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At least 109 records · Page 6

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NASA NTRS1971

Ultrasonic attenuation in superconducting molybdenum-rhenium alloys.

Investigation of longitudinal sound attenuation in superconducting Mo-Re alloys as a function of temperature, magnetic field, and frequency. Evaporated thin film CdS transducers were used for the measurements at frequencies up to 3 GHz. The normal state attenuation coefficient was found to be proportional to the square of frequency over this frequency range. Measurements in zero magnetic field yielded a value of the energy gap parameter close to the threshold value of 3.56 kTc, appropriate to a weakly coupled dirty limit superconductor.

Ashkin, M.↗

NASA NTRS1973

Studies of the inner shelf and coastal sedimentation environment of the Beaufort Sea from ERTS-1

The author has identified the following significant results. The particulate transport processes involved in the movement of surficial waters were examined using secchi disc readings, light attenuation coefficients, and particulate weights from filtration. Observations gathered during the summers of 1971 and 1972 indicate a remarkable difference in particulate matter and turbidity between the two years. ERTS-1 imagery during August 1972 showed turbid water along the northern Alaska coast. The uniformity of distribution of the turbid water and the fact that the river discharge is low at this period suggest that the turbidity is related to causes other than river effluent. Studies indicate that wave action is a more significant factor influencing particulate transport than believed heretofore. The boundary between the essentially immobile shorefast ice and the moving pack ice has been plotted from several ERTS-1 images and found to occur fairly consistently along the 20 meter contour. Considering the vast difference in the amount of ice movement shoreward and seaward of this boundary, ice-bottom action should also be different on either side of this boundary and for that matter at the shear zone that develops along the boundary.

Reimnitz, E.↗

NASA NTRS1974

A feasibility study for a remote laser water turbidity meter

A technique to remotely determine the attenuation coefficient (alpha) of the water was investigated. The backscatter energy (theta = 180 deg) of a pulse laser (lambda = 440 - 660 nm) was found directly related to the water turbidity. The greatest sensitivity was found to exist at 440 nm. For waters whose turbidity was adjusted using Chesapeake Bay sediment, the sensitivity in determining alpha at 440 nm was found to be approximately 5 - 10%. A correlation was also found to exist between the water depth (time) at which the peak backscatter occurs and alpha.

Hickman, G. D.↗

NASA NTRS1973

Some questions of an optimum probability synthesis of dynamic metalworking machine systems

Attempts were made to develop a dynamic metal working machine tool system using probability information on external factors and independent disturbances of the parameters. The problem was optimized in two stages: (1) creation of mathematical models under conditions determined by input influences, and (2) processing the results of calculations obtained on such models. Data were obtained on the patterns of distribution of dynamic quality characteristics of the tool, vibration frequencies and amplitudes, attenuation coefficients, and duration of a transition process. These data were obtained using a digital computer, statistical test methods, or logical possibility trees.

Dobrynin, S. A.↗

NASA NTRS1975

Quantitative determination of stratospheric aerosol characteristics

The author has identified the following significant results. The multiplicative scale factor needed to calibrate the recorded intensity is obtained by fitting the measured curve against a brightness model. The model was converted to the multispectral band scanner signal. Inversion of this measured signature is shown as the profile of attenuation coefficients versus altitude. Because of Gaussian noise, data were not measured directly. Data were fit with two exponential curves, one covering the lower altitude and the other covering the higher altitude. A twenty point curve was derived by selecting a data point and plotting its value from each of twenty adjacent scans. Noise from the lower altitudes was found to be erratic.

Tingey, D. L.↗

NASA NTRS1975

The feasibility of ranking material fracture toughness by ultrasonic attenuation measurements

A preliminary study was conducted to assess the feasibility of ultrasonically ranking material fracture toughness. Specimens of two grades of maraging steel for which fracture toughness values were measured were subjected to ultrasonic probing. The slope of the attenuation coefficient versus frequency curve was empirically correlated with the plane strain fracture toughness value for each grade of steel.

Vary, A.↗

NASA NTRS1975

Multiwavelength LIDAR for remote sensing of chlorophyll A in algae and phytoplankton

A theoretical and experimental analysis of laser induced fluorescence for remote detection of chlorophyll A in living algae and phytoplankton is presented. The fluorescent properties of various species of algae representative of the different color groups are described. Laboratory measurements of fluorescent scattering cross sections is discussed and quantitive data presented. A scattering matrix model is developed to demonstrate the essential requirement of multiwavelength laser excitation in order to make accurate quantitative measurements of chlorophyll A concentration when more than one color group of algae is present in the water. A practical airborne laser fluorosensor design is considered and analysis of field data discussed. Successful operation of the Langley ALOPE (airborne LIDAR oceanographic probing experiment) system is described and field measurements presented. Accurate knowledge of alpha, the optical attenuation coefficient of the water, is shown to be essential for quantitative analysis of chlorophyll A concentration. The feasibility of remotely measuring alpha by laser radar is discussed.

Mumola, P. B.↗

NASA NTRS1975

The feasibility of ranking material fracture toughness by ultrasonic attenuation measurements

A preliminary study was conducted to assess the feasibility of ultrasonically ranking material fracture toughness. Specimens of two grades of maraging steel for which fracture toughness values were measured were subjected to ultrasonic probing. The slope of the attenuation coefficient vs frequency curve was empirically correlated with the plane strain fracture toughness value for each grade of steel.

Vary, A.↗

NASA NTRS1975

Quantitative determination of stratospheric aerosol characteristics

The author has identified the following significant results. In the S192 data, a peak was apparent in the lower altitudes that was not present in the shorter wavelengths and grew with increasing wavelength beginning with band 7. For ten S192 wavelengths, the relative altitude increment was determined by knowledge of the relative position of the highest point in the scan arc. Using this scheme, results of scaling and inverting data for passes 47 and 61 were put into two models. Each result had three chart representations: (1) limb brightness measurement, (2) attenuation coefficients, and (3) ratio of the aerosol and Rayleigh coefficients to accentuate layers.

Tingey, D. L.↗

NASA NTRS1976

Correlation of chlorophyll, suspended matter, and related parameters of waters in the lower Chesapeake Bay area to LANDSAT-1 imagery

The author has identified the following significant results. An effort to relate water parameters of the lower Chesapeake Bay area to multispectral scanner images of LANDSAT 1 has shown that some spectral bands can be correlated to water parameters, and has demonstrated the feasibility of synoptic mapping of estuaries by satellite. Bands 5 and 6 were shown to be useful for monitoring total particles. Band 5 showed high correlation with suspended sediment concentration. Attenuation coefficients monitored continuously by ship along three baselines were cross correlated with radiance values on three days. Improved correlations resulted when tidal conditions were taken into consideration. A contouring program was developed to display sediment variation in the lower Chesapeake Bay from the MSS bands.

Fleischer, P.↗

NASA NTRS1975

Optical contamination evidence from Skylab and Gemini flights

Final results from a part of the T027 experiment performed on the first Skylab mission are presented. The sample array system containing 248 optical surfaces and exposed outside the orbital workshop did not collect any significant contaminants. Unfortunate performance compromises and the relative cleanliness of the assembly on the antisolar side placed the amount of available surface contaminants at or below the limiting sensitivity of the ground measuring instruments. Significant contamination was seen near the extravehicular hatch quadrant on the solar side of the orbiting assembly, and some results from returned samples are presented. Optical windows and mirrors exposed on the Gemini 12 mission showed degradation up to 35% in the UV wavelength region and solar absorptance increases up to 1.8 times the clean values. An expression for the attenuation coefficient vs wavelength is presented. The contaminant, a silicone base material, varied in thickness from 22 nm to 88 nm. The postflight scattered luminance of a contaminated Gemini 12 left-hand spacecraft hatch window was used to obtain threshold stellar visibility curves as a function of scattered and incident sunlight angles.

Muscari, J. A.↗

NASA NTRS1975

An investigation of the waters in the lower Chesapeake Bay area

Since October of 1972 the Langley Research Center and the Old Dominion University have been engaged in a cooperative effort to investigate the waters of the lower Chesapeake Bay area. During the first year an intensive effort was made to collect water data at the time of Landsat-1 overpasses. Bands 5 and 6 of the multispectral scanner (MSS) were shown to be useful for monitoring total particles, although a daily calibration was required. Band 5 had a high correlation with sediment and under some conditions an internal correction for atmospheric interference was possible. The relation of sediment to particles was established by using the MSS radiance values, since the two parameters were not monitored at the same stations. A contouring program was developed to display the sediment variation in the lower Bay at the time of the Jan. 26, 1973, overpass. Attenuation coefficients monitored continuously by ship along three baselines were cross-correlated with radiance values on three days. Evidence for tidal effects was obtained by showing that correlations improved when ship data collected during the nearest 'tidal time' instead of physical time were used

Bowker, D. E.↗

NASA NTRS1978

Neutron radiographic testing for hydrogen embrittlement

Neutron radiography (N-ray) inspection is similar to X-ray inspection in that both depend on variations in attenuation to achieve object contrast. However, effectiveness of methods differs significantly when certain combinations of elements are examined. Mass attenuation coefficient for N-rays is function of both scattering and capture possibilities for each element; thus, density of thickness of material is less important in determining its transparency to neutrons.

Dunstan, J.↗

NASA NTRS1977

Analysis of laser fluorosensor systems for remote algae detection and quantification

The development and performance of single- and multiple-wavelength laser fluorosensor systems for use in the remote detection and quantification of algae are discussed. The appropriate equation for the fluorescence power received by a laser fluorosensor system is derived in detail. Experimental development of a single wavelength system and a four wavelength system, which selectively excites the algae contained in the four primary algal color groups, is reviewed, and test results are presented. A comprehensive error analysis is reported which evaluates the uncertainty in the remote determination of the chlorophyll a concentration contained in algae by single- and multiple-wavelength laser fluorosensor systems. Results of the error analysis indicate that the remote quantification of chlorophyll a by a laser fluorosensor system requires optimum excitation wavelength(s), remote measurement of marine attenuation coefficients, and supplemental instrumentation to reduce uncertainties in the algal fluorescence cross sections.

Browell, E. V.↗

NASA NTRS1976

Magnetostrictive ultrasonic probes

The principles underlying the design and use of magnetostrictive ultrasonic probes is illustrated by oscillograms and sketches. Attention is given to such concepts as magnetostrictive transduction, broadband pulse shaping, guided wave propagation, wave impedance, reflection, transmission, and attenuation coefficients, coupling methods, and impulse-induced resonance. A number of applications of such probes are discussed including the measurement of elastic moduli, temperature, and acoustic emission and resonance studies.

Lynnworth, L. C.↗

NASA NTRS1977

Airborne bathymetric charting using pulsed blue-green lasers

Laboratory and airborne experiments have proven the feasibility and demonstrated the techniques of an airborne pulsed laser system for rapidly mapping coastal water bathymetry. Water depths of 10 plus or minus 0.25 m were recorded in waters having an effective attenuation coefficient of 0.175 m. A 2-MW peak power Nd:YAG pulsed laser was flown at an altitude of 600 m. An advanced system, incorporating a mirror scanner, a high pulsed rate laser, and a good signal processor, could survey coastal zones at the rate of several square miles per hour.

Kim, H. H.↗

NASA NTRS1977

Measured backscatter and attenuation properties, including polarization effects, of various dispersions at 0.9 micron

The optical properties of a wide variety of atmospheric dispersions were studied using a 0.9-micron lidar system which included a GaAs laser stack transmitter emitting a horizontally polarized beam of 4 milliradians vertical divergence and 1.5 milliradians horizontal divergence. A principal means for assessing optical properties was the polarization ratio, that is, the backscattered radiation power perpendicular to the transmitter beam divided by the backscattered radiation power parallel to the beam polarization. The ratio of the backscattered fraction to the attenuation coefficient was also determined. Data on the dispersion properties of black carbon smoke, road dust, fog, fair-weather cumulus clouds, snow and rain were obtained; the adverse effects of sunlight-induced background noise on the readings is also discussed.

Kohl, R. H.↗

NASA NTRS1977

LANDSAT/coastal processes

The author has identified the following significant results. Correlations between the satellite radiance values water color, Secchi disk visibility, turbidity, and attenuation coefficients were generally good. The residual was due to several factors including systematic errors in the remotely sensed data, errors, small time and space variations in the water quality measurements, and errors caused by experimental design. Satellite radiance values were closely correlated with the optical properties of the water.

James, W. P.↗