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NASA NTRS2005

Nanowire Thermoelectric Devices

Nanowire thermoelectric devices, now under development, are intended to take miniaturization a step beyond the prior state of the art to exploit the potential advantages afforded by shrinking some device features to approximately molecular dimensions (of the order of 10 nm). The development of nanowire-based thermoelectric devices could lead to novel power-generating, cooling, and sensing devices that operate at relatively low currents and high voltages. Recent work on the theory of thermoelectric devices has led to the expectation that the performance of such a device could be enhanced if the diameter of the wires could be reduced to a point where quantum confinement effects increase charge-carrier mobility (thereby increasing the Seebeck coefficient) and reduce thermal conductivity. In addition, even in the absence of these effects, the large aspect ratios (length of the order of tens of microns diameter of the order of tens of nanometers) of nanowires would be conducive to the maintenance of large temperature differences at small heat fluxes. The predicted net effect of reducing diameters to the order of tens of nanometers would be to increase its efficiency by a factor of .3. Nanowires made of thermoelectric materials and devices that comprise arrays of such nanowires can be fabricated by electrochemical growth of the thermoelectric materials in templates that contain suitably dimensioned pores (10 to 100 nm in diameter and 1 to 100 microns long). The nanowires can then be contacted in bundles to form devices that look similar to conventional thermoelectric devices, except that a production version may contain nearly a billion elements (wires) per square centimeter, instead of fewer than a hundred as in a conventional bulk thermoelectric device or fewer than 100,000 as in a microdevice. It is not yet possible to form contacts with individual nanowires. Therefore, in fabricating a nanowire thermoelectric device, one forms contacts on nanowires in bundles of the order of 10-microns wide. The fill factor for the cross-section of a typical bundle is about 1/2. Nanowires have been grown in alumina templates with pore diameters of 100 and 40 nm.

Borshchevsky, Alexander↗

NASA NTRS1984

Contamination Measurements During Ius Thermal Vacuum Tests in A Large Space Chamber

The levels of contamination that originate from inside the IUS equipment support section (ESS) due to outgassing from electronics components and wiring operating at elevated temperatures (80-160 F) were investigated. Pressure was measured inside and outside the ESS. Mass deposition measurements were made with quartz crystal microbalances (QCM) facing into and away from ESS vents. The OCM's were operated at -50 C and -180 C using thermoelectrically and cryogenically cooled QCM's. Gaseous nitrogen flow inside the ESS was used to obtain the effective molecular flow vent area of the ESS, which was evaluated to be 359 sq cm (56 sq in) compared to the 978 sq cm (150 sq in) estimated by an earlier atmosphere pressure billowing test. The total outgassing rate of the ESS materials at a temperature of 60 C (140 F) decays with a time constant of 11.5 hours based on pressure measurements during the hot cycle. A time constant of 22 hours was estimated for the fraction of the outgassing which will condense on a -50 C surface. In contrast, the time constant is only 10.1 hours for the outgassing material which condenses on a surface at -180 C. A surface at -180 C collects approximately one half of the material vented from the ESS which impinges on it. Pressure measurements show very good correlation with the mass deposition measurements.

C R Mullen↗

NASA NTRS1973

Material and structural studies of metal and polymer matrix composites

Fiber-reinforced composites and design analysis methods for these materials are being developed because of the vast potential of composites for decreasing weight and/or increasing use temperature capability in aerospace systems. These composites have potential for use in airbreathing engine components as well as aeronautical and space vehicle structures. Refractory wire-superalloy composites for use up to 2200 F or more and metal-matrix composites for lower temperature applications such as aerospace structures and turbojet fan and compressor blades are under investigation and are discussed. The development of a number of resin systems, including the polyimides and polyphenylquinoxalines, is described and their potential for use at temperatures approaching 315 C (600 F) is indicated. Various molecular modifications that improve processability and/or increase thermal and oxidative resistance of the resins are also described. Structural analysis methods are discussed for determining the stresses and deformations in complex composite systems. Consideration is also given to residual stresses resulting from the curing process and to the foreign object damage problem in fan blade applications.

Signorelli, R. A.↗

NASA NTRS1989

Relaminarization of turbulent flow on a flat plate by localized surface heating

Relaminarization of a turbulent boundary layer in air on a flat plate is demonstrated experimentally using localized surface heating. Localized heating is achieved by electrically heating a wire embedded in a thermally insulated substrate (Space Shuttle Tile) on the surface. The stability of the flow downstream of the applied control point increases with decreasing stream temperature in the flow direction. The mean and perturbation velocity profiles without control show that the flow is turbulent. With control, these profiles sequentially change from intermittently turbulent to a fully laminar state. In the relaminarization stage, the turbulent energy is dissipated by molecular transport due to viscous and conductivity mechanisms. The new profile adjusts to a lower Reynolds number based on the momentum thickness than that of the previous turbulent state.

Maestrello, Lucio↗

NASA NTRS2011

Development of an Electrostatic Precipitator to Remove Martian Atmospheric Dust from ISRU Gas Intakes During Planetary Exploration Missions

Manned exploration missions to Mars will need dependable in situ resource utilization (ISRU) for the production of oxygen and other commodities. One of these resources is the Martian atmosphere itself, which is composed of carbon dioxide (95.3%), nitrogen (2.7%), argon (1.6%), oxygen (0.13%), carbon monoxide (0.07%), and water vapor (0.03%), as well as other trace gases. However, the Martian atmosphere also contains relatively large amounts of dust, uploaded by frequent dust devils and high Winds. To make this gas usable for oxygen extraction in specialized chambers requires the removal of most of the dust. An electrostatic precipitator (ESP) system is an obvious choice. But with an atmospheric pressure just one-hundredth of Earth's, electrical breakdown at low voltages makes the implementation of the electrostatic precipitator technology very challenging. Ion mobility, drag forces, dust particle charging, and migration velocity are also affected because the low gas pressure results in molecular mean free paths that are approximately one hundred times longer than those at Earth .atmospheric pressure. We report here on our efforts to develop this technology at the Kennedy Space Center, using gases with approximately the same composition as the Martian atmosphere in a vacuum chamber at 9 mbars, the atmospheric pressure on Mars. We also present I-V curves and large particle charging data for various versions of wire-cylinder and rod-cylinder geometry ESPs. Preliminary results suggest that use of an ESP for dust collection on Mars may be feasible, but further testing with Martian dust simulant is required.

Clements, J. Sidney↗

NASA NTRS2004

Measurement of Initial Conditions at Nozzle Exit of High Speed Jets

The time averaged and unsteady density fields close to the nozzle exit (0.1 less than or = x/D less than or = 2, x: downstream distance, D: jet diameter) of unheated free jets at Mach numbers of 0.95, 1.4, and 1.8 were measured using a molecular Rayleigh scattering based technique. The initial thickness of shear layer and its linear growth rate were determined from time-averaged density survey and a modeling process, which utilized the Crocco-Busemann equation to relate density profiles to velocity profiles. The model also corrected for the smearing effect caused by a relatively long probe length in the measured density data. The calculated shear layer thickness was further verified from a limited hot-wire measurement. Density fluctuations spectra, measured using a two-Photomultiplier-tube technique, were used to determine evolution of turbulent fluctuations in various Strouhal frequency bands. For this purpose spectra were obtained from a large number of points inside the flow; and at every axial station spectral data from all radial positions were integrated. The radially-integrated fluctuation data show an exponential growth with downstream distance and an eventual saturation in all Strouhal frequency bands. The initial level of density fluctuations was calculated by extrapolation to nozzle exit.

Panda, J.↗

NASA NTRS2003

Block QCA Fault-Tolerant Logic Gates

Suitably patterned arrays (blocks) of quantum-dot cellular automata (QCA) have been proposed as fault-tolerant universal logic gates. These block QCA gates could be used to realize the potential of QCA for further miniaturization, reduction of power consumption, increase in switching speed, and increased degree of integration of very-large-scale integrated (VLSI) electronic circuits. The limitations of conventional VLSI circuitry, the basic principle of operation of QCA, and the potential advantages of QCA-based VLSI circuitry were described in several NASA Tech Briefs articles, namely Implementing Permutation Matrices by Use of Quantum Dots (NPO-20801), Vol. 25, No. 10 (October 2001), page 42; Compact Interconnection Networks Based on Quantum Dots (NPO-20855) Vol. 27, No. 1 (January 2003), page 32; Bit-Serial Adder Based on Quantum Dots (NPO-20869), Vol. 27, No. 1 (January 2003), page 35; and Hybrid VLSI/QCA Architecture for Computing FFTs (NPO-20923), which follows this article. To recapitulate the principle of operation (greatly oversimplified because of the limitation on space available for this article): A quantum-dot cellular automata contains four quantum dots positioned at or between the corners of a square cell. The cell contains two extra mobile electrons that can tunnel (in the quantummechanical sense) between neighboring dots within the cell. The Coulomb repulsion between the two electrons tends to make them occupy antipodal dots in the cell. For an isolated cell, there are two energetically equivalent arrangements (denoted polarization states) of the extra electrons. The cell polarization is used to encode binary information. Because the polarization of a nonisolated cell depends on Coulomb-repulsion interactions with neighboring cells, universal logic gates and binary wires could be constructed, in principle, by arraying QCA of suitable design in suitable patterns. Heretofore, researchers have recognized two major obstacles to realization of QCA-based logic gates: One is the need for (and the difficulty of attaining) operation of QCA circuitry at room temperature or, for that matter, at any temperature above a few Kelvins. It has been theorized that room-temperature operation could be made possible by constructing QCA as molecular-scale devices. However, in approaching the lower limit of miniaturization at the molecular level, it becomes increasingly imperative to overcome the second major obstacle, which is the need for (and the difficulty of attaining) high precision in the alignments of adjacent QCA in order to ensure the correct interactions among the quantum dots.

Firjany, Amir↗

NASA NTRS2003

Rayleigh Scattering Diagnostic Used to Measure Velocity and Density Fluctuation Spectra

A new, molecular Rayleigh-scattering-based flow diagnostic developed at the NASA Glenn Research Center has been used for the first time to measure the power spectrum of both gas density and radial velocity components in the plumes of high-speed jets. The objective of the work is to develop an unseeded, nonintrusive dynamic measurement technique for studying turbulent flows in NASA test facilities. This technique provides aerothermodynamic data not previously obtainable. It is particularly important for supersonic flows, where hot wire and pitot probes are difficult to use and disturb the flow under study. The effort is part of the nonintrusive instrumentation development program supporting propulsion research at the NASA Glenn Research Center. In particular, this work is measuring fluctuations in flow velocity, density, and temperature for jet noise studies. These data are valuable to researchers studying the correlation of flow fluctuations with far-field noise. One of the main objectives in jet noise research is to identify noise sources in the jet and to determine their contribution to noise generation. The technique is based on analyzing light scattered from molecules within the jet using a Fabry-Perot interferometer operating in a static imaging mode. The PC-based data acquisition system can simultaneously sample velocity and density data at rates to about 100 kHz and can handle up to 10 million data records. We used this system to interrogate three different jet nozzle designs in a Glenn free-jet facility. Each nozzle had a 25.4-mm exit diameter. One was convergent, used for subsonic flow measurements and to produce a screeching underexpanded jet with a fully expanded Mach number of 1.42. The other nozzles (Mach 1.4 and 1.8) were convergent-divergent types. The radial component of velocity and gas density were simultaneously measured in this work.

Seasholtz, Richard G.↗

NASA NTRS2019

Considerations for Femtosecond Laser Electronic Excitation Tagging in High-Speed Flows

Femtosecond laser electronic excitation tagging (FLEET) is an unseeded method for molecular tagging which offers valuable opportunities for measurement of high-speed (transonic, supersonic or hypersonic) flows. The unique nature of high-speed testing demands certain performance from FLEET such as satisfactory signal-to-noise ratio (SNR) at depressed static conditions (i.e., low temperatures, pressures and densities), wide dynamic range for velocity determination (especially single-shot), and measurements with acceptable accuracy and precision. This dissertation strives to evaluate FLEET in those regards and provide strategies to maximize the method's capabilities. A zero-dimensional kinetics model in nitrogen explains FLEET signal changes with pressure/density and/or temperature in terms of plasma-chemical reactions. Poorly known rate coefficients are tuned by comparing model output to measurements, with temporal agreement up to several hundred nanoseconds. Modeling reveals that initial signal peaks at reduced density because of slowed temporal evolution (and decay) of excited populations. Low temperatures enhance signal by enlarging cluster ion populations which contribute to excited species via electron-ion dissociative recombination. A purpose-built free jet facility provides experimental validation of the kinetics model and assesses FLEET velocimetry in low temperature and pressure/density conditions. Signal, lifetime, accuracy and precision results are obtained from unheated subsonic through Mach 4.0 operation of the facility, with best results noted. FLEET measurements of a sweeping jet (SWJ) actuator in compressible operation showcase its advantages in a highly unsteady jet containing subsonic through supersonic velocities. FLEET velocimetry is performed in the device's internal and external flow fields, with the latter compared to hot-wire anemometry. Internal measurements reveal the absence of shockwaves theorized to occur at high pressure ratios. Simultaneous qualitative measurements of compressible jet mixing are shown as a proof-of-concept. Overall, the work demonstrates that previous understanding of SWJ incompressible operation readily extends into the compressible realm. Practical aspects of performing FLEET velocimetry are detailed, along with strategies for improving measurement quality. Determination of a fundamental precision in nitrogen and air is attempted. Experiments show that increasing time delay and/or SNR improves velocimetry precision. A comparison of five camera systems indicates sensors with larger pixels capture higher SNR data and produce more precise results.

FLEET↗

NASA NTRS2012

Amplifier Module for 260-GHz Band Using Quartz Waveguide Transitions

Packaging of MMIC LNA (monolithic microwave integrated circuit low-noise amplifier) chips at frequencies over 200 GHz has always been problematic due to the high loss in the transition between the MMIC chip and the waveguide medium in which the chip will typically be used. In addition, above 200 GHz, wire-bond inductance between the LNA and the waveguide can severely limit the RF matching and bandwidth of the final waveguide amplifier module. This work resulted in the development of a low-loss quartz waveguide transition that includes a capacitive transmission line between the MMIC and the waveguide probe element. This capacitive transmission line tunes out the wirebond inductance (where the wire-bond is required to bond between the MMIC and the probe element). This inductance can severely limit the RF matching and bandwidth of the final waveguide amplifier module. The amplifier module consists of a quartz E-plane waveguide probe transition, a short capacitive tuning element, a short wire-bond to the MMIC, and the MMIC LNA. The output structure is similar, with a short wire-bond at the output of the MMIC, a quartz E-plane waveguide probe transition, and the output waveguide. The quartz probe element is made of 3-mil quartz, which is the thinnest commercially available material. The waveguide band used is WR4, from 170 to 260 GHz. This new transition and block design is an improvement over prior art because it provides for better RF matching, and will likely yield lower loss and better noise figure. The development of high-performance, low-noise amplifiers in the 180-to- 700-GHz range has applications for future earth science and planetary instruments with low power and volume, and astrophysics array instruments for molecular spectroscopy. This frequency band, while suitable for homeland security and commercial applications (such as millimeter-wave imaging, hidden weapons detection, crowd scanning, airport security, and communications), also has applications to future NASA missions. The Global Atmospheric Composition Mission (GACM) in the NRC Decadel Survey will need low-noise amplifiers with extremely low noise temperatures, either at room temperature or for cryogenic applications, for atmospheric remote sensing.

Padmanabhan, Sharmila↗

NASA NTRS2001

NATO Advanced Study Institute on Spectroscopy

This booklet presents an account of the course 'Spectroscopy of Systems with Spatially Confined Structures' held in Erice-Sicily, Italy, from June 15 to June 30, 2001. This meeting was organized by the International School of Atomic and Molecular Spectroscopy of the 'Ettore Majorana' Centre for Scientific Culture. The purpose of this course was to present and discuss nanometer-scale physics, a rapidly progressing field. The top-down approach of semiconductor technology will soon meet the scales of the bottom-up approaches of supramolecular chemistry and of spatially localized excitations in ionic crystals. This course dealt with the fabrication, measurement and understanding of the relevant structures and brought together the scientific communities responsible for these development. The advances in this area of physics have already let to applications in optoelectronics and will likely lead to many more. The subjects of the course included spatially resolved structures such as quantum wells, quantum wires and quantum dots, single atoms and molecules, clusters, fractal systems, and the development of related techniques like near-field spectroscopy and confocal microscopy to study such systems.

DiBartolo, Baldassare↗

NASA NTRS2005

Molecular Rayleigh Scattering Techniques Developed for Measuring Gas Flow Velocity, Density, Temperature, and Turbulence

Nonintrusive optical point-wise measurement techniques utilizing the principles of molecular Rayleigh scattering have been developed at the NASA Glenn Research Center to obtain time-averaged information about gas velocity, density, temperature, and turbulence, or dynamic information about gas velocity and density in unseeded flows. These techniques enable measurements that are necessary for validating computational fluid dynamics (CFD) and computational aeroacoustic (CAA) codes. Dynamic measurements allow the calculation of power spectra for the various flow properties. This type of information is currently being used in jet noise studies, correlating sound pressure fluctuations with velocity and density fluctuations to determine noise sources in jets. These nonintrusive techniques are particularly useful in supersonic flows, where seeding the flow with particles is not an option, and where the environment is too harsh for hot-wire measurements.

Mielke, Amy F.↗

NASA NTRS1943

A Method for Removal of Bakelite-Impregnated Wire Strain Gages

An increasing interest is being shown in the use of wire-type strain gages to measure static and dynamic stresses in aircraft-engine parts. Bakelite cement has been found satisfactory as a bonding agent for attaching the strain gages to machine parts that must operate at elevated temperatures. On many occasions, it is desired to remove Bakelite-cemented gages from the test parts for the purpose of replacing faulty gages or of returning the parts to service after strain measurements have been completed. Removal of the gages by means of scraping without prior treatment is very unsatisfactory because it is tedious and almost invariably damages the finished surface. Various solvents have been tried, but all attempts in this direction have been unsuccessful inasmuch as Bakelite cement, when properly baked, forms a polymer of very high molecular weight that resists the action of solvents. This report presents a gas-flame method of removal that is rapid and does not inure the structural part.

Kemp, Richard H.↗

NASA NTRS1979

Influence of convection on free growth of dendrite crystals from solution

The free growth of dendrites in a uniformly supercooled solution was examined using cine photography with a Schlieren optical system. Crystals were grown in the bulk of the solution from a centrally located capillary tube, nucleated at the interface with a liquid nitrogen cooled wire. Crystals propagated along the tube, the slower growing orientations eliminated, and emerged at the tip, usually growing parallel to the tube direction. For both sodium sulfate decahydrate from its solution and ice from sodium chloride solution, growth rate and fineness of dendrites increased with supercooling. In sodium sulfate, upward convection of the less dense depleted solution occurs; downward convection was observed for the rejected, more concentrated sodium chloride solution. In both cases, there was a spatial and temporal delay in the release of the convective plume from the moving dendrite tip. The role of this convection on the growth characteristics and the production of secondary crystals is examined. A proposed low-g experiment to examine differences in growth rate, crystal texture, and secondary nucleation in a reduced convective regime where molecular diffusion is the dominant transfer process is discussed.

Hallett, J.↗

NASA NTRS1989

Non-contact temperature measurements in support of microgravity combustion experiments

Recent conceptual advances in the understanding of combustion science fundamentals in the context of microgravity processes and phenomenology have resulted in an increased demand for diagnostic systems of greater sophistication. Owing primarily to the severe operational constraints that accompany the space flight environment, measurement systems to date remain fairly primative in nature. Qualitative pictures provided by photographic recording media comprise the majority of the existing data, the remainder consisting of the output of conventional transducers, such as thermocouples, hot wires, and pressure transducers. The absence of the rather strong influence of buoyant convection renders microgravity combustion phenomena more fragile than their 1-G counterparts. The emphasis was placed on nonperturbing optical diagnostics. Other factors such as limited supplies of expendable reactants, and periods of microgravity time of sufficient duration, coupled with more fundamental questions regarding inherent length and time scales and reproducibility have favored multipoint or multidimensional techniques. While the development of optical diagnostics for application to combustion science is an extremely active area at present, the peculiarities of space flight hardware severely restrict the feasibility of implementing the majority of techniques which are being utilized in terrestrial applications. The additional requirements for system reliability and operational simplicity have tended to promote somewhat less commonly emphasized techniques such as refractive index mapping and molecular Rayleigh scattering, which are briefly discussed.

Greenberg, Paul S.↗

NASA NTRS2003

Changes in Polymeric Tether Properties Due to Atomic Oxygen

The Propulsive Small Expendable Deployer System (ProSEDS) mission is designed to provide an on-orbit demonstration of the electrodynamic propulsion capabilities of tethers in space. The ProSEDS experiment will be a secondary payload on a Delta II unmanned expendable booster. A 5-km conductive tether is attached to the Delta II second stage and collects current fiom the low Earth orbit (LEO) plasma to facilitate de-orbit of the spent stage. The conductive tether is attached to a 10-km non-conductive tether, which is then attached to an endmass containing several scientific instruments. Atomic oxygen (AO) erodes most organic materials. As the orbit of the Delta II second stage decas, the AO flux (atoms/sq cm sec) increases. A nominal AO fluence of 1 x l0(exp 21) atoms/sq cm was agreed upon by the investigators as an adequate level for evaluating the performance of the tether materials. A test series was performed to determine the effect of atomic oxygen (AO) on the mechanical integrity and possible strength loss of ProSEDS tether materials. The tether materials in this study were Dyneema, an ultra-high molecular weight polyethylene material used as the non-conducting portion of the ProSEDS tether, and the Kevlar core strength fiber used in the conductive tether. Samples of Dyneema and Kevlar were exposed to various levels of atomic oxygen up to 1.07 x 10(exp 21) atoms/sq cm in the Marshall Space Flight Center Atomic Oxygen Beam Facility (AOBF). Changes in mass were noted after AO exposure. The tethers were then tensile-tested until failure. AO affected both the Dyneema and Kevlar tether material strength. Dyneema exposed to 1.07 x 10(exp 21) atoms/sq cm of atomic oxygen failed due to normal handling when removed fiom the AOBF and was not tensile-tested. Another test series was performed to determine the effect of AO on the electrical properties of the ProSEDS conductive tether. The conductive tether consists of seven individually coated strands of 28 AWG 1350-0 aluminum wire. The conductive coating, developed by Triton Systems, Inc., is a mix of polyanaline and COR, a clear AO-resistant polymer.

Finckenor, Miria M.↗

NASA NTRS1994

Silicon sample holder for molecular beam epitaxy on pre-fabricated integrated circuits

The sample holder of the invention is formed of the same semiconductor crystal as the integrated circuit on which the molecular beam expitaxial process is to be performed. In the preferred embodiment, the sample holder comprises three stacked micro-machined silicon wafers: a silicon base wafer having a square micro-machined center opening corresponding in size and shape to the active area of a CCD imager chip, a silicon center wafer micro-machined as an annulus having radially inwardly pointing fingers whose ends abut the edges of and center the CCD imager chip within the annulus, and a silicon top wafer micro-machined as an annulus having cantilevered membranes which extend over the top of the CCD imager chip. The micro-machined silicon wafers are stacked in the order given above with the CCD imager chip centered in the center wafer and sandwiched between the base and top wafers. The thickness of the center wafer is about 20% less than the thickness of the CCD imager chip. Preferably, four titanium wires, each grasping the edges of the top and base wafers, compress all three wafers together, flexing the cantilever fingers of the top wafer to accommodate the thickness of the CCD imager chip, acting as a spring holding the CCD imager chip in place.

Hoenk, Michael E.↗

NASA NTRS1999

Remote Sensing of Volcanic Clouds: Sulfur Gases and Plume Top Topography

New absorption line parameters for H2S were published and submitted to the Gestion et Etude des Informations Spectroscopiques Atmospheriques (GEISA) and high resolution transmission molecular absorption (HITRAN) databases. These new absorption line parameters will make it possible to use observations from the future Tropospheric Emission Spectrometer (TES) instrument [Earth Observing System (EOS) Chemistry Mission (CHEM) platform] to make more accurate H2S measurements if it observes an H2S-rich volcanic cloud. H2S is the second most abundant volcanic sulfur gas, and like SO2, it also converts to H2SO4 aerosols and can have a climate impact. A paper on the Moderate-resolution Imaging-Spectroradiometer (MODIS) SO2 alert is being revised. New aspects in the revision include verification of the SO2 alert during the EOS mission; factors affecting SO2 detection at thermal infrared, ultraviolet, and microwave wavelengths; radiative transfer tests; more description of satellite instruments; and thermal surface alert installed for MODIS. Her research involves the use of remote sensing to generate maps of plume top altitude. This parameter is important for models of volcanic eruption, aircraft hazards, and climate impact. The topographic shape of the top surface of a volcanic plume can provide information necessary to understand the physics controlling the injection and dispersal of a volcanic plume in the atmosphere. Glaze et al. describe the application of a photoclinometric technique to volcanic plumes. The software algorithm has been improved to account for more general plume and illumination geometries and for easily extracting position information directly from Advanced Very High-Resolution Radiometer (AVHRR) level 1B data. Testing of the algorithm has focused on acquiring AVHRR data for a variety of volcanic plumes in an effort to identify problems with the software as well as model sensitivities. The plumes chosen were erupted from volcanoes at a variety of latitudes, at different times of day, and in different seasons. Another important issue that is being investigated is the importance of plume opacity. A diagram illustrates the method for deriving phi, the angle a wind-blown plume makes with the horizontal, in the direction perpendicular to the remote sensing scan. A figure shows a sample output of the algorithm, a wire mesh map of plume top topography. Additional information is contained in the original.

Crisp, Joy A.↗