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At least 937 records · Page 52
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NASA NTRS1983

Continental land cover classification using meteorological satellite data

The use of the National Oceanic and Atmospheric Administration's advanced very high resolution radiometer satellite data for classifying land cover and monitoring of vegetation dynamics over an extremely large area is demonstrated for the continent of Africa. Data from 17 imaging periods of 21 consecutive days each were composited by a technique sensitive to the in situ green-leaf biomass to provide cloud-free imagery for the whole continent. Virtually cloud-free images were obtainable even for equatorial areas. Seasonal variation in the density and extent of green leaf vegetation corresponded to the patterns of rainfall associated with the inter-tropical convergence zone. Regional variations, such as the 1982 drought in east Africa, were also observed. Integration of the weekly satellite data with respect to time produced a remotely sensed assessment of biological activity based upon density and duration of green-leaf biomass. Two of the 21-day composited data sets were used to produce a general land cover classification. The resultant land cover distributions correspond well to those of existing maps.

Tucker, C. J.↗
NASA NTRS1983

The X-ray morphology of Abell 1367

X-ray observations of the nearby cluster Abell 1367 were made with the Imaging Proportional Counter (IPC) and High Resolution Imager (HRI) aboard the Einstein Observatory. The IPC is used to study the diffuse cluster emission. With the HRI, eight point sources are detected above the diffuse cluster emission, three of which are apparently associated with cluster galaxies. In addition, the HRI observations have resolved 13 extended features with characteristic radii of order arcmin, eight of which are associated with cluster galaxies. These extended sources have luminosities of 1.5-6.5 x 10 to the 41st per (H0)50)-squared ergs per sec in the 0.5-4.5 keV band and constitute about 60% of the total cluster emission. The ways in which these hot galactic coronae can be maintained are discussed.

Bechtold, J.↗
NASA NTRS1983

The mass of Tycho's supernova remnant as determined from a high-resolution X-ray map

High resolution Einstein Observatory X ray images of Tycho's supernova remnant (SNR) are discussed. The object has features of a shock heated shell in the interstellar medium, accompanied by an inner shell with clumped ejecta. The measurements were made for 22 hr on Feb. 8, 1979, revealing a circular SNR, a thin emission shelf at the outer edge of the remnant, no emission in the central object, and most emissions concentrated in small, clumpy objects within a spherical shell. Three components of the X ray emission were identified, and calculations of the swept-up mass, the diffuse component of the ejecta shell, and the clumpy ejecta are reported to be 2.2, 1.2, and 0.7 solar mass, respectively. The SNR is concluded to be at an evolutionary stage between uniform expansion and adiabatic changes.

Seward, F.↗
NASA NTRS1982

Fluid shifts in vascular and extravascular compartments of humans during and after simulated weightlessness

A study is presented of the transcapillary pressures and the possible fluid shifts in muscles and subcutaneous tissue of the lower leg before, during, and after head-down tilt. Results showed that the subjects experienced facial edema, headache, nasal congestion, diuresis, and decreased lower-leg volume in response to 8 hours of 5 degree head-down tilt. Also found were significant decreases in systolic and diastolic pressures 2 hours after initiation of tilt, although blood pressure normalized thereafter. The lower-leg volume, urine output and interstitial fluid pressures of the tibialis anterior muscle and overlying subcutaneous tissue also changed significantly. No significant change was found in the colloid osmotic pressures of blood or interstitial fluid. It is concluded that these results indicate the need for countermeasures to maintain precapillary-muscle tone during long space flights in order to prevent swelling of lower-leg tissues upon readjustment to earth's gravity.

Hargens, A. R.↗
NASA NTRS1983

Fluid shifts and muscle function in humans during acute simulated weightlessness

The acute effects of simulated weightlessness on transcapillary fluid balance, tissue fluid shifts, muscle function, and triceps surface reflex time were studied in eight supine human subjects who were placed in a 5 degrees head-down tilt position for 8 hr. Results show a cephalic fluid shift from the legs as indicated by facial edema, nasal congestion, increased urine flow, decreased creatinine excretion, reduced calf girth, and decreased lower leg volume. The interstitial fluid pressure in the tibialis anterior muscle and subcutaneous tissue of the lower leg was found to fall significantly, while other transcapillary pressures (capillary and interstitial fluid colloid osmotic pressures) were relatively unchanged. The total water content of the soleus muscle was unchanged during the head-down tilt. After head-down tilt, isometric strength and isokinetic strength of the plantar flexors were unchanged, while the triceps surae reflex time associated with plantar flexion movement slowed slightly. These results demonstrate a dehydration effect of head-down tilt on muscle and subcutaneous tissue of the lower leg that may affect muscle function.

Hargens, A. R.↗
NASA NTRS1983

Thermal conduction and heating by nonthermal electrons in the X-ray halo of M87

A hydrostatic model for the X-ray halo around the giant elliptical galaxy M87 is presented. It is shown that by taking into account the processes of thermal conduction, and nonthermal heating by relativistic electrons in the radio lobes, a self-consistent hydrostatic model can be constructed. There is no need to invoke radiative accretion or the suppression of thermal conductivity.

Tucker, W. H.↗
NASA NTRS1983

The relationship between the X-ray and optical luminosities for QSOs

A study of simple models for the optical and X-ray luminosities of QSOs shows that a thick accretion disk around a black hole is consistent with the observed dependence of the X-ray luminosity L(x) on the optical luminosity L(opt) to the bth power, with b roughly in the range 0.5-0.8. The disk is expected to be thick since the sources are accreting at rates near the Edington limit. Using the model of McMillan, Lightman, and Cohn (1981) for the gas supply rate, the evolution of L(opt) is predicted to be proportional to t/t(0) to the -8/3 and that of L(x) is predicted to be proportional to t/t(0) to the -2.

Tucker, W. H.↗
NASA NTRS1983

Mobile radio alternative systems study. Volume 1: Traffic model

The markets for mobile radio services in non-urban areas of the United States are examined for the years 1985-2000. Three market categories are identified. New Services are defined as those for which there are different expressed ideas but which are not now met by any application of available technology. The complete fulfillment of the needs requires nationwide radio access to vehicles without knowledge of vehicle location, wideband data transmission from remote sites, one- and two way exchange of short data and control messages between vehicles and dispatch or control centers, and automatic vehicle location (surveillance). The commercial and public services market of interest to the study is drawn from existing users of mobile radio in non-urban areas who are dissatisfied with the geographical range or coverage of their systems. The mobile radio telephone market comprises potential users who require access to the public switched telephone network in areas that are not likely to be served by the traditional growth patterns of terrestrial mobile telephone services. Conservative, likely, and optimistic estimates of the markets are presented in terms of numbers of vehicles that will be served and the radio traffic they will generate.

Tucker, W. T.↗
NASA NTRS1984

The Star Splitters: The High Energy Astronomy Observatories

The nature of the high energy universe and the design of instruments to analyze stellar and galactic radiation are described in this history of the HEAO program and its scientific and technical accomplishments. Topics covered include: creative violence, stellar explosions, cosmic rays, superbubbles, stellar coronas, collapsed stars, neutron stars, degenerate dwarf stars, black holes, X-ray images of galaxies, galactic nuclei, spiral galaxies, galactic clusters, the mystery of the missing mass, and cosmic fire.

Tucker, W. H.↗
NASA NTRS1984

Magnetically Enhanced Hydrogen Gas Dissociator: a Progress Report

The application of a sensitive hydrogen gas detector led to the observation of a significant increase in the efficiency of atom production of a magnetically enhanced dissociator. An increase of about 7000% in the production of atoms in the hyperfine state desired for maser operation is observed at certain values of the applied magnetic field. A preliminary test of the dissociator in the maser led to an observed increase of 6.18 dB in the maser power.

Lee, G.↗
NASA NTRS1983

Satellite remote sensing of total dry matter production in the Senegalese Sahel

Nine predominantly cloud-free NOAA-7 advanced very high resolution radiometer images were obtained during a three-month period during the 1981 rainy season in the Sahel of Senegal. The 0.55-0.68- and 0.725-1.10-micron channels were used to form the normalized difference green leaf density vegetation index and the 11.5-12.5-micron channel was used as a cloud mask for each of the nine images. Changes in the normalized difference values among the various dates were closely associated with precipitation events. Six of the images spanning an 8-week period were used to generate a cumulative integrated index. Ground biomas samplings in the 30,000 sq km study area were used to assign total dry biomass classes to the cumulative index.

Tucker, C. J.↗
NASA NTRS1984

Cluster of galaxies as a probe of the intergalactic medium

The use of galactic clusters as probes of the intercluster medium is discussed, and the effects of a postulated hot intercluster medium on the diffuse gas associated with clusters of galaxies is examined. It is shown that diffuse intracluster gas, which is observed at X-ray wavelengths, is a powerful probe of intergalactic space. The consequences of conduction are explored and the existence and properties of the intracluster gas are used to constrain the temperature and density of a uniform gas filling the universe. The effects of a nonuniform medium on the results are discussed and it is shown that for plausible scenarios the evaporative mass loss rates are insensitive to changes in the density and temperature of the intracluster medium in the vicinity of clusters. The parameters such a gas would have to have in order to explain the larger energy per unit mass found in the intracluster gas compared to that in galaxies are calculated.

Forman, W.↗
NASA NTRS1984

Objective assessment of Advanced Very High Resolution Radiometer data for land cover mapping

The validity of using data from the Advanced Very High Resolution Radiometer (AVHRR) of the satellites NOAA-6 and NOAA-7 for land cover mapping is assessed by making comparisons with much higher resolution LANDSAT multi-spectral scanner (MSS) data. Near synchronous data for both systems are analysed for test sites in the Imperial Valley, California, the Nile Delta, and southern Italy. The results strongly indicate that despite the very coarse resolution of the AVHRR data compared with conventional MSS data they are sufficiently strongly correlated to suggest that the former have significant potential for land cover mapping, especially at small scales and for large areas. Hence the outstanding benefits of AVHRR data, namely their high temporal frequency, relative cheapness and low data volumes for image processing, may readily be taken advantage of for such tasks.

Townshend, J. R. G.↗
NASA NTRS1984

Intensive forest clearing in Rondonia, Brazil, as detected by satellite remote sensing

Imagery from the National Oceanic and Atmospheric Administration satellite's Advanced Very High Resolution Radiometer sensor has been used to identify an area about 100 x 400 km in Rondonia (Brazil) where massive forest clearing or deforestation is occurring. A field study verified the area of the clearing, which is associated with a large colonization program.

Tucker, C. J.↗
NASA NTRS1984

Monitoring and mapping global vegetation cover using data from meteorological satellites

The role of coarse resolution meteorological satellite data for monitoring and mapping of vegetation for global, continental and regional scales is outlined. In the NOAA products used the effects of cloud cover are reduced by the generation of temporal composites of images of the normalized difference vegetation index. Different land cover types are shown to have characteristic spectral phenological curves. Such data have the disadvantage of effectively increasing the apparent areal extent of small areas of green vegetation.

Townshend, J. R. G.↗