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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 613 records · Page 34
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NASA NTRS1996

Repeat Pass Aircraft Interferometry Results at Portage Lake, Maine and Innisfail, Australia

The NASA/JPL AIRSAR/TOPSAR instruments have the capability of collecting fully polarimetric radar data at three wavelengths (C, L, and P-bands) and dual antenna interferometry at C-band, and more recently, L-band. In order to understand frequency and baseline dependent scattering effects in vegetated regions, repeat pass interferometry data was collected for two vegetated regions in 1993. Portage Lake, Maine is a primarily coniferous forested region with some clear cutting from logging activities in the region. The second site at Innisfail, Australia borders a tropical rain forest and is situated adjacent to some major clear cut regions and banana plantations. Preliminary analysis of repeat pass data collected in these areas shows that the smaller the wavelength the greater the temporal decorrelation between passes, the longer the wavelength the greater the penetration depth for some types of vegetation canopy, yet for some vegetation canopy types, in particular for a banana plantation, there appears to be no frequency dependent penetration into the canopy.

Hensley, Scott↗
NASA NTRS1996

Repeat Pass Aircraft Interferometry Results at Portage Lake, Maine and Innisfail, Australia

The NASA/JPL AIRSAR/TOPSAR instruments have the capability of collecting fully polarimetric radar data at three wavelengths (C, L and P-Bands) and dual antenna interferometry at C-Band, and more recently L-Band. In order to understand frequency and baseline dependent scattering effects in vegetated regions repeat pass interferometry data was collected for two vegetated regions in 1993. Portage Lake, Maine is a primarily coniferous forested region with some clear cutting from logging activities in the region. The second site at Innisfail, Australia borders a tropical rain forest and is situated adjacent to some major clear cut regions and banana plantations. Preliminary analysis of repeat pass data collected in these areas shows that the smaller the wavelength the greater the temporal decorrelation between passes, the longer the wavelength the greater the penetration depth for some types of vegetation canopy, yet for some vegetation canopy types, in particular for a banana plantation there appears to be no frequency dependent penetration into the canopy.

Hensley, Scott↗
NASA NTRS2010

CBSIT 2009: Airborne Validation of Envisat Radar Altimetry and In Situ Ice Camp Measurements Over Arctic Sea Ice

The past few years have seen the emergence of satellite altimetry as valuable tool for taking quantitative sea ice monitoring beyond the traditional surface extent measurements and into estimates of sea ice thickness and volume, parameters that arc fundamental to improved understanding of polar dynamics and climate modeling. Several studies have now demonstrated the use of both microwave (ERS, Envisat/RA-2) and laser (ICESat/GLAS) satellite altimeters for determining sea ice thickness. The complexity of polar environments, however, continues to make sea ice thickness determination a complicated remote sensing task and validation studies remain essential for successful monitoring of sea ice hy satellites. One such validation effort, the Arctic Aircraft Altimeter (AAA) campaign of2006. included underflights of Envisat and ICESat north of the Canadian Archipelago using NASA's P-3 aircraft. This campaign compared Envisat and ICESat sea ice elevation measurements with high-resolution airborne elevation measurements, revealing the impact of refrozen leads on radar altimetry and ice drift on laser altimetry. Continuing this research and validation effort, the Canada Basin Sea Ice Thickness (CBSIT) experiment was completed in April 2009. CBSIT was conducted by NOAA. and NASA as part of NASA's Operation Ice Bridge, a gap-filling mission intended to supplement sea and land ice monitoring until the launch of NASA's ICESat-2 mission. CBIST was flown on the NASA P-3, which was equipped with a scanning laser altimeter, a Ku-band snow radar, and un updated nadir looking photo-imaging system. The CB5IT campaign consisted of two flights: an under flight of Envisat along a 1000 km track similar to that flown in 2006, and a flight through the Nares Strait up to the Lincoln Sea that included an overflight of the Danish GreenArc Ice Camp off the coast of northern Greenland. We present an examination of data collected during this campaign, comparing airborne laser altimeter measurements with (1) Envisat RA-2 returns retracked optimally for sea ice and (2) in situ measurements of sea ice thickness and snow depth gathered from ice camp surveys. Particular attention is given to lead identification and classification using the continuous photo-imaging system along the Envisat underflight as well as the performance of the snow radar over the ice camp survey lines.

Connor, Laurence↗
NASA NTRS1982

The results of initial analysis of OSTA-1/Ocean Color Experiment (OCE) imagery

Ocean view images from the Ocean Color Experiment (OCE) were produced at three widely separated locations on the Earth. Digital computer enhancement and band ratioing techniques were applied to radiometrically corrected OCE spectral data to emphasize patterns of chlorophyll distribution and, in one shallow, clear water case, bottom topography. The chlorophyll pattern in the Yellow Sea between China and Korea was evident in a scene produced from Shuttle Orbit 24. The effects of the discharge from the Yangtze and other rivers were also observed. Two scenes from orbits 30 and 32 revealed the movement of patches of plankton in the Gulf of Cadiz. Geometrical corrections to these images permitted the existing ocean current velocities in the vicinity to be deduced. The variability in water depth over the Grand Bahama Bank was estimated by using the blue-green OCE channel. The very clear water conditions in the area caused bottom reflected sunlight to produce a sensor signal which was related inversely to the depth of the water.

Kim, H. H.↗
NASA NTRS1991

Assessment of surface penetration with polarimetric radar

An airborne P-, L-, and C-band polarimetric radar dataset acquired over the Atchafalaya Bay study site was used to assess its surface penetration capabilities. The dataset was decompressed and reformatted to form a three-wavelength and three-polarization nine-channel dataset. All nine channels were filtered for speckle noise removal, using the 7-by-7 local-statistics moving-window filtering. Significant smoothing of data was obtained so that the data can be classified using the SRCH and M234 ELAS programs. Preliminary assessment of the PLC images indicated that the radar waves penetrated muddy water. Therefore the radar can measure the water depth and can be used to map the submerged sediments. A statistical analysis of the digital data provided insight on the depth of muddy water penetration.

Wu, Shih-Tseng↗
NASA NTRS2000

Creep Properties of NiAl-1Hf Single Crystals Re-Investigated

NiAl-1Hf single crystals have been shown to be quite strong at 1027 C, with strength levels approaching those of advanced Ni-based superalloys. Initial testing, however, indicated that the properties might not be reproducible. Study of the 1027 C creep behavior of four different NiAl-1Hf single-crystal ingots subjected to several different heat treatments indicated that strength lies in a narrow band. Thus, we concluded that the mechanical properties are reproducible. Recent investigations of the intermetallic NiAl have confirmed that minor alloying additions combined with single-crystal growth technology can produce elevated temperature strength levels approaching those of Ni-based superalloys. For example, General Electric alloy AFN 12 {Ni-48.5(at.%) Al-0.5Hf-1Ti-0.05Ga} has a creep rupture strength equivalent to Rene 80 combined with a approximately 30-percent lower density, a fourfold improvement in thermal conductivity, and the ability to form a self-protective alumina scale in aggressive environments. Although the compositions of strong NiAl single crystals are relatively simple, the microstructures are complex and vary with the heat treatment and with small ingot-toingot variations in the alloy chemistry. In addition, initial testing suggested a strong dependence between microstructure and creep strength. If these observations were true, the ability to utilize NiAl single-crystal rotating components in turbine machinery could be severely limited. To investigate the possible limitations in the creep response of high-strength NiAl single crystals, the NASA Glenn Research Center at Lewis Field initiated an in depth investigation of the effect of heat treatment on the microstructure and subsequent 1027 C creep behavior of [001]-oriented NiAl-1Hf with a nominal chemistry of Ni-47.5Al-1Hf-0.5Si. This alloy was selected since four ingots, grown over a number of years and possessing slightly different compositions, were available for study. Specimens taken from the ingots were subjected to several heat treatment schedules, examined by transmission electron microscopy, and tested in both compression and tension. An example of the microstructure found in a [001]-oriented NiAl-1Hf specimen after a solution treatment at 1317 C for 50 hr followed by air cooling is illustrated in the image on the left, where the NiAl matrix contains a uniform distribution of nanometer-scale Gphase (Ni16Hf6Si7) precipitates. Other heat treating schedules produced microstructures with nanometer-sized G-phase cubes and plates or, in an extreme case, produced a microstructure with all the G-phase converted to Heusler (Ni2AlHf) particles. The results of 1027 C creep strength and strain rate testing are illustrated which summarizes data from tensile and compressive testing of samples cut from all four NiAl-1Hf ingots and subjected to a variety of heat treatment schedules. With one exception, all the strength values lie in a narrow band that spans six orders of magnitude in strain rate. The only factor that produced results outside of this band was the heat treatment schedule that dissolved all the G-phase and replaced it with Heusler precipitates. The results portrayed in this figure lead to the important practical conclusion that the elevated-temperature creep properties of NiAl-1Hf single crystals are reproducible and are not affected by small variations in alloy chemistry from ingot to ingot or by different initial distributions of G-phase in the heat-treated alloy. The only variable in this study that produced a significant and delerious effect on mechanical strength was a post-solution heat treatment that lead to the complete disappearance of the G-phase in favor of Heusler precipitates.

Whittenberger, J. Daniel↗
NASA NTRS1980

A physical model of Titan's clouds

A physical model of the formation and growth of aerosols in the atmosphere of Titan has been constructed in light of the observed correlation between variations in Titan's albedo and the sunspot cycle. The model was developed to fit spectral observations of deep methane bands, pressures, temperature distributions, and cloud structure, and is based on a one-dimensional physical-chemical model developed to simulate the earth's stratospheric aerosol layer. Sensitivity tests reveal the model parameters to be relatively insensitive to particle shape but sensitive to particle density, with high particle densities requiring larger aerosol mass production rates to produce compatible clouds. Solution of the aerosol continuity equations for particles of sizes 13 A to about 3 microns indicates the importance of a warm upper atmosphere and a high-altitude mass injection layer, and the production of aerosols at very low aerosol optical depths. Limits are obtained for the chemical production of aerosol mass and the eddy diffusion coefficient, and it is found that an increase in mass input causes a decrease in mean particle size.

Toon, O. B.↗
NASA NTRS1986

A continental rift model for the La Grande greenstone belt

Stratigraphic relationships and the geochemistry of volcanic rocks contrain the nature and timing of the tectonic and magmatic processes in the pre-deformational history of the La Grande greenstone belt in the Superior Province of north-central Quebec. The lowermost supracrustals in this belt are obscured by syntectonic granitoid intrusives. The supracrustal succession in the western part of the belt consists of a lower sequence of immature clastic sediments and mafic volcanoclastics, overlain by pillowed and massive basalts. Further east, along tectonic strike, a lower sequence of mafic volcanoclastics and immature clastic sediments is overlain by a thick sequence of pillowed and massive basalts, and resedimented coarse clastic sediments and banded iron formation. These are overlain by assive basaltic andesites, andesites and intermediate volcanoclastics intercalated with immature clastic sediments. In contrast, in the eastern part of the belt lenses of felsic volcanics and volcanoclastics occur at the base of the succession and pillowed and massive basalts are overlain by komatiites at the top. The La Grande greenstone belt can be explained as the product of continental rifting. The restricted occurence of komatiites, and eastwardly directed paleocurrents in clastic sediments in the central part of the belt are consistent with rifting commencing in the east and propagating westward with time. The increase in depth of emplacement and deposition with time of the lower three units in the central part of the belt reflects deposition in a subsiding basin. These supracrustal rocks are believed to represent the initial rift succession.

Skulski, T.↗
NASA NTRS2006

Improvements in Raman Lidar Measurements Using New Interference Filter Technology

Narrow-band interference filters with improved transmission in the ultra-violet have been developed under NASA-funded research and used in the Raman Airborne Spectroscopic Lidar (RASL) in ground-based, upward-looking tests. Measurements were made of atmospheric water vapor, cirrus cloud optical properties and carbon dioxide that improve upon any previously demonstrated using Raman lidar. Daytime boundary and mixed layer profiling of water vapor mixing ratio up to an altitude of approximately 4 h is performed with less than 5% random error using temporal and spatial resolution of 2-minutes and 60 - 210, respectively. Daytime cirrus cloud optical depth and extinction-to-backscatter ratio measurements are made using 1 -minute average. Sufficient signal strength is demonstrated to permit the simultaneous profiling of carbon dioxide and water vapor mixing ratio into the free troposphere during the nighttime. A description of the filter technology developments is provided followed by examples of the improved Raman lidar measurements.

Whiteman, David N.↗
NASA NTRS2020

NuSTAR Observation of GROJ1744−28 at Low Mass Accretion Rate

Context.Neutron stars in low-mass X-ray binaries (LMXBs) are important systems to study the physics of accretion onto compact ob-jects. The system GRO J1744−28 is particularly interesting, as it usually shows clear pulsations as well as X-ray bursts. Additionally,there are claims for a magnetic field of 5×1011G through the detection of a Cyclotron Resonant Scattering Feature (CRSF).Aims.We present the spectral analysis of GRO J1744−28 using∼29 ks of NuSTAR data taken in 2017 February at a low luminosityof 3.2×1036erg s−1(3–50 keV). Our goal is to study the variability of the source spectrum with pulse phase and to search for the claimed CRSF. Methods.The continuum spectrum is modeled with an absorbed power-law with exponential cut-off, and an additional iron line component. We find no obvious indications for a CRSF and therefore perform a detailed cyclotron line search using statistical methods.We perform this search on pulse phase-averaged as well as phase-resolved spectra. Results.GRO J1744−28 was observed at one of the lowest luminosities studied so far. The previously detected Type II X-ray bursts re absent. Clear pulsations at a period of 2.141124(9) Hz are detected. The pulse profile shows an indication of a secondary peak,which was not seen at higher flux. The 4σupper limit for the strength of a CRSF in the 3–20 keV band is 0.07 keV, lower than the strength of the line found at higher luminosity. Conclusions.The detection of pulsations shows that the source did not enter the “propeller” regime, even though the source flux of4.15×10−10erg cm−2s−1was almost one order of magnitude below the threshold for the propeller regime claimed in previous studies on this source. The transition into the propeller regime in GRO J1744−28 must therefore be below a luminosity of 3.2×1036erg s−1(3–50 keV), which implies a surface magnetic field.2.9×1011G and mass accretion rate.1.7×1016g s−1. A change of the CRSF depth as function of luminosity is not unexpected and has been observed in other sources. This result possibly implies a change in emission geometry as function of mass accretion rate to reduce the depth of the line below our detection limit.

Ole König↗
NASA NTRS1982

Mars' atmospheric behavior from Viking infra-red thermal mapper measurements

Data from the 15 micron band of CO2 readings with the two Viking IR thermal mappers are discussed. Contrasts were observed to be strong between clear and dusty conditions, with a latitudinal gradient and a diurnal amplitude variation in the winter southern hemisphere. Consistency was found in zonal mean temperatures in the absence of dust, with a peak temperature of 180 K at the poles and a diurnal amplitude of 15 K at the equator. Large temperature increases occur in dusty conditions, with global dust storms being present in the northern, but not southern, hemisphere. Estimations of the surface and atmospheric temperatures are calculated in order to derive optical depths from the IR measurements of atmospheric opacity. The optical depth around the whole planet is found to be relatively uniform at any given moment. Finally, the diurnal behavior of the brightness temperature is outlined for 1.4 Mars years.

Martin, T. Z.↗
NASA NTRS1973

Ultraviolet reflectivity and geometrical albedo of Titan

Titan's geometrical albedo of 0.094 plus or minus 0.012 was measured at 4255 A with a 50-A bandpass. From this and the spectral measurements, the geometrical albedo was derived as a function of wavelength. It is found that the wavelength dependences of Titan's UV spectrum and of the spectrum of Saturn's Rings are remarkably similar. No trace of any absorption bands is apparent. These results imply that UV gaseous absorption and Rayleigh scattering play a strongly subdued role in Titan's atmosphere. Any homogeneous atmospheric model implies that the absorber responsible for Titan's UV spectral albedo varies strongly with wavelength. On the other hand, it is found that the UV observations can be satisfied by an absorber having a relatively weak dependence upon wavelength if an inhomogeneous atmospheric model is employed. In particular, a fine dust, which absorbs as the reciprocal of the wavelength, can explain the UV observations, provided that it is preferentially distributed high up in Titan's atmosphere where the optical depth from Rayleigh scattering is low.

Barker, E. S.↗
NASA NTRS1979

Spatially resolved methane band photometry of Jupiter. I - Absolute reflectivity and center-to-limb variations in the 6190-, 7250-, and 8900-A bands. II - Analysis of the south equatorial belt and south tropical zone reflectivity

Spatially resolved measurements of the absolute reflectivity and center to limb variations of Jupiter in the 6190, 7250 and 8900 A methane bands and nearby continuum regions are presented and analyzed for the south equatorial belts (SEBs) and south tropical zone (STrZ). It is found that the polar hoods, equatorial zone, Red Spot and north tropical zone have highest methane reflectivities, with the temperate zones and polar regions having low reflectivity and the STrZ and SEBs having intermediate values. The data on the SEB and STrZ are analyzed in terms of diffuse reflecting-scattering and two-cloud models of the vertical distribution of aerosols in the Jovian atmosphere. To fit observations, the STrZ cloud top must have between 0.55 and 0.43 bar total pressure and optical depth between 1.5 and 2.5. The reflecting-scattering models are not suitable for the SEBs. The SEB upper cloud is deeper, cloud thickness is less and the lower cloud is deeper than in the STrZ. A forward scattering haze layer accounts for limb darkening in the continuum.

West, R. A.↗
NASA NTRS1993

A Study of Saturn's E-Ring Particles Using the Voyager 1 Plasma Wave Instrument

The flyby of Voyager 1 at Saturn resulted in the detection of a large variety of plasma waves, e.g., chorus, hiss, and electron cyclotron harmonics. Just before the outbound equator crossing, at about 6.1 R(sub s), the Voyager 1 plasma wave instrument detected a strong, well-defined low-frequency enhancement. Initially it was suggested that plasma waves might be responsible for the spectral feature but more recently dust was suggested as at least a partial contributor to the enhancement. In this report we present evidence which supports the conclusion that dust contributes to the low-frequency enhancement. A new method has been used to derive the dust impact rate. The method relies mainly on the 16-channel spectrum analyzer data. The few wide band waveform observations available (which have been used to study dust impacts during the Voyager 2 ring plane crossing) were useful for calibrating the impact rate from the spectrum analyzer data. The mass and, hence, the size of the dust particles were also obtained by analyzing the response of the plasma wave spectrum analyzer. The results show that the region sampled by Voyager 1 is populated by dust particles that have rms masses of up to few times 10(exp -11) g and sizes of up to a few microns. The dust particle number density is on the order of 10(exp -3) m(exp 3). The optical depth of the region sampled by the spacecraft is 1.04 x 10(exp -6). The particle population is centered about 2500 km south of the equatorial plane and has a north-south thickness of about 4000 km. Possible sources of these particles are the moons Enceladus and Tethys whose orbits lie within the E-ring radial extent. These results are in reasonable agreement with photometric studies and numerical simulations.

Tsintikidis, D.↗
NASA NTRS1978

The blue-to-green reflectance ratio and lake water quality

Correlations between the relative values of the blue and green reflectances of a lake and water quality indices, such as depth of photic zone, Secchi disk transparency, attenuation coefficient, and chlorophyll concentration, have been observed during an intensive satellite, aircraft, and surface vessel study of Lake Ontario and Conesus Lake. Determinations of blue and green reflectances from Skylab S190A color imagery are in excellent agreement with values obtained from small-scale color imagery from aircraft. Further, the accuracy of the satellite data appears within that required for extrapolation to the water quality indices. The study has also determined that changes in chlorophyll, lignin, and humic acid concentration can be discriminated by the behavior of the blue-to-green reflectance ratio and the reflectances of the green and red bands.

Piech, K. R.↗
NASA NTRS1996

Aeropropulsion Technology (APT). Task 23 - Stator Seal Cavity Flow Investigation

The focus of NASA Contract NAS3-25950 Task 23 was to numerically investigate the flow through an axial compressor inner-banded stator seal cavity. The Allison/NASA developed ADPAC code was used to obtain all flow predictions. Flow through a labyrinth stator seal cavity of a high-speed compressor was modeled by coupling the cavity flow path and the main flow path of the compressor. A grid resolution study was performed to guarantee adequate grid spacing was used. Both unsteady rotor-stator-rotor interactions and steady-state isolated blade calculations were performed with and without the seal cavity present. A parameterized seal cavity study of the high-speed stator seal cavity collected a series of solutions for geometric variations. The parameter list included seal tooth gap, cavity depth, wheel speed, radial mismatch of hub flowpath, axial trench gap, hub corner treatments, and land edge treatments. Solution data presented includes radial and pitchwise distributions of flow variables and particle traces describing the flow character.

Heidegger, N. J.↗
NASA NTRS2005

3-D Highway in the Sky

If it were 50 years ago, NASA's contribution to rock and roll could have been more than just the all-astronaut rock band, Max Q, composed of six NASA astronauts, all of whom have flown aboard the Space Shuttle. If it were 50 years ago, a new NASA spinoff technology, Synthetic Vision, would likely have been able to prevent the fateful, small plane crash that killed rock and roll legends Buddy Holly, Ritchie Valens, and The Big Bopper on that stormy night in 1959. Synthetic Vision is a new cockpit display system that helps pilots fly through bad weather, and it has incredible life-saving potential. In 1997, the White House Commission on Aviation Safety and Security created NASA s Aviation Safety and Security Program (AvSSP) with the aim of sounding the depths of NASA s cutting-edge aviation advances and history of successes. The AvSSP decided to use NASA technology to cut the rate of fatal aviation accidents that occur because of lowered visibility and spatial disorientation, common problems that arise in poor weather conditions, in the dark, or with inexperienced pilots.

Source record↗
NASA NTRSDate not supplied

Towards a more realistic representation of NASA CERES-derived surface radiative fluxes during polar night: a comparison with the MOSAiC field campaign

The Arctic is one of the most sensitive regions of Earth to climate change, and yet remains one of the more difficult regions to both observe and simulate. The high latitude of the Arctic gives it some unusual features compared with much of Earth, such as large and variable sea ice cover, extensive mixed phase cloud cover, and the polar day/night cycle. These features significantly influence the radiative environment of the Arctic as well as the ability to observe it. The remoteness of the Arctic from most of civilization makes large volumes of in situ observations difficult to collect, and so satellite observations are a critical tool for observing the region, such as those from Clouds and the Earth’s Radiant Energy System (CERES). But validating the satellite radiative flux estimates is difficult because of the lack of in situ measurements. A useful remedy is utilizing measurements from field campaigns, such as the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition during 2019-2020. The extensive high-quality surface radiative flux and meteorological measurements collected from MOSAiC provide a useful check on flux retrievals from CERES instruments. Previous work compared MOSAiC and CERES surface radiative fluxes during the 2020 melt season (April-September). Errors in CERES fluxes were related to errors in estimated atmospheric optical depth and surface albedo. We conduct a similar assessment of CERES surface flux retrievals using MOSAiC data, but for the months of October through March instead. As this time period is mostly during polar night and twilight, the focus of the study is on longwave surface fluxes. To better understand the reasons for errors in CERES fluxes, we use the large set of meteorological measurements also collected by MOSAiC, including surface temperature, thermodynamic vertical profiles, surface turbulent fluxes, and cloud properties. For example, one notable possible source of error in the CERES estimate of surface downwelling longwave flux is the estimate of cloud base height when compared with MOSAiC W-band radar measurements – an overestimate of cloud base height yields an underestimate of the downwelling flux on the order of tens of W m2.

J. Brant Dodson↗