Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Tucker”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Some thoughts on the implementation of pilot night vision devices for helicopters

Night vision enhancement devices greatly expand the range and quality of services by extending night operational capabilities. Evolving military tactical concepts for helicopters survivability and battlefield effectiveness necessitate nap-of-the-earth (NOE) flying under both day and night conditions. From a pilot workload standpoint, flying a helicopter NOE in day VFR conditions with minimum clearance between rotors and obstacles is quite demanding. Doing the same job at night is several times more difficult. There are two general categories of night vision devices in operation in helicopter aviation: the Night Vision Goggles (NVG) and forward looking infrared (FLIR) system. The capabilities and limitations of those two devices are discussed.

Tucker, G. E.↗
NASA NTRS1985

North American vegetation patterns observed with the NOAA-7 advanced very high resolution radiometer

Spectral vegetation index measurements derived from remotely sensed observations show great promise as a means to improve knowledge of land vegetation patterns. The daily, global observations acquired by the advanced very high resolution radiometer, a sensor on the current series of U.S. National Oceanic and Atmospheric Administration meteorological satellites, may be particularly well suited for global studies of vegetation. Preliminary results from analysis of North American observations, extending from April to November 1982, show that the vegetation index patterns observed correspond to the known seasonality of North American natural and cultivated vegetation. Integration of the observations over the growing season produced measurements that are related to net primary productivity patterns of the major North American natural vegetation formations. Regions of intense cultivation were observed as anomalous areas in the integrated growing season measurements. Significant information on seasonality, annual extent and interannual variability of vegetation photosynthetic activity at continental and global scales can be derived from these satellite observations.

Goward, S. N.↗
NASA NTRS1984

Considerations of and improvements to large-scale vegetation monitoring

The NOAA-7 polar orbiting sun-synchronous operational satellite carries the 5-channel advanced very high-resolution radiometer which acquires data globally at a spatial resolution of 4 km on a daily basis. These data provide a means for frequently monitoring global vegetation at continental scales. Techniques for compositing and cloud screening a green leaf density vegetation index product for Africa are presented for 9 sequential days beginning August 16, 1982 and are compared with a semi-operational vegetation index product produced by NOAA.

Gatlin, J. A.↗
NASA NTRS1983

Monitoring global vegetation using NOAA-7 AVHRR data

The NOAA-7 polar orbiting, sun-synchronous, operational satellite carries the 5 channel Advanced Very High Resolution Radiometer (AVHRR). Data are acquired globally at a resolution of 4 km on a daily basis. This data provides the means of frequently monitoring global vegetation on continental scales. Techniques for compositing and cloud screening a vegetation index for Africa are presented. The sample data set covers 9 days beginning August 16, 1983 and is compared with a semi-operational vegetation index product produced by NOAA.

Gatlin, J. A.↗
NASA NTRS1984

Optimal directional view angles for remote-sensing missions

The present investigation is concerned with the directional, off-nadir viewing of terrestrial scenes using remote-sensing systems from aircraft and satellite platforms, taking into account advantages of such an approach over strictly nadir viewing systems. Directional reflectance data collected for bare soil and several different vegetation canopies in NOAA-7 AVHRR bands 1 and 2 were analyzed. Optimum view angles were recommended for two strategies. The first strategy views the utility of off-nadir measurements as extending spatial and temporal coverage of the target area. The second strategy views the utility of off-nadir measurements as providing additional information about the physical characteristics of the target. Conclusions regarding the two strategies are discussed.

Kimes, D. S.↗
NASA NTRS1985

Free tropospheric measurements of CS2 over a 45 deg N to 45 deg S latitude range

The mean value obtained from 52 free tropospheric measurements of CS2 over the 45 deg N-45 deg S latitude range was 5.7 pptv, with standard deviation and standard error of 1.9 and 0.3 pptv, respectively. Large fluctuations in the CS2 concentration are observed which reflect the apparent short atmospheric residence time and inhomogeneities in the surface sources of CS2. The amounts of CS2 in the Northern and Southern Hemispheres are statistically equal.

Tucker, B. J.↗
NASA NTRS1985

African land-cover classification using satellite data

Data from the advanced very high resolution radiometer sensor on the National Oceanic and Atmospheric Administration's operational series of meteorological satellites were used to classify land cover and monitor vegetation dynamics for Africa over a 19-month period. There was a correspondence between seasonal variations in the density and extent of green leaf vegetation and the patterns of rainfall associated with the movement of the Intertropical Convergence Zone. Regional variations, such as the 1983 drought in the Sahel of western Africa, were observed. Integration of the weekly satellite data with respect to time for a 12-month period produced a remotely sensed estimate of primary production based upon the density and duration of green leaf biomass. Eight of the 21-day composited data sets covering an 11-month period were used to produce a general land-cover classification that corresponded well with those of existing maps.

Tucker, C. J.↗
NASA NTRS1984

Regional analysis from data from heterogeneous pixels - 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 eight-week period were used to generate a cumulative integrated index. Ground biomass 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 NTRS1985

Satellite measurements of surface albedo and temperatures in semi-desert

Measurements of surface parameters in an arid steppe (the semi-desert of the northern Sinai) were made from the NOAA-6 satellite to assess the effects of the vegetation recovery in a fenced-off area. The radiances measured in the solar wavelengths over the vegetated area were about 25 percent lower than those measured over the surrounding bare sandy soil (where the surface albedo measured from Landsat is about 0.42). This implies a reduction in the albedo by the vegetation also by about 25 percent if both surfaces are regarded as Lambertian, but by as much as 42 percent if the vegetated area is modeled as a plane of soil with vertically protruding plants. The radiation temperatures in the 11 micron channel at approximately 0730 LST measured over the vegetated area were by as much as 2.5 K higher than over the surrounding sands.

Otterman, J.↗
NASA NTRS1985

Hot coronae around early-type galaxies

The analysis of the X-ray emission from a sample of 55 bright early-type galaxies shows that hot gaseous coronae are a common and perhaps ubiquitous feature of such systems. The X-ray emission can be explained most naturally as thermal bremsstrahlung from hot gas which may be accumulated from mass loss during normal stellar evolution. The presence of these coronae shows that matter previously thought to be expelled in a galactic wind is instead stored in a hot galactic corona which may be heated and powered by supernova explosions. Perhaps the single most important feature of these coronae is that they provide a unique tracer of the gravitational potential in the outer regions of bright early-type galaxies. In this paper the X-ray properties of these coronae and their implications for the presence of massive dark halos around individual early-type galaxies are discussed. Total masses of early-type galaxies up to 5 trillion solar masses are found.

Forman, W.↗
NASA NTRS1985

Determination of volcanic dust deposition from El Chichon using ground and satellite data

Major volcanic eruptions of El Chichon on 28 March 1982, 3 April 1982 and 4 April 1982 produced heavy tephra falls in surrounding areas. Data from the NOAA-6 and NOAA-7 satellites were used to determine the extent of the tephra falls. The satellite data showed a larger area of tephra deposition than was reported from conventional ground measurements.

Tucker, C. J.↗
NASA NTRS1985

Directional reflectance factor distributions for cover types of Northern Africa

Directional reflectance factors that spanned the entire exitance hemisphere were collected on the ground throughout the morning period for common cover types in Tunisia, Africa. NOAA 7/8 AVHRR bands 1(0.58-0.68 micron) and 2 (0.7301.1 micron) were used in data collection. The cover types reported were a plowed field, annual grassland, steppe grassland, hard wheat, salt plain, and irrigated wheat. Several of these cover types had geometric structures that are extreme as compared to those reported in the literature. Comparisons were made between the dynamics of the observed reflectance distributions and those reported in the literature. It was found that the dynamics of the measured data could be explained by a combination of soil and vegetation scattering components. The data and analysis further validated physical principles that cause the reflectance distribution dynamics as proposed by field and simulation studies in the literature. Finally, the normalized difference transformation (Band 2 - Band 1)/(Band 1 + Band 2), which is useful in monitoring vegetation cover, generally decreased the variation in signal with changing view angle. However, several exceptions were noted.

Kimes, D. S.↗
NASA NTRS1985

Boolean integral calculus for digital systems

The concept of Boolean integration is introduced and developed. When the changes in a desired function are specified in terms of changes in its arguments, then ways of 'integrating' (i.e., realizing) the function, if it exists, are presented. Boolean integral calculus has applications in design of logic circuits.

Tucker, J. H.↗
NASA NTRS1985

Application of AVHRR vegetation index to study atmosphere-biosphere exchange of CO2

The Advanced Very High Resolution Radiometer (AVHRR) satellite-borne sensor is presently used, together with field data, to determine the geographic distributions of the seasonal exchange of CO2 between the earth's atmosphere and the terrestrial biota. The exchange functions thus obtained are validated in virtue of the ability to reproduce the observed annual cycle of atmospheric CO2 in a three-dimensional tracer transport model. The AVHRR is carried by the TIROS-N series of polar-orbiting satellites.

Fung, I. Y.↗
NASA NTRS1985

Continental land cover classification using satellite data

Four different approaches to the classification of land cover for whole continents using multitemporal images of the normalized difference vegetation index derived from the Advanced Very High Resolution Radiometer of the NOAA series of satellites are discussed. The first approach uses only two dates from different seasons and classification dependent upon subdivision of the resultant two-dimensional feature space by an analyst using a track ball. The second approach involves a similar method of partitioning the feature space, but with the two dimensions being the first and second principal components derived from 13 four-week composite images. The third approach uses the maximum likelihood rule to derive the classified map. In the fourth approach, the amount of deviation from characteristic curves is used as a basis for classification.

Townshend, J. R. G.↗
NASA NTRS1985

Multitemporal dimensionality of images of normalized difference vegetation index at continental scales

Two sets of multitemporal data derived from NOAA world data product are analyzed by means of principal components analysis in order to examine their underlying multitemporal dimensionality. Specifically, images of the normalized difference vegetation index (NDVI) were analyzed for eight 3-week periods for Africa and ten 3-week periods for North America sampled from throughout the year extending from April 1982 to March 1983. The two multitemporal sets of images displayed remarkable similarities in terms of their first two components, the first corresponding very closely to the annualized integrated NDVI and the second to the seasonality of the NDVI. In particular, for the African data set the feature space defined by the first two components allows separation of the main cover types.

Townshend, J. R. G.↗