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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Bulk Insolation Models as Predictors for Locations for High Lunar Hydrogen Concentrations

In this study we consider the bulk effects of surface illumination on topography (insolation) and the possible thermodynamic effects on the Moon's hydrogen budget. Insolation is important as one of the dominant loss processes governing distributions of hydrogen volatiles on the Earth, Mars and most recently Mercury. We evaluated three types of high latitude > 65 deg., illumination models that were derived from the Lunar Observing Laser Altimetry (LOLA) digital elevation models (DEM)'s. These models reflect varying accounts of solar flux interactions with the Moon's near-surface. We correlate these models with orbital collimated epithermal neutron measurements made by the Lunar Exploration Neutron Detector (LEND). LEND's measurements derive the Moon's spatial distributions of hydrogen concentration. To perform this analysis we transformed the topographic model into an insolation model described by two variables as each pixels 1) slope and 2) slope angular orientation with respect to the pole. We then decomposed the illumination models and epithermal maps as a function of the insolation model and correlate the datasets.

Hydrogen Concentrations↗
DOE OSTI2022

Spatial Trends and Drivers of Bedload and Suspended Sediment Fluxes in Global Rivers

Abstract Bedload is notoriously challenging to measure and model; its dynamics, therefore, remains largely unknown in most fluvial systems worldwide. We present results from a global scale bedload flux model as part of the WBMsed modeling framework that well predict the distribution of water discharge, suspended sediment and bedload. The sensitivity of bedload predictions to river slope, particle size, discharge, river width, and suspended sediment were analyzed, showing the model to be most responsive to spatial dynamics in river discharge and slope. The relationship between bedload and total sediment flux is analyzed globally, and for representative longitudinal river profiles (Amazon, Mississippi, and Lena Rivers). The results show that while the proportion of bedload decreases from headwaters to the coasts, there is considerable variability between basins and along river corridors. The topographic and hydrological longitudinal profiles of rivers are shown to be the key drivers of bedload trends, with fluctuations in slope controlling its more local dynamics. Estimates of water and sediment fluxes to global oceans from 2,067 largest river outlets (draining 67% of the global continental area) are provided. Estimated water discharge at 30,579 km 3 /y corresponds well to past estimates; however, sediment flux is higher. Total global particulate load of 17.8 Gt/y is delivered to global oceans, 14.8 Gt/y as washload, 1.1 Gt/y as bedload, and 2.6 Gt/y as suspended bed material. The largest 25 rivers are predicted to transport more than half of the total sediment flux to global oceans.

Cohen, Sagy↗
NASA NTRS2020

Temporal and spatial variability in surface roughness and accumulation rate around 88° S from repeat airborne geophysical surveys

We use repeat high-resolution airborne geophysical data consisting of laser altimetry, snow, and Ku-band radar and optical imagery acquired in 2014, 2016, and 2017 to analyze the spatial and temporal variability in surface roughness, slope, wind deposition, and snow accumulation at 88° S, an elevation bias validation site for ICESat-2 and potential validation site for CryoSat-2. We find significant small-scale variability (<10 km) in snow accumulation based on the snow radar subsurface stratigraphy, indicating areas of strong wind redistribution are prevalent at 88° S. In general, highs in snow accumulation rate correspond with topographic lows, resulting in a negative correlation coefficient of r(exp 2)=−0.32 between accumulation rate and MSWD (mean slope in the mean wind direction). This relationship is strongest in areas where the dominant wind direction is parallel to the survey profile, which is expected as the geophysical surveys only capture a two-dimensional cross section of snow redistribution. Variability in snow accumulation appears to correlate with variability in MSWD. The correlation coefficient between the standard deviations of accumulation rate and MSWD is r(exp 2)=0.48, indicating a stronger link between the standard deviations than the actual parameters. Our analysis shows that there is no simple relationship between surface slope, wind direction, and snow accumulation rates for the overall survey area. We find high variability in surface roughness derived from laser altimetry measurements on length scales smaller than 10 km, sometimes with very distinct and sharp transitions. Some areas also show significant temporal variability over the course of the 3 survey years. Ultimately, there is no statistically significant slope-independent relationship between surface roughness and accumulation rates within our survey area. The observed correspondence between the small-scale temporal and spatial variability in surface roughness and backscatter, as evidenced by Ku-band radar signal strength retrievals, will make it difficult to develop elevation bias corrections for radar altimeter retrieval algorithms.

Michael Studinger↗
NASA NTRS1972

Haystack Observatory

Radio astronomy programs comprise three very-long-baseline interferometer projects, ten spectral line investigations, one continuum mapping in the 0.8 cm region, and one monitoring of variable sources. A low-noise mixer was used in mapping observations of 3C273 at 31 GHz and in detecting of a new methyl alcohol line at 36,169 MHz in Sgr B2. The new Mark 2 VLBI recording terminal was used in galactic H2O source observations using Haystack and the Crimean Observatory, USSR. One feature in W29 appears to have a diameter of 0.3 millisec of arc and a brightness temperature of 1.4 x 10 to the 15th power K. Geodetic baseline measurements via VLBI between Green Bank and Haystack are mutually consistent within a few meters. Radar investigations of Mercury, Venus, Mars, and the Moon have continued. The favorable opposition of Mars and improvements in the radar permit measurements on a number of topographic features with unprecedented accuracy, including scarps and crater walls. The floor of Mare Serenitatis slopes upward towards the northeast and is also the location of a strong gravitational anomaly.

Source record↗
NASA NTRS1978

Mars - Topographic control of clouds, 1907-1973

Mariner 9 high-resolution photos and topographic information were used to make a topographic analysis of 'blue' and 'red' cloud positions reported over a 66-year period. A sample of 77 'blue' cloud sites lay preferentially at the highest Martian elevations; 60% centered precisely on the seven major volcanic mountain peaks (unknown when the clouds were observed); another 16% lay on substantial slopes or contacts between cratered terrain and lower plains. The median altitude of blue cloud sites was 2.1 km above the global topographic median. These results agree with other evidence that most earth-detected blue clouds are orographic uplift clouds, composed of condensates. Over half of 131 sporadic yelowish or red clouds were associated with blue clouds or volcanoes, and thus probably did not represent dust storm phenomena. Of 88 'possible dust clouds', about two-thirds occur at borders between light and dark areas, in the light regions. These sites may have thin veneers of dust, and current depositional or denudational activity. Median altitude of 'possible dust cloud' sites was 0.5 km below the global topographic median.

Hartmann, W. K.↗
DOE OSTI2022

Orthoimagery and Shapefiles Documenting Pre- and Post-August 2019 Slope Disturbances, Teller Road Site, Seward Peninsula, Alaska, 2018-2019

This dataset was derived from UAS aerial photos and dGPS data collected at the Teller mile marker 47 site in 2018 and 2019 and used to support research quantifying the timing and rate of surface movements and analyze soil transport process in Arctic landscapes. In July 2018, a Phantom uncrewed aerial system (UAS) collected >6800 high resolution aerial photos of the lower portion of the Teller 47 watershed (see for raw photos; pending archive NGA281). During the UAS survey, 25 x 25 cm tile ground control points (GCPs) were laid out and secured with one rebar rod in the center. The four corners and rebar tops were surveyed with differential GPS, and these coordinates were used to construct and validate an orthomosaic of the site. These points were resurveyed in August 2019 and used to track annual movement. Changes in position between the two surveys are reported in (Lathrop et al. 2022; NGA254). Agisoft Metashape photogrammetry software was used to construct a georeferenced orthomosaic image (*.tif file) of a portion (0.68 km2) of the watershed with a final resolution of ~1 cm. Manual delineation of the perimeters of failures visible in the UAS imagery (*.tif files) was conducted to create shapefile polygons (two *.zip files). The failures were identified by the exposure of bare mineral soils, which were made visible by disruption of the overlying tundra vegetation. The shapefiles were then used to analyse the topographic distribution and sizes of the failures. In August 2019 an additional ~300 georeferenced UAS images of slope instability features were collected (data pending submission) and compared with the 2018 orthomosaic. Overview maps of the failure locations included as a *.pdf.The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a research effort to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy's Office of Biological and Environmental Research.The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska.Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy's Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2004

Relaxation of the Martian Crustal Dichotomy Boundary in the Ismenius Region

The origin of the Martian crustal dichotomy remains a puzzle that when solved can provide an insight to the geological and geophysical evolution of Mars. In this study we model crustal relaxation in order to better constrain the original topographic shape, rheology, and temperature of the Martian crust. Our approach is to model the detailed geologic history of the Ismenius region of Mars, including slope, strain, and timing of faulting [1]. This region may contain the best preserved section of the dichotomy boundary as it is relatively unaffected by large impacts and erosion. So far the only study Martian crustal relaxation [2] suggests that the original topographic shape of the dichotomy is preserved. However, in this area strain from faulting implies at least some relaxation [1].

Guest, A.↗
NASA NTRS1978

Improving forest cover classification accuracy from Landsat by incorporating topographic information

The paper shows that accuracies of computer classification of species-specific forest cover types from Landsat imagery can be improved by 27% or more through the incorporation of topographic information from digital terrain tapes registered to multidate Landsat imagery. The topographic information improves classification accuracies because many common forest tree species have preferred elevation ranges and slope aspects. These preferences allow the separation of forest cover types which have similar spectral signatures but different species compositions. It is noted that the development of a classification system which uses prior probabilities and sets of prior probabilities conditioned by one or two external variables represents a significant increase in classification power.

Strahler, A. H.↗
NASA NTRS1979

Wetland classification on the Alaskan North Slope

An interactive supervised wetland classification was performed on Landsat digital data for three sites on the North Slope of Alaska. Color-coded classification maps identifying 10 wetland subcategories were produced. Field observations, topographic maps, and aerial photographs were employed as collateral data in classifying and verifying the Landsat information.

Morrow, J. W.↗
NASA NTRS2016

Fir Decline and Mortality in the Southern Siberian Mountains

Increased dieback and mortality of dark needle conifer (DNC) stands (composed of fir (Abies sibirica),Siberian pine (Pinus sibirica) and spruce (Picea obovata))were documented in Russia during recent decades. Here we analyzed spatial and temporal patterns of fir decline and mortality in the southern Siberian Mountains based on satellite, in situ and dendrochronological data. The studied stands are located within the boundary between DNC taiga to the north and forest-steppe to the south. Fir decline and mortality were observed to originate where topographic features contributed to maximal water-stress risk, i.e., steep (1825),convex, south-facing slopes with a shallow well-drained root zone. Fir regeneration survived droughts and increased stem radial growth, while upper canopy trees died. Tree ring width(TRW) growth negatively correlated with vapor pressure deficit (VPD), drought index and occurrence of late frosts, and positively with soil water content. Previous year growth conditions (i.e., drought index, VPD, soil water anomalies)have a high impact on current TRW (r 0.600.74). Fir mortality was induced by increased water stress and severe droughts (as a primary factor) in synergy with bark-beetles and fungi attacks (as secondary factors). Dendrochronology data indicated that fir mortality is a periodic process. In a future climate with increased aridity and drought frequency, fir (and Siberian pine) may disappear from portions of its current range (primarily within the boundary with the forest steppe)and is likely to be replaced by drought-tolerant species such as Pinus sylvestris and Larix sibirica.

Kharuk, Viacheslav I.↗
DOE OSTI2023

Topographic Evolution of Nb Surfaces Subjected to Electropolishing

Surface quality plays an important role in the performance of SRF cavities. We report the topographic evolution of H degassed, N and O doped Nb surfaces subjected to electropolishing using atomic force microscopy. N doped Nb shows a substantial increase in roughness due to formation of niobium nitrides into the surface. Implications of the topography on magnetic field enhancement and vortex entry are discussed.

Lechner, E.M.↗
NASA NTRS1994

A structural fabric defined by topographic lineaments: Correlation with Tertiary deformation of Ellesmere and Axel Heiberg Islands, Canadian Arctic

Digital topographic contours from four 1:250000 scale maps have been gridded to produce a digital elevation model for part of Ellesmere and Axel Heiberg islands in the Canadian Arctic Islands. Gradient calculations were used to define both east and west dipping slopes defining a pattern of lineaments that have been compared with mapped geological structures. In ice-covered areas, where geological mapping was not possible, well-defined topographic lineaments have been identified and are correlated to extensions of major structural features. The northeast-southwest patterns of both topographic lineaments and mapped structures are strongly unimodal and support a single compressive event oriented at 67 deg west of north. This orientation is coincidental with the convergence direction calculated from the kinematic poles of rotation for Greenland relative to North America between 56 and 35 Ma. A minor secondary peak at 70 east of north is observed for thrust and normal fault solutions and is not directly related to the predicted convergence direction. Whether this represents a unique phase of deformation or is a subcomponent of a single event is not known. The agreement of structural components, lineament orientations, and convergence direction suggests an overwhelming over print of Eurekan deformation on any preexisting structural fabric. This study confirms, for the first time, an excellent compatibility between geological and geophysical constraints for the timing and geometry of the Eurekan orogeny.

Oakey, Gordon↗
NASA NTRS2007

SPOT-VEG Based Analysis of Siberian Silkmoth Outbreak

The spatial and temporal dynamics of an outbreak of the Siberian silkmoth were correlated with topographic features of the affected area using SPOT-VEG data and a high resolution digital elevation model (DEM). In 2002-2003 an outbreak affected approximately 20,000 ha in the South Siberian mountains of Russia. The outbreak began between the elevations of approximately 430- 480 m and on southwest slopes with steepness < 5 degrees. As the pest searched for food it moved up and down slope, resulting in an elevation distribution split within a range of approximately 390-540 m and slope steepness up to 15 degrees. In the final phase the azimuth distribution of damaged stands became even. The correlation between the initial phase and topographic features can be used to prioritize monitoring forest areas most vulnerable to destruction by pests.

Kharuk, Viatcheslav I.↗
NASA NTRS1973

Remote sensing of permafrost and geological hazards in Alaska

The author has identified the following significant results. The study of the ERTS-1 imagery of Alaska indicates the following: that areas of different topographic expression affecting the distribution and character of permafrost can be distinguished clearly; that on the Arctic North Slope, regional differences in the distribution and character of permafrost-related oriented thaw lakes can be observed; that the distribution of certain types of geologic materials having a significant effect on the character of permafrost can be delineated on a regional scale; and that the resolution of the imagery is adequate to identify large scale geologic hazards such as landslides, glacier-dammed lakes, aufeis fields, etc. The information concerning the distribution and character of permafrost and geologic hazards to the gained in accomplishing the objectives of this project will be an invaluable aid in solving engineering-geologic and environmental problems related to route and site selection for structures such as roads, railroads, pipelines, and large installations; to distribution of natural construction materials; and to construction and maintenance.

Ferrians, O. J., Jr.↗
NASA NTRS1993

Local topography of Mars and its relationship to surface weathering processes

There is a growing body of evidence in favor of the importance of aqueous sedimentary processes on Mars. It is important to understand the role that surface weathering processes have played in the development of the present morphology of the Martian surface. Such an understanding is important not only for its relevance to the study of volatile sources and sinks on Mars through time, but also for its relevance to Martian geologic and tectonic history. Starting in the fall of this year, the Mars Observer Laser Altimeter will begin sending back to Earth data on the topography of Mars that is of a higher quality than most of the topography data available for the Earth. This data will be invaluable, not only for understanding global and large-scale regional processes and landforms on Mars, but also for the study of local and smaller-scale regional processes and landforms. Digital topography is an important part of geologic and geomorphic studies, useful in distinguishing between different lithologies and between different types of weathering. Digital topography data may be used to study a wide variety of local and regional-scale landforms, including valleys, sand dunes, lava flows, landslides, and slopes. Topography data are also essential to the analysis of spectral response patterns, especially in areas of high topographic relief. Geomorphic classification can be significantly improved by the addition of topographic information.

Schaefer, M. W.↗
NASA NTRS2021

Hydraulic Jump Dynamics Above Supercell Thunderstorms

The strongest supercell thunderstorms typically feature an above-anvil cirrus plume (AACP), which is a plume of ice and water vapor in the lower stratosphere that occurs downwind of the ambient stratospheric flow in the lee of overshooting deep convection. AACP-origin hydration of the stratosphere has a poorly constrained role in ozone destruction and surface warming. In this study, we use large eddy simulations corroborated by radar observations to understand the physics of AACP generation. We show that the overshooting top of a simulated supercell can act as a topographic obstacle and drive a hydraulic jump downstream at the tropopause, similar to a windstorm moving down the slope of a mountain but without solid topography. Once the jump is established, water vapor injection deep into the stratosphere may exceed 7 tonnes per second.

Gerald M Heymsfield↗
NASA NTRS1992

Topography of Apollinaris Patera and Ma'adim Vallis

Digital elevation models of the northern part of Ma'adim Vallis (603a41 607m/pix, 639a91 721m/pix), and Apollinaris Patera (603a42 612m/pix, 639a92 717m/pix), covering the area between 180 degrees to 190 degrees long and -2 degrees to -20 degrees lat. were obtained using a method described here. The results for the Ma'adim Vallis area show broad agreement with the United States Geological Survey (USGS) topographic map of the area with a channel depth of 1 to 2 km. A detailed study of the variations in the channel depth along its course and calculations of its discharge rate from channel cross section and slope are currently being undertaken. Results for Apollinaris Patera have been obtained, although the absolute heights relative to the Mars datum are not well constrained. However, the relative heights are sufficient for some analysis. Again, the topographic map is in reasonable agreement with the USGS map of the area, although there are significant differences.

Thornhill, G. D.↗