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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Vortex Rings Generated by a Shrouded Hartmann-Sprenger Tube

The pulsed flow emitted from a shrouded Hartmann-Sprenger tube was sampled with high-frequency pressure transducers and with laser particle imaging velocimetry, and found to consist of a train of vortices. Thrust and mass flow were also monitored using a thrust plate and orifice, respectively. The tube and shroud lengths were altered to give four different operating frequencies. From the data, the radius, velocity, and circulation of the vortex rings was obtained. Each frequency corresponded to a different length to diameter ratio of the pulse of air leaving the driver shroud. Two of the frequencies had length to diameter ratios below the formation number, and two above. The formation number is the value of length to diameter ratio below which the pulse converts to a vortex ring only, and above which the pulse becomes a vortex ring plus a trailing jet. A modified version of the slug model of vortex ring formation was used to compare the observations with calculated values. Because the flow exit area is an annulus, vorticity is shed at both the inner and outer edge of the jet. This results in a reduced circulation compared with the value calculated from slug theory accounting only for the outer edge. If the value of circulation obtained from laser particle imaging velocimetry is used in the slug model calculation of vortex ring velocity, the agreement is quite good. The vortex ring radius, which does not depend on the circulation, agrees well with predictions from the slug model.

DeLoof, Richard L.↗
NASA NTRS1983

Fiber optics for astronomical spectroscopy - The Medusa Spectrograph

An instrument has been built to obtain simultaneous spectra of 32 objects in the field of view of the Steward Observatory 2.3 m telescope. Short lengths of optical fiber are used to bring light from galaxy images at the focus of the telescope into a line at the spectrograph slit. This multi-fiber aperture plate instrument has been dubbed the Medusa Spectrograph. The Medusa is now producing spectra of about 100 galaxies per clear night. An optimized version of the instrument called the MX Spectrometer is being constructed to record spectra at a higher rate. This new instrument will have remotely positioned fibers under computer control. A Charge Coupled Device will be used as the spectrograph detector to allow sky subtraction, give increased dynamic range and provide more accurate wavelength calibration. Transmission characteristics of some commercial fibers are discussed, and the microlens optics used to match the telescope and the spectrograph to the fibers to avoid focal ratio degradation are described.

Hill, J. M.↗
NASA NTRS1992

SkICAT: A cataloging and analysis tool for wide field imaging surveys

We describe an integrated system, SkICAT (Sky Image Cataloging and Analysis Tool), for the automated reduction and analysis of the Palomar Observatory-ST ScI Digitized Sky Survey. The Survey will consist of the complete digitization of the photographic Second Palomar Observatory Sky Survey (POSS-II) in three bands, comprising nearly three Terabytes of pixel data. SkICAT applies a combination of existing packages, including FOCAS for basic image detection and measurement and SAS for database management, as well as custom software, to the task of managing this wealth of data. One of the most novel aspects of the system is its method of object classification. Using state-of-theart machine learning classification techniques (GID3* and O-BTree), we have developed a powerful method for automatically distinguishing point sources from non-point sources and artifacts, achieving comparably accurate discrimination a full magnitude fainter than in previous Schmidt plate surveys. The learning algorithms produce decision trees for classification by examining instances of objects classified by eye on both plate and higher quality CCD data. The same techniques will be applied to perform higher-level object classification (e.g., of galaxy morphology) in the near future. Another key feature of the system is the facility to integrate the catalogs from multiple plates (and portions thereof) to construct a single catalog of uniform calibration and quality down to the faintest limits of the survey. SkICAT also provides a variety of data analysis and exploration tools for the scientific utilization of the resulting catalogs. We include initial results of applying this system to measure the counts and distribution of galaxies in two bands down to Bj is approximately 21 mag over an approximate 70 square degree multi-plate field from POSS-II. SkICAT is constructed in a modular and general fashion and should be readily adaptable to other large-scale imaging surveys.

Weir, N.↗
NASA NTRS1982

Geologic observations of the northern boundary of the Caribbean plate across central America as seen by Seasat and SIR-A

The radar data analyzed here extend from the Amatique Bay (Golfo de Honduras) in the northeast to the Pacific Ocean (Puenta Remedios) in the southwest. Space Shuttle Imaging Radar (SIR-A) data-take 18 overlaps the principal part of the Seasat mosaic. SIR-A data make possible more observations over the Central American Cordillera, where strong layover limited the amount of information obtained by Seasat. The radar coverage delineates the principal strike-slip faults of the region (Cuilco-Chixoy-Polochic, Motagua and Jocotan), which have acted as the Caribbean-Americas plate boundary. It also demarcates volcanic terranes related to subduction of the Cocos Plate under the Caribbean Plate. Within pumice fields of the Tertiary volcanic belt, the use of two Seasat look directions (rev 759 and rev 1211), in conjunction with SIR-A data, makes possible some rock discrimination.

Rebillard, P.↗
NASA NTRS1981

Imaging X-ray spectrophotometers

A new instrument which combines the good energy resolution of the gas scintillation proportional counter with the high position resolution of the microchannel plate is proposed. A study of the factors which determine the combined energy and position resolution of the new instrument is discussed. Submillimeter position resolution along with good energy resolution (8% fwhm at 6 keV) should be achievable.

Hailey, C. J.↗
NASA NTRS1979

Recent developments at JPL in the application of image processing to astronomy

Four applications of image processing to astronomy, automated location and analysis of star and galaxy images, geometric and radiometric decalibration of vidicon spectra, display of multiband radio images, and generation of high resolution polarization direction and magnitude maps from images are presented with illustrative examples. The technique by which a digital image can be analyzed automatically to locate and segregate between stars and galaxies and the steps performed by the classifier to determine the nature of each object are outlined. The classification program executed on a 48 inch Schmidt plate of the cluster of galaxies 655 is described. The calibration and decalibration steps to remove geometric and radiometric distortions from a silicon vidicon camera digital spectra are discussed. Three methods of displaying multispectral radio data, generating a mosaic of each image, producing a color coded image to depict radio velocity, and producing a stereo pair with radial velocity as depth are described. The generation of polarization information from images obtained through linear polarizing filters is illustrated, and it is concluded that in each case information was displayed using digital techniques which could not readily have been provided visually.

Lorre, J. J.↗
NASA NTRS1995

Stokes problems for moving half-planes

New exact solutions of the Navier-Stokes equations are obtained for the unbounded and bounded oscillatory and impulsive tangential edgewise motion of touching half-infinite plates in their own plane. In contrast to Stokes classical solutions for the harmonic and impulsive motion of an infinite plane wall, where the solutions are separable or have a simple similarity form, the present solutions have a two-dimensional structure in the near region of the contact between the half-infinite plates. Nevertheless, it is possible to obtain relatively simple closed-form solutions for the flow field in each case by defining new variables which greatly simplify the r- and theta- dependence of the solutions in the vicinity of the contact region. These solutions for flow in a half-infinite space are then extended to bounded flows in a channel using an image superposition technique. The impulsive motion has application to the motion near geophysical faults, whereas the oscillatory motion has arisen in the design of a novel oscillating half-plate flow chamber for examining the effect of fluid shear stress on cultured cell monolayers.

NASA Discipline Musculoskeletal↗
NASA NTRS2006

Solar CIV Vacuum-Ultraviolet Fabry-Perot Interferometers

Aims: A tunable, high spectral resolution, high effective finesse, vacuum ultraviolet (VUV) Fabry-Perot interferometer (PPI) is designed for obtaining narrow-passband images, magnetograms, and Dopplergrams of the transition region emission line of CIV (155 nm). Methods: The integral part of the CIV narrow passband filter package (with a 2-10 pm FWHM) consists of a multiple etalon system composed of a tunable interferometer that provides high-spectral resolution and a static low-spectral resolution interferometer that allows a large effective free spectral range. The prefilter for the interferometers is provided by a set of four mirrors with dielectric high-reflective coatings. A tunable interferometer, a VUV piezoelectric-control etalon, has undergone testing using the surrogate F2 eximer laser line at 157 nm for the CIV line. We present the results of the tests with a description of the overall concept for a complete narrow-band CIV spectral filter. The static interferometer of the filter is envisioned as being hudt using a set of fixed MgF2 plates. The four-mirror prefilter is designed to have dielectric multilayer n-stacks employing the design concept used in the Ultraviolet Imager of NASA's Polar Spacecraft. A dual etalon system allows the effective free spectral range to be commensurate with the prefilter profile. With an additional etalon, a triple etalon system would allow a spectrographic resolution of 2 pm. The basic strategy has been to combine the expertise of spaceflight etalon manufacturing with VUV coating technology to build a VUV FPI which combines the best attributes of imagers and spectrographs into a single compact instrument. Results. Spectro-polarimetry observations of the transition region CIV emission can be performed to increase the understanding of the magnetic forces, mass motion, evolution, and energy release within the solar atmosphere at the base of the corona where most of the magnetic field is approximately force-free. The 2D imaging of the full vector magnetic field at the height of maximum magnetic influence (minimum plasma beta) can be accomplished, albeit difficult, by measuring the Zeeman splitting of the CIV resonance pair. Designs of multiple VUV FPIs can be developed for integration into future orbiting solar observatories to obtain rapid cadence, spectral imaging of the transition region.

Gary, G. Allen↗
NASA NTRS2013

The Effects of Surfaces on the Aerodynamics and Acoustics of Jet Flows

Aircraft noise mitigation is an ongoing challenge for the aeronautics research community. In response to this challenge, low-noise aircraft concepts have been developed that exhibit situations where the jet exhaust interacts with an airframe surface. Jet flows interacting with nearby surfaces manifest a complex behavior in which acoustic and aerodynamic characteristics are altered. In this paper, the variation of the aerodynamics, acoustic source, and far-field acoustic intensity are examined as a large at plate is positioned relative to the nozzle exit. Steady Reynolds-Averaged Navier-Stokes solutions are examined to study the aerodynamic changes in the field-variables and turbulence statistics. The mixing noise model of Tam and Auriault is used to predict the noise produced by the jet. To validate both the aerodynamic and the noise prediction models, results are compared with Particle Image Velocimetry (PIV) and free-field acoustic data respectively. The variation of the aerodynamic quantities and noise source are examined by comparing predictions from various jet and at plate configurations with an isolated jet. To quantify the propulsion airframe aeroacoustic installation effects on the aerodynamic noise source, a non-dimensional number is formed that contains the flow-conditions and airframe installation parameters.

Smith, Matthew J.↗
NASA NTRS1974

Electronographic photometry of extended objects. I - Reduction procedures

Attention is given to the reduction of electronographic camera images obtained with the aid of the Kron camera. A description is given of the equipment used to digitize the plate material. The response of the camera-emulsion-microdensitometer system is discussed along with present system performance figures. An outline is presented of existing and future computer reduction techniques.

Benedict, G.↗
NASA NTRS1988

Monocular electro-optical stereo scanner

MEOSS is a single optics and single spectral band camera. Three CCD's working in pushbroom mode are mounted perpendicular to the flight direction on a common focal plate. Their oblique views of + and - 23 degrees forward and backward, as well as nadir oriented, lead to threefold stereoscopic images. This principle allows a nearly simultaneous generation of all three images of a stereo triplet. The time gap between the forward and aft looking images guarantees constant illumination conditions. The ground resolution of MEOSS will be 52 by 80 m ground pixel size, height resolution of 55 m and swath width of 255 km. The drifting ground coverage pattern of MEOSS is unique compared to polar orbiting satellites and will allow images of an area to be taken at different times of the day. A scene will consist of 3144 scan lines, with each having 3236 pixels. The data will be received by the Deep Space Network of JPL Goldstone and mailed to Goddard.

Vermillion, C.↗
NASA NTRS1990

ORFEUS-SPAS - The Berkeley EUV spectrometer

The Berkeley EUV spectrometer of ORFEUS-SPAS, a joint project of NASA and the BMFT, incorporates a set of four novel spherically figured, varied line-space gratings used in a geometry that is similar to that of the classic Rowland mount to span an interval of 390 and 1200 A. Two spectral detector units containing curved microchannel plates and delay-line anodes encode the arriving photons in digital format for telemetry. An additional optic directs the image of the source in the entrance aperture onto a sealed FUV detector which is used to track the source as it drifts during an observation, enabling a postflight reconstruction of the spacecraft pointing vector. This in turn makes it possible to define with precision the wavelength of each recorded photon.

Bowyer, Stuart↗
NASA NTRS2000

Reflective Focused Schlieren System Improved for Use in 10- by 10-Foot Supersonic Wind Tunnel

The reflective focused schlieren system that was developed for use in the 10- by 10-Foot Supersonic Wind Tunnel (10x10 SWT) at the NASA Glenn Research Center at Lewis Field as part of the Unstart Test Program was improved this past year. In April 1999, the development and use of the system was presented at the Supersonic Tunnel Association International in Bedford, England. A focused schlieren system is similar to a standard schlieren system in that shock waves coming from an object in supersonic flow can be seen using a standard video camera. Unlike the standard schlieren system, which produces a two-dimensional schlieren image, a focused schlieren system can produce a threedimensional image. The preceding drawing shows the components of the reflective focused schlieren system being developed for use in the 10x10 SWT. Although the system worked well for the Unstart Test Program, it was not sensitive enough to be classified as a facility capability. Therefore, a program was implemented to improve the sensitivity of the reflective focused schlieren system so that it could be a facility capability for Glenn's 10x10 SWT. Several techniques were implemented to increase the sensitivity and to improve the overall operation of the system. These included refinement of the source grid, improvement in the cutoff grid production, improvement of the source grid and cutoff grid alignment, installation of an improved light source, and incorporation of an image-enhancing system. These changes are being implemented with the system set up in the laboratory. A checkout test of the system is planned in the 10x10 SWT in March 2000. Of these techniques, the most developed is the refinement of the source grid. The original system had a pattern of -in. by -in. squares on -in. centers (distance between the center points of adjacent squares). This gave a ratio of light to dark (reflective to nonreflective area) of 3:1. The recommended ratio is 1:1. In order to accomplish this, a pattern of -in.-diameter dots on 3/8-in. centers was developed. Preliminary tests with this pattern showed an increase in system sensitivity and image clarity. Further testing and refinement are scheduled. The former and improved dot patterns are shown. The use of glass plates to produce the cutoff grid improved the cutoff grid's quality and helped to align it with the source grid. The cutoff grid, which is the negative of the source grid, is made by exposing photography film (or glass plates) to the proper light while it is installed in the focused schlieren system. The exposed film or plate is removed from the system and then developed as a photograph negative. Because the glass plates are rigid, they eliminate the risk of distortion when the negative is reinstalled in the system and realigned with the source grid.

Williamson, Gary Scott↗
NASA NTRS2010

Phase and Pupil Amplitude Recovery for JWST Space-Optics Control

This slide presentation reviews the phase and pupil amplitude recovery for the James Webb Space Telescope (JWST) Near Infrared Camera (NIRCam). It includes views of the Integrated Science Instrument Module (ISIM), the NIRCam, examples of Phase Retrieval Data, Ghost Irradiance, Pupil Amplitude Estimation, Amplitude Retrieval, Initial Plate Scale Estimation using the Modulation Transfer Function (MTF), Pupil Amplitude Estimation vs lambda, Pupil Amplitude Estimation vs. number of Images, Pupil Amplitude Estimation vs Rotation (clocking), and Typical Phase Retrieval Results Also included is information about the phase retrieval approach, Non-Linear Optimization (NLO) Optimized Diversity Functions, and Least Square Error vs. Starting Pupil Amplitude.

Dean, B. H.↗
NASA NTRS1999

KWIC: A Widefield Mid-Infrared Array Camera/Spectrometer for the KAO

The Kuiper Widefield Infrared Camera (KWIC) is an imaging spectrometer designed for use on the Kuiper Airborne Observator between 18 and 40 microns. The spectral resolution achieving devices are two fully tunable and scanning cryogenic Fabry-Perot interferometers that employ free standing metal mesh as the reflective surfaces. The detective device is a 128 x 128 pixel Si:Sb BIB array manufactured by Rockwell/Boeing for the SIRTF project. The plate scale for KWIC (one pixel subtends 2.73" x 2.73") was chosen so as to more than fully sample the KAO beam (approximately 9" at 31.5 microns), to enable effective image restoration techniques to be applied. Even so, KWIC has a rather large (5.8' x 5.8') field of view. KWIC has both high and low spectral resolution modes that are interchangeable in a few minutes time in flight on the KAO. The high resolution (R = lambda/(delta)lambda = 1000 to 6000) mode is suitable for detecting weak lines in the presence of strong continuum for Galactic sources, and for resolving broad extragalactic lines. The low resolution (R approximately 30 to 100) mode is suitable for imaging in the thermal dust continuum.

Stacey, Gordon J.↗
NASA NTRS1983

Image plane detector for the dynamics explorer Fabry-Perot interferometer

A compact twelve-channel photon-counting device based on existing Generation II imaging technology has been developed for use as the image-plane detector of the Dynamics Explorer Fabry-Perot interferometer. The device has an S-20 photocathode, three-microchannel plate electron multiplication stages, and an equal-area concentric-ring segmented anode whose geometry mimics that of the interference ring pattern produced by a plane etalon. The twelve channels sample equal and contiguous intervals in the spectrum. The purpose of the delopment has been to utilize the signal multiplex advantage of a multichannel detector in the measurement of Doppler shifts and line-broadening effects for naturally occurring atmospheric emission features of low intensity. The design, testing, calibration, and flight performance of the novel detector system are presented. In addition, measured emission line profiles at high resolution from the satellite instrument are presented to illustrate the operation of the device.

Killeen, T. L.↗
NASA NTRS1985

Coma morphology and dust-emission pattern of periodic comet Halley. III - Additional high-resolution images taken in 1910

High-resolution photographic images of comet Halley obtained at Lick, Helwan, Lowell, and Vienna observatories during May-June 1910 are analyzed using the image-processing algorithm of Larson and Sekanina (1984). The results are presented in tables and compared with analyses of Mt. Wilson plates for the same period (Sekanina and Larson, 1984), and good general agreement is noted. Consideration is given to the position of the rotation pole, features indicative of the nucleus spin rate, the spokelike structure observed on May 21-22, and the expanding gas halo.

Larson, S. M.↗
NASA NTRS1985

Quantitative analysis of hard X-ray 'footpoint' flares observed by the solar maximum mission

Amplifier gain and collimator hole size variations across the field of view, amplifier/filter efficiency, variations in effective collimator hole size and angular response with photon energy, dead-time, and hard X-ray plate transmission, are among the factors for which instrumental corrections have to be incorporated to effect reliable correction and deconvolution of images from the SMM satellite's Hard X-ray Imaging Spectrometer (HXIS). Attention is given to the substantial Poisson noise in these energy bands. The maximum entropy deconvolution/correction routine developed for establishing the spatial structure reliably inferrable from HXIS data is presented, together with the results of the application of this routine to the three impulsive flares reported by Duijemian et al. (1982) from April 10, May 21, and November 5, 1980.

Mackinnon, A. L.↗