3,508 research outputs found
LIBRA: An inexpensive geodetic network densification system
A description is given of the Libra (Locations Interposed by Ranging Aircraft) system, by which geodesy and earth strain measurements can be performed rapidly and inexpensively to several hundred auxiliary points with respect to a few fundamental control points established by any other technique, such as radio interferometry or satellite ranging. This low-cost means of extending the accuracy of space age geodesy to local surveys provides speed and spatial resolution useful, for example, for earthquake hazards estimation. Libra may be combined with an existing system, Aries (Astronomical Radio Interferometric Earth Surveying) to provide a balanced system adequate to meet the geophysical needs, and applicable to conventional surveying. The basic hardware design was outlined and specifications were defined. Then need for network densification was described. The following activities required to implement the proposed Libra system are also described: hardware development, data reduction, tropospheric calibrations, schedule of development and estimated costs
The 1990 Johnson Space Center bibliography of scientific and technical papers
Abstracts are presented of scientific and technical papers written and/or presented by L. B. Johnson Space Center (JSC) authors, including civil servants, contractors, and grantees, during the calendar year of 1990. Citations include conference and symposium presentations, papers published in proceedings or other collective works, seminars, and workshop results, NASA formal report series (including contractually required final reports), and articles published in professional journals
Tracer Applications of Noble Gas Radionuclides in the Geosciences
The noble gas radionuclides, including 81Kr (half-life = 229,000 yr), 85Kr
(11 yr), and 39Ar (269 yr), possess nearly ideal chemical and physical
properties for studies of earth and environmental processes. Recent advances in
Atom Trap Trace Analysis (ATTA), a laser-based atom counting method, have
enabled routine measurements of the radiokrypton isotopes, as well as the
demonstration of the ability to measure 39Ar in environmental samples. Here we
provide an overview of the ATTA technique, and a survey of recent progress made
in several laboratories worldwide. We review the application of noble gas
radionuclides in the geosciences and discuss how ATTA can help advance these
fields, specifically determination of groundwater residence times using 81Kr,
85Kr, and 39Ar; dating old glacial ice using 81Kr; and an 39Ar survey of the
main water masses of the oceans, to study circulation pathways and estimate
mean residence times. Other scientific questions involving deeper circulation
of fluids in the Earth's crust and mantle also are within the scope of future
applications. We conclude that the geoscience community would greatly benefit
from an ATTA facility dedicated to this field, with instrumentation for routine
measurements, as well as for research on further development of ATTA methods
A rapid prototyping/artificial intelligence approach to space station-era information management and access
Applications of rapid prototyping and Artificial Intelligence techniques to problems associated with Space Station-era information management systems are described. In particular, the work is centered on issues related to: (1) intelligent man-machine interfaces applied to scientific data user support, and (2) the requirement that intelligent information management systems (IIMS) be able to efficiently process metadata updates concerning types of data handled. The advanced IIMS represents functional capabilities driven almost entirely by the needs of potential users. Space Station-era scientific data projected to be generated is likely to be significantly greater than data currently processed and analyzed. Information about scientific data must be presented clearly, concisely, and with support features to allow users at all levels of expertise efficient and cost-effective data access. Additionally, mechanisms for allowing more efficient IIMS metadata update processes must be addressed. The work reported covers the following IIMS design aspects: IIMS data and metadata modeling, including the automatic updating of IIMS-contained metadata, IIMS user-system interface considerations, including significant problems associated with remote access, user profiles, and on-line tutorial capabilities, and development of an IIMS query and browse facility, including the capability to deal with spatial information. A working prototype has been developed and is being enhanced
COBE's search for structure in the Big Bang
The launch of Cosmic Background Explorer (COBE) and the definition of Earth Observing System (EOS) are two of the major events at NASA-Goddard. The three experiments contained in COBE (Differential Microwave Radiometer (DMR), Far Infrared Absolute Spectrophotometer (FIRAS), and Diffuse Infrared Background Experiment (DIRBE)) are very important in measuring the big bang. DMR measures the isotropy of the cosmic background (direction of the radiation). FIRAS looks at the spectrum over the whole sky, searching for deviations, and DIRBE operates in the infrared part of the spectrum gathering evidence of the earliest galaxy formation. By special techniques, the radiation coming from the solar system will be distinguished from that of extragalactic origin. Unique graphics will be used to represent the temperature of the emitting material. A cosmic event will be modeled of such importance that it will affect cosmological theory for generations to come. EOS will monitor changes in the Earth's geophysics during a whole solar color cycle
Site and Basin Effects on Seismic Hazard in Indonesia:Sulawesi and Jakarta Case Studies
Earthquakes are among the most costly, devastating and deadly
natural hazards. The
extent of the seismic hazard is often influenced by factors like
the source location and site
characteristics, while the susceptibility of assets is influenced
by the population density,
building design, infrastructure and urban planning. A
comprehensive knowledge of the
nature of source and local geology enables the establishment of
an effective urban planning
that takes into account the potential seismic hazard, which in
turn may reduce the degree
of vulnerability.
The first probabilistic seismic hazard assessment (PSHA)
incorporating the effects of local site characteristic for the
island of Sulawesi in Indonesia has been conducted.
Most of the island, with the exception of South Sulawesi, is
undergoing rapid deformation.
This leads to high hazard in most regions (such that PGA > 0.4g
at 500 year return period
including site effects) and extremely high hazard (like PGA > 0.8
g at 500 year return
period) along fast-slipping crustal fault. On the other hand, a
distant site relative to fault
might suffer higher ground motion if that site is composed of
soft soil. This research has
proven that incorporating near-surface physical properties, in
this case is represented by
VS30, surface geology contribute significantly to ground motions,
consequently, responsible
for potential building damage.
The PSHA study that took place in Sulawesi took us move further,
investigate
the effect of deep structure on seismic waves. Jakarta was chosen
for its location sitting
on less known deep sediment basin and economic and political
importances. A dense
portable-seismic-broadband network, comprising 96 stations, has
been operated within
four months covering the Jakarta. The seismic network sampled
broadband seismic-noise
mostly originating from ocean waves and anthropogenic activity.
We used Horizontal-toVertical Spectral Ratio (HVSR) measurements
of the ambient seismic noise to estimate the
fundamental-mode Rayleigh wave ellipticity curves, which were
used to infer the seismic
velocity structure of the Jakarta Basin. By mapping and modeling
the spatial variation of
low-frequency (0.124{0.249 Hz) HVSR peaks, this study reveals
variations in the depth to
the Miocene basement. To map these velocity profiles of unknown
complexity, we employ
a Transdimensional-Bayesian framework for the inversion of HVSR
curves for 1D profiles
of velocity and density beneath each station. The inverted
velocity profiles show a sudden
change of basement depth from 400 to 1350 m along N-S profile
through the center of the
city, with an otherwise gentle increase in basin depth from south
to north.
Seismic wave modelings are conducted afterward and shows that for
very deep
basin of Jakarta, available ground motion prediction equation
(GMPE) is less sufficient
in capturing the effect of basin geometry on seismic waves.
Earrthquake scenario modeling using SPECFEM2D is performed to
comprehend the effect of deep basin on ground
motions. This modeling reveals that the city may experience high
peak ground velocity
(PGV) during large megathrust earthquake. The complexity of the
basin is responsible
for magnifying ground motions observed in the basin
Geodynamics Branch research report, 1982
The research program of the Geodynamics Branch is summarized. The research activities cover a broad spectrum of geoscience disciplines including space geodesy, geopotential field modeling, tectonophysics, and dynamic oceanography. The NASA programs which are supported by the work described include the Geodynamics and Ocean Programs, the Crustal Dynamics Project, the proposed Ocean Topography Experiment (TOPEX) and Geopotential Research Mission. The individual papers are grouped into chapters on Crustal Movements, Global Earth Dynamics, Gravity Field Model Development, Sea Surface Topography, and Advanced Studies
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