Sentinel Range Research Articles

High-Precision Measurement of Height Differences from Shadows in Non-Stereo Imagery: New Methodology and Accuracy Assessment

The shadow-height method has been extensively used to extract the heights of buildings from the shadows they cast in non-stereo (single view) aerial and satellite imagery. However, the use of this method in Earth sciences has been limited, partially due to the relatively low accuracy reported, the fuzziness of shadow edges, the complexities of the scanning sensors, and a lack of software tools. In this paper, we present an enhanced shadow-height methodology offering significant accuracy improvement. These improvements are mainly the result of using a physical approach to model the illumination gradient through the edge of shadows and by leveraging meteorological data to precisely estimate atmospheric refraction. We validated 91 shadow-derived height estimations from images obtained by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) at three sites with latitudes between 33 and 78°S: The Andes Mountains, Sentinel Range, and Abbot ice shelf. Reference measurements were obtained from Global Navigation Satellite System (GNSS) surveys and the Ice, Cloud, and land Elevation Satellite (ICESat). The observed errors fell below 6% for small height differences (∼20 m) and below 2% for larger height differences (≳300 m). Our validation data cover solar elevations ranging from 3.7 to 42.2°, and we observed smaller absolute errors at lower solar elevations. This novel information can be valuable for studying surface elevation changes in present and old imagery and extending glacier volume variation time-series.

The influence of dynamic environmental interactions on detection efficiency of acoustic transmitters in a large, deep, freshwater lake

BackgroundAcoustic telemetry is an increasingly common method used to address ecological questions about the movement, behaviour, and survival of freshwater and marine organisms. The variable performance of acoustic telemetry equipment and ability of receivers to detect signals from transmitters have been well studied in marine and coral reef environments to inform study design and improve data interpretation. Despite the growing use of acoustic telemetry in large, deep, freshwater systems, detection efficiency and range, particularly in relation to environmental variation, are poorly understood. We used an array of 90 69-kHz acoustic receivers and 8 sentinel range transmitters of varying power output deployed at different depths and locations approximately 100–9500 m apart for 215 days to evaluate how the detection efficiency of acoustic receivers varied spatially and temporally in relation to environmental conditions.ResultsThe maximum distance that tags were detected ranged from 5.9 to 9.3 km. Shallow tags consistently had lower detection efficiency than deep tags of the same power output and detection efficiency declined through the winter months (December–February) of the study. In addition to the distance between tag and receiver, thermocline strength, surface water velocity, ice thickness, water temperature, depth range between tag and receiver, and number of fish detections contributed to explaining variation in detection efficiency throughout the study period. Furthermore, the most significant models incorporated interactions between several environmental variables and tag–receiver distance, demonstrating the complex temporal and spatial relationships that exist in heterogeneous environments.ConclusionsRelying on individual environmental variables in isolation to interpret receiver performance, and thus animal behaviour, may be erroneous when detection efficiency varies across distances, depths, or tag types. As acoustic telemetry becomes more widely used to study ecology and inform management, it is crucial to understand its limitations in heterogeneous environments, such as freshwater lakes, to improve the quality and interpretation of data. We recommend that in situ range testing and retrospective analysis of detection efficiency be incorporated into study design for telemetry projects. Furthermore, we caution against oversimplifying the dynamic relationship between detection efficiency and environmental conditions for the sake of producing a correction that can be applied directly to detection data of tagged animals when the intended correction may not be justified.

Active layer thermal monitoring of a Dry Valley of the Ellsworth Mountains, Continental Antarctica

The Ellsworth Mountains are located along the southern edge of the Ronne-Filchner Ice Shelf and are subdivided by the Minnesota Glacier into the Heritage Range to the east, and the Sentinel Range to the west (Figure 1). The climate of the Ellsworth Mountains is strongly controlled by proximity to the Ronne-Filchner Ice Shelf and elevation. The entire ice free area is underlain by continuous permafrost of unknown thickness, most in the form of dry permafrost. Active-layer depths in drift sheets of the Ellsworth Mountains range from 15 to 50cm. Detailed knowledge on Antarctic permafrost is patchy, especially at the continent. Two adjacent active layer monitoring sites were installed at Mt. Dolence, Ellsworth Mountains, in the summer of 2012. Two dry-valley soils at Mt. Dolence area, on quartzite drift deposits were studied: (i) a convex-slope site exposed to the wind (Lithic Haplorthel 886m asl, 5cm, 10cm, 30cm); and a sheltered concave-slope site protected from winds (Lithic Anhyorthel 850m asl, 5cm, 10cm, 30cm). Data was recorded at hourly intervals from January 2nd 2012 until December 29th 2013. The soil climate temperature at 5cm reaches a maximum daily mean in late December, reaching a minimum in mid July at both sites. Active layer thickness reaches a maximum of 48.4cm at P1 on January 17th 2013 and 47.8cm at P2 on January 7th 2012. The soil thermal regime at the dry valley of Mt. Dolence, Ellsworth Mountains is characteristic of cold desert affected by dry-frozen permafrost. Although air temperature does not reach elevated positive values, variations in soil temperature are intense, showing the soil's response to solar radiation. The origins of typical surface periglacial features and landform on the widespread Ellsworth drifts may be inherited from past events of warmer climates, since liquid water is unlikely to play any significant role under the present climate.

Mt. Vinson and the evolution of US policy on Antarctic mountaineering, 1960–1966

ABSTRACTThe full extent of the height and scale of the Sentinel Range, Antarctica, was not known until reconnaissance flights and scientific traverses in the International Geophysical Year (IGY), 1957–1958. These explorations revealed the range to be twenty miles in length, with a large number of high peaks culminating in Mt. Vinson, the highest on the Antarctic continent at nearly 4900 meters. The discoveries captured the interest of the U.S. and world mountaineering communities setting off a competition to achieve the first climb of Vinson. The challenge was tempered only by the range's remoteness from the coast of Antarctica and the formidable logistics of mounting a mountaineering expedition. The US which had the most advanced ski-equipped cargo aircraft, had an established post-IGY policy that prohibited adventure expeditions that could divert logistic resources from the scientific programme. This paper discusses Mt. Vinson competition within the US and international climbing communities, mounting national pressures to achieve the first climb, and a reversal in policy by the US Antarctic Policy Group that resulted in the 1966–1967 American Antarctic Mountaineering Expedition's first ascents of Vinson and five other high peaks. Today, between 100 and 200 persons climb Mt. Vinson each austral summer.

Airborne tourism in the Antarctic

ABSTRACTThere are two classes of airborne tourism in Antarctica: overflights without landing, and fl ights including landing. The earliest overflight was in 1956, but there were no regular flights until 1977, when Qantas and Air New Zealand began overflights with wide-bodied aircraft. A crash on Mount Erebus in 1979 that killed 257 people drew attention to the absence of effective planning, air traffic control, and rescue services. Landings began in the South Shetland Islands in 1982, when C-130 aircraft of Fuerza Aerea de Chile brought passengers from Punta Arenas. Since 1983, tourists have been accommodated in a Chilean government hostel. Flights to the interior began in 1984 when climbers were taken to the Sentinel Range by ski-equipped aircraft. Unmodified transport aircraft have been used since 1987, making wheel landings on naturally occurring bare ice in the Heritage Range. Tourists were taken from this site to the South Pole in 1988 by smaller, ski-equipped aircraft. Owing to the lack of conventional airfields in Antarctica, the future of intercontinental operations may depend on the development of additional airfields on bare ice. There are many possible sites. Most are near the periphery of the continent but some are in high latitudes, one only 300 km from the South Pole. A few of these will allow direct flights of unmodified passenger aircraft from South America, South Africa, Australia, or New Zealand. The possibility of 300 day-trippers stepping onto the ice from a Boeing 747 raises a variety of safety and environmental concerns. The challenge to the Antarctic Treaty System will be to reconcile the interests of governments, scientists, airlines, tour operators, tourists, and environmentalists.

Logistic aspects of geological studies in the Ellsworth Mountains, Antarctica, 1979–80

The most ambitious field project of the 1979–80 austral summer season in Antarctica was conducted in the Ellsworth Mountains (Fig 1), when 42 scientists and technicians studied a variety of geological problems in an area which included both the Sentinel Range to the north and the Heritage Range to the south (Fig 2), from about 77°15'S to 80°30'S and 80°W to 87°30'W.

Fossils from the Ellsworth Mountains, Antarctica

THE Ellsworth Mountains are centred at 79° S., 85° W. in West Antarctica south of the eastern Pacific Ocean (sec Fig. 1). They extend about 220 miles in a north-north-west direction and are divided into a northern Sentinel Range and a southern Heritage Range. Widespread rock exposure and critical location make these mountains important in seeking an understanding of the structural evolution of West Antarctica. One of us (C. C.) visited the Ellsworth Mountains briefly in 1959 during an airborne traverse, and University of Minnesota expeditions worked there during the 1961–62 and 1962–63 summer seasons. Few fossils were found by the first expedition1, and none has proved identifiable even to genus. Significant palseontological discoveries were made, however, during the 1962–63 season when one of us (G. F. W.) led a party in the Heritage Range and the other a party in the Sentinel Range. Although the new material was only briefly examined and the field work is continuing, it seems desirable to make available a summary of the fossil discoveries so far.

Seismic measurements on the ice sheet of the Antarctic Peninsula

The results of seismic measurements made during the Antarctic Peninsula over-snow traverse of 1961–1962 are presented and discussed. Maps of snow surface and bedrock elevation are presented. The Antarctic Peninsula is shown to be an island separated from the Sentinel Range by a channel 1000 m below sea level and from the Eights Coast of Ellsworth Land by a channel 500 m deep. A reflection horizon 450 m above the base of the ice near Eights Station was observed. Wide-angle reflections showed the existence of a low-velocity layer below this reflecting horizon which is interpreted as the result of moraine within the ice. An 18-km refraction profile showed a velocity of 3.87 km/sec in the top 0.9 km of ice, a velocity of 4.39 krn/sec in the next 0.2 km, a velocity of 5.29 krn/sec in the next 3.5 km, and a possible velocity of 6.0 km/sec in the rock below.

Probable Disintegration of Antarctica

The writer's research life has coincided fairly closely with the vast discoveries made in thi c ntury s nce he first joined the Sc tt Expedition to Antarctica in 1910. Nothing was known within the coasts of Antarctica until Scott had returned; indeed, until the end of 1904 the map merely showed a pear-shaped outline extending around the South Pole. In my first long memoir, which appeared in this Journal in 1914, I discussed generally the structure of Antarctica, and I especially stressed the resemblance between Antarctic and Australian structure ('Physiography and glacial geology of East Antarctica'; Geogr. J. 44 (1914) 365-82; 452-67; 553-71). I suggested that a broad syncline or downfold below sea level might extend from the Ross Sea to the Weddell Sea?somewhat as the Tasman Sea separated the folded New Zealand Ridge from the Horsts of Australia. Possibly this marine channel was present in midTertiary times. I have seen these suggestions to a considerable degree corroborated by the con? clusions ofthe I.G.Y. researches as seen in the recent topographic map published by the Scientific American in September 1962 (Antarctica: prepared by the American Geographical Society for the United States Antarctic Research Program, with a grant from the National Science Foundation: 1:5M. 1962). Two techniques have been developed in the Antarctic in the last thirty years? exploration by air, and echo-sounding through the ice cap. I may instance a few errors on the earlier maps. In 1914 Amundsen, as he sledged over the Ross Ice Shelf to the Pole, gave it as his opinion that 'Carmen Land' blocked my hypothetical geosyncline. This land was illusory: Scott's ship sailed over several so-called 'lands' in 1911 near Cape Adare (near d Fig. 1). Mawson found that many landfalls cited by Wilkes in 1840 were greatly out of position in this area. Wilkins, on his first flight in December 1928 charted 'Stefansson Strait' in approximately lat. 71 ? in such a position as to divide Graham Land from the Continent; this was later found to be an error. In 1940 was published in the Regionale Geologie der Erde of Leipzig (Bd. I: Die alten Kerne) my geological account of Antarctica which, though written in 1934, was more complete than anything that had been published before, and which was illustrated by a block diagram of Antarctica. In 1935 Ellsworth flew across from the Weddell Sea to the Ross Sea, and found that his 'Sentinel Range' (c) much prolonged the 'Antarctic-Andes' towards the Ross Sea. However, Byrd's aviator (Anderson) in 1936 reported that the 'Great Horst' extended for some 180 miles beyond the South Pole towards the Weddell Sea. The new sonic data reported as late as 1960 gave sonic and other inform? ation which seemed wholly to block the suggested geosyncline. The latest map, the American one discussed here, shows that the geosyncline, some 2000 miles long, and varying in width from 200 miles downwards until it narrows near the Horlick Mountains at the point marked * on Figure 1, is an actual feature. Recent soundings have shown that the Ross Shelf extends south-east for some 500 miles to the

Paleozoic Stratigraphy Along Alaska Highway in Northeastern British Columbia

Excellent exposures of Paleozoic rocks are present along the Alaska Highway between Summit Lake (mile 392) and the Liard River (mile 497) in British Columbia. Silurian, Devonian, and Mississippian beds have been studied in detail in this area. The names McConnell and Muncho are proposed for two unnamed Devonian formations in the area, and the name Kindle is introduced for all of the Mississippian rocks along this part of the highway. Marine limestones and black shales make up most of the Paleozoic section although local sandstones are developed. The geologic record indicates that at least several hundred irregular but clearly cyclic sedimentary alternations occurred here during the Paleozoic era. In addition, several groups of cycles give evidence of megacyclic sedimentation. The area is divided into three physiographic provinces: the Stone Range and the Sentinel Range, each of which is composed of tightly folded, overthrust, Paleozoic limestones, and the Racing River Valley, a relatively low gently folded zone of soft Upper Paleozoic and Mesozoic rocks which separates the two ranges. The Stone Range, on the east side of the area, is characterized by a thinner, more sandy, more variable sequence of Paleozoic rocks than the Sentinel Range, which seems to indicate closer proximity to the eastern shore of the Cordilleran geosyncline.