieval schemes, such as the bispectral method used by the International Satellite Cloud Climatology Project (ISCCP), have no way of determining whether overlapping cloud layers exist in any group of satellite pixels. Coakley (1983) used a spatial coherence method to determine whether a region contained more than one cloud layer. Baum et al. (1995) developed a scheme for detection and analysis of daytime multiple cloud layers using merged AVHRR (Advanced Very High Resolution Radiometer) and HIRS (High-resolution Infrared Radiometer Sounder) data collected during the First ISCCP Regional Experiment (FIRE) Cirrus 2 field campaign. Baum et al. (1995) explored the use of a cloud classification technique based on AVHRR data. This study examines the feasibility of applying the cloud classifier to global satellite imagery.

Welch, Ronald M.↗
NASA NTRS2004

Using the GeoFEST Faulted Region Simulation System

GeoFEST (the Geophysical Finite Element Simulation Tool) simulates stress evolution, fault slip and plastic/elastic processes in realistic materials, and so is suitable for earthquake cycle studies in regions such as Southern California. Many new capabilities and means of access for GeoFEST are now supported. New abilities include MPI-based cluster parallel computing using automatic PYRAMID/Parmetis-based mesh partitioning, automatic mesh generation for layered media with rectangular faults, and results visualization that is integrated with remote sensing data. The parallel GeoFEST application has been successfully run on over a half-dozen computers, including Intel Xeon clusters, Itanium II and Altix machines, and the Apple G5 cluster. It is not separately optimized for different machines, but relies on good domain partitioning for load-balance and low communication, and careful writing of the parallel diagonally preconditioned conjugate gradient solver to keep communication overhead low. Demonstrated thousand-step solutions for over a million finite elements on 64 processors require under three hours, and scaling tests show high efficiency when using more than (order of) 4000 elements per processor. The source code and documentation for GeoFEST is available at no cost from Open Channel Foundation. In addition GeoFEST may be used through a browser-based portal environment available to approved users. That environment includes semi-automated geometry creation and mesh generation tools, GeoFEST, and RIVA-based visualization tools that include the ability to generate a flyover animation showing deformations and topography. Work is in progress to support simulation of a region with several faults using 16 million elements, using a strain energy metric to adapt the mesh to faithfully represent the solution in a region of widely varying strain.

Geophyical Finite Element Simulation Tool (GeoFEST↗
NASA NTRS2019

Long-Lived In-Situ Solar System Explorer (LLISSE): Potential Contributions to the Next Decade of Solar System Exploration

Venus, while having similar size, mass, and location in the solar system to Earth, varies from Earth in many ways and holds many scientific mysteries despite many missions that have focused on it in the past. Primary differences include Venus' climate, atmosphere, and perhaps most notably the extreme surface conditions. The layers of sulfuric acid clouds and high pressure CO2 laden atmosphere make remote sensing at Venus much less effective than at other solar system bodies. In addition, surface conditions present formidable engineering challenges due to the high temperature, pressure, and reactive chemistry. To date, landed missions have not been able to last more than about 2 hours on the surface [1]. This has resulted in significant knowledge gaps about the surface conditions of this important body in the solar system. The science community has effectively no in-situ temporal data at the Venus surface. These data are critical for the development of a thorough understanding of Venus' weather and the processes by which chemical species interact with each other and are transported throughout the atmospheric column. The LLISSE platform, and its variants, are a foundation for future mission concepts based on a core set of long-lived technologies providing significant new science as well as demonstrating new technical capabilities. After completion, LLISSE has the potential to be a complimentary element to missions going to Venus and would provide unique and important science to missions whether they be orbiters or short duration landers.

Kremic, Tibor↗
NASA NTRS2019

Long-Lived In-Situ Solar System Explorer (LLISSE)

Venus, while having similar size, mass, and location in the solar system to Earth, varies from Earth in many ways and holds many scientific mysteries despite many missions that have focused on it in the past. Primary differences include Venus' climate, atmosphere, and perhaps most notably the extreme surface conditions. The layers of sulfuric acid clouds and high pressure CO2 laden atmosphere make remote sensing at Venus much less effective than at other solar system bodies. In addition, surface conditions present formidable engineering challenges due to the high temperature, pressure, and reactive chemistry. To date, landed missions have not been able to last more than about 2 hours on the surface [1]. This has resulted in significant knowledge gaps about the surface conditions of this important body in the solar system. The science community has effectively no in-situ temporal data at the Venus surface. These data are critical for the development of a thorough understanding of Venus' weather and the processes by which chemical species interact with each other and are transported throughout the atmospheric column. The LLISSE platform, and its variants, are a foundation for future mission concepts based on a core set of long-lived technologies providing significant new science as well as demonstrating new technical capabilities. After completion, LLISSE has the potential to be a complimentary element to missions going to Venus and would provide unique and important science to missions whether they be orbiters or short duration landers.

Kremic, Tibor↗
NASA NTRS2023

Space Weather Investigation Frontier (SWIFT)

The Space Weather Investigation Frontier (SWIFT) mission will aim at making major discoveries on the three-dimensional structure and dynamics of heliospheric structures that drive space weather. The focus will be on Interplanetary Coronal Mass Ejections (ICMEs) that originate from massive expulsions of plasma and magnetic flux from the solar corona. They cause the largest geomagnetic storms and solar energetic particle events, threatening to endanger life and disrupt technology on Earth and in space. A big current problem, both regarding fundamental solar-terrestrial physics and space weather, is that we do not yet understand spatial characteristics and temporal evolution of ICMEs and that the existing remote-sensing and in-situ observatories are not suited for resolving multi-layered and evolutionary structures in these massive storm drivers. Here, we propose a groundbreaking mission concept study using solar sail technology that, for the first time, will make continuous, in-situ multi-point observations along the Sun-Earth line beyond the Lagrange point L1 (sub-L1). This unique position, in combination with L1 assets, will allow distinguishing between local and global processes, spatial characteristics, temporal evolution, and particle energization mechanisms related to ICMEs. In addition, measurements of the magnetic field in earthbound ICMEs and their sub-structures from the SWIFT location will double the current forecasting lead-times from L1. This concept also paves the way for missions with increasingly longer forecasting lead-times, addressing NASA and NOAA’s space weather goals, as set forth by the Decadal Survey. The objective of this communication is to inform the community of the ongoing effort, including plans to further develop the mission concept, supported by the Heliophysics Flight Opportunities Studies (HFOS) program under NASA’s Research Opportunities in Space and Earth Sciences (ROSES).

M. Akhavan-Tafti↗