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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

A preliminary study of the feasibility of detecting the floating macrophytes by means of digital processing of MSS/LANDSAT data

The feasibility of mapping the floating macrophytes (mostly water hyacinth: (Eichornia crassipes) in the Salto Grande reservoir in Americana, SP, by means of digital processing of MSS/LANDSAT data is described. The area occupied by the macrophytes was extracted by exclusion after the merging of two thematic masks representing the area of vegetation free water surface. One of the masks was obtained from a date when the vegetal cover is insignificant, while the other represents a large infestation episode. The utilization of digital processing of MSS/LANDSAT data techniques for the documentation of macrophytes infestation is feasible only when the phenomenon occurs in large areas.

Valeriano, D. D.↗
NASA NTRS1984

Ground-based Measurements of Mesosphere Temperatures by Optical Means

The determination of the rotatinal temperature of the molecular emissions of OH or O2 offers a means of observing from the ground the mesosphere temperature at about 90 km throughout the night. The techniques and optical instrumentation developed to carry out these measurements are described. In comparison with other methods for the observation of this important geophysical quantity the optical technique is inexpensive and readily applicable for automatic operations over a long time period.

Meriweather, J. W., Jr.↗
NASA NTRS1985

Comparisons of monthly mean cosmic ray counting rates observes from worldwide network of neutron monitors

In order to examine the stability of neutron monitor observation, each of the monthly average counting rates of a neutron monitors is correlated to those of Kiel neutron monitor. The regression coefficients thus obtained are compared with the coupling coefficients of isotropic intensity radiation. The results of the comparisons for five year periods during 1963 to 1982, and for whole period are given. The variation spectrum with a single power law with an exponent of -0.75 up to 50 GV is not so unsatisfactory one. More than one half of the stations show correlations with the coefficient greater than 0.9. Some stations have shifted the level of mean counting rates by changing the instrumental characteristics which can be adjusted.

Ryu, J. Y.↗
NASA NTRS1985

The method for the study of the inelastic cross-section for high energy protons by means of shower arrays with the large calorimetric area

Proton initiated showers could be reliably separated from showers initiated by cosmic ray nuclei by means of arrays with large calorimetric area, using distributions of energy fractions for EAS electromagnetic muon and hadron components. Proton initiated showers penetrate deeper into the atmosphere and have relatively lower energy fraction in muons. Distribution of that energy fraction is sensitive to the value of the proton inelastic cross-section. It is shown that the analysis of this distribution let one distinguish between log sup 2 S -rise and log S -rise of the cross-section at energies above 10 to the 15th power eV.

Danilova, T. V.↗
NASA NTRS1984

Covalent bonding effect on the mean excitation energy of H2 with the local plasma model

Chemical bonding is taken into account explicitly in the determination of the mean excitation energy (I) for stopping power of H2 with the local plasma approximation by employing molecular electronic wave functions for H2 for the first time. This procedure leads to a new value for IH2 that is higher than all accepted experimental and theoretical values.

Kamaratos, E.↗
NASA NTRS1984

Intercomparison of planetary-scale diagnostics derived from separate satellite and radiosonde time-mean temperature fields

The planetary-scale components of the extratropical Northern Hemisphere troposphere-stratosphere 1973-74 winter circulation are diagnosed using separate time-mean temperature fields based on radiosonde and satellite observations. Meridional cross-sections of zonal wind together with, for zonal wavenumbers 1, 2 and 3, the streamfunction amplitude, phase and Eliassen-Palm flux are displayed, with the relative accuracy of the satellite-derived diagnostics assessed through comparison with the 'ground-truth' radiosonde information. The satellite and radiosonde diagnostics compare most favourably in terms of zonal wind speed and shear, direction of wave propagation and meridional wave structure - all of which are closely related to the differential properties of the atmospheric temperature field. The intensity of the satellite-derived patterns of tropospheric wave propagation is underestimated due to the effects of spatial smoothing and residual cloud contamination present in the satellite radiance measurements.

Miles, T.↗
NASA NTRS1983

Estimates of vertical crustal movements along the coast of Greece, based on mean sea level data

Mean Annual Sea Level (MASL) data from Greek coastal stations, for the 1969-1982 period, showed crustal stability to a standard deviation of + or - 1.8 cm at 10 of the 18 useful stations, supporting the contention that crustal movements greater than 5 cm can be detected by relative MASL. A comparison of MASL data with gravity changes measured in the Peloponnese and Central regions of Greece suggests that vertical movements occurred along a gradient equal to, or larger than, the free air gradient. MASL data from active volcanic islands have high potential for the detection of uplift prior to eruption.

Lagios, E.↗
NASA NTRS1985

Mean Winds of the Upper Middle Atmosphere (60-110 Km): a Global Distribution from Radar Systems (MF, Meteor, VHF)

During the last decade a large number of radars have been developed, which have produced substantial quantities of tidally corrected mean winds data in the upper middle atmosphere. The distribution of the radars is not global, but many areas are well covered. Zonal and meridional wind height-time cross sections from 60 to 80 km (MF/meteor radar) to approx. 110 km were preared for the last 5 to 6 years. They are compared with cross sections from CIRA 1972 for zonal winds, and GROVES (1969) for meridional winds. It is shown that while CIRA 1972 is still a useful model for many purposes, significant differences exist between it and the new radar data. The latter demonstrate important seasonal, latitudinal, longitudinal and hemispheric variations. The new meridional cross sections are of great value. The common features with GROVES (1969) are the equatorward cells in summer near 85 km; however, their strength (approx. 10 m/s) and size are less. Systematic and somewhat different variations emerge at (higher 52 N) and lower (35 to 44 deg) latitudes.

Manson, A. H.↗
NASA NTRS1986

Passive eddy-current damping as a means of vibration control in cryogenic turbomachinery

Lateral shaft vibrations produced by a rotating unbalance weight were damped by means of eddy currents generated in copper conductors that were precessing cyclicly in the gap formed by the pole faces of C-shaped, permanent magnets. The damper assembly, which was located at the lower bearing support of a vertically oriented rotor was completely immersed in liquid nitrogen during the test run. The test rotor was operated over a speed range from 800 to 10,000 rpm. Three magnet/conductor designs were evaluated. Experimental damping coefficients varied from 180 to 530 N sec/m. Reasonable agreement was noted for theoretical values of damping for these same assemblies. Values of damping coefficients varied from 150 to 780 N sec/m. The results demonstrate that passive eddy-current damping is a viable candidate for vibration control in cryogenic turbomachinery.

Cunningham, R. E.↗
NASA NTRS1986

Pressure probe and hot-film probe rsponses to acoustic excitation in mean flow

An experiment was conducted to compare the relative responses of a hot-film probe and a pressure probe positioned in a flow duct carrying mean flow and progressive acoustic waves. The response of each probe was compared with that of a condenser-type microphone flush mounted in the duct wall for flow Mach numbers up to about 0.5. The response of the pressure probe was less than that of the flush-mounted microphone by not more than about 2.1 dB at the highest centerline Mach number. This decreased response of the probe can likely be attributed to flow-induced impedance changes at the probe sensor orifices. The response of the hot-film probe, expressed in terms of fluctuating pressure, was greater than that of the flush-mounted microphone by as much as 6.0 dB at the two higher centerline Mach numbers. Removal of the contribution from fluctuating temperature in the hot-film analytical model greatly improved the agreement between the two transducer responses.

Parrott, T. L.↗
NASA NTRS1985

Mean winds of the upper middle atmosphere (60-110 km): A global distribution from radar systems (M.F., METEOR, VHF)

Since the development of the last CIRA in 1972, the number of radars providing winds in the upper middle atmosphere has increased significantly. These systems fill the data gap between 60 km and 110 km. The radars include medium frequency (MF) radars or partial reflection systems giving data from 60/70 to 100/110 km; meteor radars, 80 to 110 km, and M.S.T. radars operating as meteor radars. Data from 12 locations are shown, which represent a good Northern Hemispheric (NH) North American chain, an Oceanian chain which is mainly in the Southern Hemisphere (SH), and some Western Europe data. Generally tidal oscillations have been removed from days or groups of days, and the remaining mean winds and longer period oscillations plotted as height-time contours. Composite cross sections from the years 1978 to 1982 were formed where possible so that only the major temporal features remain.

Manson, A. H.↗
NASA NTRS1985

Mean zonal winds and planetary waves induced by internal gravity wave packets

The generation of mean zonal winds and planetary waves induced by internal gravity wave packets are investigated by numerical experiments. The numerical model is a 3-dimensional primitive equation model on the equatorial beta-plane with boundaries at the equator and North Pole. Because of equatorial boundary conditions, equatorial symmetric modes only are included in the model. Internal gravity wave packets are produced by thermal heating at the bottom boundary. Because of restriction of grid size, convective instability is parameterized by time-independent vertical and horizontal eddy viscosity. Other dissipation mechanisms (e.g., Newtonian cooling, ion drag, molecular viscosity etc.) are also included in the model.

Takahashi, M.↗
NASA NTRS1985

A numerical study of nonlinear interactions between mean flow and breaking internal gravity waves

Internal gravity waves are one of the important phenomena in understanding the general circulation as well as eddy motions in the atmosphere, particularly in the mesosphere and lower thermosphere. Therefore, in order to reproduce the middle atmospheric general circulation, it is necessary to incorporate vertically propagating internal gravity waves into general circulation models (GCMs). Results from numerical simulations on nonlinear interactions between mean flow and internal gravity waves are briefly presented.

Kida, H.↗
NASA NTRS1986

Design of adaptive control systems by means of self-adjusting transversal filters

The design of closed-loop adaptive control systems based on nonparametric identification was addressed. Implementation is by self-adjusting Least Mean Square (LMS) transversal filters. The design concept is Model Reference Adaptive Control (MRAC). Major issues are to preserve the linearity of the error equations of each LMS filter, and to prevent estimation bias that is due to process or measurement noise, thus providing necessary conditions for the convergence and stability of the control system. The controlled element is assumed to be asymptotically stable and minimum phase. Because of the nonparametric Finite Impulse Response (FIR) estimates provided by the LMS filters, a-priori information on the plant model is needed only in broad terms. Following a survey of control system configurations and filter design considerations, system implementation is shown here in Single Input Single Output (SISO) format which is readily extendable to multivariable forms. In extensive computer simulation studies the controlled element is represented by a second-order system with widely varying damping, natural frequency, and relative degree.

Merhav, S. J.↗
NASA NTRS1985

Monthly mean distribution of ozone and temperature

Global monthly mean charts for both hemispheres are given for four mid-season months, and for the pressure levels 30, 10, 1, and 0.1 mbar for temperature and 0.4 mbar for ozone. Charts of total ozone are provided separately. This set of charts shows clearly the very close coupling between the temperature and ozone distributions and demonstrates the influence of the large-scale planetary waves which give rise to very large longitudinal variations. The regular and interannual variability of temperature and ozone are discussed.

Labitzke, K.↗
NASA NTRS1985

Mean-flow measurements in a supersonic three-dimensional turbulent boundary layer

Measurements are presented of the mean flow in a supersonic turbulent boundary layer subjected to a constant weak transverse pressure gradient. The temperature and longitudinal velocity and the axial shear stress were only slightly affected by the three-dimensionality but a clearly defined crossflow component appeared, in the manner suggested by theory and confirmed in earlier experiments. The flow deflection angle and transverse-velocity component achieved a self-preserving form so long as the transverse-pressure gradient remained constant, and both achieved a maximum at the sublayer edge; the deflection angle seemed to decrease again between the latter and the surface. An empirical relation was found between the pressure-gradient strength and the maximum in the crossflow, and the dependence of the latter on distance from the surface was used to test analytical crossflow predictions. The data are in general agreement with Van Den Berg's law of the wall. The data also support the so-called parabolic law following a relaxation distance, especially if inviscid gradients are accounted for, and if the normal coordinate is contracted by the compressibility transformation.

Demetriades, A.↗
NASA NTRS1986

Statistical characterization of sea surface geometry for a wave slope field discontinuous in the mean square

Statistics of two-dimensional wave groups, of steep wave events, and of a cascade pattern manifested in the surface geometry in a developed sea state are derived. A systematic view is presented of the spectral moment problem, highlighting its physical meaning and showing its relationship with the theory of random fields. A solution of this problem is suggested that is appropriate to the case of wind-generated surface waves. The solution method treats the surface elevation field as specified on a spatial (temporal) running grid, developing an averaging procedure which employs the Taylor microscale as the mesh size. The technique is illustrated by first exposing errors in direct calculations of the effective surface impedance for a coherently reflected L-band radio wave. The technique is then used to study wave groups and steep waves for a Gaussian, two-dimensional, time-varying surface. Finally, the theory is applied to estimate breaking wave statistics,

Glazman, R. E.↗