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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Measuring Airflow With Digital Holographic Interferometry

Digital image-processing system assists in analysis of holographic interferometric images of flow about airfoil. Operating semiautomatically, identifies, counts, and labels interference fringes, then processes distances between fringes into distribution of pressure on surface of airfoil. Yields data on pressure faster than manual image-analyses techniques, and data compares favorably with those obtained by manual analysis and by probe measurements of pressure. Uses computer programs evaluating interferograms along straight or curved lines represented by polygon segments. User prompted for such inputs as reference points and fringe number. Digitizes holographic interferograms of flow and processes them into data of pressure or other properties of flow.

Torres, Francisco J.↗
NASA NTRS2010

UAVSAR Active Electronically-Scanned Array

The Uninhabited Airborne Vehicle Synthetic Aperture Radar (UAVSAR) L-band (1.2-1.3 GHz) repeat pass, interferometric synthetic aperture radar (InSAR) used for Earth science applications. Using complex radar images collected during separate passes on time scales of hours to years, changes in surface topography can be measured. The repeat-pass InSAR technique requires that the radar look angle be approximately the same on successive passes. Due to variations in aircraft attitude between passes, antenna beam steering is required to replicate the radar look angle. This paper describes an active, electronically steered array (AESA) that provides beam steering capability in the antenna azimuth plane. The array contains 24 transmit/receive modules generating 2800 W of radiated power and is capable of pulse-to-pulse beam steering and polarization agility. Designed for high reliability as well as serviceability, all array electronics are contained in single 178cm x 62cm x 12 cm air-cooled panel suitable for operation up 60,000 ft altitude.

Sadowy, Gregory↗
NASA NTRS1980

Interferometry of Saturn and its rings at 1.30-cm wavelength

Interferometric observations of Saturn and its rings at a wavelength of 1.30 cm are presented in an attempt to place constraints upon the amount of thermal radiation emitted by the ring particles. Model-fitting and aperture synthesis techniques were used to analyze the data obtained on nine baselines at a frequency of 23 GHz. Ring optical depth is found to be close to that observed at visible wavelengths, while ring brightness temperature is only 7 + or - 1 K, requiring the ring particles to be nearly conservative scatterers at this wavelength and implying an upper limit of 2.4 m to the radius of a typical ring particle with a lower limit of 0.95 to its single scattering albedo. An observed difference between planetary radii observed at 1.30 and 3.71 cm is interpreted in terms of limb darkening and found to be marginally different from the predictions of atmospheric models in which NH3 is the principal source of microwave opacity.

Schloerb, F. P.↗
NASA NTRS1982

The Jovian ammonia abundance from interferometric observations of limb darkening at 3.4 mm

The relative abundances of the various atomic and molecular constituents in the Jovian atmosphere are important data for studies of the origin of the solar system. The determination of the ammonia abundance presents a number of difficulties. However, difficulties related to a use of the microwave sensing technique can be largely overcome by measuring the brightness distribution across the disk. In particular, information about the atmosphere can be obtained from the degree of limb darkening, which requires only a relative brightness measurement as opposed to an absolute measurement. Valdes and Welch (1978) have used the considered approach in a study of Jupiter at 1.3 cm. In the present investigation a more general relation between the amount of limb darkening in the broad 1.25-cm inversion band of ammonia and the ammonia abundance is derived. The model is applied to new measurements of Jupiter's limb darkening at 3.4 mm.

Valdes, F.↗
NASA NTRS2009

Astronomical Studies at Infrared Wavelengths

Astronomical studies at infrared wavelengths have dramatically improved our understanding of the universe, and observations with Spitzer, Herschel, and SOFIA will continue to provide exciting new discoveries. The relatively low angular resolution of these missions, however, is insufficient to resolve the physical scale on which mid-to far-infrared emission arises, resulting in source and structure ambiguities that limit our ability to answer key science questions. Interferometry enables high angular resolution at these wavelengths - a powerful tool for scientific discovery. We will build the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII), an eight-meter baseline Michelson stellar interferometer to fly on a high-altitude balloon. BETTII's spectral-spatial capability, provided by an instrument using double-Fourier techniques, will address key questions about the nature of disks in young star clusters and active galactic nuclei and the envelopes of evolved stars. BETTII will also lay the technological groundwork for future balloon programs, paving the way for interferometric observations of exoplanets.

Rinehart, Stephen A.↗
NASA NTRS1985

A technique to measure the size of particles in laser Doppler velocimetry applications

A method to measure the size of particles in Laser Doppler Velocimeter (LDV) applications is discussed. Since in LDV the velocity of the flow is assocated with the velocity of particles to establish how well they follow the flow, in the present method the interferometric probe volume is surrounded by a larger beam of different polarization or wavelength. The particle size is then measured from the absolute intensity scattered from the large beam by particles crossing the fringes. Experiments using polystrene particles between 1.1 and 3.3 microns and larger glass beads are reported. It is shown that the method has an excellent size resolution and its accuracy is better than 10% for the particle size studied.

Hess, C. F.↗
NASA NTRS1992

Interferometric reconstruction of three-dimensional high-speed aerodynamic flows

Holographic interferometry can be a very useful diagnostic tool in high-speed aerodynamic testing. During this summer research period, various possible approaches for accurately reconstructing three-dimensional flows from limited data were examined. The approach based on the combination of the following three techniques appears to be promising: (1) Continuous Local Basis Function Method - this computational tomographic method has a power to accurately reconstruct continuous regions and is appropriate from well-conditioned to moderately limited data; (2) Variable Basis Method - this computational tomographic method provides accuracy near discontinuities, i.e., shock regions, and is appropriate from moderately-limited to severely-limited data; and (3) Complementary Field Method - this is a general iterative reconstructor that can be coupled with any computational tomographic techniques. Mathematically, it can be shown that this method can provide better accuracy than the direct reconstruction as in a conventional approach. Our numerical simulation of experiments demonstrated improved reconstruction results even when these techniques were individually tested.

Cha, Soyoung Stephen↗
NASA NTRS2014

Microwave Interferometric Radiometry in Remote Sensing: an Invited Historical Review

The launch of the Soil Moisture and Ocean Salinity (SMOS) mission on 2 November 2009 marked a milestone in remote sensing for it was the first time a radiometer capable of acquiring wide field of view images at every single snapshot, a unique feature of the synthetic aperture technique, made it to space. The technology behind such an achievement was developed, thanks to the effort of a community of researchers and engineers in different groups around the world. It was only because of their joint work that SMOS finally became a reality. The fact that the European Space Agency, together with CNES (Centre National d'Etudes Spatiales) and CDTI (Centro para el Desarrollo Tecnológico e Industrial), managed to get the project through should be considered a merit and a reward for that entire community. This paper is an invited historical review that, within a very limited number of pages, tries to provide insight into some of the developments which, one way or another, are imprinted in the name of SMOS.

Microwave↗
NASA NTRS1974

Interferometric scans of interstellar K I lines

Results of interferometric scans of the interstellar 7669 wavelength line of neutral potassium are reported toward 26 stars at 1.2 km/sec resolution. The advantages of the K I line, as compared with other optical interstellar lines, are discussed. Recent progress in photoanalytical techniques are shown to make possible the effective realization in practice of the inherent advantages of the K I line.

Hobbs, L. M.↗
NASA NTRS1977

Infrared and millimeter wave techniques for the Cosmic Background Explorer Satellite

The Cosmic Background Explorer Satellite will employ infrared and microwave techniques to gain information about the very early universe. Three instruments will cover the spectral range from 8 microns to 13 mm, determining both the spectrum and angular distribution of the large scale background radiation fields. A cryogenic polarizing Michelson interferometric spectrometer will measure the spectrum of the 3 deg K relic radiation from the big bang with precision. Four differential microwave radiometers will map the sky from 23 to 90 GHz in a search for anisotropy of the universe. A broadband cryogenic IR photometer will map zodiacal dust emission, galactic dust, and an extragalactic residual component.

Mather, J. C.↗
NASA NTRS1988

Few-nanoradian deep space navigation in local reference frames

Angular navigation with Very Long Baseline Interferometry is performed at the 15-100 nanoradian level by differencing the interferometric delays of a spacecraft and nearby radio source. Clock rate, earth orientation and atmospheric effects limit the accuracy. By observing several radio sources along with the spacecraft, these dominant errors can be reduced by parameter estimation. Using improved instrumentation, the technique analyzed below, which can potentially yield 1-3 nanoradian accuracy, locates the spacecraft in a local reference frame of radio sources. In this paper, observation strategies and covariance results will be presented for the local reference frame technique. The error contributions of system noise and tropospheric fluctuations will be evaluated. An application of this few-nanoradian technique to Jovian approach is also presented.

Treuhaft, R. N.↗
NASA NTRS1992

A new-speckle interferometry system for the MAMA detector

We have developed a new system for making speckle observations with the multianode microchannel array (MAMA) detector. This system is a true photon-counting imaging device which records the arrival time of every detected photon and allows for reconstruction of image features near the diffraction limit of the telescope. We present a description of the system and summary of observational results obtained at the Lick Observatory 1-m reflector in 1991 September. The diffraction limit of the 1-m telescope at 5029 A is about 0.125 arcsec and we have successfully resolved the catalogued interferometric binary HD 202582 with a separation of 0.157 +/- 0.031 arcsec. A pair of stars in the open cluster Chi Persei separated by 2.65 +/- 0.22 arcsec with approximate V magnitudes 8.6 and 11.5 has also been successfully analyzed with the speckle technique.

Horch, E.↗
NASA NTRS1980

Data acquisition for measuring the wind on Venus from Pioneer Venus

The Pioneer Venus Differential Long Baseline Interferometry experiment was designed to measure the motion in three dimensions of the Pioneer probes during their fall to the surface of Venus, using a combination of Doppler and long baseline ratio interferometric methods. The altitude profiles of wind speed and direction that may be deduced from these data are expected to contribute significantly to the understanding of the dynamics of the Venus atmosphere. The design of the experiment and the equipment and software techniques that were developed specially for this experiment are described.

Smith, J. R.↗
NASA NTRS1996

Waveguides in Thin Film Polymeric Materials

Results on the fabrication of integrated optical components in polymeric materials using photo printing methods will be presented. Optical waveguides were fabricated by spin coating preoxidized silicon wafers with organic dye/polymer solution followed by soft baking. The waveguide modes were studied using prism coupling technique. Propagation losses were measured by collecting light scattered from the trace of a propagation mode by either scanning photodetector or CCD camera. We observed the formation of graded index waveguides in photosensitive polyimides after exposure of UV light from a mercury arc lamp. By using a theoretical model, an index profile was reconstructed which is in agreement with the profile reconstructed by the Wentzel-Kramers-Brillouin calculation technique using a modal spectrum of the waveguides. Proposed mechanism for the formation of the graded index includes photocrosslinking followed by UV curing accompanied with optical absorption increase. We also developed the prototype of a novel single-arm double-mode interferometric sensor based on our waveguides. It demonstrates high sensitivity to the chance of ambient temperature. The device can find possible applications in aeropropulsion control systems.

Sakisov, Sergey↗
NASA NTRS1984

Analysis and application of Fourier transform spectroscopy in atmospheric remote sensing

An analysis method for Fourier transform spectroscopy is summarized with applications to various types of distortion in atmospheric absorption spectra. This analysis method includes the fast Fourier transform method for simulating the interferometric spectrum and the nonlinear least-squares method for retrieving the information from a measured spectrum. It is shown that spectral distortions can be simulated quite well and that the correct information can be retrieved from a distorted spectrum by this analysis technique.

Park, J. H.↗
NASA NTRS1993

Techniques and Applications of SAR interferometry for ERS-1: Topographic Mapping, Change Detection, and Slope Measurement

SAR (Synthetic Aperture Radar) interferometry allows the measurement of high resolution topography of terrain from repeat orbit SAR data sets obtained by the ERS-1 AMI (Active Microwave Instrument). The system parameters which affect the accuracy of the topographic maps are errors in determination of the interferometric baseline, non parallel orbit tracks, decorrelation caused by baseline length, thermal noise, and surface change. Surface change can be observed in the interferograms either through decorrelation of the interferometric phase, or coherent phase shifts caused by locally uniform surface displacements. Phase gradient maps can be derived directly from the complex interferograms and can be transformed into surface slopes mapped onto a geometrically corrected grid.

Charles L Werner↗
NASA NTRS1974

The 1974 NASA-ASEE summer faculty fellowship aeronautics and space research program

Research activities by participants in the fellowship program are documented, and include such topics as: (1) multispectral imagery for detecting southern pine beetle infestations; (2) trajectory optimization techniques for low thrust vehicles; (3) concentration characteristics of a fresnel solar strip reflection concentrator; (4) calaboration and reduction of video camera data; (5) fracture mechanics of Cer-Vit glass-ceramic; (6) space shuttle external propellant tank prelaunch heat transfer; (7) holographic interferometric fringes; and (8) atmospheric wind and stress profiles in a two-dimensional internal boundary layer.

Obrien, J. F., Jr.↗
NASA NTRS1988

A simplified oil-film skin-friction meter

The oil-film method of skin friction measurement, which does not require calibration, nevertheless entails that interferometric measurements of the oil film be obtained. The oil-film method is presently simplified by eliminating interferometry and its requisite polished surface, by taking direct and dynamic measurements of the oil-film slope with a small position-sensing photodiode. This technique has undergone verification in incompressible turbulent and laminar flows in flat-plate boundary layers and pipe flows; the meter is judged to be inexpensive, simple, and robust.

Bandyopadhyay, P. R.↗