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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Using computers to analyze continuous data.

Dynamic field measurements often involve large quantities of continuous data, which must be analyzed and interpreted to obtain meaningful information. The processing can often be accomplished by tape-recording the data in analog form, performing off-line digitalization, and using the result as an input to statistical programs on a digital computer. A time series analysis was used to obtain power spectral density (PSD) curves to identify dominant frequencies. Representative PSD plots were obtained for STOL aircraft during cruise. Vibrational energy was clearly concentrated below 0.1 Hz, and was much higher in the vertical than in the lateral direction.

Catherines, J. J.↗
NASA NTRS1979

Analyses of mean and turbulent motion in the tropics with the use of unequally spaced data

Wind velocities from 25 km to 60 km over Ascension Island, Fort Sherman and Kwajalein for the period January 1970 to December 1971 are analyzed in order to achieve a better understanding of the mean flow, the eddy kinetic energy and the Eulerian time spectra of the eddy kinetic energy. Since the data are unequally spaced in time, techniques of one-dimensional covariance theory were utilized and an unequally spaced time series analysis was accomplished. The theoretical equations for two-dimensional analysis or wavenumber frequency analysis of unequally spaced data were developed. Analysis of the turbulent winds and the average seasonal variance and eddy kinetic energy of the turbulent winds indicated that maximum total variance and energy is associated with the east-west velocity component. This is particularly true for long period seasonal waves which dominate the total energy spectrum. Additionally, there is an energy shift for the east-west component into the longer period waves with altitude increasing from 30 km to 50 km.

Kao, S. K.↗
NASA NTRS1979

Radar observation of known and unknown clear echoes

Target cross-section as a function of wavelength for known insects, known bird, and dot targets is presented. Tracking data using the time series analysis was tabulated for known birds. Examples were selected from these early works to give entomologists some indication of the types of information that are available by radar as well as examples of the different sources of clear-air radar backscatter.

Glover, K. M.↗
NASA NTRS1980

Lightning source locations from VHF radiation data for a flash at Kennedy Space Center

Three dimensional locations are presented for the VHF (30-50 MHz) radiation sources generated by a three-stroke lightning flash at the Kennedy Space Center. The locations were obtained by calculating the difference in time of arrival (DTOA) of radiated pulses at four ground stations. A computer-implemented multiple time series analysis was used in calculating DTOA data. The locations of the approximately 48,000 sequential VHF sources are compared with wide band electric-field records to provide a better understanding of the physics of lightning discharge.

Rustan, P. L.↗
NASA NTRS1981

Computational problems in autoregressive moving average (ARMA) models

The choice of the sampling interval and the selection of the order of the model in time series analysis are considered. Band limited (up to 15 Hz) random torque perturbations are applied to the human ankle joint. The applied torque input, the angular rotation output, and the electromyographic activity using surface electrodes from the extensor and flexor muscles of the ankle joint are recorded. Autoregressive moving average models are developed. A parameter constraining technique is applied to develop more reliable models. The asymptotic behavior of the system must be taken into account during parameter optimization to develop predictive models.

Agarwal, G. C.↗
NASA NTRS1982

Identification of multivariable high performance turbofan engine dynamics from closed loop data

The multivariable instrumental variable/approximate maximum likelihood (IV/AML) method or recursive time-series analysis is used to identify the multivariable (four inputs-three outputs) dynamics of the Pratt and Whitney F100 engine. A detailed nonlinear engine simulation is used to determine linear engine model structures and parameters at an operating point using open loop data. Also, the IV/AML method is used in a direct identification mode to identify models from actual closed loop engine test data. Models identified from simulated and test data are compared to determine a final model structure and parameterization that can predict engine response for a wide class of inputs. The ability of the IV/AML algorithm to identify useful dynamic models from engine test data is assessed.

Merrill, W.↗
NASA NTRS1984

L band push broom microwave radiometer: Soil moisture verification and time series experiment Delmarva Peninsula

The verification of a multi-sensor aircraft system developed to study soil moisture applications is discussed. This system consisted of a three beam push broom L band microwave radiometer, a thermal infrared scanner, a multispectral scanner, video and photographic cameras and an onboard navigational instrument. Ten flights were made of agricultural sites in Maryland and Delaware with little or no vegetation cover. Comparisons of aircraft and ground measurements showed that the system was reliable and consistent. Time series analysis of microwave and evaporation data showed a strong similarity that indicates a potential direction for future research.

Jackson, T. J.↗
NASA NTRS1984

Geological rhythms and cometary impacts

Time series analysis reveals two dominant, long-term periodicities approximately equal to 32 and 260 million years in the known series of geological and biological upheavals during the Phanerozoic Eon. The cycles of these episodes agree in period and phase with the cycles of impact cratering on Earth, suggesting that periodic comet impacts strongly influence Earth processes.

Rampino, M. R.↗
NASA NTRS1983

Identification of multivariable high performance turbofan engine dynamics from closed loop data

The multivariable instrumental variable/approximate maximum likelihood (IV/AML) method of recursive time-series analysis is used to identify the multivariable (four inputs-three outputs) dynamics of the Pratt and Whitney F100 engine. A detailed nonlinear engine simulation is used to determine linear engine model structures and parameters at an operating point using open loop data. Also, the IV/AML method is used in a direct identification made to identify models from actual closed loop engine test data. Models identified from simulated and test data are compared to determine a final model structure and parameterization that can predict engine response for a wide class of inputs. The ability of the IV/AML algorithm to identify useful dynamic models from engine test data is assessed. Previously announced in STAR as N82-20339

Merrill, W.↗
NASA NTRS1984

Effect of jet exit vanes on flow pulsations in an open-jet wind tunnel

An investigation was conducted of various jet exit vane configurations in the open test section of the Langley 4- by 7-Meter Tunnel to determine their effectiveness in reducing flow pulsations. The data consist of the instantaneous velocity fluctuations measured with hot-wire anemometers located at the tunnel centerline, 39.5 ft (12.0) downstream of the jet exit. The data are presented in the form of measured root-mean-square turbulence levels in the test section and a time series analysis for the baseline jet exit configuration (without vanes) and forthe most effective vane configuration, which consisted of triangular vanes alternating into and out of the flow around the jet exit.

Sellers, W. L., III↗
NASA NTRS1984

NIMBUS-7 SBUV (Solar Backscatter Ultraviolet) observations of solar UV spectral irradiance variations caused by solar rotation and active-region evolution for the period November 7, 1978 - November 1, 1980

Observations of temporal variations of the solar UV spectral irradiance over several days to a few weeks in the 160-400 nm wavelength range are presented. Larger 28-day variations and a second episode of 13-day variations occurred during the second year of measurements. The thirteen day periodicity is not a harmonic of the 28-day periodicity. The 13-day periodicity dominates certain episodes of solar activity while others are dominated by 28-day periods accompanied by a week 14-day harmonic. Techniques for removing noise and long-term trends are described. Time series analysis results are presented for the Si II lines near 182 nm, the Al I continuum in the 190 nm to 205 nm range, the Mg I continuum in the 210 nm to 250 nm range, the MgII H & K lines at 280 nm, the Mg I line at 285 nm, and the Ca II K & H lines at 393 and 397 nm.

Heath, D. F.↗
NASA NTRS1984

Geological rhythms and cometary impacts

Time-series analysis reveals two dominant, stable long-term periodicities approximately equal to 33 + or - 3 and 260 + or - 25 million years in the known series of geological and biological upheavals during the Phanerozoic Eon. Because the cycles of these episodes agree in period and phase with the cycles of impact cratering on earth, these results suggest that periodic comet impacts strongly influence global tectonism and biological evolution. These two periodicities could arise from interactions of the solar system with interstellar clouds as the solar system moves cyclically through the Galaxy.

Rampino, M. R.↗
NASA NTRS1986

Description of data on the Nimbus 7 LIMS map archive tape: Ozone and nitric acid

The Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) data set has been processed into a Fourier coefficient representation with a Kalman filter algorithm applied to profile data at individual latitudes and pressure levels. The algorithm produces synoptic data at noon Greenwich Mean Time (GMT) from the asynoptic orbital profiles. This form of the data set is easy to use and is appropriate for time series analysis and further data manipulation and display. Ozone and nitric acid results are grouped together in this report because the LIMS vertical field of views (FOV's) and analysis characteristics for these species are similar. A comparison of the orbital input data with mixing ratios derived from Kalman filter coefficients indicates errors in mixing ratio of generally less than 5 percent, with 15 percent being a maximum error. The high quality of the mapped data was indicated by coherence of both the phases and the amplitudes of waves with latitude and pressure. Examples of the mapped fields are presented, and details are given concerning the importance of diurnal variations, the removal of polar stratospheric cloud signatures, and the interpretation of bias effects in the data near the tops of profiles.

Remsberg, E. E.↗
NASA NTRS1986

Temporal frequency of radio emissions for the April 25, 1984 flare

The National Geophysical Data Center archives data of the solar-terrestrial environment. The USAF Radio Solar Telescope Network (RSTN) data allow performance of time series analysis to determine temporal oscillations as low as three seconds. The X13/3B flare which erupted in region 4474 (S12E43) on the 24 to 25 of April 1984, was selected. The soft X-rays, 1 to 8 A, remained above X-levels for 50 minutes and the radio emissions measured at Learmonth Solar Observatory reached a maximum of 3.15 x 10 to the 5th power SFUs at 410 MHz at 0000UT. A power spectral analysis of the fixed frequency RSTN data from Learmonth shows possible quasi-periodic fluctuations in the range two to ten seconds. Repetition rates or quasi-periodicities, in the case of the power spectral analysis, generally showed the same trends as the average solar radio flux at 245 and 8800 MHz. The quasi-periodicities at 1415 MHz showed no such trends.

Wells, G. D.↗
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.↗