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At least 937 records · Page 52

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NASA NTRS1974

Magnetisation of comets

Construction of a model explaining the means by which the interplanetary magnetic field could mix with the plasma of a comet tail. It is suggested that the magnetic fields in comet tails derive from the hydromagnetic conversion of kinetic energy into magnetic energy in the nuclear region of the comet. In particular, it is shown that, if the nuclear region consists of a supplementary distributed source for the coma gases, a turbulent flow with maximum velocities of the order of thermal velocity may be expected in this region, with the necessary ordering in the turbulent velocity field provided by the rotation of the nuclear region. It is concluded that a comet, when sufficiently close to the sun, may be able to generate an appreciable magnetic field and that the magnetic fields observed in the tail may then result from processes analogous to those producing the earth's magnetotail.

Mendis, A.↗

NASA NTRS1974

Polarized magnetic field fluctuations at the Apollo 15 site - Possible regional influence on lunar induction

High-frequency (5 to 40 millihertz) induced lunar magnetic fields, observed at the Apollo 15 site near the southeastern boundary of Mare Imbrium and the southwestern boundary of Mare Serenitatis, show a strong tendency toward linear polarization in a direction radial to the Imbrium basin and circumferential to the Serenitatis basin, a property that could be indicative of a possible regional influence on the induction.

Schubert, G.↗

NASA NTRS1973

Surface configuration as an explanation for lithology-related cross-polarized radar image anomalies

One problem that has persisted since the development of multipolarized radar is the cause or causes of differential depolarization which is expressed as tonal reversals between like- and cross-polarized images of certain outcrops. Rocks producing anomalously low returns on the cross-polarized image could be classed into three general types: (1) certain geologically recent lava flows (late Pleistocene and Holocene), (2) some tertiary volcanics and (3) certain massive sandstones. Differential depolarization has been produced by volcanic rocks of various compositions including rhyolite, rhyodacite, dacite, andesite, and basalt. This has led to the conclusion that differential depolarization is not directly caused by any compositional factor. However, the study of aerial photos and subsequent field observation have led to the conclusion that the weathering and other surface characteristics of the outcrops are responsible for their appearance on multipolarized imagery.

Mccauley, J. R.↗

NASA NTRS1975

Real time solar magnetograph Skylab mission Atlas

An atlas of all magnetic field observations made during the Skylab missions with the Real Time Solar Magnetograph system located at the Marshall Space Flight Center is presented. Also included are a description of the system and its operation; an outline of the data reductions performed; and a discussion of probable errors, noise, magnetic sensitivity, and system reliability.

Hagyard, M. J.↗

NASA NTRS1974

Satellite detection of vegetative damage and alteration caused by pollutants emitted by a zinc smelter

The author has identified the following significant results. Field observations and data collected by low flying aircraft were used to verify the accuracy of maps produced from the satellite data. Although areas of vegetation as small as six acres can accurately be detected, a white pine stand that was severely damaged by sulfur dioxide could not be differentiated from a healthy white pine stand because spectral differences were not large enough. When winter data were used to eliminate interference from herbaceous and deciduous vegetation, the damage was still undetectable. The analysis was able to produce a character map that accurately delineated areas of vegetative alteration due to high zinc levels accumulating in the soil. The map depicted a distinct gradient of less damage and alteration as the distance from the smelter increased. Although the satellite data will probably not be useful for detecting small acreages of damaged vegetation, it is concluded that the data may be very useful as an inventory tool to detect and delineate large vegetative areas possessing differing spectral signatures.

Mcmurtry, G. J.↗

NASA NTRS1974

Coastal wetlands analysis from ERTS MSS digital data and field spectral measurements

Classification, delineation and evaluation of coastal wetlands can be made on the basis of major vegetative associations. To produce wetland maps, two vegetation-analysis look-up tables were developed for use in the ERTS ANALYSIS System. These look-up tables are based on Earth Resources Technology Satellite (ERTS) digital values in Multispectral Scanner (MSS) bands 4, 5, and 7 and were developed using seasonal spectral reflectance measurements from field observations. Computer-generated maps at an approximate scale of 1:20,000 were produced for the primary test site, Chincoteague Marsh, Virginia. There is a high degree of accuracy in the identification of wetland features and plant associations. The classification was also tested on other Atlantic coast salt marshes and a brackish marsh in the Chesapeake Bay.

Carter, V.↗

NASA NTRS1975

Interplanetary streams and their interaction with the earth

Plasma and magnetic field observations of interplanetary streams near 1 AU are summarized. Two types of streams have been identified - corotating streams and flare-associated, and other flow patterns are present due to interactions among streams. The theory of corotating streams, which attributes them to a high temperature region near the sun, satisfactorily explains many of the effects observed at 1 AU. A correspondingly complete theory of flare-associated streams does not exist. Streams are a key link in the chain that connects solar and geomagnetic activity. The factors that most influence geomagnetic activity are probably related to streams and determined by the dynamics of streams. The evolution of streams on scales of 27 days and 11 years probably determines the corresponding variations of geomagnetic activity.

Burlaga, L. F.↗

NASA NTRS1975

Error enhancement in geomagnetic models derived from scalar data

An investigation conducted by Backus (1970) regarding the possible existence of two harmonic functions of certain characteristics in three-dimensional space is considered. The derivation of a model of the main geomagnetic field from scalar data is discussed along with a numerical simulation study. It is found that experimental discrepancies between vector field observations and the predictions of the model may have a mathematical origin, related to the work of Backus.

Stern, D. P.↗

NASA NTRS1976

A study of some effects of vertical shear on thunderstorms

Evidence is presented for the existence of vortices and vortex pairs in thunderstorms. A preliminary parameterized model of the nonthermal generation of thunderstorm vortices derived from field observations of storms and laboratory observations of a jet in crossflow is reported, together with an explanation of how such a model might be used to guide analysis of mesoscale rawinsonde, radar, and satellite data toward an improved capability for prediction of thunderstorm motion and growth. Preliminary analyses of radar and satellite data from Atmospheric Variability Experiment IV are used with available rawinsonde data to develop a correlation between wind shears, instability, and thunderstorm motion and development. Specific studies are recommended for best development of concepts and utilization of data from Atmospheric Variability and Atmospheric Variability Severe Storms Experiments.

Connell, J.↗

NASA NTRS1976

Remote sensing of soil moisture by a 21-cm passive radiometer

Microwave sensors on Skylab collected data as part of the Earth Resources Experiment Package. An investigation was designed to obtain field observations of soil moisture content for comparison with data from Skylab. The 21-cm radiometer has been shown to be highly responsive to the moisture content of the upper 2.5-cm layer of soil. A composite relationship between the radiometric temperature and soil moisture content has been determined from five data sets obtained over Kansas and Texas. This relationship, having a correlation index of -0.96, has been used as a basis for calculating the soil moisture content of large areas across the United States.

Eagleman, J. R.↗

NASA NTRS1976

The Jovian magnetosphere and magnetopause

The characteristics of the planet Jupiter's inner magnetosphere are examined, taking into account the Pioneer 10 and 11 magnetometer data. Data on the reliability of spherical harmonic expansions are presented in a table. The properties of the Jovian magnetosheath and magnetopause are described. Bow shock and magnetopause crossings were securely identified in plasma data and were usually identified in plasma data and were usually identifiable in the magnetometer data. Explanations for the large number of observed crossings are discussed. It is pointed out that in the case of the outer magnetosphere the observed field strength is nearly an order of magnitude larger than would be expected from Jupiter's dipole moment. The distinguishing characteristics of the magnetic field in the middle magnetosphere are also considered.

Davis, L., Jr.↗

NASA NTRS1977

A technique for the determination of Louisiana marsh salinity zone from vegetation mapped by multispectral scanner data: A comparison of satellite and aircraft data

Vegetation in selected study areas on the Louisiana coast was mapped using low altitude aircraft and satellite (LANDSAT) multispectral scanner data. Fresh, brackish, and saline marshes were then determined from the remotely sensed presence of dominant indicator plant associations. Such vegetational classifications were achieved from data processed through a standard pattern recognition computer program. The marsh salinity zone maps from the aircraft and satellite data compared favorably within the broad salinity regimes. The salinity zone boundaries determined by remote sensing compared favorably with those interpolated from line-transect field observations from an earlier year.

Butera, M. K.↗

NASA NTRS1977

The internal magnetic fields created by diffusion

Electrical resistance along with internal and external loop voltages were considered in a calculation of internal magnetic fields observed in aircraft structures following a lightning strike. The geometry of cylindrical bodies, both circular and elliptical, was utilized in the computation in order to model fuselage and wing cross sections.

Franklin A Fisher↗

NASA NTRS1977

Application of LANDSAT satellite imagery for iron ore prospecting in the Western Desert of Egypt

Prospecting for iron ore occurrences was conducted by the Remote Sensing Center in Bahariya Oasis-El Faiyum area covering some 100,000 km squared in the Western Desert of Egypt. LANDSAT-1 satellite images were utilized as the main tool in the regional prospecting of the iron ores. The delineation of the geological units and geological structure through the interpretation of the images corroborated by field observations and structural analysis led to the discovery of new iron ore occurrences in the area of investigation.

Elshazly, E. M.↗

NASA NTRS1977

Application of LANDSAT satellite imagery for iron ore prospecting in the western desert of Egypt

The author has identified the following significant results. The delineation of the geological units and geological structures through image interpretation, corroborated by field observations and structural analysis, led to the discovery of new iron ore deposits. A new locality for iron ore deposition, namely Gebel Qalamun, was discovered, as well as new occurrences within the already known iron ore region of Bahariya Oasis.

Elshazly, E. M.↗

NASA NTRS1978

Multiple-satellite studies of magnetospheric substorms - Distinction between polar magnetic substorms and convection-driven negative bays

Two types of prolonged auroral zone magnetic bay activity are studied. The first manifests frequent substorm expansions and the second (a convection bay) shows weak and infrequent substorm onset signatures during intense auroral zone bays. Data are obtained by multiple satellite recordings during a 5-hour interval of persistent auroral zone activity. The results are discussed in terms of: magnetic activity on the ground, solar wind and tail lobe conditions, onset and recovery of the 1122 UT substorm, plasma sheet variations during the convection bay, reappearance of substorm signatures in the tail of about 1613 UT, and magnetic field observations at synchronous orbit.

Pytte, T.↗

NASA NTRS1979

Operational activities

A short description of the observational field program as carried out in the Canal Zone during July 1977 is presented. The people responsible for organizing the activity and those deployed to the Canal Zone, who were responsible for various aspects of the field activity (including the experiments) are listed. The ozonesonde balloon and rocketsonde launches and the aircraft flight track are shown. The daily activity schedule during the 16-day Intertropical Convergence Zone study is shown. The instrument configuration of the U-2 research aircraft used during the experiment is also shown.

Page, W. A.↗

NASA NTRS1978

Environmental testing of flat plate solar cell modules

Commercially available flat-plate solar cell modules have been subjected to a variety of environmental tests designed to simulate service conditions. Among the tests are those simulating heat and rain, wind-driven rains, humidity and freezing, humidity and heat, humidity with a voltage bias, salt fog, hail impact, and fungus infestation. Tests for optical surface soiling and the combined effects of temperature, humidity and UV irradiation are under development. A correlation has been demonstrated between degradation caused by the qualification tests and such observed field effects as power loss.

Griffith, J.↗