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NASA NTRS1988

Lab tests of a thermomechanical pump for shoot

Laboratory tests of a thermomechanical (TM) pump utilizing a commercially available porous disk have been conducted. Various size disks, heater configurations, and outlet flow impedances have been used to characterize scale models of the pump proposed for the Superfluid Helium On-Orbit Transfer (SHOOT) Flight Experiment. The results yield the scalability of the TM pump to larger diameters, and hence larger pumping rates, the dependence of flow rate on back pressure and heater power, and the limits of pumping speed due to internal losses within the porous disk due to mutual and superfluid friction. Analysis indicates that for low back pressures the flow rate is limited by the superfluid friction rather than the mutual friction. For the porous plug used in the early tests this amounts to a practical limit of 4.4 liters per hour per square centimeter. For a baselined flight plug area of 180 sq cm this yields 790 liters per hour.

Dipirro, Michael J.↗

NASA NTRS1988

Robustness margin calculation with dynamic and real parametric uncertainty

The problem of robust stability in feedback control systems with real uncertain parameters and unmodeled dynamics, where the latter takes the form of one complex block dynamic uncertainty, is considered. A robustness margin Tm is defined with respect to such model uncertainty structure and robust stability is characterized in terms of it. An algorithm to calculate Tm and the closely related multivariable stability margin km and structured singular value mu measures of robust stability is developed. It is shown that other control problems, such as robust performance for real parametric uncertainty, can also be handled in this framework.

Sideris, Athanasios↗

NASA NTRS1987

Operational use of Landsat data for timber inventory

Landsat TM data, digital elevation model (DEM) data, and field observations were used to generate a timber type/structure and land-cover strata map of the Sequoia National Forest in California, U.S. and to create a classification data set. The spectral classes were identified as 32 information classes of land cover or timber type and structure. DEM data were used for the determination of major timber specie types by topographic regions of natural occurrence. The results suggest that, for inventories over large areas, traditional per-pixel classifiers are not appropriate for TM-resolution data sets over spatially complex regions such as forest lands; either resolution must be degraded, or more context-dependent classifiers, such as the ECHO classifier described by Landgrebe (1979), must be used.

Price, Curtis V.↗

NASA NTRS1987

Improvement of cloud cover assessment of Landsat Thematic Mapper data

Various methods for cloud cover assessment of Landsat TM data are compared and evaluated. A total of 3906 TM 241-mm black-and-white photo prints of different seasons and regions were assessed manually. These images were mostly in band 4 (0.76-0.90 microns) for daytime data and band 6 (10.4-12.5 microns) for nighttime data. The results of this manual assessment are compared to available automated and manual assessments, and the differences between results obtained by various methods are discussed.

Ludwig, R.↗

NASA NTRS1988

TE/TM decomposition of electromagnetic sources

Three methods are given by which bounded EM sources can be decomposed into two parts radiating transverse electric (TE) and transverse magnetic (TM) fields with respect to a given constant direction in space. The theory applies source equivalence and nonradiating source concepts, which lead to decomposition methods based on a recursive formula or two differential equations for the determination of the TE and TM components of the original source. Decompositions for a dipole in terms of point, line, and plane sources are studied in detail. The planar decomposition is seen to match to an earlier result given by Clemmow (1963). As an application of the point decomposition method, it is demonstrated that the general exact image expression for the Sommerfeld half-space problem, previously derived through heuristic reasoning, can be more straightforwardly obtained through the present decomposition method.

Lindell, Ismo V.↗

NASA NTRS1988

Mapping in the Oman ophiolite using enhanced Landsat Thematic Mapper images

The level of apparent lithological discrimination possible with Landsat TM images in the Oman are discussed. It is found that by using parts of the short-wavelength IR spectrum, the discrimination revealed by the TM data is sufficiently uniform throughout the Oman ophiolite to produce lithological maps at 1:100,000 scale. Decorrelation stretching of the data produces images in which allows for the recognition of variations in gabbro composition, the identification of small acidic, gabbroic, and ultramafic intrusions, the discrimation of the uppermost mantle from the deeper mantle, the precise location of the Moho, and the delineation of gossans and areas subject to choritic-epidotic alteration.

Abrams, M. J.↗

NASA NTRS1989

Remote sensing of evaporite mineral zonation in salt flats (salars)

Compositional zoning within Salar de Atacama and Salar de Llulliallaco has been mapped from Landsat Thematic Mapper (TM) data. The data were enhanced using decorrelation stretching of TM bands 7, 5, and 4, which were considered to possess the majority of the mineralogical information. The resulting 7, 5, 4 (red, green, blue) color composites provide excellent discrimination of evaporite mineral zones within the salar. The interpretation is supported by fieldwork at the Salar de Atacama and spectral considerations. A strong relationship between the mineralogy of a unit and surface roughness was observed in the field, hence there is potential for imaging radar to provide complementary zonal data.

Chapman, J. E.↗

NASA NTRS1989

Thulium YAG laser operation at 2.01 microns

Variable temperature laser experiments were performed with two compositions of Tm:Cr:YAG (5.0:1.0 and 1.5:2.0 percent substitutions), with special attention given to the spectroscopic details of energy transfer and quasi-3 level lasing. Differences in laser threshold and flashlamp degradation were found in lasing the two compositions, and it is suggested that the difference is due to the 1.5:2.0 rod having much less efficient energy transfer than the 5.0:1.0 Tm:Cr crystals. To first order, the thermal occupation factor is found to dominate laser threshold determination at temperatures betwen 120 and 240 K.

Storm, Mark E.↗

NASA NTRS1988

Volcano monitoring by short wavelength infrared satellite remote sensing

The use of short wavelength IR Landsat TM data for volcano monitoring is examined. By determining the pixel-integrated from the TM data, it is possible to estimate the temperature and size of hot areas which occupy less than one complete pixel. Examples of volcano monitoring with remote sensing data are discussed. It is suggested that the entire volcanic temperature range (100-1200 C) could be accomplished by decreasing the band 6 gain by just one order of magnitude so that it was sensitive to radiance from 1 to 100 mW/sq cm/sr/micron.

Rothery, D. A.↗

NASA NTRS1988

A Landsat Thematic Mapper investigation of the geobotanical relationships in the northern spruce-fir forest, Mt. Moosilauke, New Hampshire

This investigation, in the northern spruce-fir forest at Mt. Moosilauke, NH, indicates that Landsat TM data can be used to distinguish between and map major vegetation zones. Principal components analysis can be used to reduce the dimensionality of the TM data; and in this simpler spectral space, it is easier to visualize the discrimination between major vegetation zones: the northern hardwoods zone, spruce-fir zone, fir zone, and alpine tundra zone. The moisture stress index highlights areas of heavy forest damage (fir waves), but does not correlate with low levels of damage in the mixed, background forest at Mt. Moosilauke. Care must be taken to avoid confusion between high-elevation climatically-stressed vegetation (normal krummholz forest) and damaged lower elevation forests, both of which have similar TM5/TM4 ratio values.

Torcoletti, Paul J.↗

NASA NTRS1989

Application of Landsat Thematic Mapper data for coastal thermal plume analysis at Diablo Canyon

The possibility of using Landsat Thematic Mapper (TM) thermal data to derive absolute temperature distributions in coastal waters that receive cooling effluent from a power plant is demonstrated. Landsat TM band 6 (thermal) data acquired on June 18, 1986, for the Diablo Canyon power plant in California were compared to ground truth temperatures measured at the same time. Higher-resolution band 5 (reflectance) data were used to locate power plant discharge and intake positions and identify locations of thermal pixels containing only water, no land. Local radiosonde measurements, used in LOWTRAN 6 adjustments for atmospheric effects, produced corrected ocean surface radiances that, when converted to temperatures, gave values within approximately 0.6 C of ground truth. A contour plot was produced that compared power plant plume temperatures with those of the ocean and coastal environment. It is concluded that Landsat can provide good estimates of absolute temperatures of the coastal power plant thermal plume. Moreover, quantitative information on ambient ocean surface temperature conditions (e.g., upwelling) may enhance interpretation of numerical model prediction.

Gibbons, D. E.↗

NASA NTRS1989

Small scale patches of suspended matter and phytoplankton in the Elbe River estuary, German Bight and tidal flats

Landsat 5 TM measurements are found suitable for study of small scale features in coastal waters; three independent factors, namely suspended matter concentration, atmospheric scattering, and sea-surface temperature, were extracted from all seven TM channels on the basis of factor analysis. The distribution of suspended matter in near-surface water layer and sea surface temperature is observable with a spatial resolution of at least 120 x 120 sq m. The high correlation between water depth and suspended matter distribution established by ship-gathered data supports the presently hypothesized control by bottom topography and wind-modified tidal currents of eddy and front formation.

Doerffer, R.↗

NASA NTRS1989

Investigations of microwave plasmas - Applications in electrothermal thruster systems

Experimental studies which have been conducted to develop understanding of plasma processes used for spacecraft propulsion are reviewed. The techniques discussed are calorimetry and volume measurements using the TM 011 and TM 012 modes in the microwave cavity system. The use of plasmas in electrical propulsion and microwave induction is reviewed. Plasma containment, microwave power production, energy distribution, and the pressure and flow dependence of the energy distribution are addressed. The plasma dimensions and their dependence on pressure, flow, and power are considered.

Haraburda, Scott S.↗

NASA NTRS1988

Numerical Arc Segmentation Algorithm for a Radio Conference (NASARC), version 4.0: User's manual

The information in the NASARC (Version 4.0) Technical Manual (NASA-TM-101453) and NASARC (Version 4.0) User's Manual (NASA-TM-101454) relates to the state of Numerical Arc Segmentation Algorithm for a Radio Conference (NASARC) software development through November 1, 1988. The Technical Manual describes the NASARC concept and the algorithms used to implement the concept. The User's Manual provides information on computer system considerations, installation instructions, description of input files, and program operation instructions. Significant revisions were incorporated in the Version 4.0 software over prior versions. These revisions have further enhanced the modeling capabilities of the NASARC procedure and provide improved arrangements of predetermined arcs within the geostationary orbit. Array dimensions within the software were structured to fit within the currently available 12-megabyte memory capacity of the International Frequency Registration Board (IFRB) computer facility. A piecewise approach to predetermined arc generation in NASARC (Version 4.) allows worldwide planning problem scenarios to be accommodated within computer run time and memory constraints with enhanced likelihood and ease of solution.

Whyte, Wayne A., Jr.↗

NASA NTRS1989

Comparison of in situ and Landsat derived reflectance of Alaskan glaciers

Reflectances calculated from TM data and corrected for atmospheric effects correspond with in situ measured reflectances in the nadir-viewing mode, and are shown to be related to a glacier's mass balance if measured over a period of years. A reflectance of 0.895 for a test site in the Wrangell Mountains, Alaska, was calculated from TM Band 4 (0.76 - 0.90 micron) data and corrected for atmospheric effects. This value was comparable to the in situ reflectance of 0.90 measured in the same 0.76 - 0.90 micron wavelength region. For the same site, a reflectance value of 0.79 derived from integrating over most (0.40 - 3.0 micron) of the reflective portion of the electromagnetic spectrum was quite different from the integrated reflectance of 0.95 calculated for the spectral range 0.40 - 1.0 micron. This demonstrates the importance of using the full reflective energy spectrum for calculating the albedo of snow, and for obtaining a meaningful computation of a glacier's energy and mass balance change.

Hall, D. K.↗

NASA NTRS1989

Spectral mapping of Alaskan ophiolites using Landsat Thematic Mapper data

Ophiolites are sections of oceanic lithosphere that have been exposed by thrusting in mountain belts. Thematic Mapper three-band color composites have been used to differentiate the main rock types of the ophiolites of the western Brooks Range, Alaska, and to map mineralogic variations produced by processes that affect oceanic lithosphere, such as mantle partial melting, hydration of ultramafic rock, formation of cumulate layers, and hydrothermal alteration and metamorphism of basalt. Scaled composites of TM Bands 7, 3, 1 and 5, 4, 2, and 3, 2, 1, displayed in red, green, and blue are most useful for visually differentiating rocks of the ophiolites. Ternary diagrams of digital number values are used to evaluate color variations observed in the three-band composites. Geologic maps, interpreted from TM images and reconnaissance field studies, are presented for the Asik Mountain, Maiyumerak Mountains, Avan Hills, and Misheguk Mountain ophiolites. The mapping results are being used to guide additional studies of the tectonics of the Brooks Range ophiolites.

Harding, David J.↗

NASA NTRS1989

Tectonics and volcanism in central Mexico - A Landsat Thematic Mapper perspective

Digitally enhanced Landsat Thematic Mapper (TM) images were used to map neotectonic deformation in central Mexico. This region has been studied for decades using a variety of geological and geophysical techniques, but synoptic mapping of neotectonic activity and major fault zones there, and an evaluation of their regional relationship to the character and location of volcanism were not previously possible until the application of synoptic, high resolution satellite imagery. Interpretation of the TM images shows that the tectonic deformation is closely linked in time and space to the dominantly calc-alkaline volcanics of the Mexican Volcanic Belt (MVB). The eruptive style and distribution of the volcanics is clearly related to the deformation resulting from relative motions of three large crustal blocks south of the MVB. Therefore, zones of weakness within the crust of central Mexico, which may be inherited from earlier episodes of deformation, are a principal factor controlling the oblique orientation of the MVB relative to the Acapulco Trench.

Johnson, C. A.↗

NASA NTRS1989

Reflectance characteristics and surface processes in stabilized dune environments

Analysis of multitemporal TM data for three environmentally related field areas yields information on the response characteristics of stabilized dunes and desert-fringe environments. The three field sites studied include dune fields in Egypt, Mali, and Botswana, ranging in climate from hyperarid to semiarid, and may be classed as an environmental series relating surface processes under Saharan, Sahelian, and Savanna conditions. Sites were field mapped and monitored with TM data for lengths of time up to a year. The complexity of spectral response characteristics is greatest where vegetation is dense and diverse, but study of the three environments together places constraints on the importance of vegetation to spectral response as well as to mechanisms of sand transport. In both Mali and Botswana, the Sahelian and Savanna environments, contrast reversals occur on dune crests and reflectance patterns change through the dry season to resemble the response curves of the hyperarid study site in Egypt. In these analyses, overall surface brightness is controlled by sand composition, while spectral features are controlled by vegetation dynamics.

Jacobberger, P. A.↗