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At least 379 records · Page 21

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NASA NTRS1978

Sublimate morphology on 74001 and 74002 orange and black glassy droplets

SEM-EDX analysis of the surface morphology of the 74001 and 74002 orange and black glassy droplets has revealed the presence of ubiquitous micromound coatings. Assuming that the diameter of an individual micromound is an indication of total coating thickness, then the thickness of this volatile and metal-rich layer ranges from less than 20 A to over 300 A in thickness. On rare droplets the micromound coating is partially covered by a sparse population of crystals and masses that are essentially NaCl in composition. Additionally, an irregular mass on the surface of one black droplet may contain free sulfur. Amoeboid masses of iron, some with incipient crystal faces, are also present on a few droplet surfaces. The above features, i.e., halite crystals, sulfur-rich masses and amoeboid iron, are rare; the more common occurrence of metals and volatiles is in the micromound coating. Based on our observations of several hundred spheres from both Apollo and Luna missions, the classic micromound coating is unique to the Apollo 15 green and Apollo 17 orange and black droplets. Although some investigators have proposed various impact sequences to produce these unique droplets, the volcanic fire fountain origin is favored.

Clanton, U. S.↗

NASA NTRS1979

A Geos 3 Orbit determination experiment

The purpose of this experiment was to investigate the value of altimetry data in high-precision satellite orbit determination. To accomplish this, software was developed to process laser, C-band, doppler and altimeter data singly or jointly. Initially, orbit determination studies were undertaken using synthetic data to validate the software. As data became available, preliminary experiments were carried out. When all the data became available, an intensive study was made covering a 4-day span in 1976. The results showed that even with sparse altimeter data it was possible to accurately determine the semimajor axis and eccentricity with altimeter data only. When altimeter data was supplemented with (as few as) two C-band passes, high-precision ephemerides were obtained. Using two laser passes to supplement the altimetry data did not achieve that same high precision. This is probably because the geographic location (mid-Atlantic) of the highly accurate laser data were such that they did not ideally complement the available (south Atlantic and Indian Ocean) altimeter data.

Pisacane, V. L.↗

NASA NTRS1979

FORTRAN subroutines for out-of-core solutions of large complex linear systems

The design and usage of two main subprograms using direct methods to solve large linear complex systems, of the form Ax = b, whose coeffficient matrices are too large to be stored in core are described. The first main subprogram is for systems whose coefficient matrices are of a particular sparse structure, namely, the matrix A can be written in the form B + D, where B is a block-banded system, and D has only a few columns of nonzeros. Key elements of the algorithms used in the subprograms include: the data structure, the strategy for preserving numerical stability, the adaptability of the algorithms for dense systems as well as for block-profile systems.

Yip, E. L.↗

NASA NTRS1980

Skylab reactivation mission report

On July 11, 1979, Skylab impacted the Earth's surface. The debris dispersion area stretched from the South Eastern Indian Ocean across a sparsely populated section of Western Australia. The events leading to the reentry of Skylab are discussed and a final assessment of the Skylab debris impact footprint is presented. Also included are detailed evaluations of the various Skylab systems that were reactivated when control of Skylab was regained in mid-1978 after having been powered down since February 4, 1974.

Chubb, W. B.↗

NASA NTRS1980

Electromagnetic backscattering from a random distribution of lossy dielectric scatterers

Electromagnetic backscattering from a sparse distribution of discrete lossy dielectric scatterers occupying a region 5 was studied. The scatterers are assumed to have random position and orientation. Scattered fields are calculated by first finding the mean field and then by using it to define an equivalent medium within the volume 5. The scatterers are then viewed as being embedded in the equivalent medium; the distorted Born approximation is then used to find the scattered fields. This technique represents an improvement over the standard Born approximation since it takes into account the attenuation of the incident and scattered waves in the equivalent medium. The method is used to model a leaf canopy when the leaves are modeled by lossy dielectric discs.

Lang, R. H.↗

NASA NTRS1980

A preliminary assessment of the accuracy of selected meteorological parameters determined from Nimbus 6 satellite profile data

Published rms errors in rawinsonde data and discrepancies between satellite and rawinsonde profile data for temperature, dewpoint temperature, mixing ratio, and wind speed. Satellite rms errors were found to be 2 to 3 times as large as those for rawinsonde data. Gradients of the preceding parameters were computed for both rawinsonde and satellite data and compared with means and near extreme values computed from the AVE 2 and AVE 4 experiments. In all cases, it was found that satellite data can be used to determine with relatively good accuracy the near extreme gradients but not those whose value does not exceed the average. Synoptic charts were prepared to show that patterns of temperature could be determined with relatively good accuracy, while those of dew point were not as good as those for temperature. Winds represented by cloud motion vectors (satellite winds) were compared with rawinsonde winds, and it was found that large gaps exist in satellite values for a given pressure level and that errors in the satellite determined concluded that satellite profile data are very useful in synoptic analysis, particularly in data sparse regions as well as regions where near extreme gradients exist in the measured parameters.

Scoggins, J. R.↗

NASA NTRS1980

Investigation of the application of HCMM thermal data to snow hydrology

The author has identified the following significant results. Comparison of the thermal IR band temperatures over the rapidly melting snowcover in a number of locations in the Salt-Verde Arizona watershed by the U-2 high altitude multispectral scanner, with temperatures for these same locations measured by the corresponding HCMM pass, indicate that the U-2 temperatures are typically 5 C higher than the values analyzed from the HCMM infrared digital printout. Results tend to substantiate findings of other investigators that with the offset that has been applied to all HCMM data, the HCMM temperature values may, in fact, actually be 5 C too low. Analysis of differences between the HCMM day and night temperatures for selected snowcovered areas in the Sierra Nevada Mountains, derived from the daytime and nighttime printouts, show greater delta tau values for the sparsely vegetated higher elevations than for the lower elevation, more densely forested terrain. The differences for the 12 hour sequence are also greater in most instances than the 36 hour difference.

Barnes, J. C.↗

NASA NTRS1980

A hill-sliding strategy for initialization of Gaussian clusters in the multidimensional space

A hill sliding technique was devised to extract Gaussian clusters from the multivariate probability density estimate of sample data for the first step of iterative unsupervised classification. Each cluster was assumed to posses a unimodal normal distribution. A clustering function proposed distinguished elements of a cluster under formation from the rest in the feature space. Initial clusters were extracted one by one according to the hill sliding tactics. A dimensionless cluster compactness parameter was proposed as a universal measure of cluster goodness and used satisfactorily in test runs with LANDSAT multispectral scanner data. The normalized divergence, defined by the cluster divergence divided by the entropy of the entire sample data, was utilized as a general separability measure between clusters. An overall clustering objective function was set forth in terms of cluster covariance matrices, from which the cluster compactness measure could be deduced. Minimal improvement of initial data partitioning was evaluated by this objective function in eliminating scattered sparse data points. The hill sliding clustering technique developed herein has the potential applicability to decomposition any multivariate mixture distribution into a number of unimodal distributions when an appropriate distribution function to the data set is employed.

Park, J. K.↗

NASA NTRS1980

Survey of the plasma electron environment of Jupiter: A view from Voyager

The plasma environment within Jupiter's bow shock is considered in terms of the in situ, calibrated electron plasma measurements made between 10 eV and 5.95 keV by the Voyager plasma science experiment (PLS). Measurements were analyzed and corrected for spacecraft potential variations; the data were reduced to nearly model independent macroscopic parameters of the local electron density and temperature. It is tentatively concluded that the radial temperature profile within the plasma sheet is caused by the intermixing of two different electron populations that probably have different temporal histories and spatial paths to their local observation. The cool plasma source of the plasma sheet and spikes is probably the Io plasma torus and arrives in the plasma sheet as a result of flux tube interchange motions or other generalized transport which can be accomplished without diverting the plasma from the centrifugal equator. The hot suprathermal populations in the plasma sheet have most recently come from the sparse, hot mid-latitude "bath" of electrons which were directly observed juxtaposed to the plasma sheet.

Scudder, J. D.↗

NASA NTRS1979

UHF coplanar-slot antenna for aircraft-to-satellite data communications

The initiative for starting the Aircraft-to-Satellite Data Relay (ASDAR) Program came from a recognition that much of the world's weather originates in the data sparse area of the tropics which are primarily ocean. The ASDAR system consists of (1) a data acquisition and control unit to acquire, store and format these data; (2) a clock to time the data sampling and transmission periods; and (3) a transmitter and low-profile upper hemisphere coverage antenna to relay the formatted data via satellite to the National Weather Service ground stations, as shown schematically. The low-profile antenna is a conformal antenna based on the coplanar-slot approach. The antenna is circular polarized and has an on-axis gain of nearly 2.5 dB and a HPBW greater than 90 deg. The discussion covers antenna design, radiation characteristics, flight testing, and system performance.

Myhre, R. W.↗

NASA NTRS1979

A scheme for computing surface fluxes from mean flow observations

A computational method for estimating turbulent surface stress, sensible heat flux, and humidity flux from mean velocity, temperature, and humidity at a single height in the atmospheric surface layer is presented. The method is based on coupling a Monin-Obukhov similarity profile to a 'force-restore' formulation for the evolution of surface soil temperature to yield the local values of shear stress, heat flux, and surface temperature. In addition to reference-level mean flow properties, the parameters required to implement this method are the thermal heat capacity of the soil, the surface aerodynamic roughness, latitude, solar declination, surface albedo, surface emissivity, and atmospheric transmissivity. Sample calculations are presented for (1) constant atmospheric forcing at the reference level, and (2) variable atmospheric forcing corresponding to Kahle's (1977) measurements of windspeed, air temperature, and radiometer soil surface temperature under dry vegetatively sparse conditions in the Mohave Desert, Calif.

Hoffert, M. I.↗

NASA NTRS1978

Treatment of cloudiness in regional scale - Numerical weather prediction models

A numerical weather prediction model is considered in which cloud water and precipitation are explicitly predicted as functions of three space dimensions and time. Approximations in the thermodynamic and continuity equations are discussed in detail, as well as the cumulus parameterization and the cloud microphysics parameterization. An example of a real-data forecast indicates that very accurate quantitative precipitation and cloud cover forecasts are possible using initial observations from only the relatively sparse rawinsonde network in the U.S.

Kreitzberg, C. W.↗

NASA NTRS1979

Morphology and distribution of common 'sand' dunes on Mars - Comparison with the earth

A comparative study of Martian and terrestrial dunes was made based on Viking Orbiter pictures and aerial pictures of terrestrial deserts. The morphological similarity between the Martian dunes and terrestrial crescentic dunes implies that the dynamics of dune formation are similar on the two planets, despite Martian constraints on dune formation that include much higher velocity winds required to move 'sand' in saltation, the possible inhibition of sand movement by absorbed water vapor, the seasonal 'snow' cover in the north circumpolar erg, and a probably sparse sand supply. The absence of longitudinal dunes and the restriction of massive crescentic dunes to a few sites on Mars suggests that Mars may have a long eolian history in which much of the sand suitable for saltation has already been transported to the north polar erg and crater floor fields.

Breed, C. S.↗

NASA NTRS1979

Subjective evaluation of the combined influence of satellite temperature sounding data and increased model resolution on numerical weather forecasting

The present evaluation is concerned with (1) the significance of prognostic differences resulting from the inclusion of satellite-derived temperature soundings, (2) how specific differences between the SAT and NOSAT prognoses evolve, and (3) comparison of two experiments using the Goddard Laboratory for Atmospheric Sciences general circulation model. The subjective evaluation indicates that the beneficial impact of sounding data is enhanced with increased resolution. It is suggested that satellite sounding data posses valuable information content which at times can correct gross analysis errors in data sparse regions.

Atlas, R.↗

NASA NTRS1980

Korean coastal water depth/sediment and land cover mapping /1:25,000/ by computer analysis of Landsat imagery

Computer analysis was applied to single data Landsat MSS imagery of a coastal area near Seoul, Korea equivalent to a 1:50,000 topographic map, and featuring large dynamic sediment transport processes. Supervised image processing yielded a test classification map containing five water depth/sediment classes, two shoreline/tidal classes and five coastal land cover classes at a scale of 1:25,000 and with a training set accuracy of 76%; the training sets were selected by direct examination of the digitally displayed imagery. The unsupervised ISOCLAS (Senkus, 1976) clustering analysis was performed to assess the relative value of this approach to image classification in areas of sparse or nonexistent ground control. Results indicate that it is feasible to produce quantitative maps for detailed study of dynamic coastal processes given a Landsat image data base at sufficiently frequent time intervals.

Park, K. Y.↗

NASA NTRS1980

Microwave radiometric determination of oceanographic and meteorological parameters

The thermal microwave brightness from the atmosphere over an ocean in the range 5-40 GHz is influenced primarily by the distribution of vapor and liquid water in the atmosphere and the temperature and wind speed at the sea surface. The Scanning Multichannel Microwave Radiometer (SMMR), which was carried aboard both the Nimbus-7 and Seasat satellites (both launched in 1978), measures this radiation at five frequencies to find these four parameters. A retrieval algorithm has been developed which, on simulated data, yields accuracies of 1.5 C in sea surface temperature, 0.9 m/s in wind speed, 4 mg/ sq cm of cloud liquid water content and 0.14gm/sq cm of precipitable water vapor. Results from the Seasat SMMR, while both preliminary and sparse, are consistent with these simulations.

Wilheit, T. T.↗

NASA NTRS1980

The evaluation of 3cm-wavelength radar for mapping surface deposits in the Bristol Lake/Granite Mountain area, Mojave Desert, California

Surface deposits in the Bristol Lake/Granite Mountains area, Mojave Desert, California were mapped using high resolution 3 cm wavelength radar images. The surface deposits range from silt to boulders in size and were separated into six radar-rock units on the basis of radar return signatures (brightness and texture) and geomorphic expression. Field reconnaissance of the six units showed that the brightness of the radar signatures on the images correlates with the surface roughness of each unit. Two major radar signatures anomalies were noted during the study. A dark radar signature for the large sand ridges in the Kelso Dunes area and a distinct northwest trending contrast boundary between bright and dark radar signatures in the Bristol Dry Lake area. Field reconnaissance of the two areas indicated that near surface moisture may be the cause of dark signatures. Dune areas with little to no vegetation produce a dark signature, whereas areas with sparse to moderate vegetation produce an intermediate to dark signature.

Sugiura, R.↗

NASA NTRS1980

First Scientific Working Group Meeting of Airborne Doppler Lidar Wind Velocity Measurement Program, appendix C

The problem is to operate on two scalar fields to produce a vector field, to produce user products from the vector field, and to establish reliability of results. Data problems encountered include sparse measurements, irregular distribution, varying quality, imperfect orthogonality, aliasing due to sampling volume, and measurements not simultaneous. Desired algorithm characteristics, solution elements, and characteristics of the model are listed. The seven simulation elements, eight algorithm steps and the required user inputs are given.

Lee, R. W.↗