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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Transformation from proper time on earth to coordinate time in solar system barycentric space-time frame of reference. I. II

It is noted that in order to obtain accurate computed values of earth-based range and Doppler observables of a deep space probe, an expression is required for the difference between coordinate time (t) in the solar system barycentric space-time frame of reference and proper time (tau) recorded on a fixed atomic clock on earth. This is part 1 of a two-part article which obtains an expression for the coordinate time/proper time difference that can be used in deriving computed values of observations of a spacecraft or celestial body located anywhere in the solar system. The expression can also be used in computing Very Long Baseline Interferometry data types. In part 1, expression for the coordinate time/proper time difference is obtained that is a function of position and velocity vectors of the major celestial bodies of the solar system and the atomic clock on earth which reads proper time. This expression is transformed in part 2 to a function of time and the earth-fixed coordinates of the atomic clock.

Moyer, T. D.↗
NASA NTRS1997

Detecting Small-Scale Topographic Changes and Relict Geomorphic Features on Barrier Islands Using SAR

The shapes and elevations of barrier islands may change dramatically over a short period of time during a storm. Coastal scientists and engineers, however, are currently unable to measure these changes occurring over an entire barrier island at once. This three-year project, which is funded by NASA and jointly conducted by the Bureau of Economic Geology and the Center for Space Research at The University of Texas at Austin, is designed to overcome this problem by developing the use of interferometry from airborne synthetic aperture radar (AIRSAR) to measure coastal topography and to detect storm-induced changes in topography. Surrogate measures of topography observed in multiband, fully polarimetric AIRSAR (This type of data are now referred to as POLSAR data.) are also being investigated. Digital elevation models (DEM) of Galveston Island and Bolivar Peninsula, Texas obtained with Topographic SAR (TOPSAR) are compared with measurements by Global Positioning System (GPS) ground surveys and electronic total station surveys. In addition to topographic mapping, this project is evaluating the use of POLSAR to detect old features such as storm scarps, storm channels, former tidal inlets, and beach ridges that have been obscured by vegetation, erosion, deposition, and artificial filling. We have also expanded the work from the original proposal to include the mapping of coastal wetland vegetation and depositional environments. Methods developed during this project will provide coastal geologists with an unprecedented tool for monitoring and understanding barrier island systems. This understanding will improve overall coastal management policies and will help reduce the effects of natural and man-induced coastal hazards. This report summarizes our accomplishments during the second year of the study. Also included is a discussion of our planned activities for year 3 and a revised budget.

Gibeaut, James C.↗
NASA NTRS2000

Estimation of EOP From VLBI: Direct Approach

The currently adopted strategy of Earth Orientation Parameters (EOP) estimation from Very Long Baseline Interferometry (VLBI) is to estimate six parameters: Universal Time 1 (UT1), UT1 rate, pole positions, and nutation offsets for each 24-hour session independently. Then the resulting time series of raw EOP are filtered and a regression analysis is performed to obtain nutation coefficients, polhode of the pole, and other physical parameters. Thus, the latter parameters are obtained indirectly in two stages. An alternative approach of direct estimation of the final EOP is presented. Pole coordinates and UT1 are considered as a sum of three components: the low-period component that is modeled by a cubic spline, the harmonic component that includes forced nutation, precession and sub-daily variations of EOP, and the stochastic component that is modeled by a linear spline with segment length 1-2 hours. All parameters are obtained in a single LSQ solution using all available data.

POLAR MOTION↗
NASA NTRS2002

Boot strapping star position and baseline knowledge with uncalibrated SIM observations

An external calibration technique for SIM involves measurement of calibration stars whose positions must already be known to an accuracy of 2 milliarcseconds. We demonstrate a procedure that effectively 'bootstraps' calibration star positions from an ab initio catalog to the required accuracy by observing them with the uncalibrated SIM instrument.

astrometry↗
NASA NTRSDate not supplied

High-Temperature MEMS Based Venus Seismometer

Seismology is the method of choice for studying a planet’s interior and assessing current tectonic activity. With a single strategically placed seismometer, or preferably a network of seismometers, a variety of key aspects of a planet can be evaluated. The level and nature of seismicity observed provides a gauge of current geologic, especially tectonic, activity. Where tectonic activity is and is not occurring illuminates what regions and geologic features on the planet are currently active, thus, constraining global geodynamics. Larger distal earthquakes can be used to determine major compositional and structural boundaries within a planet’s interior, providing major constraints on planet formation and interior evolution. Seismometers have been deployed successfully on the Moon and Mars. Only small subsets of the scientific knowledge that can be gained from seismology can be obtained from alternative scientific approaches, such as global gravity solutions or repeat-pass interferometry. By virtue of its similar size to Earth, Venus is likely to be highly seismically active (Fig. 1). Even at Earth-like levels of seismology, returning meaningful data would require observation over a period that is at least 2–3 orders of magnitude longer than the 1–2 h lifetime of previous Soviet landers. Clever insulation could extend the lifetime of standard electronics in a modern lander to perhaps 24 h. While active cooling of electronics for a Venusian lander is plausible, this approach would require considerable technological advancement and will likely come at a high monetary and mass cost. The high density of the Venusian atmosphere at the surface should mean that there is good coupling of seismic energy into the atmosphere, such that seismology using infrasound from a balloon platform is currently being explored, and observations of the upper levels of the atmosphere from orbit has also been proposed [3]. Besides losing all shear wave information with these two methods, calibrating and interpreting seismic information that has been distorted by, and convolved with, atmospheric phenomena will be challenging without existing seismology data collected through surface seismometers (optimally, simultaneous surface seismological observations would be made).

silicon carbide↗
NASA NTRS1996

Interferometric Estimation of theThree-Dimensional Ice-Flow Velocity Vector Using Ascending and Descending Passes

Satellite radar interferometry provides an importatn new tool for determining ice-flow velocity. Interferometric measurements made from a single track direction are sensitive only to a single component of the three-dimensional velocity vector. Observations from along thre different track directions would allow the full velocity vector to be determined. A north/south-looking SAR could provide these observations over large portions of the globe but not over large areas of the polar ice sheets. We develop and demonstrate a technique that allows the full three-component velocity vector to be determined from data acquired along two track directions (ascending and descending) under a surface-parallel flow assumption.

interferometry satellite radar interferometry ice-↗
NASA NTRS1981

An analysis of radio interferometry with the block O system

The form and flow of information from signal reception to recorded bits at each station, through cross-correlation, phase-tracking, phase calibration, and bandwidth synthesis, to final observable formation are traced. In this process the data volume is greatly compressed for each observation, from approx. 10 to the 9th power bits on the station tapes to only four final observables: amplitude, delay, phase-delay rate and RF phase. After phase calibration and propagation media calibrations, the final delay observable is shown to be the sum of a geometric delay and a clock synchronization offset.

Thomas, J. B.↗
NASA NTRS1990

Pacific-North American plate motion from very long baseline interferometry compared with motion inferred from magnetic anomalies, transform faults, and earthquake slip vectors

Geodetic VLBI measurements were used to test whether the Pacific-North American plate velocity averaged over several years of direct observation (1984-1987) equals that averaged over millions of years. It was also tested whether this velocity parallels the San Andreas fault, transform faults and earthquake slip vectors in the Gulf of California, and earthquake slip vectors along the Queen Charlotte fault, along the Alaskan peninsula, and along the Kamchatkan peninsula. The VLBI data provide an estimate of the direction of plate motion that is independent of estimates from fault azimuths and earthquake slip vectors. The Euler vector determined from VLBI was found to be nearly identical to the Euler vector of plate motion model NUVEL-1, which is based on the trends of transform faults, earthquake slip vectors, and spreading rates from marine magnetic anomalies that average motion since 3 Ma. The velocity between the Pacific and North American plates averaged over the past several years equals or nearly equals its velocity averaged over the past several million years, the difference along their boundary nowhere exceeding 4 + or - 7 mm/yr.

Argus, Donald F.↗
DOE OSTI2021

Utilizing distributed acoustic sensing and ocean bottom fiber optic cables for submarine structural characterization

The sparsity of permanent seismic instrumentation in marine environments often limits the availability of subsea information on geohazards, including active fault systems, in both time and space. One sensing resource that provides observational access to the seafloor environment are existing networks of ocean bottom fiber optic cables; these cables, coupled to modern distributed acoustic sensing (DAS) systems, can provide dense arrays of broadband seismic observations capable of recording both seismic events and the ambient noise wavefield. Here, we report a marine DAS application which demonstrates the strength and limitation of this new technique on submarine structural characterization. Based on ambient noise DAS records on a 20 km section of a fiber optic cable offshore of Moss Landing, CA, in Monterey Bay, we extract Scholte waves from DAS ambient noise records using interferometry techniques and invert the resulting multimodal dispersion curves to recover a high resolution 2D shear-wave velocity image of the near seafloor sediments. We show for the first time that the migration of coherently scattered Scholte waves observed on DAS records can provide an approach for resolving sharp lateral contrasts in subsurface properties, particularly shallow faults and depositional features near the seafloor. Our results provide improved constraints on shallow submarine features in Monterey Bay, including fault zones and paleo-channel deposits, thus highlighting one of many possible geophysical uses of the marine cable network.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Polymorphism of gold under laser-based ramp compression to 690 GPa

The high-pressure behavior and polymorphism of gold has attracted strong recent interest from theory as well as from both static and dynamic experiments. In this study, gold was dynamically ramp-compressed to 690 GPa via laser ablation using the Omega Laser Facility (U. Rochester) in order to investigate the stability regions of this noble metal's polymorphs. Here, stresses were determined from measurements of surface or interface velocities by laser interferometry. In situ X-ray diffraction was carried out to constrain the structure and density. The ambient face-centered-cubic (fcc) phase was observed at 162 GPa, followed by a mixed phase region consisting of the fcc and body-centeredcubic (bcc). The presence of only the bcc phase was observed between 377 and 690 GPa. Our results are consistent with recent shock compression experiments and demonstrate that gold transforms to the bcc phase under conditions of both ramp and shock loading.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1990

Analytical and experimental studies on creep behavior of polymeric matrix composites

The creep behavior of graphite/epoxy composites is studied both analytically and experimentally. In the analytical study, a special finite element procedure was developed for the accurate and efficient analysis of creep response in anisotropic materials. This procedure was used to study the stress and strain distributions and histories in composite laminates containing circular holes. In the experimental study, creep tests were performed to investigate the time-dependent response of graphite/epoxy composites at elevated temperature. The moire interferometry technique was employed to determine the deformation histories in notched composites. The experimental results were compared with the analytical predictions and good agreement was observed.

Lin, K. Y.↗
NASA NTRS2020

CzeV1731: The Unique Doubly Eclipsing Quadruple System

We report the discovery of the relatively bright (V=10.5 mag), doubly eclipsing 2+2 quadruple system CzeV1731. This is the third known system of its kind, in which the masses are determined for all four stars and both the inner and outer orbits are characterized. The inner eclipsing binaries are well-detached systems moving on circular orbits: pair A with period PA=4.10843 d and pair B with PB=4.67552 d. The inner binaries contain very similar components (q≈1.0), making the whole system a so-called double twin. The stars in pair B have slightly larger luminosities and masses and pair A shows deeper eclipses. All four components are main-sequence stars of F/G spectral type. The mutual orbit of the two pairs around the system barycenter has a period of about 34yr and an eccentricity of about 0.38. However, further observations are needed to reveal the overall architecture of the whole system, including the mutual inclinations of all orbits. This is a promising target for interferometry to detect the double at about 59 mas and Mbol<1 mag.

Stars↗
NASA NTRS1995

Combinations of Earth Orientation Observations: SPACE94, COMB94, and POLE94

A Kalman filter has been used to combine all publicly available, independently determined measurements of the Earth's orientation taken by the modern, space-geodetic techniques of very long baseline interferometry, satellite laser ranging, lunar laser ranging, and the global positioning system. Prior to combining the data, tidal terms were removed from the UT1 measurements, outlying data points were deleted, series-specific corrections were applied for bias and rate, and the stated uncertainties of the measurements were adjusted by multiplying them by series-specific scale factors. Values for these bias- rate corrections and uncertainty scale factors were determined by an iterative, round-robin procedure wherein each data set is compared, in turn, to a combination of all other data sets. When applied to the measurements, the bias-rate corrections thus determined make the data sets agree with each other in bias and rate, and the uncertainty scale factors thus determined make the residual of each series (when differenced with a combination of all others) have a reduced chi-square of one. The corrected and adjusted series are then placed within an IERS reference frame by aligning them with the IERS Earth orientation series EOP (IERS)90C04. The result of combining these corrected, adjusted and aligned series is designated SPCE94 and spans October 6.0, 1976 to January 27.0, 1995 at daily intervals.

SPACE94 COMB94↗
NASA NTRS2008

Observations and Mitigation of RFI in ALOS PALSAR SAR Data; Implications for the Desdyni Mission

Initial examination of ALOS PALSAR synthetic aperture radar (SAR) data has indicated significant radio frequency interference (RFI) in several geographic locations around the world. RFI causes significant reduction in image contrast, introduces periodic and quasi-periodic image artifacts, and introduces significant phase noise in repeat pass interferometric data reduction. The US National Research Council Decadal Survey of Earth Science has recommended DESDynI, a Deformation, Ecosystems, and Dynamics of Ice satellite mission comprising an L-band polarimetric radar configured for repeat pass interferometry. There is considerable interest internationally in other future L-band and lower frequency systems as well. Therefore the issues of prevalence and possibilities of mitigation of RFI in these crowded frequency bands is of considerable interest. RFI is observed in ALOS PALSAR in California, USA, and in southern Egypt in data examined to date. Application of several techniques for removing it from the data prior to SAR image formation, ranging from straightforward spectral normalization to time-domain, multi-phase filtering techniques are considered. Considerable experience has been gained from the removal of RFI from P-band acquired by the GeoSAR system. These techniques applied to the PALSAR data are most successful when the bandwidth of any particular spectral component of the RFI is narrow. Performance impacts for SAR imagery and interferograms are considered in the context of DESDynI measurement requirements.

InSAR↗