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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Radar penetration in the Amazonian rain forest

Radar return from vegetation covered terrains is due to three components: the scattering resulting from the top surface of the vegetation canopy (surface scattering); the scattering which occurs within the vegetation layer (volume scattering); and the scattering which takes place at the surface below the vegetation canopy (ground scattering). Through the studies of selected areas in the Amazon Region a case is presented where most of the radar returns observed in radar imagery results from the scattering at the surface below vegetation layer (ground scattering). Thus, radar penetration occurred.

Pereiradacunha, Roberto↗
NASA NTRS1988

Structure and growth of the mixing layer over the Amazonian rain forest

The structure and growth of the atmospheric mixed layer over the Amazonian rain forest were examined using measurements obtained during the NASA Amazon Boundary Layer Experiment. Measurements of temperature, moisture, and horizontal wind were carried out in and above the mixed layer by means of a tethered balloon, rawinsonde, and aircraft; fluxes of sensible and latent heat were measured at the top of the canopy. It was found that the mixing layer grows rapidly, at 5-8 cm/sec, soon after sunrise to a mean maximum height of 1200 m by 1300 LT; during undisturbed conditions, mixed layer heights of 1000 are common between 1000 and 1600 LT. No horizontal inhomogeneities in the mixed layer structure or depth were found over large distances. A simple mixed layer model was applied to show how fluxes of species might be estimated using only quantities measured at the surface and prescribing an initial condition and boundary condition for the mixed layer.

Martin, Charles L.↗
NASA NTRS1988

Emission of NO and deposition of O3 in a tropical forest system

Rates for emission of NO and deposition of O3 were measured at a tropical forest site in Reserve Adolfo Ducke, near Manaus, Brazil. Two independent techniques were used to determine the NO flux: (1) a soil enclosure method and (2) a method based on simultaneous observations of NO and O3 vertical profiles at night, when NO is irreversibly removed by reaction with O3. Results obtained using the two techniques agreed well, giving an average NO flux of 5.2 + or - 1.7 x 10 to the 10th molecules/sq cm per sec and an average vertical exchange coefficient of 2.2 x 10 to the 3rd cu cm/sec. Sources of NO from tropical forest soils may be important for global atmospheric chemistry. Rapid removal of O3 was observed in the lowest levels of the forest. The nocturnal deposition rate was estimated to be 5.6 + or - 2.5 x 10 to the 11th molecules/sq cm per sec through the 6-m level. The large deposition rate for O3 is consistent with the strong sink inferred from observations of ozone in the Amazon region.

Kaplan, W. A.↗
NASA NTRS1988

Tropospheric methane from an Amazonian floodplain lake

The sources of methane and its flux to the troposphere from the Amazonian floodplain were investigated during the dry season of July and August 1985, using measurements of methane concentration gradients obtained aboard a houseboat laboratory anchored in Lago Calado, a stratified dendritic lake of about 6-sq km area located near the center of the Amazon Basin. Methane concentrations in the mixed layer of the lake were found to vary from 0.0001 to 0.0055 mM, with no consistent temporal trend. The measured methane flux from the surface of the open lake to the atmosphere averaged 27 mg CH4/sq m per day, consistent with the buildup in ambient methane in the nocturnal surface mixed layer of the troposphere. Ebullition contributed 70 percent to the average total flux. The source of methane to the lake and, ultimately, to the troposphere is the benthic sediments.

Crill, Patrick M.↗
NASA NTRS1988

Methane flux from the central Amazonian floodplain

A total of 186 methane measurements from the three primary Amazon floodplain environments of open water lakes, flood forests, and floating grass mats were made over the period 18 July through 2 September 1985. These data indicate that emissions were lowest over open water lakes. Flux from flooded forests and grass mats was significantly higher. At least three transport processes contribute to tropospheric emissions: ebullition from sediments, diffusion along the concentration gradient from sediment to overlaying water to air, and transport through the roots and stems of aquatic plants. Measurements indicate that the first two of these processes are most significant. It was estimated that on the average bubbling makes up 49 percent of the flux from open water, 54 percent of that from flooded forests, and 64 percent of that from floating mats. If the measurements were applied to the entire Amazonian floodplain, it is calculated that the region could supply up to 12 percent of the estimated global natural sources of methane.

Bartlett, Karen B.↗
NASA NTRS1988

Emissions of N2O from tropical forest soils - Response to fertilization with NH4(+), NO3(-), and PO4(3-)

Undisturbed oxisols in a central Amazon tropical forest were fertilized with ammonium, nitrate, or phosphate. Enhanced emissions of N2O were observed for all treatments within one day of fertilization, with the response NO3(-) much greater than NH4(+) much greater than PO4(3-). Approximately, 0.5 percent of applied NO3(-) was converted to N2O within two weeks after application, with less than 0.1 percent of the NH4(+) converted to N2O. These experiments reveal a potentially large source of N2O from microbial reduction of NO3(-) in the clay soils of Amazonia.

Keller, M.↗
NASA NTRS1988

Shuttle imaging radar A analysis of land use in Amazonia

Over large areas in the tropics, satellite imagery is the principal source of data on the area, current stature, and extent of disturbance of the forests. The information from imagery that covers large areas at low resolution is greatly enhanced when different types of imagery can be compared. The paper presents a comparison of data from Landsat MSS and from the Shuttle Imaging Radar (SIR-A) L band HH polarization data for sites in the Amazon Basin. Results indicate that SIR-A backscatter from the undisturbed forest was lower than that from some disturbed areas and from flooded forests and that SIR-A brightness, increases nonlinearly with the Landsat normalized difference vegetation index. It is hypothesized that the brightest radar returns in southern Amazonia are from newly cleared forests that are littered with standing and fallen tree boles that function as corner reflectors; and that backscatter will diminish from disturbed areas over time as fields are burned repeatedly.

Stone, Thomas A.↗
NASA NTRS1988

Temporal variations of particle fluxes in the deep subtropical and tropical North Atlantic - Eulerian versus Lagrangian effects

The flux of particles measured by sediment traps in the deep water of the Sargasso Sea and western tropical North Atlantic undergoes pronounced temporal variation. In the Sargasso Sea the variability is largely due to seasonal changes in mixed-layer depth and attendant changes in primary productivity affecting a wide region. By contrast, the variability in the western tropical Atlantic appears to be caused by patches of elevated nutrient and pigment concentrations which have their origin in the plumes of the Amazon and Orinoco rivers. Coastal zone color scanner scenes demonstrate the great seasonal and interannual differences in the direction and dispersal patterns of the plumes. The river plumes break up into irregular patches which may pass through the catchment area of a sediment trap at varying rates, thereby creating the impression of almost random temporal flux variability at a fixed trap site.

Deuser, W. G.↗
NASA NTRS1988

Rare earth elements in river waters

To characterize the input to the oceans of rare earth elements (REE) in the dissolved and the suspended loads of rivers, the REE concentrations were measured in samples of Amazon, Indus, Mississippi, Murray-Darling, and Ohio rivers and in samples of smaller rivers that had more distinct drainage basin lithology and water chemistry. It was found that, in the suspended loads of small rivers, the REE pattern was dependent on drainage basin geology, whereas the suspended loads in major rivers had relatively uniform REE patterns and were heavy-REE depleted relative to the North American Shale composite (NASC). The dissolved loads in the five major rivers had marked relative heavy-REE enrichments, relative to the NASC and the suspended material, with the (La/Yb)N ratio of about 0.4 (as compared with the ratio of about 1.9 in suspended loads).

Goldstein, Steven J.↗
NASA NTRS1988

Ozone measurements in the troposphere of an Amazonian rain forest environment

Ozone concentration profiles from the ground to above the stratospheric peak were obtained in an equatorial rain forest environment near Manaus in the Amazon Basin between July and August of 1985. The peak ozone concentration (4.4 x 10 to the 22 molecules/cu cm) was found at 20 mbar (26.6 km). A major pollution (biomass-burning) event which occurred near the end of the experiment was responsible for large changes in ozone concentration.

Kirchhoff, V. W. J. H.↗
NASA NTRS1989

AVHRR for monitoring global tropical deforestation

Advanced Very High Resolution Radiometer (AVHRR) data have been used to assess the dynamics of forest trnsformations in three parts of the tropical belt. A large portion of the Amazon Basin has been systematically covered by Local Area Coverage (LAC) data in the 1985-1987 period. The analysis of the vegetation index and thermal data led to the identification and measurement of large areas of active deforestation. The Kalimantan/Borneo forest fires were monitored and their impact was evaluated using the Global Area Coverage (GAC) 4 km resolution data. Finally, High Resolution Picture Transmission (HRPT) data have provided preliminary information on current activities taking place at the boundary between the savanna and the forest in the Southern part of West Africa. The AVHRR approach is found to be a highly valuable means for carrying out deforestation assessments in regional and global perspectives.

Malingreau, J. P.↗
NASA NTRS1989

Monitoring tropical environments with Space Shuttle photography

Orbital photography from the Space Shuttle missions (1981-88) and earlier manned spaceflight programs (1962-1975) allows remote sensing time series to be constructed for observations of environmental change in selected portions of the global tropics. Particular topics and regions include deforestation, soil erosion, supersedimentation in streams, lacustrine, and estuarine environments, and desertification in the greater Amazon, tropical Africa and Madagascar, South and Southeast Asia, and the Indo-Pacific archipelagoes.

Helfert, Michael R.↗
NASA NTRS1989

Calibrating the simple biosphere model for Amazonian tropical forest using field and remote sensing data. I - Average calibration with field data

Using meteorological and hydrological measurements taken in and above the central-Amazon-basin tropical forest, calibration of the Sellers et al. (1986) simple biosphere (SiB) model are described. The SiB model is a one-dimensional soil-vegetation-atmosphere model designed for use within GCMs models, representing the vegetation cover by analogy with processes operating within a single representative plant. The experimental systems and the procedures used to obtain field data are described, together with the specification of the physiological parameterization required to provide an average description of data. It was found that some of the existing literature on stomatal behavior for tropical species is inconsistent with the observed behavior of the complete canopy in Amazonia, and that the rainfall interception store of the canopy is considerably smaller than originally specified in the SiB model.

Sellers, Piers J.↗
NASA NTRS1989

Seasat over-land scatterometer data. II - Selection of extended area land-target sites for the calibration of spaceborne scatterometers

The post-launch performance verification for future scatterometers can use extended area land targets to calibrate antenna gain patterns and to verify and monitor deployment configurations. For the Ku-band Seasat scatterometer, a region of tropical rain forest in the Amazon basin was used as a homogeneous extended-area land target. As this region is continuously being deforested, other regions are investigated for calibrating scatterometers. The global backscatter coefficients (sigma0) are compared to classifications of natural vegetation and cultivation intensity and the variability with time during the three-month mission is studied. The statistical variability of sigma0 is compared with prior estimates resulting from the known variability of the instrument parameters and communication noise. Data from selected forested regions with relatively homogeneous sigma0 and little time-dependence are presented.

Kennett, Rosemary G.↗
NASA NTRS1989

Cumulus cloud model estimates of trace gas transports

Draft structures in convective clouds are examined with reference to the results of the NASA Amazon Boundary Layer Experiments (ABLE IIa and IIb) and calculations based on a multidimensional time dependent dynamic and microphysical numerical cloud model. It is shown that some aspects of the draft structures can be calculated from measurements of the cloud environment. Estimated residence times in the lower regions of the cloud based on surface observations (divergence and vertical velocities) are within the same order of magnitude (about 20 min) as model trajectory estimates.

Garstang, Michael↗
NASA NTRS1989

Earth observations during Space Shuttle flight STS-29 - Discovery's voyage to the earth

The environmental, geologic, meteorologic, and oceanographic phenomena documented by earth photography during the Space Shuttle STS-29 mission are reviewed. A map of the nadir point positions of earth-viewing photographs from the mission is given and color photographs of various regions are presented. The mission photographs include atmospheric dust and smoke over parts of Africa and Asia, Sahelian water sites, center pivot irrigation fields in the Middle East, urban smog over Mexico City, isolated burning in the Bolivian Amazon, and various ocean features and cloud formations.

Lulla, Kamlesh↗
NASA NTRS1989

Nitrous oxide flux following tropical land clearing

The importance of seasonal cycles of N2O flux from tropical ecosystems and the possibility that tropical deforestation could contribute to the ongoing global increase in N2O concentrations were assessed by measuring N2O flux from forest, cleared land, and pasture over an annual cycle in the central Amazon. A pasture that had been converted from tropical forest had threefold greater annual N2O flux than a paired forest site; similar results were obtained in spot measurements in other pastures. If these results are general, such tropical pastures represent a globally significant source of increased N2O.

Luizao, Flavio↗
NASA NTRS1990

The variations of CO and O3 concentrations in a region subject to biomass burning

Carbon monoxide (CO) and ozone (O3) concentrations have been observed in the Brazilian Amazon region, at a site strongly affected by biomass burning (Cuiaba, 16 deg S, 58 deg W). Time variations are described for the first long-term program of studying the effect of biomass burning on O3 and CO over a complete seasonal cycle, including the seasonal maxima of 1987 and 1988. In order to obtain elements for comparison, an identical observational program was maintained at a site totally outside of the direct influence of biomass burning (Natal, 6 deg S, 35 deg W). The biomass burning contribution to the Cuiaba concentrations of CO and O3 is very large. Diurnal maxima concentrations exceeded 90 ppbv O3 in 1987 and 120 ppbv O3 in 1988, in September. For the wet season, the monthly average ozone concentration in March-April is about 10 ppbv. During the month of maxima, September, the O3 concentration average was 41 ppbv for 1987 and 71 ppbv for 1988. The CO concentrations are about 90 ppbv in the wet season. In September, 460 ppbv and 660 ppbv of CO were observed for 1987 and 1988, respectively. At Natal the seasonal variation is of the order of a factor of 2. During the wet season, the concentrations of CO and O3 at both stations are about the same.

Kirchhoff, V. W. J. H.↗