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At least 127 records · Page 7

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DOE OSTI2025

Brief communication: Decadal changes in topography, surface water and subsurface structure across an Arctic coastal tundra site

Abstract. In ice-rich polygonal tundra, spatiotemporal heterogeneity in ground-ice melt reshapes topography, impacting infrastructure, water and carbon cycles. This study evaluates changes in topography and subsurface structure at a coastal Arctic site by comparing data from two surveys conducted a decade apart. Each survey includes electrical resistivity tomography, active layer thickness, photogrammetry, and topographic data. Results reveal subsidence and decrease in permafrost table elevation with varying intensity and spatial distribution across polygons, alongside diverse thermal-hydrological responses, such as thermokarst pool formation in high-centered-polygons and more even subsidence in flat-centered-polygons. The study also underscores the value and limitations of sporadic surveys.

Bachman, Jonathan A↗

NASA NTRS1972

Lunar topography - First radar-interferometer measurements of the Alphonsus-Ptolemaeus-Arzachel region.

Radar interferometry is a new technique for accurately measuring the topography of the lunar surface from the earth. Measurements have been made with this technique of an area including the craters Ptolemaeus, Alphonsus, and Arzachel and a portion of Mare Nubium. There is evidence for a late episode of volcanism that partially filled two of the craters through a crustal fault of Imbrian origin. Several other features of the topography, particularly those coinciding with local gravitational anomalies, can be correlated with flow events.

Zisk, S. H.↗

NASA NTRS1973

A comparison of Martian albedo features with topography.

Martian albedo features photographed from the earth are compared with the topography observed by Mariner 9. Three Lambert azimuthal equal-area charts prepared to facilitate the comparison are presented. No correlation between large-scale albedos and topography can be generalized, but several different kinds of relationships seem to be indicated in particular regions. Examples of these are discussed.

Inge, J. L.↗

NASA NTRS1975

A numerical circulation model with topography for the Martian Southern Hemisphere

A quasi-geostrophic numerical model, including friction, radiation, and the observed planetary topography, is applied to the general circulation of the Martian atmosphere in the Southern Hemisphere at latitudes south of about 35 deg. Near equilibrium weather systems developed after about 5 model days. To avoid violating the quasi-geostrophic approximation, only 0.8 of the already smoothed relief was employed. Weather systems and velocity fields are strikingly tied to topography. A 2mb middle latitude jet stream is found of remarkably terrestrial aspect. Highest surface velocities, both horizontal and vertical, are predicted in western Hellas Planitia and eastern Argyre Planitia, which are observed to be preferred sites of origin of major Martian dust storms. Mean horizontal velocities and vertical velocities are found just above the surface velocity boundary layer.

Mass, C.↗

NASA NTRS1976

Rotating stratified flow over finite isolated topography

Inviscid, steady, stratified rotating flow over a finite, isolated topographic feature is critically analyzed. The formulation is based on approximating the horizontal momentum by the geostrophic momentum. A boundary value problem governs the perturbation pressure field. The solution is an anticyclonic, topographically-bound vortex whose characteristics are independent of the upstream velocity but do depend on stratification, rotation, and the nature of the topography. The vortex is baroclinic in the vicinity of the mountain but barotropic in the far field. The velocity field is a combination of the bound vortex and an upstream velocity interacting with the perturbation pressure field. The effects of stratification, upstream velocity and the nature of the topography are investigated, and fluid trajectories are plotted.

Merkine, L.-O.↗

NASA NTRS1976

A numerical circulation model with topography for the Martian southern hemisphere

A two-level numerical model taking account of the observed planetary topography is applied to the general circulation of the Martian atmosphere in the southern hemisphere. The physics of this model is based on the assumption of a hydrostatic quasi-geostrophic ideal-gas atmosphere composed entirely of carbon dioxide; radiative transfer among the atmosphere, space, and the ground is included along with surface friction. The calculations indicate the development of near-equilibrium weather systems after about five model days, weather systems and velocity fields whose positions appear to be connected with topography, and a midlatitude jet stream strikingly similar to the terrestrial case. The results also suggest that the vertical and horizontal wind components in western Hellas and eastern Argyre produce copious amounts of suspendible dust each year, that both major and minor dust storms should be a common occurrence on Mars, and that the entire south circumpolar zone appears to be a dust sink in winter.

Mass, C.↗

NASA NTRS1977

Radial variation of lunar crater rim topography

The paper presents results of determinations of variations of rim topography as a function of range from the crater rim for a group of morphologically fresh craters. It is found that the rate at which exterior crater topography converges with the surrounding surface is highly variable among different radial directions at individual craters as well as between different craters, and that at several craters, oblique impact appears to have contributed to azimuthal elevation/range variations.

Settle, M.↗

NASA NTRS1978

Computed and observed ocean topography - A comparison

The Goddard Space Flight Center's latest Gravity Earth Model, GEM-8, was used to construct a static sea surface. Such a surface corresponds to the surface of an ocean without the time-varying effects of atmospheric pressure, surface wind friction, tides, and currents. It conforms to a surface dictated by the earth's gravitational and rotational forces. The sea surface model is the result of analyzing more than 500,000 satellite observations together with about 1600 5 deg x 5 deg and about 38,000 1 deg x 1 deg surface gravity anomalies. Preliminary comparisons between the computed and measured sea surface topography indicate that they agree quite well and differ by less than 1 m in many places including the Atlantic test area. Sea-surface features such as undulations caused by trenches and ridges are clearly and accurately detectable. The use of altimeter data for orbit computation reduces the uncertainty of the spacecraft height and thus the errors of the sea-surface topography.

Vonbun, F. O.↗

NASA NTRS1980

Maintenance of quasi-stationary waves in a two-level quasi-geostrophic spectral model with topography

A study of the maintenance of the quasistationary waves forced by topography using a truncated two-level quasigeostrophic spectral model in a zonal channel on a beta-plane is presented. The model's motion contains wavenumbers 0, n, and 2n in the zonal direction, where n is the lowest eddy wavenumber and also the wavenumber of the topography. The study covered the two cases defined by n=2 and n=3; the spectral mode was integrated by initially perturbing the stationary solution of the equations governing the spectral coefficients, and a detailed energetics study was made of the quasiequilibrium state to study the maintenance of the quasistationary waves. The energy conversions required for maintaining these waves when n=3 imply that they are generated mainly by baroclinic stability of the forced waves; this type of baroclinic wave tends to become stationary to draw efficiently on the available energy of the forced wave.

Yao, M.-S.↗

NASA NTRS1979

Photogrammetric portrayal of Mars topography

Special photogrammetric techniques have been developed to portray Mars topography, using Mariner and Viking imaging and nonimaging topographic information and earth-based radar data. Topography is represented by the compilation of maps at three scales: global, intermediate, and very large scale. The global map is a synthesis of topographic information obtained from Mariner 9 and earth-based radar, compiled at a scale of 1:25,000,000 with a contour interval of 1 km; it gives a broad quantitative view of the planet. At intermediate scales, Viking Orbiter photographs of various resolutions are used to compile detailed contour maps of a broad spectrum of prominent geologic features; a contour interval as small as 20 m has been obtained from very high resolution orbital photography. Imagery from the Viking lander facsimile cameras permits construction of detailed, very large scale (1:10) topographic maps of the terrain surrounding the two landers; these maps have a contour interval of 1 cm. This paper presents several new detailed topographic maps of Mars.

Wu, S. S. C.↗

NASA NTRS1979

Dynamic sea surface topography from GEOS-3 altimetry - Determination of some dominant parameters

The second, third and fourth degree zonal harmonics of the quasi-stationary dynamic sea surface topography can be recovered from the GEOS-3 altimetry despite the adverse levels of noise indicated by the crossover discrepancies generated from the best orbits available at the end of 1977 and the GEOS-3 altimetry. Techniques for modelling the global sea surface topography are discussed along with methods for signal recovery in the presence of significant levels of noise. The analysis also provides a means of defining the geocentricity of the system of reference used in preparing the GEOS-3 ephemeris.

Mather, R. S.↗

NASA NTRS1981

A Martian general circulation experiment with large topography

A three-layer general circulation model of the Martian atmosphere is described, and the assumptions governing the model are discussed. The simulated, zonally averaged circulation is found to have only limited sensitivity to differences between this model and an earlier general circulation model; this circulation compares reasonably well with observations. It is also found that the meridional mass flow produced by the seasonal condensation of CO2 in the winter polar region has a major influence on the circulation; owing to the weak influence of atmospheric heat transport, however, the mass flow is governed almost entirely by radiation. Quasi-barotropic stationary waves, which are forced kinematically by the topography and which resemble topographically forced terrestrial planetary waves, are generated by the model in the winter hemisphere region of strong eastward flow, while baroclinic stationary waves are thermally forced by topography in the tropics and summer subtropics. It is also concluded that transient baroclinically unstable waves, of somewhat lower dominant wavenumber than those found on the earth, are generated in winter midlatitudes; their amplitudes, wavenumbers, and phase speeds closely agree with what has been deduced from the Viking lander observations.

Pollack, J. B.↗

NASA NTRS1981

Role of membrane stresses in the support of planetary topography

The role of membrane stresses and bending stresses in supporting topographic loads on planetary elastic lithospheres is examined. A dimensionless parameter is introduced in order to determine the ability of a spherical shell to support loads through membrane stresses. It is determined that when this parameter is large, membrane stresses can fully support topographic loads with flexure, and when it is small the influence of the membrane stresses can be neglected. Equations governing the behavior of a spherical shell are solved for a topographic load expressed in terms of spherical harmonics, and spherical harmonic expansions of the measured gravity and topography for Mars and the moon are compared with the theory. It is concluded that membrane stresses play an important role in the support of topographic loads on the moon and Mars. The correlation of observed gravitational potential anomalies with the topography on Mars is explained by membrane stresses in the elastic lithosphere.

Turcotte, D. L.↗

NASA NTRS1980

Estimation of the thickness of the Tharsis lava flows and implications for the nature of the topography of the Tharsis plateau

An attempt to estimate the thickness of the volcanics which cover the large part of the Tharsis region is reported. Estimates for the thickness of the flows were made using the numerous occurrences of the partially buried craters throughout the region and a relation between the crater diameter and crater rim height. Estimates were made along the southern contact with the heavily cratered terrain in the Phoenicis Lacus and Memnonia quadrangles, and along the northeast contact with older plains units in the Tharsis and Lunae Palus quadrangles. In these distal regions the thickness estimates range from 0 to 600-700 m of lava. This would indicate that only 20-30% of the topography is the result of volcanic construction. If the 20-30% estimate is representative of Tharsis as a whole then lava thickness would reach only 2-3 km near the center of the region. Thus only a small fraction of the topography presently observed can be attributed to units readily identifiable as volcanic. This additional evidence indicates that the model for Tharsis of a pre-existing elevated region of heavily cratered crust, capped by a veneer of volcanics is correct.

Plescia, J. B.↗

NASA NTRS1982

New radar-derived topography for the northern hemisphere of Mars

Earth-based radar altimetry data for the northern equatorial belt of Mars (6 deg S-23 deg N) have recently been reduced to a common basis corresponding to the 6.1-mbar reference surface. A first look at these data indicates that the elevations of Tharsis, Elysium, and Lunae Planum are lower (by 2-5 km) than has been suggested by previous estimates. These differences show that the required amount of tectonic uplift (or constructional volcanism) for each area is less than has been previously envisioned. Atmospheric or surficial conditions are suggested which may explain the discrepancies between the radar topography and elevations measured by other techniques. The topographies of Chryse Planitia, Syrtis Major, and Valles Marineris are also described.

Downs, G. S.↗

NASA NTRS1983

Critique of 'Elastic thickness of the Venus lithosphere estimated from topography and gravity' by A. Cazenave and K. Dominh

A critique of a model of the near-surface structure of Venus by Cazenave and Dominh (1981) based on Pioneer Venus data on gravity and topography is presented. Two objections are raised, the first an assumption of Airy compensation at a depth of 6 km, and the second that a gravity-topography relation is sufficient to study the subsurface characteristics. It is shown that determination of the gravity field along the line of sight, and not along the vertical, is necessary for a valid geophysical model with the available data. It is concluded that the spacecraft data are sufficient to define constraints on models of the subsurface characteristics, but are not sufficient for actually describing the substrate.

Reasenberg, R. D.↗

NASA NTRS1983

Venus gravity anomalies and their correlations with topography

This report provides a summary of the high-resolution gravity data obtained from the Pioneer Venus Orbiter radio tracking data. Gravity maps, covering a 70 deg latitude band through 360 deg of longitude, are displayed as line-of-sight and vertical gravity. Topography converted to gravity and Bouguer gravity maps are also shown in both systems. Topography to gravity ratios are made over several regions of the planet. There are markedly different ratios for the Aphrodite area as compared to the Beta and Atla areas.

Sjogren, W. L.↗

NASA NTRS1983

The relationship between surface topography, gravity anomalies, and temperature structure of convection

Consideration is given to the relationship between the temperature structure of mantle convection and the resulting surface topography and gravity anomalies, which are used in its investigation. Integral expressions relating the three variables as a function of wavelength are obtained with the use of Green's function solutions to the equations of motion for the case of constant-viscosity convection in a plane layer subject to a uniform gravitational field. The influence of the boundary conditions, particularly at large wavelengths, is pointed out, and surface topographies and gravity produced by convection are illustrated for a number of simple temperature distributions. It is shown that the upper thermal boundary layer plays an important role in determining the surface observables, while temperatures near the bottom of the layer affect mainly that boundary. This result is consistent with an explanation of geoid anomalies over mid-ocean swells in terms of convection beneath the lithosphere.

Parsons, B.↗