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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 199 records · Page 11
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NASA NTRS1987

Numerical simulations and the problem of periodicity in the cratering record

Ages of craters in the record of impacts on earth may be uniformly periodic, totally random, or a mixture of the two. These alternatives are studied through numerical simulation wherein time-series analysis is performed on real and simulated sequences to which random noise has been added to represent age-dating uncertainty. It is concluded that the real record is most likely to have been generated by a mixture of random and periodic impacts, with the random events constituting the majority.

Trefil, J. S.↗
NASA NTRS1987

Chemistry of the global troposphere - Fluorocarbons as tracers of air motion

Winds and convective mixing from a general circulation model of the atmosphere have been applied in a chemical tracer model (CTM) to simulate the global distribution and temporal variability of chlorofluorocarbons (CFCs). The seasonal cycle in moist convection, with maximum activity over continents in summer, leads to an annual cycle in the surface concentration of CFCs. Emissions are retained in the lowest levels of the atmosphere during winter, and surface concentrations peak near sources. In this season, CFCs from European sources are carried by low-level winds into the Arctic. During summer, vertical exchange is more efficient, and pollutants are transported more rapidly to the middle atmosphere. Consequently, concentrations of CFCs during summer are relatively low near the surface and elevated in the middle troposphere. Time series analysis of data from Adrigole, Ireland, indicates that the model accurately simulates long-range transport of air pollution. The model reproduces global distributions and trends for CFC-11 and CFC-12 observed by the ALE experiment; however, subgrid diffusion must be introduced into the model in order to reproduce the observed interhemispheric gradient. Interhemispheric exchange occurs mainly in the upper tropical troposphere, producing a profile which increases with altitude in the Southern Hemisphere, in agreement with observations. The distribution of CFCs is such that it is necessary to apply important corrections to observations at surface stations in order to derive global distributions.

Prather, Michael↗
NASA NTRS1987

Characteristics of atmospheric disturbances with a quasi-two day period

In 1968 the Soviet equatorial meteor expedition measured, at an altitude of 80 to 105 km, wind velocity disturbances in the equatorial atmosphere with a quasi-two day period. An example of such disturbances is provided which shows time series of wind velocity in the meridional and zonal directions. The results of the time series analysis are discussed.

Kalchenko, B. V.↗
NASA NTRS1987

New approaches to some methodological problems of meteor science

Several low cost approaches to continuous radioscatter monitoring of the incoming meteor flux are described. Preliminary experiments were attempted using standard time frequency stations WWVH and CHU (on frequencies near 15 MHz) during nighttime hours. Around-the-clock monitoring using the international standard aeronautical beacon frequency of 75 MHz was also attempted. The techniques are simple and can be managed routinely by amateur astronomers with relatively little technical expertise. Time series analysis can now be performed using relatively inexpensive microcomputers. Several algorithmic approaches to the analysis of meteor rates are discussed. Methods of obtaining optimal filter predictions of future meteor flux are also discussed.

Meisel, David D.↗
NASA NTRS1990

Analytical concepts for health management systems of liquid rocket engines

Substantial improvement in health management systems performance can be realized by implementing advanced analytical methods of processing existing liquid rocket engine sensor data. In this paper, such techniques ranging from time series analysis to multisensor pattern recognition to expert systems to fault isolation models are examined and contrasted. The performance of several of these methods is evaluated using data from test firings of the Space Shuttle main engines.

Williams, Richard↗
NASA NTRS1992

Long-term source monitoring with BATSE

The uncollimated Burst and Transient Source Experiment (BATSE) large area detectors (LADs) are well suited to nearly continuous monitoring of the stronger hard x-ray sources, and time series analysis for pulsars. An overview of the analysis techniques presently being applied to the data are discussed, including representative observations of the Crab Nebula, Crab pulsar, and summaries of the sources detected to data. Results of a search for variability in the Crab Pulsar pulse profile are presented.

Wilson, R. B.↗
NASA NTRS1993

Control of unsteady shock-induced turbulent boundary layer separation upstream of blunt fins

Fluctuating wall pressure measurements have been made on centerline upstream of blunt fins in a Mach 5 turbulent boundary layer. Standard time series analysis and conditional sampling algorithms have been used to examine the effects of leading edge sweepback, leading edge shape, and fin root modifications on the fluctuating pressures. Leading edge sweep considerably reduces the mean and rms pressure loading at the fin root, the extent of the region of unsteady separation shock motion, and the separation length. The frequency of pressure fluctuations in the intermittent region increases with leading edge sweepback, while the spectral content of pressure fluctuations in the separated region is virtually unchanged by leading edge sweep. A swept hemicylindrically blunted root fillet reduces the centerline upstream influence and intermittent region length by 50 percent, and reduces the mean and rms pressure loading at the fin root by about 75 percent and 95 percent respectively. Experiments using hemicylindrical, wedge shaped and flat leading edges show that while separated flow scales increase with increasing 'bluntness', intermittent region length and root loading decrease, and separation shock frequency increases.

Kleifges, K.↗
NASA NTRS1994

The tropical semiannual oscillations in temperature and ozone as observed my the MLS

The first two years of Microwave Limb Sounder (MLS) temperature and ozone data are used to examine the tropical upper-stratospheric semiannual oscillation (SAO). Time series analysis revealed that the strongest amplitudes of the SAO occurred near the equator at 2 mb for temperature and 5 mb for ozone, consistent with previous observations. The first cycle of each calendar year was observed to have a much higher amplitude than the second cycle except for the warm phase in late 1991. Interannual variability in the strength of the SAO, such as the much stronger warm phase of late 1991 as compared to late 1992, was significant and could be partly attributed to the Quasi-Biennial Oscillation (QBO) in zonal wind.

Ray, Eric A.↗
NASA NTRS1994

Satellite remote sensing of H2SO4 aerosol using the 8- to 12-microns window region: Application to Mount Pinatubo

Monitoring stratospheric aerosols containing H2SO4 using the brightness temperature (BT) difference between 11 and 8.3 microns (BT(sub 8)-BT(sub 11)) spectral channels is demonstrated using theoretical calculations and satellite observations. Assuming an aqueous solution of 50% and 75% sulfuric acid, radiative transfer calculations indicate that over oceans an increase in the optical depth of the stratospheric aerosol results in an increase in BT(sub 8)-BT(sub 11). Theoretical simulations suggest that the technique is sensitive to visible optical depths greater than approximately 0.15. The simulations also demonstrate a lack of sensitivity to the particle size distribution. Changes in pre- and post-Pinatubo observations by the High-resolution Infrared Radiation Sounder 2 (HIRS2) on board the NOAA 10 are consistent with observed optical depth measurements and confirm the sensitivity of these channels to the presence of the aerosol. The technique is also applied to cold tropical convective clouds and desert regions where the signal, though evident, is less conclusive. Time series analysis is applied to the NOAA 10 and NOAA 12 combined BT(sub 8-BT(sub 11) observations to detect the periodicity of the spread of the volcanic aerosol. Over a region of the southern Pacific a 18- to 26-day period is present. Model simulations were conducted to demonstrate a trispectral with observations near 8, 11, and 12 microns. The trispectral approach has high potential in that the spectral signature of cirrus, water vapor, and H2SO4 aerosols are different. Observations from NOAA 10 and NOAA 11 are combined to demonstrate the capabilities of these infrared wavelengths of detecting the aerosol. The signal is clearly evident when a region of the South Atlantic is compared for pre- and post-Pinatubo conditions.

Ackerman, Steven A.↗
NASA NTRS1995

Periodicities of hard x-ray burst during the last solar cycle

By using power spectrum and standard FFT time series analysis, the Hard X-ray burst during solar cycle -22 were studied. This data of Hard X-ray burst spectrometer (HXRBS) on the solar maximum mission from Launch and February 14, 1980, through re-entry on December 2, 1989, by NASA artificial satellite. The results indicate that there are short and intermediate solar periodicities. Also it is found that there is a relation between the short periodicities (few minutes) with similar periodicities in solar radio emissions and in good agreement with the theoretical mode of solar oscillations.

Hady, Ahmed A.↗
NASA NTRS1996

Interdisciplinary Investigations in Support of Project DI-MOD

Various concepts from time series analysis are used as the basis for the development of algorithms to assist in the analysis and interpretation of remote sensed imagery. An approach to trend detection that is based upon the fractal analysis of power spectrum estimates is presented. Additionally, research was conducted toward the development of a software architecture to support processing tasks associated with databases housing a variety of data. An algorithmic approach which provides for the automation of the state monitoring process is presented.

Starks, Scott A.↗
NASA NTRS1995

Composition/Structure/Dynamics of comet and planetary satellite atmospheres

This research program addresses two cases of tenuous planetary atmospheres: comets and Io. The comet atmospheric research seeks to analyze a set of spatial profiles of CN in comet Halley taken in a 7.4-day period in April 1986; to apply a new dust coma model to various observations; and to analyze observations of the inner hydrogen coma, which can be optically thick to the resonance scattering of Lyman-alpha radiation, with the newly developed approach that combines a spherical radiative transfer model with our Monte Carlo H coma model. The Io research seeks to understand the atmospheric escape from Io with a hybrid-kinetic model for neutral gases and plasma given methods and algorithms developed for the study of neutral gas cometary atmospheres and the earth's polar wind and plasmasphere. Progress is reported on cometary Hydrogen Lyman-alpha studies; time-series analysis of cometary spatial profiles; model analysis of the dust comae of comets; and a global kinetic atmospheric model of Io.

Combi, Michael R.↗
NASA NTRS1993

Climate Sensitivity Studies of the Greenland Ice Sheet Using Satellite AVHRR, SMMR, SSM/I and in Situ Data

The feasibility of using satellite data for climate research over the Greenland ice sheet is discussed. In particular, we demonstrate the usefulness of Advanced Very High Resolution Radiometer (AVHRR) Local Area Coverage (LAC) and Global Area Coverage (GAC) data for narrow-band albedo retrieval. Our study supports the use of lower resolution AVHRR (GAC) data for process studies over most of the Greenland ice sheet. Based on LAC data time series analysis, we can resolve relative albedo changes on the order of 2-5%. In addition, we examine Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave Imager (SSM/I) passive microwave data for snow typing and other signals of climatological significance. Based on relationships between in situ measurements and horizontally polarized 19 and 37 GHz observations, wet snow regions are identified. The wet snow regions increase in aerial percentage from 9% of the total ice surface in June to a maximum of 26% in August 1990. Furthermore, the relationship between brightness temperatures and accumulation rates in the northeastern part of Greenland is described. We found a consistent increase in accumulation rate for the northeastern part of the ice sheet from 1981 to 1986.

Steffen, K.↗
NASA NTRS2000

"Cloud Slicing" : A New Technique to Derive Tropospheric Ozone Profile Information from Satellite Measurements

A new technique denoted cloud slicing has been developed for estimating tropospheric ozone profile information. All previous methods using satellite data were only capable of estimating the total column of ozone in the troposphere. Cloud slicing takes advantage of the opaque property of water vapor clouds to ultraviolet wavelength radiation. Measurements of above-cloud column ozone from the Nimbus 7 total ozone mapping spectrometer (TOMS) instrument are combined together with Nimbus 7 temperature humidity and infrared radiometer (THIR) cloud-top pressure data to derive ozone column amounts in the upper troposphere. In this study tropical TOMS and THIR data for the period 1979-1984 are analyzed. By combining total tropospheric column ozone (denoted TCO) measurements from the convective cloud differential (CCD) method with 100-400 hPa upper tropospheric column ozone amounts from cloud slicing, it is possible to estimate 400-1000 hPa lower tropospheric column ozone and evaluate its spatial and temporal variability. Results for both the upper and lower tropical troposphere show a year-round zonal wavenumber 1 pattern in column ozone with largest amounts in the Atlantic region (up to approx. 15 DU in the 100-400 hPa pressure band and approx. 25-30 DU in the 400-1000 hPa pressure band). Upper tropospheric ozone derived from cloud slicing shows maximum column amounts in the Atlantic region in the June-August and September-November seasons which is similar to the seasonal variability of CCD derived TCO in the region. For the lower troposphere, largest column amounts occur in the September-November season over Brazil in South America and also southern Africa. Localized increases in the tropics in lower tropospheric ozone are found over the northern region of South America around August and off the west coast of equatorial Africa in the March-May season. Time series analysis for several regions in South America and Africa show an anomalous increase in ozone in the lower troposphere around the month of March which is not observed in the upper troposphere. The eastern Pacific indicates weak seasonal variability of upper, lower, and total tropospheric ozone compared to the western Pacific which shows largest TCO amounts in both hemispheres around spring months. Ozone variability in the western Pacific is expected to have greater variability caused by strong convection, pollution and biomass burning, land/sea contrast and monsoon developments.

Ziemke, J. R.↗
NASA NTRS2000

A Bridge Health Monitoring Method Using the Hilbert-Huang Transform: A Case Study

We have developed a new method for nondestructive instrument method to monitor the health of a bridge. This new method is based on a transient test load and simple data collection. The nuclear of the method is the new invented nonstationary and nonlinear time series analysis method, the Empirical Mode Decomposition and Hilbert Spectral Analysis. The final decision on the health of the bridge structure is based on the nonlinear characteristic of the data, and on the comparison between the free and the forced vibration frequencies. Thus this alternative method enjoys many advantages: (1) no a priori data required, (2) simple data collection, and (3) minimum traffic disruption. Results from a case study of the Shing-Nan Bridge in Hou-Wei will be reported.

Huang, Norden E.↗
NASA NTRS2001

Changes in the Earth's UV Reflectivity (1979 to 1992)

Measurements of the Earth,s 380 nm UV reflectivity combine the effects of surface reflectivity, aerosols, haze, cloud optical thickness, and the fraction of the scene covered by clouds. Since the 380 nm surface reflectivity is low (2 to 8%) over most surfaces, water and land, the observed reflectivity changes are mostly caused by changes in the amount of snow/ice, cloudiness and aerosols. Time-series analysis of TOMS reflectivity over the period from 1979 to 1992 shows that there were no significant changes in annually-averaged zonal-average reflectivity at latitudes within 60 degrees S to 60 degrees N, even though there were changes at higher latitudes (e.g., 3% per decade, in reflectivity units, between 60 degrees N and 70 degrees N). When the effects of the 11-year solar cycle and ENSO (El Nino Southern Oscillation) are removed from the data, statistically significant reflectivity changes are observed poleward of both 40 degrees S and 40 degrees N. The solar-cycle results suggest a possible Sun-weather relationship.

Hermana, J. R.↗
NASA NTRS2001

Cloud Slicing: A New Technique to Derive Upper Tropospheric Ozone from Satellite Measurements

A new technique denoted cloud slicing has been developed for measuring upper tropospheric ozone. Cloud slicing takes advantage of the opaque property of water vapor clouds to ultraviolet wavelength radiation. Measurements of above-cloud column ozone from the Nimbus 7 total ozone mapping spectrometer (TOMS) instrument are combined together with Nimbus 7 temperature humidity and infrared radiometer (THIR) cloud-top pressure data to derive ozone column amounts in the upper troposphere. In this study tropical TOMS and THIR data for the period 1979-1984 are analyzed. By combining total tropospheric column ozone (denoted TCO) measurements from the convective cloud differential (CCD) method with 100-400 hPa upper tropospheric column ozone amounts from cloud slicing, it is possible to estimate 400-1000 hPa lower tropospheric column ozone and evaluate its spatial and temporal variability. Results for both the upper and lower tropical troposphere show a year-round zonal wave number 1 pattern in column ozone with largest amounts in the Atlantic region (up to 15 DU in the 100-400 hPa pressure band and around 25-30 DU in the 400-1000 hPa pressure band). Upper tropospheric ozone derived from cloud slicing shows maximum column amounts in the Atlantic region in the June-August and September-November seasons which is similar to the seasonal variability of CCD derived TCO in the region. For the lower troposphere, largest column amounts occur in the September-November season over Brazil in South America and also southern Africa. Localized increases in the tropics in lower tropospheric ozone are found over the northern region of South America around August and off the west coast of equatorial Africa in the March-May season. Time series analysis for several regions in South America and Africa show an anomalous increase in ozone in the lower troposphere around the month of March which is not observed in the upper troposphere. The eastern Pacific indicates weak seasonal variability of upper, lower, and total tropospheric ozone compared to the western Pacific which shows largest TCO amounts in both hemispheres around spring months. Ozone variability in the western Pacific is expected to have greater variability caused by strong convection, pollution and biomass burning, land/sea contrast and monsoon developments.

Ziemke, J. R.↗
NASA NTRS2004

Perspectives on African Ozone from Sondes, Dobson and Aircraft Measurements

We have been studying variability in ozone over Africa using data from ozonesondes (vertical profiles from surface to stratosphere), aircraft (the MOZAIC dataset with cruise altitude and landing/takeoff profiles) and the ground (Dobson spectrophotometer total ozone column measurement). The following may give context for ozone investigations during AMMA: 1. Total ozone measurements since 1989 show considerable variability in mean value among the African stations in Algeria, Kenya, Egypt, South Africa, as well as in seasonal cycles and year-to-year. Trends are not evident. 2. The impacts of convection, stratospheric injection, biomass burning and lightning appear in ozone sounding profile data. Time-series analysis and case studies point to periodic influences of long-range interactions with the Atlantic ("ozone paradox," wave-one") and Indian Oceans. 3. Tropospheric ozone variations, observed in tropospheric profiles and integrated column amount, follow general seasonal patterns but short- term variability is so strong that simple averages are inadequate for describing "climatology" and statistical classification approaches may be required.

Thompson, A. M.↗