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At least 217 records · Page 12

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.

Orbiting and In-Situ Lidars for Earth and Planetary Applications

At NASA Goddard Space Flight Center (GSFC), we have been developing spaceborne lidar instruments for Earth and planetary sciences. We have successfully flown a several missions in the past based on mature diode pumped solid-state laser transmitters. In recent years we have been developing advanced laser technologies for applications such as laser spectroscopy, laser communications, and interferometry. In this paper, we will discuss recent experimental progress on these systems and instrument prototypes for ongoing development efforts.

Space instruments

Holographic interferometry

Holographic interferometry application to laser NDT of objects with nonoptical surfaces, describing techniques and industrial uses

Wuerker, R. F.

The gravity and shape of the moon

This review discusses the current knowledge of the gravity and geometry of the moon, and their implications as to lunar structure. Measurements pertaining to the gravity field are, first and foremost, Doppler tracking of spacecraft that have orbited the moon, but also the laser ranging from the earth to the moon and the gravity meters and accelerometers landed with the Apollo spacecraft. Measurements pertaining to the geometry include (1) those related to the shape: the metric photography and laser altimeters on Apollo 15, 16, and 17; the electromagnetic sounder on Apollo 17; the landmark tracking from earlier Apollo orbiters; and occupations, plus (2) measurements related to the orientation: the laser ranging and interferometry from the earth. The review does not cover determinations of topography from photography taken for geologic or landing reconnaissance purposes. The discussion of tectonic implications is limited to inferences of a quantitative nature. The emphasis is on work since 1970; see Kaula [1969, 1971] for reviews of earlier work.

William M. Kaula

VLBI/Laser Intercomparison Project: Session 2

Recent experiments are described which directly intercompare very long baseline interferometry (VLBI) with laser ranging to artificial satellites by measuring the vector lengths of the same intercontinental baselines. These experiments are part of the VLBI/Laser-Intercomparison Project, a continuing task to assess the suitability of VLBI to various geophysical applications.

Fliegel, H. F.

Transonic flow past a symmetrical airfoil at high angle of attack

The results of an experimental investigation of shock-induced stall and leading-edge stall on a 64A010 airfoil section are presented. Advanced nonintrusive techniques - laser velocimetry, holographic interferometry, and buried-wire anemometry - were used in characterizing the inviscid and viscous flow regions. The measurements include Mach contours of the inviscid flow regions, and mean velocity, flow direction and Reynolds shear stress profiles in the separated regions. The experimental observations of this study are relevant to efforts to improve surface pressure prediction methods for airfoils at or near stall.

Johnson, D. A.

Time and frequency stability for the Crustal Dynamics Project

Very long base interferometry (VLBI) and laser ranging to artificial satellites and the Moon were used to determined vector baselines between stations with precisions of about one part in 10 to the 8th power. Deformations and strain accumulations in active earthquake regions were determined by making frequent measurements of baselines between many stations in active areas near plate boundaries.

Coates, R. J.

Measurements in liquid fuel sprays

Techniques for studying the events directly preceding combustion in the liquid fuel sprays are being used to provide information as a function of space and time on droplet size, shape, number density, position, angle of flight and velocity. Spray chambers were designed and constructed for: (1) air-assist liquid fuel research sprays; (2) high pressure and temperature chamber for pulsed diesel fuel sprays; and (3) coal-water slurry sprays. Recent results utilizing photography, cinematography, and calibration of the Malvern particle sizer are reported. Systems for simultaneous measurement of velocity and particle size distributions using laser Doppler anemometry interferometry and the application of holography in liquid fuel sprays are being calibrated.

Chigier, N.

Length of day and atmospheric angular momentum - A comparison of 1981-1983

In connection with the availability of observations of increasingly greater accuracy and higher time resolution, studies have been conducted regarding the relationship between the earth's rotation and the angular momentum of its atmosphere. The present paper reports an investigation conducted on the basis of earth rotation values determined during the time from 1981 to 1983 with the aid of very long baseline interferometry (VLBI), lunar laser ranging (LLR), and satellite laser ranging (SLR). The values obtained with the different techniques were compared, and a combined series of length of day (LOD) values were computed. A similar computation procedure was applied to the atmospheric angular momentum (AAM) values of U.S. and European origin to obtain corresponding series of LOD values.

Morgan, P. J.

Daily estimates of the earth's pole position with the Global Positioning System

Daily estimates of the earth's pole position have been obtained with measurements from a worldwide network of GPS receivers, obtained during the three week GIG '91 experiment in January-February 1991. For this short-term study, the GPS based polar motion series agrees with the other space based geodetic techniques (Very Long Baseline Interferometry and Satellite Laser Ranging) to about 0.4 mas rms, after the removal of mean biases of order 1-3 mas. The small error in day-to-day variability is not sensitive to the fiducial strategy used, nor are fiducial sites even necessary for monitoring high frequency pole position variability. The small biases indicate that the applied reference frames of the three geodetic techniques are nearly aligned, that the GPS fiducial errors are small, and that systematic errors in GPS are also small (of order 5 ppb). A well determined reference frame is necessary for monitoring the long-term stability of polar motion and for separating it from other long-term signals such as tectonic motion and internal systematic errors.

Lindqwister, Ulf J.

Tectonic deformation in southern California

Our objectives were to use modem geodetic data, especially those derived from space techniques like Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and the Global Positioning System (GPS) to infer crustal deformation in southern California and relate it to plate tectonics and earthquake hazard. To do this, we needed to collect some original data, write computer programs to determine positions of survey markers from geodetic observables, interpret time dependent positions in terms of velocity and earthquake caused episodic displacements, and construct a model to explain these velocities and displacements in terms of fault slip and plate movements.

Jackson, David D.

Miniature Loop Heat Pipe (MLHP) Thermal Management System

The MLHP Thermal Management System consists of a loop heat pipe (LHP) with multiple evaporators and condensers, thermal electrical coolers, and deployable radiators coated with variable emittance coatings (VECs). All components are miniaturized. It retains all the performance characteristics of state-of-the-art LHPs and offers additional advantages to enhance the functionality, versatility, and reliability of the system, including flexible locations of instruments and radiators, a single interface temperature for multiple instruments, cooling the on instruments and warming the off instruments simultaneously, improving. start-up success, maintaining a constant LHP operating temperature over a wide range of instrument powers, effecting automatic thermal switching and thermal diode actions, and reducing supplemental heater powers. It can fully achieve low mass, low power and compactness necessary for future small spacecraft. Potential applications of the MLHP thermal technology for future missions include: 1) Magnetospheric Constellation; 2) Solar Sentinels; 3) Mars Science Laboratory; 4) Mars Scouts; 5) Mars Telecom Orbiter; 6) Space Interferometry Mission; 7) Laser Interferometer Space Antenna; 8) Jupiter Icy Moon Orbiter; 9) Terrestrial Planet Finder; 10) Single Aperture Far-Infrared Observatory, and 11) Exploration Missions. The MLHP Thermal Management System combines the operating features of a variable conductance heat pipe, a thermal switch, a thermal diode, and a state-of-the-art LHP into a single integrated thermal system. It offers many advantages over conventional thermal control techniques, and can be a technology enabler for future space missions. Successful flight validation will bring the benefits of MLHP technology to the small satellite arena and will have cross-cutting applications to both Space Science and Earth Science Enterprises.

Ku, Jentung

Modernizing and Expanding the NASA Space Geodesy Network to Meet Future Geodetic Requirements

NASA maintains and operates a global network of Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and Global Navigation Satellite System ground stations as part of the NASA Space Geodesy Program. The NASA Space Geodesy Network (NSGN) provides the geodetic products that support Earth observations and the related science requirements as outlined by the US National Research Council (NRC in Precise geodetic infrastructure: national requirements for a shared resource, National Academies Press, Washington, 2010. http://nap.edu/12954, Thriving on our changing planet: a decadal strategy for Earth observation from space, National Academies Press, Washington, 2018. http://nap.edu/24938). The Global Geodetic Observing System (GGOS) and the NRC have set an ambitious goal of improving the Terrestrial Reference Frame to have an accuracy of 1 mm and stability of 0.1 mm per year, an order of magnitude beyond current capabilities. NASA and its partners within GGOS are addressing this challenge by planning and implementing modern geodetic stations colocated at existing and new sites around the world. In 2013, NASA demonstrated the performance of its next-generation systems at the prototype next-generation core site at NASA’s Goddard Geophysical and Astronomical Observatory in Greenbelt, Maryland. Implementation of a new broadband VLBI station in Hawaii was completed in 2016. NASA is currently implementing new VLBI and SLR stations in Texas and is planning the replacement of its other aging domestic and international legacy stations. In this article, we describe critical gaps in the current global network and discuss how the new NSGN will expand the global geodetic coverage and ultimately improve the geodetic products. We also describe the characteristics of a modern NSGN site and the capabilities of the next-generation NASA SLR and VLBI systems. Finally, we outline the plans for efficiently operating the NSGN by centralizing and automating the operations of the new geodetic stations.

Merkowitz, S. M.

Orbiting and In-Situ Lidars for Earth and Planetary Applications

At NASA Goddard Space Flight Center (GSFC), we have been developing spaceborne lidar instruments for space sciences. We have successfully flown several missions in the past based on mature diode pumped solid-state laser transmitters. In recent years we have been developing advanced laser technologies for applications such as laser spectroscopy, laser communications, and interferometry. In this paper, we will discuss recent experimental progress on these systems and instrument prototypes for ongoing development efforts.

Anthony W. Yu

Phase-Dependent Squeezing in Dual-Comb Interferometry

Manipulating the quantum noise of continuous-wave lasers through squeezing has reshaped optical interferometry. However, progress in optical frequency comb interferometry with pulsed squeezed sources has been limited, despite the role of frequency combs in ultraprecise optical metrology. Here, we introduce a new time-domain approach to characterizing squeezed femtosecond light pulses using dual-comb interferometry. Time-domain interferograms are generated via multiheterodyne beating between the modes of a Kerr soliton-squeezed frequency comb and a coherent state comb. The interferogram noise reveals phase-dependent squeezing and antisqueezing, dipping as much as 3.8 ± 0.2 dB below the shot noise level at alternating zero crossings. We model this nonstationary quantum noise as a periodic optical displacement of the squeezed comb by the coherent comb. These results support a route toward quantum-enhanced dual-comb timing applications and high-speed quantum state tomography with dual-comb interferometers.

Herman, Daniel Issac [University of Colorado, Boul

Holographic interferometry.

Review of the techniques and applications of holographic interferometry. The recording of a 'reflected-light' hologram with a gas laser is described in order to illustrate the unique optical properties of a hologram. Special types of interferometric measurement, such as stored-beam holographic interferometry and double-exposure holographic interferometry, are then discussed. Applications of gas-laser holographic interferometry to the detection of internal flaws in steel tubing are cited, as well as applications involving the testing of aircraft and automotive tires and aircraft honeycomb composites for bond integrity and the prediction of failure in mechanical components. Finally, applications of the pulsed solid-state ruby laser in holographic interferometry are considered.

Wuerker, R. F.

Lunar dynamics and selenodesy - Results from analysis of VLBI and laser data

Very long base line interferometry (VLBI) observations of lunar radio transmitters have been combined with data from laser ranging to lunar retroreflectors to estimate simultaneously (1) parameters in models of the lunar orbit and libration and (2) the selenodetic coordinates of the radio transmitters and retroreflectors. For the ratio of the mass of the sun to that of the earth plus moon, a value of approximately 328,900.5 is obtained. The lunar moment-of-inertia ratios beta and gamma are also determined. The values and most of the uncertainties obtained for the third-degree harmonics of the moon's gravity field are comparable to those which have been obtained by others from observations of lunar-orbiting spacecraft. However, the results for the two third-degree gravity coefficients have much less uncertainty than determinations based on laser data alone. For the relative position vectors of the lunar radio transmitters and the retroreflectors, the estimates have uncertainties of about 30 m along the earth-moon direction and about 10 m in each of the two transverse coordinates.

King, R. W.