Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “INTERFEROMETRY”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Satellite radar interferometry - Two-dimensional phase unwrapping

Interferometric synthetic aperture radar observations provide a means for obtaining high-resolution digital topographic maps from measurements of amplitude and phase of two complex radar images. The phase of the radar echoes may only be measured modulo 2 pi; however, the whole phase at each point in the image is needed to obtain elevations. An approach to 'unwrapping' the 2 pi ambiguities in the two-dimensional data set is presented. It is found that noise and geometrical radar layover corrupt measurements locally, and these local errors can propagate to form global phase errors that affect the entire image. It is shown that the local errors, or residues, can be readily identified and avoided in the global phase estimation. A rectified digital topographic map derived from the unwrapped phase values is presented.

Goldstein, Richard M.↗
NASA NTRS1989

Fast Laser Holographic Interferometry For Wind Tunnels

Proposed system makes holographic interferograms quickly in wind tunnels. Holograms reveal two-dimensional flows around airfoils and provide information on distributions of pressure, structures of wake and boundary layers, and density contours of flow fields. Holograms form quickly in thermoplastic plates in wind tunnel. Plates rigid and left in place so neither vibrations nor photgraphic-development process degrades accuracy of holograms. System processes and analyzes images quickly. Semiautomatic micro-computer-based desktop image-processing unit now undergoing development moves easily to wind tunnel, and its speed and memory adequate for flows about airfoils.

Lee, George↗
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 NTRS1988

Astronomical interferometry on the Moon

Optical interferometric arrays are particularly attractive candidates for a manned lunar base. A permanent lunar can provide support for a variety of astronomical investigations. An optical interferometric array, perhaps of the general form of the VLA but designed for optical instead of radio wavelengths, would lead to a qualitative advance in the understanding of the universe. A wide variety of scientific problems could be addressed by such an instrument. The stellar analogs of the solar cycle, the behavior of sunspots on other stars, the magnetic field configurations of other stars, and the behavior of dynamic plasma phenomena such as flares and winds are examples of star related problems that ultimately would lead to both increased understanding of our Sun and fundamental knowledge of the manner in which stars form and evolve.

Burke, Bernard F.↗
NASA NTRS1989

Holographic interferometry with an injection seeded Nd:YAG laser and two reference beams

The performance of twin injection seeded Nd:YAG lasers is compared with the performance of an argon-ion laser for recording dual-reference-beam holograms in AGFA 8E56 emulsion. Optical heterodyning is used to measure interference, and the results are expressed in terms of heterodyning signal level and intensity signal-to-noise. The Nd:YAG laser system is to be used for optical inspections of structures for cracks, defects, gas leaks, and structural changes.

Decker, Arthur J.↗
NASA NTRS1989

Speckle interferometry using fiber optic phase stepping

A system employing closed-loop phase-stepping is used to measure the out-of-plane deformation of a diffusely reflecting object. Optical fibers are used to provide reference and object beam illumination for a standard two-beam speckle interferometer, providing set-up flexibility and ease of alignment. Piezoelectric fiber-stretchers and a phase-measurement/servo system are used to provide highly accurate phase steps. Intensity data is captured with a charge-injection-device camera, and is converted into a phase map using a desktop computer. The closed-loop phase-stepping system provides 90 deg phase steps which are accurate to 0.02 deg, greatly improving this system relative to open-loop interferometers. The system is demonstrated on a speckle interferometer, measuring the rigid-body translation of a diffusely reflecting object with an accuracy + or - 10 deg, or roughly + or - 15 nanometers. This accuracy is achieved without the use of a pneumatically mounted optics table.

Mercer, Carolyn R.↗
NASA NTRS1989

Skin-friction measurements by laser interferometry

The measurement of skin friction in rapidly distorted compressible flows is difficult, and very few reliable techniques are available. A recent development, the laser interferometer skin friction (LISF) meter, promises to be useful for this purpose. This technique interferometrically measures the time rate of thinning of an oil film applied to an aerodynamic surface. Under the proper conditions the wall shear stress may thus be found directly, without reference to flow properties. The applicability of the LISF meter to supersonic boundary layers is examined experimentally. Its accuracy and repeatability are assessed, and conditions required for its successful application are considered.

Kim, K.-S.↗
NASA NTRS1988

Geodesy by radio interferometry - Determination of vector motions for sites in the western United States

The use of VBLI to study plate tectonic motion, plate boundary deformation, earth dynamics, and the crustal motions in the western U.S. is discussed. Results from dual frequency (S and X band) mobile VLBI experiments between October 1982 and February 1987 are presented. It is suggested that significant northwest motion is occurring well east of the San Andreas fault.

Gordon, David↗
NASA NTRS1988

Very long baseline interferometry observations using the tracking and data relay satellite as an orbiting radio telescope

An antenna in geostationary orbit was used for VLBI observations at 2.3 GHz, in combination with ground antennas in Australia and Japan. 23 of the 25 observed sources were detected on orbiter-ground baselines, with baseline lengths as large as 2.15 earth diameters. Brightness temperatures between 10 to the 12th K and 4 x 10 to the 12th K were measured for 10 sources.

Linfield, R. P.↗
NASA NTRS1988

Global fringe fitting for space interferometry

Global fringe fitting for VLBI has been incorporated into the NRAO Astronomical Image Processing System as the VBFIT program. A generalized program, called VBGFF, has been developed for use with VLBI arrays that include orbiting radio telescopes. Various aspects of these programs are discussed.

Jones, Dayton L.↗
NASA NTRS1988

Mark III very long baseline interferometry positions of eight stellar systems and astrometric comparisons

Accurate positions of eight stellar systems have been obtained from Mark III VLBI observations performed with multistation arrays, and the quality of the celestial frames used by different techniques is compared. The satisfactory agreement found between VLBI and optical positions indicates that the preliminary FK5 optical frame defined by Fricke (1982) is aligned with the VLBI extragalactic reference frame. The VLBI and VLA right ascensions agree, while a large discrepancy is noted between the VLBI and VLA declinations.

Lestrade, Jean-Francois↗
NASA NTRS1988

Analysis of the light scattering interferometry for spheres larger than the light wavelength

A theoretical model, based on the geometrical optics approach, has been developed to simulate various aspects of the phase Doppler particle analyzer (PDPA). The model has taken into consideration the non-uniform (Gaussian) illumination of the particles as they pass through the probe volume. Instrument response curves have been generated for various scattering angles by performing spatial and temporal integration of the scattered intensity distribution over the receiver surface. Experimental and theoretical investigations have established the applicability of this instrument to both forward and backscatter angles.

Bachalo, W. D.↗
NASA NTRS1989

Real time processor for array speckle interferometry

The authors are constructing a real-time processor to acquire image frames, perform array flat-fielding, execute a 64 x 64 element two-dimensional complex FFT (fast Fourier transform) and average the power spectrum, all within the 25 ms coherence time for speckles at near-IR (infrared) wavelength. The processor will be a compact unit controlled by a PC with real-time display and data storage capability. This will provide the ability to optimize observations and obtain results on the telescope rather than waiting several weeks before the data can be analyzed and viewed with offline methods. The image acquisition and processing, design criteria, and processor architecture are described.

Chin, Gordon↗
NASA NTRS1989

Orbital elements of Charon from speckle interferometry

The semimajor axis and the inclination are the two most important quantities presently determined from 56 well-calibrated speckle-interferometric observations of the position of Charon, which are presented in conjunction with an orbit solution that incorporates them. Both values in the best solution obtained are noted to significantly differ from earlier determinations. The new value for the semimajor axis represents a 2.7 percent increase over the previously accepted value; the mean density of the system, however, remains unaltered.

Beletic, J. W.↗
NASA NTRS1989

Angular navigation on short baselines using phase delay interferometry

Results are presented for two recent short baseline experiments, with baseline lengths of 6 and 253 km, showing delay residuals of 10 ps or less for angularly close sources. On the 6-km baseline, a fiber-optic link was used to distribute a common frequency reference, enabling coherent operation of the two stations. The observed delay residuals correspond to a differential angular accuracy of about 10 nrad on the 253-km baseline. Future plans are discussed, including the development of a realtime correlation capability on a 22-km baseline at Goldstone, CA.

Edwards, Charles D.↗
NASA NTRS1989

Tracking requirements to support space very long baseline interferometry

The use of VLBI with a radio telescope in space is exmained. The concept of space VLBI and Soviet, Japanese, and U.S./European studies for developing space VLBI observatories are reviewed. The proposed NASA/ESA Quasat mission is described, including the potential ground tracking sites for high earth orbiters.

Jordan, J. Frank↗