Prominent Topographic Features Research Articles

Decadal long simulations of mesoscale structures in the northern North Sea/Skagerrak using two ocean models

We consider results from two 27-year-long simulation pairs derived using two different ocean models. We focus on the Skagerrak/North Sea area. Each pair consists of the two terrain-following coordinate models ROMS and MIPOM. The first pair utilizes an eddy-permitting grid, that is, a grid in which the Rossby radius is barely resolved. The second pair utilizes an eddy-resolving grid in which the Rossby radius is truly resolved. The goal is to compare the quality of the two models and the two pairs. To this end we derive statistical properties such as probability density functions and compare them with similar statistics derived from observations. Thereby we obtain insight into whether a truly eddy-resolving model is required to realistically capture the mesoscale statistics. We find that eddy resolution is critical to get the mesoscale statistics correct, in particular, the strength of the current jets. Our results also indicate that the improvement gained by employing the eddy-resolving grid is mostly due to a better resolved topography. In particular, we find that this is the case in areas exhibiting prominent topographic features, such as the deep Norwegian Trench cutting into the heart of the northern North Sea/Skagerrak area. The results also highlight the advantage of first performing quality assurance investigations when implementing a new model for a new area.

Gumusut-Kakap Project: Geohazard Characterization and Effect on Field Development

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper IPTC 12554, "Gumusut-Kakap Project: Geohazard Characterisation and Impact on Field- Development Plans," by C. Hadley, D. Peters, and A. Vaughan, SPE, Shell International E&P, and D. Bean, Sarawak Shell Sdn. Bhd., originally prepared for the 2008 International Petroleum Technology Conference, Kuala Lumpur, 3-5 December. The paper has not been peer reviewed. Shell and venture partners encountered numerous seafloor and near-seafloor geohazards at the deepwater Gumusut-Kakap field on the continental slope offshore Malaysia. Early identification of the geohazards, by interpretation of exploration 3D-seismic data and evaluation of discovery and appraisal-well logs, provided the impetus necessary to undertake an extensive data-acquisition program to determine the extent of the hazards and the mitigation needed for a successful development. Introduction The Gumusut-Kakap field in the Malaysian deepwater province offshore northwest Borneo was discovered in 2003 with the drilling of the Gumusut-1B well. The field is 120 km offshore, in the southern portion of Sabah Block J and Block K. Four appraisal wells, Gumusut-2 and Gumusut-3 in Block J and Kakap-1 and Kakap-2 in Block K, were drilled during 2004–05. The seafloor slopes regionally to the southwest, with a gradient of approximately 5°, and water depths within the development area vary from 900 to 1200 m. Seafloor and near-seafloor sediments are hemipelagic, interbedded with turbidites and mass-transport deposits (MTDs). Exploration 3D-seismic data and data from the discovery and appraisal wells were interpreted in 2005 to identify geohazards that could influence field-development plans and to screen potential surface well locations. The seafloor extraction from the 3D-seismic data set revealed a variable seafloor topography. The most prominent topographic features are a series of upper-slope canyons, which are interpreted to be the seafloor expression of buried mass-transport complexes and a steep-sided seafloor bulge. The bulge rises 120 to 150 m above the surrounding seafloor and is approximately 8 km wide. The bulge is the surface expression of one of a series of deep-seated anticlines, which are common in the region. Both flanks of the bulge have been eroded by downslope mass failures. Appraisal wells Gumusut-2, Kakap-1, and Kakap-2 were drilled on the bulge. Anomalies in the subsurface data included a bottom-simulating reflector (BSR) between 150 and 180 m below the seafloor, which underlies the downdip portion of the bulge and coincides with an extensive seismic wipeout zone.

Observations of the Fawn Trough Current over the Kerguelen Plateau from instrumented elephant seals

Due to its great meridional extent and relatively shallow depths, the Kerguelen Plateau constitutes a major barrier to the eastward flowing Antarctic Circumpolar Current in the Indian sector of the Southern Ocean. While most of the Antarctic Circumpolar Current transport is deflected north of the Kerguelen Islands, the remainder (∼ 50 Sv, 1 Sv = 10 6 m 3 s − 1 ) must pass south of the islands, most probably through the Fawn and Princess Elizabeth Troughs. However, the paucity of finely resolved quasi-synoptic hydrographic data in this remote and infrequently sampled area has limited the progress in our knowledge of the regional circulation. Since 2004, a new approach using elephant seals from the Kerguelen Islands as autonomous oceanographic profilers has provided new information on the hydrography over the Kerguelen Plateau, covering the entire Antarctic Zone between the Polar Front and Antarctica, with a mean along-track resolution of about 25 km. These finely resolved bio-logged data revealed details of a strong northeastward current found across the Fawn Trough (sill depth: 2600 m; 56°S, 78°E). This so-called Fawn Trough Current transports cold Antarctic waters found mostly south of the Elan Bank, between the Ice Limit (58°S) and the Antarctic Divergence (64°S) in the eastern Enderby Basin, toward the Australian–Antarctic Basin. Our analysis also demonstrates that the Deep Western Boundary Current, which carries cold Antarctic water along the eastern flank of the southern Kerguelen Plateau collides with Fawn Trough Current at the outlet of the Fawn Trough sill. In other words, the Fawn Trough constitutes a veritable bottleneck, channelling the quasi-totality of the Antarctic Circumpolar flow found south of the Polar Front. Thanks to the unprecedented fine resolution of seal-borne data, a branch of flow centered at the Winter Water isotherm of 1 °C is also revealed along the northern escarpment of the Elan Bank, and then along the southern edge of Heard Island. Further analysis of different supplementary data reveals a complex circulation pattern in the entire Enderby Basin, with several distinctive branches of flow being strongly controlled by prominent topographic features such as the Southwest Indian Ridge, Conrad Rise, Elan Bank, and Kerguelen Plateau. This newly emerged frontal structure refines considerably previous large-scale circulation schematics of the area.

An Assessment of the Biases of Satellite Rainfall Estimates over the Tibetan Plateau and Correction Methods Based on Topographic Analysis

AbstractThe hydrological processes over the Tibetan Plateau have significant implications on regional macroscale atmospheric circulation patterns and the Asian monsoon system. Because of its remote setting and lack of ground observations, it is difficult to study the spatial and temporal patterns of precipitation over the plateau, and satellite remote sensing technology can be used to fill in the gaps where station data are not available. In this study the authors examine monthly 1° × 1° rainfall estimates obtained from the Special Sensor Microwave Imager (SSM/I) [National Environmental Satellite, Data, and Information Service (NESDIS) algorithm] and Tropical Rainfall Measuring Mission (TRMM) 3B42 version 5 (V5) products for the months of April–October 1998–2002 over the Tibetan Plateau. By comparing the satellite estimates with ground observations at 94 weather stations in the study region, the authors derived regression models that produced significant improvements to satellite estimates based on various levels of correction efforts, using geographic location and topographic variables extracted from digital elevation models using geographic information systems (GIS) technology. The explained variance in observed precipitation was improved from 34% to 38% by SSM/I and TRMM 3B42 V5 products alone to over 70% when location and topographic variables were added. These topographic variables reflect micro- to mesoscale surface roughness, height of topographic features or relief, slopes facing toward or away from the moisture pathways, and relative locations or directions to prominent topographic features such as mountain peaks and ridgelines.

Climate change over the past 2000 years in Western China

Western China, defined here as the land falling within the geographical boundaries of the People's Republic of China in the west, south and north, and the approximate eastern extent of the Tibetan and Alaxa Plateaux to the east, occupies an important climatic region, influenced by the Asian and Indian summer monsoons, the mid-latitude westerlies and the dry, cold central Asian winter monsoon. The Tibetan Plateau itself is a prominent topographic feature that exerts major control on regional atmospheric circulation. Previous compilations of meteorological data and documentary sources suggest that western China, and the Tibetan Plateau in particular, is highly sensitive to anthropogenically induced climate change. Temperature increases appear to be greatest at higher altitudes: moreover, precipitation variations seem to have been marked, although spatially complex. The region contains a wealth of information about past climate derived from instrumental, documentary and proxy sources although meteorological time series are generally too short to capture the full range of recent climatic variability. Documentary and proxy sources are therefore important. We review studies of climate change in western China for the past two millennia. Documentary records are complemented by proxy data from ice cores, tree rings, lake sediments, groundwater profiles and glacial geomorphology. Although general patterns of change can be identified, proxy records of past climate are often semi-quantitative at best, open to alternative interpretations and sometimes poorly dated. Despite evidence for marked variations in climate over the past 2000 years, changes during the 20th century, especially in temperature, may have been unprecedented. The density of data points over western China is currently too low for spatial patterns to be identified, especially in precipitation variation. However, there does seem to have been an increase in warming with altitude over the most recent past.

Paleogeographic and paleotopographic evolution of the Swiss and Eastern Alps since the Oligocene

The Alps are representing the most prominent topographic feature of central Europe in the last 30 Million years. Integration of sediment budget and thermochronological data show that crustal blocks within the Swiss and Eastern Alps experienced differential erosion and uplift, with eastward decreasing rates. Since 30Ma, in the course of collision and slab breakoff, the Swiss and western Eastern Alps were uplifted and formed a mountain range. Moderate erosion rates stabilized ∼2Myr later after adaption to the new base level. Between 28Ma and 5Ma, erosion rates shifted above and below different regional mean levels. These shifts of erosion rates were governed by changes of the tectonic setting. Moderate temporary drops of erosion rates and lowering of topography occurred at ∼21Ma and ∼15Ma in the course of lateral extension. Temporary rises occurred between 24 and 22Ma during thrust loading and between 18 and 16Ma during axial updoming of core complexes. By 5Ma, a sustainable strong increase of erosion rates occurred in the Swiss and Western Alps. A much weaker increase is detected in the Eastern Alps somewhat later, which makes a tectonic trigger, probably a 2nd slab breakoff, more reasonable than a climatic trigger. However, this controversial 5-Ma event is superimposed by accelerated erosion after 2.7Ma, governed by the onset of cyclic glaciations. Effective valley incision and sediment evacuation by glacial erosion caused isostatic compensation and pronounced young uplift of the Alps.The post-Eocene paleotopographic evolution of key areas is indirectly assessed on the base of erosion rates. Spatial change of paleotopography of the Alps and central Europe is estimated and illustrated in 3 paleogeographic maps.

The cause for the north–south orientation of the crustal dichotomy and the equatorial location of Tharsis on Mars

The crustal dichotomy and the Tharsis rise are the most prominent topographic features on Mars. The dichotomy is largely an expression of different crustal thicknesses in the northern and southern hemispheres, while Tharsis is centered near the equator at the dichotomy boundary. However, the cause for the orientation of the dichotomy and the equatorial location of Tharsis remains poorly understood. Here we show that the crustal thickness variations associated with the dichotomy may have driven true polar wander, establishing the north–south orientation of the dichotomy very early in martian history. Such a reorientation that placed the dichotomy boundary near the equator would also have constrained the Tharsis region on the dichotomy boundary to have originated near the equator. We present a scenario for the early generation and subsequent reorientation of the hemispheric dichotomy, although the reorientation is independent of the formation mechanism. Our results also have implications for the sharply different remanent magnetizations between the two hemispheres.

Global mapping of diapycnal diffusivity in the deep ocean based on the results of expendable current profiler (XCP) surveys

Based on the results of the extensive XCP surveys in the North Pacific, we first examine the empirical relationship between the estimated diapycnal diffusivity in the thermocline and the numerically predicted, available energy density of the semidiurnal internal tide (major energy source for diapycnal diffusivity) at each location. The diapycnal diffusivity is estimated by applying the parameterization of Gregg (1989) to the fine‐scale vertical shear of horizontal velocity measured by XCP. Next, the numerically predicted energy density of the semidiurnal internal tide at each longitude and latitude in the world's oceans is incorporated into the resulting empirical relationship to obtain the global distribution of diapycnal diffusivity in the thermocline. This model predicts that strong diapycnal mixing (mixing hotspot) is limited to the prominent topographic features at latitudes between 20° and 30°.

Recent fold growth and drainage development: The Janauri and Chandigarh anticlines in the Siwalik foothills, northwest India

The active growth of a fault-and-thrust belt in frontal zones of Himalaya is a prominent topographical feature, extending 2500 km from Assam to Pakistan. In this paper, kinematical analysis of frontal anticlines and spatial mapping of active faults based on geomorphological features such as drainage pattern development, fault scarps and uplifted Quaternary alluvial fans are presented. We analyse the geomorphic and hydrographic expressions of the Chandigarh and the Janauri active anticlines in the NW India Siwaliks. To investigate the morphological scenario during the folding process, we used spatial imagery, geomorphometric parameters extracted from digital elevation models and fieldwork. Folding between the Beas and Sutlej Rivers gives clear geomorphological evidence of recent fold growth, presumably driven by movements of blind thrust faults. Structural style within the Janauri and Chandigarh anticlines is highly variable (fault-propagation folds, pop-up structures and transfer faults). The approach presented here involves analysis of topography and drainage incision of selected landforms to detect growth of active anticlines and transfer faults. Landforms that indicate active folding above a southwest-dipping frontal thrust and a northeast-dipping back-thrust are described. Along-strike differences in ridge morphology are measured to describe the interaction of river channel patterns with folds and thrust faults and to define history of anticline growth. The evolution of the apparently continuous Janauri ridge has occurred by the coalescence of independent segments growing towards each other. By contrast, systematic drainage basin asymmetry shows that the Chandigarh anticline ridge has propagated laterally from NW to SE.

28th DeBeers Alex. Du Toit Memorial Lecture, 2004. On Cryogenian (Neoproterozoic) ice-sheet dynamics and the limitations of the glacial sedimentary record

28th DeBeers Alex. Du Toit Memorial Lecture, 2004. On Cryogenian (Neoproterozoic) ice-sheet dynamics and the limitations of the glacial sedimentary record

A Tibetan Taylor Cap and a halo of stratospheric ozone over the Himalaya

[1] With an average elevation in excess of 4000 m asl, the Tibetan Plateau is one of the Earth's most prominent topographic features. The plateau plays an important role in the global climate system by acting as a heat source during the summer and a heat sink during the winter. There also exists evidence that its influence extends into the upper-troposphere and lower-stratosphere through the existence of a region of low total column ozone over the plateau. We report on observations of ozone concentration from the Bhutanese Himalaya that support the hypothesis that a Taylor Cap exists over the plateau. We argue that the presence of this cap results in the formation of a halo of ozone-rich air in the upper-troposphere around the perimeter of Tibet. The Himalaya are within this halo and the higher peaks may be exposed to ozone concentrations similar to those found in industrialized cities.

The Agulhas Ridge, South Atlantic: The Peculiar Structure of a Fracture Zone

The Agulhas Ridge is a prominent topographic feature that parallels the Agulhas-Falkland Fracture Zone (AFFZ). Seismic reflection and wide angle/refraction data have led to the classification of this feature as a transverse ridge. Changes in spreading rate and direction associated with ridge jumps, combined with asymmetric spreading within the Agulhas Basin, modified the stress field across the fracture zone. Moreover, passing the Agulhas Ridge’s location between 80 and 69 Ma, the Bouvet and Shona Hotspots may have supplied excess material to this part of the AFFZ thus altering the ridge’s structure. The low crustal velocities and overthickened crust of the northern Agulhas Ridge segment indicate a possible continental affinity that suggests it may be formed by a small continental sliver, which was severed off the Maurice Ewing Bank during the opening of the South Atlantic. In early Oligocene times the Agulhas Ridge was tectono-magmatically reactivated, as documented by the presence of basement highs disturbing and disrupting the sedimentary column in the Cape Basin. We consider the Discovery Hotspot, which distributes plume material southwards across the AAFZ, as a source for the magmatic material.

Three‐dimensional numerical simulation of M2 internal tides in the East China Sea

The East China Sea and adjacent seas are one of the most significant generation regions of the M2 internal tide in the world's oceans. In the present study, we investigate the distribution and energetics of the M2 internal tide around the continental shelf edge in the East China Sea using a three‐dimensional numerical model. The numerical experiment shows that M2 internal tides are effectively generated over prominent topographic features such as the subsurface ridges in the Bashi/Luzon and Tokara Straits, the ridges along the Ryukyu Island chain, and the continental shelf slope in the East China Sea, the former particularly so. All of these topographic features are characterized by steep slopes at the depth of the thermocline onto which the M2 barotropic tide is almost normally incident. The M2 internal tides propagating away from these multiple source regions interfere with each other to create a complicated wave pattern. It is found that the calculated pattern of the M2 internal tide agrees well with TOPEX/Poseidon altimeter observations. The conversion rate from M2 barotropic to baroclinic energy over the whole analyzed model domain is estimated to be 35 GW. Roughly 10% of the energy in the M2 surface tide incident on the prominent topographic features is converted to the M2 internal tide, although about half of the M2 internal tidal energy is subject to local dissipation in close proximity to the generation sites.

Latitudinal dependence of diapycnal diffusivity in the thermocline estimated using a finescale parameterization

The spatial distribution of diapycnal diffusivity in the thermocline over a large area in the interior of the North Pacific is obtained by incorporating the finescale vertical shear of horizontal velocity measured by expendable current profilers into the empirical formula proposed by Gregg [1989]. It is clearly shown that diapycnal diffusivity in the North Pacific strongly depends on the latitude. For example, the estimated diapycnal diffusivities near the Hawaiian Ridge and the Izu‐Ogasawara Ridge exceed 10−4 m2 s−1, whereas those near the Aleutian Ridge and the Emperor Seamounts are of the order of 0.1 × 10−4 m2 s−1, even though the available semidiurnal internal tidal energy is similar among all of these prominent topographic features. The observed results are consistent with the numerical prediction that the cascade of internal tidal energy down to dissipation scales is dominated by parametric subharmonic instability which is expected to occur only below 30°N.

Surface-piercing salt domes of interior North Oman, and their significance for the Ara carbonate ‘stringer’ hydrocarbon play

ABSTRACT The six surface-piercing salt domes of interior North Oman form prominent topographic and geological features in an otherwise flat, rocky desert environment. These domes in the central part of the Ghaba Salt Basin have been known since the 1950s but very little data has been published on them. Our geological survey in 2001 provided significant new lithological, stratigraphic, and sedimentological information on the rocks exposed in the domes. This paper provides a comprehensive overview of the morphology, geometry, structural geology and geological evolution of the salt domes. Furthermore, it incorporates relevant information from unpublished subsurface studies to place the new geological field data in the context of ongoing exploration for deep hydrocarbon plays in Oman. A wide variety of rocks is exposed in the salt domes: carbonates, clastics (conglomerates, sandstones, siltstones and clays), volcanics, evaporites and ‘caprocks’. Constituent rocks and structural style vary considerably from one dome to another, but at the surface the main lithological elements of the diapirs are carbonates and evaporites of the ‘Infracambrian’ (Late Precambrian to Early Cambrian) Ara Group, the uppermost unit of the Huqf Supergroup. Very large exotic blocks of bedded Ara carbonates––commonly hundreds of meters long––are well-exposed and form distinctive hills and ridges, thus allowing detailed field observations on intra-salt carbonate ‘stringers’ that have been carried up by rising diapiric salt. A close correlation exists between the facies of the carbonate exotics in the salt domes and Ara ‘stringer’ carbonates penetrated and extensively cored in recent deep exploration wells in the South Oman Salt Basin. This demonstrates the regional significance of the salt domes for the intra-salt ‘stringer’ hydrocarbon play in Oman. Our work has implications for the prospectivity of other ‘Infracambrian’ evaporite basins in Oman, and possibly also for time-equivalent (‘Hormuz’) salt basins elsewhere in the Middle East.

Land ownership and other landscape-level effects on biodiversity in southern Ontario’s Niagara Escarpment Biosphere Reserve, Canada

We investigated effects of landscape-level factors on measures of biodiversity using published descriptions for 98 significant natural areas along the Niagara Escarpment. This is a 725 km, largely forested, Paleozoic limestone escarpment that, excepting the Great Lakes, is the most prominent topographical feature of southern Ontario, Canada. Results show highly significant differences in mean site size and extent of forest interior among natural areas of different ownership classes, with larger and more forested sites being under mixed (private + public) ownership, but no significant difference between sites of public and private ownership. Analysis of covariance demonstrated that after controlling for differences in landscape-level factors (total size of natural area, extent of forest interior, extent of landform heterogeneity and geographic location), most measures of biotic diversity (including the number of vegetation community types, provincially rare vascular plants, and regionally and locally rare breeding birds) differed significantly among sites of private, public and mixed ownership. In general, values at public and mixed ownership sites were greatest, with significantly lower biodiversity values at privately-owned sites. Furthermore it would seem not to be a product of public bodies having historically purchased the largest sites or most-forested sites, since there is no significant difference between the mean size of publically-owned and privately-owned sites. Results of stepwise multiple regression confirm the well known relation between size of a natural area and variation in both total, and rare species diversity. Since public sites have generally more species than private sites, they are essential elements of any conservation network.

Paterae on Io: A new type of volcanic caldera?

Paterae, defined by the International Astronomical Union as “irregular crater[s], or complex one[s] with scalloped edges,” are some of the most prominent topographic features on Io. Paterae on Io are unique, yet in some aspects they resemble calderas known and studied on Earth, Mars, and Venus. They have steep walls, flat floors, and arcuate margins and sometimes exhibit nesting, all typical of terrestrial and Martian basalt shield calderas. However, they are much larger, many are irregular in shape, and they typically lack shields. Their great sizes (some >200 km diameter) and lack of associated volcanic edifices beg comparison with terrestrial ash flow calderas; however, there is no convincing evidence on Io for the high‐silica erupted products or dome resurgence associated with this type of caldera. Ionian paterae seem to be linked with the eruption of large amounts of mafic to ultramafic lavas and colorful sulfur‐rich materials that cover the floors and sometimes flow great distances away from patera margins. They are often angular in shape or are found adjacent to mountains or plateaus, indicating tectonic influences on their formation. A database of 417 paterae on Io measured from images with <3.2 km pixel−1 resolution (80% of its surface) reveals that their mean diameter of 41.0 km is close to that for calderas of Mars (47.7 km), is smaller than that for Venus (∼68 km), but dwarfs those for terrestrial basalt shield calderas (6.6 km) and ash flow calderas (18.7 km). Thirteen percent of all paterae are found adjacent to mountains, 42% have straight or irregular margins, and 8% are found atop low shields. Abundant, smaller paterae with more continuously active lava eruptions are found between 25°S and 25°N latitude, whereas fewer and larger paterae are found poleward of these latitudes. Patera distribution shows peaks at 330°W and 150°W longitude, likely related to the direction of greatest tidal massaging by Jupiter. Ionian patera formation may be explained by portions or combinations of models considered for formation of terrestrial calderas, yet their unusual characteristics may require new models with a greater role for tectonic processes.

Numerical study of the spatial distribution of the M2 internal tide in the Pacific Ocean

As a first step toward numerical modeling of global internal tides, we clarify the distribution of the M2 internal tide in the Pacific Ocean using a three‐dimensional primitive equation numerical model. The numerical simulation shows that energetic internal tides are generated over the bottom topographic features in the Indonesian Archipelago, the Solomon Archipelago, the Aleutian Archipelago, and the Tuamotu Archipelago, the continental shelf slope in the East China Sea, and the mid‐oceanic ridges such as the Izu‐Ogasawara Ridge, the Hawaiian Ridge, the Norfolk Ridge, the Kermadec Ridge, and the Macquarie Ridge. The calculated spatial patterns of the M2 internal tide around the Hawaiian Ridge and the Izu‐Ogasawara Ridge agree well with the TOPEX/Poseidon altimetric observation. The conversion rate from the M2 surface to internal tide energy integrated over the whole model domain amounts to 338 GW (1 GW = 109 W), 84% of which are found to be generated over the prominent topographic features mentioned above. Reflecting the spatial distribution of the prominent topographic features in the Pacific Ocean, the energy level of the M2 internal tide in the western and central Pacific is 2–3 orders of magnitude higher than that in the eastern Pacific. This remarkable asymmetry shows that extensive microstructure measurements in the western and central Pacific are indispensable to determining the representative value of diapycnal mixing rates in the global ocean.

The shape of Mars before Global Surveyor: Results from reanalysis of the Viking control point network

Three‐dimensional coordinates of 3739 globally distributed control points derived from photogrammetric analysis of Viking Orbiter image data are studied with respect to the shape and large‐scale morphology of Mars. Spheres, spheroids, spherical functions, and a Digital Terrain Model (DTM) of 50 km grid spacing are fitted to the data. Prominent topographic features in the terrain model include the Tharsis volcanoes, Olympus Mons, Alba Patera and prominent mare and highland regions as well as the major impact basins. While the global dichotomy is clearly visible in our data, our model does not reveal any distinct signature associated with the presumed dichotomy boundary at this global scale. Rather, it suggests a smooth topographic transition from southern to northern hemisphere. This model is unique among existing topographic data sets for Mars, as it combines global coverage, a spatial resolution sufficient to resolve regional topography, and absolute elevation data more accurate than in previous control point network analyses. Formal errors and a comparison with the first released topographic profiles obtained by Mars Global Surveyor's Laser Altimeter (MOLA) suggest that 70% and 90% of the DTM grid elements represent the topography of the planet to better than 1000 m and 2000 m, respectively.

Photogrammetric analysis of horizon panoramas: The Pathfinder landing site in Viking orbiter images

Tiepoint measurements, block adjustment techniques, and sunrise/sunset pictures were used to obtain precise pointing data with respect to north for a set of 33 IMP horizon images. Azimuth angles for five prominent topographic features seen at the horizon were measured and correlated with locations of these features in Viking orbiter images. Based on this analysis, the Pathfinder line/sample coordinates in two raw Viking images were determined with approximate errors of 1 pixel, or 40 m. Identification of the Pathfinder location in orbit imagery yields geological context for surface studies of the landing site. Furthermore, the precise determination of coordinates in images together with the known planet‐fixed coordinates of the lander make the Pathfinder landing site the most important anchor point in current control point networks of Mars.