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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Terrestrial kilometric radiation: 3-average spectral properties

A study is presented of the average spectral properties of terrestrial kilometric radiation (TKR) derived from observations made by radio astronomy experiments onboard the IMP-6 and RAE-2 spacecraft. As viewed from near the equatorial plane, TKR is most intense and most often observed in the 21-24 hr local time zone and is rarely seen in the 09-12 hr zone. The peak flux density usually occurs near 240 kHz, but there is evidence that the peak occurs at a somewhat lower frequency on the dayside. The frequency of the peak in the average flux spectrum varies inversely with increasing substorm activity as inferred from the auroral electrojet index (AE) from a maximum near 300 kHz during very quiet times to a minimum below 200 kHz during very disturbed times. The absolute flux levels in the 100-600 kHz TKR band increase significantly with increasing AE. The average power associated with a particular source region seems to decrease rapidly with increasing source altitude.

Kaiser, M. L.↗
NASA NTRS1977

Terrestrial kilometric radiation. III - Average spectral properties

The spectral properties of terrestrial kilometric radiation (TKR) derived from observations made during radio-astronomy experiments on board the Imp 6 and Radio Astronomy Explorer 2 spacecraft are studied. As viewed from near the equatorial plane, TKR is most intense and most often observed in the 2100-2400 LT zone and is rarely seen in the 0900-1200 LT zone. The absolute flux levels in the 100- to 600-kHz TKR band increase significantly with increasing substorm activity as inferred from the auroral electrojet index (AE). In the late-evening sector the median power increases by about 3 orders of magnitude between quiet periods (AE less than 75 gammas) and disturbed periods (AE above 200 gammas). The peak flux density usually occurs near 250 kHz, although the frequency of the peak in the flux spectrum appears to vary inversely with AE from a maximum near 300 kHz during very quiet times to a minimum below 200 kHz during very disturbed times. The half-power bandwidth is typically 100% of the peak frequency. The variation of TKR flux density with apparent source altitude indicates that source strength decreases more rapidly than the inverse square of distance.

Kaiser, M. L.↗
NASA NTRS1983

Effects of high energy radiation on the mechanical properties of epoxy graphite fiber reinforced composites

The effects of high energy radiation on mechanical properties and on the molecular and structural properties of graphite fiber reinforced composites are assessed so that durability in space applications can be predicted. A listing of composite systems irradiated along with the maximum radiation dose applied and type of mechanical tests performed is shown. These samples were exposed to 1/2 MeV electrons.

Gilbert, R. D.↗
NASA NTRS1973

Atmospheric effects on remote sensing of non-uniform temperature sources

The equations of transfer, for a plane-parallel scattering atmosphere with a point source of energy on the lower bounding surface, were solved for various values of sensor/point source orientation and optical depths. Applications of this analysis to Skylab and ERTS mission are discussed, and requirements for atmospheric property data and radiation transfer properties are considered.

Mcneill, W. A.↗
NASA NTRS1973

Properties of optical radiation of variables and quasars

Photoelectric observations in the system UBV are considered for 42 variable stars, six quasars and Sco XR-1 with U-B and B-V colors of different type radiations. There are regressive dependences for nearly all the objects. On the Delta V/Delta B, Delta U/Delta B plane the objects were divided according to the types and situated along the bands. The directions of these bands are in agreement with values of A for different types of radiation.

Lukatskaya, F. I.↗
NASA NTRS2006

Visual Risk Assessment of Space Radiation Exposure for Future Space Exploration Missions

Protecting astronauts from space radiation exposure during an interplanetary mission is an important challenge for mission design and operations. If sufficient protection is not provided near solar maximum, the risk can be significant due to exposure to sporadic solar particle events (SPEs) as well as to the continuous galactic cosmic radiation (GCR). Polyethylene shielded "storm shelters" inside spacecraft have been shown to limit total exposure from a large SPE to a permissible level, preventing acute risks and providing a potential approach to fulfill the ALARA (as low as reasonably achievable) requirement. For accurate predictions of radiation dose to astronauts involved in future space exploration missions, detailed variations of radiation shielding properties are required. Radiation fluences and doses vary considerably across both the spacecraft geometry and the body-shielding distribution. A model using a modern CAD tool ProE(TradeMark), which is the leading engineering design platform at NASA, has been developed to account for these local variations in the radiation distribution. Visual assessment of radiation distribution at different points inside a spacecraft module and in the human body for a given radiation environment are described. Results will ultimately guide in developing requirements for maximal protection for astronauts from space radiation.

Hussein, Hesham F.↗
NASA NTRS2007

Remote Sensing of the Radiative and Microphysical Properties of Clouds during TC4: Results from MAS, MASTER, MODIS, and MISR

The MODIS Airborne Simulator (MAS) and MODIS/ASTER Airborne Simulator (MASTER) were used to obtain measurements of the bidirectional reflectance and brightness temperature of clouds at 50 discrete wavelengths between 0.47 and 14.3 (12.9 m for MASTER). These observations were obtained from the NASA ER-2 aircraft as part of the Tropical Composition, Clouds and Climate Coupling Experiment (TC4) conducted over Central America and surrounding Pacific and Atlantic Oceans between July 17 and August 8, 2007. Multispectral images in eight distinct bands were used to derive a confidence in clear sky (or alternatively the probability of cloud) over land and ocean ecosystems. Based on the results of individual tests run as part of this cloud mask, an algorithm was developed to estimate the phase of the clouds (liquid water, ice, or undetermined phase). Finally, the cloud optical thickness and effective radius were derived for both liquid water and ice clouds that were detected during each flight, using a nearly identical algorithm as that implemented operationally to process MODIS cloud data from the Aqua and Terra satellites (Collection 5). This analysis shows that the cloud mask developed for operational use on MODIS, and tested using MAS and MASTER date in TC4, is quite capable of distinguishing both liquid water and ice clouds during daytime conditions over both land and ocean. The cloud optical thickness and effective radius retrievals used three distinct bands of the MAS (or MASTER), and these results were compared with nearly simultaneous retrievals of MODIS on the Terra spacecraft. Finally, this MODIS-based algorithm was adapted to MISR data to infer the cloud optical thickness of liquid water clouds from MISR. Results of this analysis will be presented and discussed.

King, Michael D.↗
NASA NTRS2010

Remote Sensing of Radiative and Microphysical Properties of Clouds During TC (sup 4): Results from MAS, MASTER, MODIS, and MISR

The Moderate Resolution Imaging Spectroradiometer (MODIS) Airborne Simulator (MAS) and MODIS/Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Airborne Simulator (MASTER) were used to obtain measurements of the bidirectional reflectance and brightness temperature of clouds at 50 discrete wavelengths between 0.47 and 14.2 microns (12.9 microns for MASTER). These observations were obtained from the NASA ER-2 aircraft as part of the Tropical Composition, Cloud and Climate Coupling (TC4) experiment conducted over Central America and surrounding Pacific and Atlantic Oceans between 17 July and 8 August 2007. Multispectral images in eleven distinct bands were used to derive a confidence in clear sky (or alternatively the probability Of cloud) over land and ocean ecosystems. Based on the results of individual tests run as part of the cloud mask, an algorithm was developed to estimate the phase of the clouds (liquid water, ice, or undetermined phase). The cloud optical thickness and effective radius were derived for both liquid water and ice clouds that were detected during each flight, using a nearly identical algorithm to that implemented operationally to process MODIS Cloud data from the Aqua and Terra satellites (Collection 5). This analysis shows that the cloud mask developed for operational use on MODIS, and tested using MAS and MASTER data in TC(sup 4), is quite capable of distinguishing both liquid water and ice clouds during daytime conditions over both land and ocean. The cloud optical thickness and effective radius retrievals use five distinct bands of the MAS (or MASTER), and these results were compared with nearly simultaneous retrievals of marine liquid water clouds from MODIS on the Terra spacecraft. Finally, this MODIS-based algorithm was adapted to Multiangle Imaging SpectroRadiometer (MISR) data to infer the cloud optical thickness Of liquid water clouds from MISR. Results of this analysis are compared and contrasted.

King, Michael D.↗
NASA NTRS2014

Column Aerosol Optical Properties and Aerosol Radiative Forcing During a Serious Haze-Fog Month over North China Plain in 2013 Based on Ground-Based Sunphotometer Measurements

In January 2013, North China Plain experienced several serious haze events. Cimel sunphotometer measurements at seven sites over rural, suburban and urban regions of North China Plain from 1 to 30 January 2013 were used to further our understanding of spatial-temporal variation of aerosol optical parameters and aerosol radiative forcing (ARF). It was found that Aerosol Optical Depth at 500 nm (AOD500nm) during non-pollution periods at all stations was lower than 0.30 and increased significantly to greater than 1.00 as pollution events developed. The Angstrom exponent (Alpha) was larger than 0.80 for all stations most of the time. AOD500nm averages increased from north to south during both polluted and non-polluted periods on the three urban sites in Beijing. The fine mode AOD during pollution periods is about a factor of 2.5 times larger than that during the non-pollution period at urban sites but a factor of 5.0 at suburban and rural sites. The fine mode fraction of AOD675nm was higher than 80% for all sites during January 2013. The absorption AOD675nm at rural sites was only about 0.01 during pollution periods, while 0.03-0.07 and 0.01-0.03 during pollution and non-pollution periods at other sites, respectively. Single scattering albedo varied between 0.87 and 0.95 during January 2013 over North China Plain. The size distribution showed an obvious tri-peak pattern during the most serious period. The fine mode effective radius in the pollution period was about 0.01-0.08 microns larger than during nonpollution periods, while the coarse mode radius in pollution periods was about 0.06-0.38 microns less than that during nonpollution periods. The total, fine and coarse mode particle volumes varied by about 0.06-0.34 cu microns, 0.03-0.23 cu microns, and 0.03-0.10 cu microns, respectively, throughout January 2013. During the most intense period (1-16 January), ARF at the surface exceeded −50W/sq m, −180W/sq m, and −200W/sq m at rural, suburban, and urban sites, respectively. The ARF readings at the top of the atmosphere were approximately −30W/sq m in rural and −40-60W/sq m in urban areas.

Atmosphere↗
NASA NTRS2003

Cloud Property Retrieval and 3D Radiative Transfer

Cloud thickness and photon mean-free-path together determine the scale of "radiative smoothing" of cloud fluxes and radiances. This scale is observed as a change in the spatial spectrum of cloud radiances, and also as the "halo size" seen by off beam lidar such as THOR and WAIL. Such of beam lidar returns are now being used to retrieve cloud layer thickness and vertical scattering extinction profile. We illustrate with recent measurements taken at the Oklahoma ARM site, comparing these to the-dependent 3D simulations. These and other measurements sensitive to 3D transfer in clouds, coupled with Monte Carlo and other 3D transfer methods, are providing a better understanding of the dependence of radiation on cloud inhomogeneity, and to suggest new retrieval algorithms appropriate for inhomogeneous clouds. The international "Intercomparison of 3D Radiation Codes" or I3RC, program is coordinating and evaluating the variety of 3D radiative transfer methods now available, and to make them more widely available. Information is on the Web at: http://i3rc.gsfc.nasa.gov/. Input consists of selected cloud fields derived from data sources such as radar, microwave and satellite, and from models involved in the GEWEX Cloud Systems Studies. Output is selected radiative quantities that characterize the large-scale properties of the fields of radiative fluxes and heating. Several example cloud fields will be used to illustrate. I3RC is currently implementing an "open source" 3d code capable of solving the baseline cases. Maintenance of this effort is one of the goals of a new 3DRT Working Group under the International Radiation Commission. It is hoped that the 3DRT WG will include active participation by land and ocean modelers as well, such as 3D vegetation modelers participating in RAMI.

Cahalan, Robert F.↗
NASA NTRS1984

Effects of high energy radiation on the mechanical properties of epoxy-graphite fiber reinforced composites

The effects of high energy radiation on the mechanical properties and on the molecular and structural properties of graphite fiber reinforced composites were assessed so that the durability of such composites in space applications could be predicted. Investigative techniques including ESR and infrared spectroscopy, ESCA, contact angle measurements, and dynamic and static mechanical testing (3-point bending and interlaminar shear) were employed. The results using these different techniques are individually described, and the implications of the data are discussed. The proposed plan of work for the next fiscal year is outlined.

Fornes, R. E.↗
NASA NTRS1985

Effects of high energy radiation on the mechanical properties of epoxy-graphite fiber reinforced composites

In an effort to elucidate the changes in molecular structural and mechanical properties of epoxy/graphite fiber composites upon exposure to ionizing radiation in a simulated space environment, spectroscopic and surface properties of tetraglycidyl-4,4'-diamino diphenyl methane (TGDDM) red with diamino diphenyl sulfone (DDS) and T-300 graphite fiber were investigated following exposure to ionizing radiation. Cobalt-60 gamma radiation and 1/2 MeV electrons were used as radiation sources. The system was studied using electron spin resonance (ESR) spectroscopy, infrared absorption spectroscopy, contact angle measurements, and electron spectroscopy for chemical analysis.

Fornes, R. E.↗
NASA NTRS2022

The impacts of immersion ice nucleation parameterizations on Arctic mixed-phase stratiform cloud properties and the Arctic radiation budget in GEOS-5

The influence of four different immersion freezing parameterizations on Arctic clouds and the top-of-the atmosphere (TOA) and surface radiation fluxes is investigated in the fifth version of the National Aeronautics and Space Administration (NASA) Goddard Earth Observing System (GEOS-5) with sea surface temperature, sea ice fraction and aerosol emissions held fixed. The different parameterizations were derived from a variety of sources, including classical nucleation theory, field and laboratory measurements. Despite the large spread in the ice-nucleating particle (INP) concentrations in the parameterizations, the cloud properties and radiative fluxes had a tendency to form two groups, with the lower INP concentration category producing larger water path and low-level cloud fraction during winter and early spring, whereas the opposite occurred during the summer season. The stability of the lower troposphere was found to strongly correlate with low-cloud fraction, and along with the effect of ice nucleation, ice sedimentation and melting rates, appears to explain the spring-to-summer reversal pattern in the relative magnitude of the cloud properties between the two categories of simulations. The strong modulation effect of the liquid phase on immersion freezing led to the successful simulation of the characteristic Arctic cloud structure, with a layer rich in supercooled water near cloud top and ice and snow at lower levels. Comparison with satellite retrievals and in situ data suggest that simulations with low INP concentrations more realistically represent Arctic clouds and radiation.

Arctic↗