Journal articles on the topic 'Surface elevations'
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1
Jezek, Kenneth C. "Surface elevation and velocity changes on the south-central Greenland ice sheet: 1980–2011." Journal of Glaciology 58, no. 212 (2012): 1201–11. http://dx.doi.org/10.3189/2012jog12j031.
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AbstractWe extend through 2011 an ice-sheet elevation and surface velocity record across three measurement networks established in south-central Greenland by The Ohio State University in 1980/81. Surface parameters are derived from repeat GPS in situ observations, elevations measured by airborne laser altimetry and by the Ice, Cloud and land Elevation Satellite (ICESat). Elevations at the western network steadily rose early in the record by 0.10 ± 0.02 m a-1, but an eastward-progressing thinning trend began in the mid-1990s followed by a ~1m elevation drop at all stations from 2005 to 2011. Measurements weakly suggest a surface velocity increase at the western cluster from 1980 to 2005. At the central network, elevations rose by 0.08 ± 0.02 m a-1 through 2005 and surface speed increased by 0.5–0.7 m a-1. Surface elevations at the central network remained nearly constant thereafter. Thickening occurred at the southern ice divide by 0.05 ± 0.02 m a-1, while east of the divide the ice sheet thinned with increasing rate from the divide, likely because of decreasing accumulation rate trends and drawdown into rapidly retreating coastal glaciers. Our most recent data show that thinning rates are slowing at several sites just east of the divide and that the elevation at the divide continues to increase.
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Dixon, Lester S., and Belinda A. Sullivan. "Selecting Terminal Water Surface Elevations." Journal of Hydraulic Engineering 112, no. 5 (May 1986): 428–31. http://dx.doi.org/10.1061/(asce)0733-9429(1986)112:5(428).
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Molnar, Peter, and Lina C. Pérez-Angel. "Constraints on the paleoelevation history of the Eastern Cordillera of Colombia from its palynological record." Geosphere 17, no. 4 (June 21, 2021): 1333–52. http://dx.doi.org/10.1130/ges02328.1.
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Abstract We attempted to make an objective assessment of whether fossil pollen assemblages from the Sabana de Bogotá require surface uplift of ~2000 m since 6–3 Ma, as has been argued. We relied on recently published elevation ranges of plants for which fossil pollen has been found in sites 2000–2500 m high in the Sabana de Bogotá. The elevation ranges of fossil plants do not overlap, suggesting that those ranges may be too narrow. By weighting these elevation ranges by percentages of corresponding fossil pollen and summing them, we estimated probability density functions for past elevations. These probability distributions of past elevations overlap present-day elevations and therefore do not require surface uplift since deposition of the pollen. Fossil pollen assemblages include pollen from some plant taxa for which we do not know present-day elevation ranges, and therefore, with a more complete knowledge of elevation distributions, tighter constraints on elevations should be obtainable. The elevation of the oldest assemblage, from Tequendama, which lies at the southern edge of the Sabana de Bogotá and is thought to date from 16 to 6 Ma, is least well constrained. Although our analysis permits no change in elevation since the pollen was deposited, we consider 1000–2000 m of elevation gain since 15 Ma to be likely and consistent with an outward growth of the Eastern Cordillera.
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Bidschadler, R. A., and P. L. Vornberger. "Detailed elevation map of Ice Stream C, Antarctica, using satellite imagery and airborne radar." Annals of Glaciology 20 (1994): 327–35. http://dx.doi.org/10.3189/1994aog20-1-327-335.
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Surface elevations collected by airborne radar arc interpolated between flight lines using Landsat I'M image data to produce a detailed digital elevation model of a part of Ice Stream C, West Antarctica. The photodinometric method developed is general and allows the derivation of surface elevation along any line parallel to the solar illumination from a single known elevation on that line. Accuracies of the derived elevations are improved with additional elevation control that permits an empirical determination of parameters in the photoclinometric equation accounting for albedo and atmospheric scattering. Elevation errors increase approximately linearly with the integration distance. An explicit relationship is derived that shows the image brightness is insensitive to the cross-Sun component of small surface slopes typical of ice sheets. The greatest impediment to the accuracy of this technique is the radiance resolution of the sensor which limits the signal-to-noise ratio of the image data and can mask variations in albedo that are falsely converted to variations in surface slope.
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Bidschadler, R. A., and P. L. Vornberger. "Detailed elevation map of Ice Stream C, Antarctica, using satellite imagery and airborne radar." Annals of Glaciology 20 (1994): 327–35. http://dx.doi.org/10.1017/s0260305500016645.
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Surface elevations collected by airborne radar arc interpolated between flight lines using Landsat I'M image data to produce a detailed digital elevation model of a part of Ice Stream C, West Antarctica. The photodinometric method developed is general and allows the derivation of surface elevation along any line parallel to the solar illumination from a single known elevation on that line. Accuracies of the derived elevations are improved with additional elevation control that permits an empirical determination of parameters in the photoclinometric equation accounting for albedo and atmospheric scattering. Elevation errors increase approximately linearly with the integration distance. An explicit relationship is derived that shows the image brightness is insensitive to the cross-Sun component of small surface slopes typical of ice sheets. The greatest impediment to the accuracy of this technique is the radiance resolution of the sensor which limits the signal-to-noise ratio of the image data and can mask variations in albedo that are falsely converted to variations in surface slope.
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Tang, Jiale, Xincan Lan, Yuanyuan Lian, Fang Zhao, and Tianqi Li. "Estimation of Urban–Rural Land Surface Temperature Difference at Different Elevations in the Qinling–Daba Mountains Using MODIS and the Random Forest Model." International Journal of Environmental Research and Public Health 19, no. 18 (September 11, 2022): 11442. http://dx.doi.org/10.3390/ijerph191811442.
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Land surface temperature (LST) variations are very complex in mountainous areas owing to highly heterogeneous terrain and varied environment, which complicates the surface urban heat island (SUHI) in mountain cities. Previous studies on the urban heat island (UHI) effect mostly focus on the flat terrain areas; there are few studies on the UHI effect in mountainous areas, especially on the influence of elevation on the SUHI effect. To determine the SUHI in the Qinling–Daba mountains (China), MODIS LST data were first preprocessed and converted to the same elevations (1500 m, 2000 m, 2500 m, 3000 m, and 3500 m) using a digital elevation model and the random forest method. Then, the average LSTs in urban land, rural land, and cultivated land were calculated separately based on the ranges of the invariable urban, rural, and cultivated areas during 2010–2018, and the urban, rural, and cultivated land LST difference were estimated for the same elevations. Results showed that the accuracy of LST estimated using the random forest method is very high (R2 ≥ 0.9) at elevations of 1500 m, 2000 m, 2500 m, 3000 m and 3500 m. The difference in urban, rural, and cultivated lands’ LST has a trend of decrease with increasing elevation, meaning that the SUHI weakens at higher elevations. The average LST of urban areas is 0.52–0.59 °C (0.42–0.57 °C) higher than that of rural and cultivated areas at an elevation of 1500 m (2000 m). The average LST of urban areas is 0.10–1.25 °C lower than that of rural and cultivated areas at elevations of 2500 m, 3000 m, and 3500 m, indicating absence of the SUHI at those elevations.
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Minocha, Rakesh, Alexandra R. Contosta, Gregory B. Lawrence, Ravinder K. Kohli, Subhash C. Minocha, and Stephanie Long. "Changes in Soil Chemistry and Foliar Metabolism of Himalayan Cedar (Cedrus deodara) and Himalayan Spruce (Picea smithiana) along an Elevational Gradient at Kufri, HP, India: The Potential Roles of Regional Pollution and Localized Grazing." Forests 12, no. 4 (March 28, 2021): 400. http://dx.doi.org/10.3390/f12040400.
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We investigated changes in soil chemistry and foliar metabolism of Himalayan cedar [Cedrus deodara (Roxb. Ex Lamb.) G.Don] and Himalayan spruce [Picea smithiana (Wall.) Boiss] trees along a steep elevational gradient in the lower Himalayan Mountains at Kufri, Himachal Pradesh (HP), India. The foliar and soil samples were collected from four locations along a 300 m elevational gradient at ridge, high-, mid-, and low-elevation sites within the forested Shimla Water Catchment Wildlife Sanctuary that provides water for the city of Shimla, HP,. Observations at the time of sampling revealed that the high-elevation site was being heavily grazed. Soils collected at the four sites showed differences in soil chemistry along the gradient. Surface soils (top 10 cm) at the high-elevation site had the highest concentrations of carbon, nitrogen, calcium, magnesium, phosphorus, organic matter, and effective cation exchange capacity, possibly caused by grazing. Mineral soils were slightly acidic at all sites except the mid-elevation site, which was extremely acidic in the upper mineral soil. Similar to surface soil chemistry, foliar metabolism was also comparatively unique for high elevation. In Himalayan cedar foliage, higher concentrations of soluble proteins, polyamines, amino acids, and potassium were observed at the high-elevation site as compared to the ridge, mid and low elevations. No major differences were observed in the metabolic profiles of cedar between the ridge and low elevation ranges. Spruce foliage was sampled only from the ridge and low elevations and its metabolic profiles suggested healthier conditions at the low elevation. The results of the study demonstrate the impact of the interplay between local and regional drivers of forest health on cedar and spruce trees in a forested catchment that acts as a water source for downstream communities.
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Levinsen, J. F., I. M. Howat, and C. C. Tscherning. "Improving maps of ice-sheet surface elevation change using combined laser altimeter and stereoscopic elevation model data." Journal of Glaciology 59, no. 215 (2013): 524–32. http://dx.doi.org/10.3189/2013jog12j114.
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AbstractWe combine the complementary characteristics of laser altimeter data and stereoscopic digital elevation models (DEMs) to construct high-resolution (∼100 m) maps of surface elevations and elevation changes over rapidly changing outlet glaciers in Greenland. Measurements from spaceborne and airborne laser altimeters have relatively low errors but are spatially limited to the ground tracks, while DEMs have larger errors but provide spatially continuous surfaces. The principle of our method is to fit the DEM surface to the altimeter point clouds in time and space to minimize the DEM errors and use that surface to extrapolate elevations away from altimeter flight lines. This reduces the DEM registration errors and fills the gap between the altimeter paths. We use data from ICESat and ATM as well as SPOT 5 DEMs from 2007 and 2008 and apply them to the outlet glaciers Jakobshavn Isbræ (JI) and Kangerdlugssuaq (KL). We find that the main trunks of JI and KL lowered at rates of 30–35 and 7–20 m a−1,respectively. The rates decreased inland. The corresponding errors were 0.3–5.2 m a−1for JI and 0.3–5.1 m a−1for KL, with errors increasing proportionally with distance from the altimeter paths.
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Lee, W. L., Y. Gu, K. N. Liou, L. R. Leung, and H. H. Hsu. "A global model simulation for 3-D radiative transfer impact on surface hydrology over Sierra Nevada and Rocky Mountains." Atmospheric Chemistry and Physics Discussions 14, no. 22 (December 15, 2014): 31603–25. http://dx.doi.org/10.5194/acpd-14-31603-2014.
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Abstract. We investigate 3-D mountain effects on solar flux distributions and their impact on surface hydrology over the Western United States, specifically the Rocky Mountains and Sierra Nevada using CCSM4 (CAM4/CLM4) global model with a 0.23° × 0.31° resolution for simulations over 6 years. In 3-D radiative transfer parameterization, we have updated surface topography data from a resolution of 1 km to 90 m to improve parameterization accuracy. In addition, we have also modified the upward-flux deviation [3-D − PP (plane-parallel)] adjustment to ensure that energy balance at the surface is conserved in global climate simulations based on 3-D radiation parameterization. We show that deviations of the net surface fluxes are not only affected by 3-D mountains, but also influenced by feedbacks of cloud and snow in association with the long-term simulations. Deviations in sensible heat and surface temperature generally follow the patterns of net surface solar flux. The monthly snow water equivalent (SWE) deviations show an increase in lower elevations due to reduced snowmelt, leading to a reduction in cumulative runoff. Over higher elevation areas, negative SWE deviations are found because of increased solar radiation available at the surface. Simulated precipitation increases for lower elevations, while decreases for higher elevations with a minimum in April. Liquid runoff significantly decreases in higher elevations after April due to reduced SWE and precipitation.
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Nieto-Reyes, Alicia. "On the Non-Gaussianity of Sea Surface Elevations." Journal of Marine Science and Engineering 10, no. 9 (September 15, 2022): 1303. http://dx.doi.org/10.3390/jmse10091303.
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The sea surface elevations are generally stated as non-Gaussian processes in the current literature, being considered Gaussian for short periods of relatively low wave heights. The objective here is to study the evolution of the distribution of the sea surface elevation from Gaussian to non-Gaussian as the period of time in which the associated time series is recorded increases. To do this, an empirical study based on the measurements of the buoys in the US coast downloaded at a casual day is performed. This study results in rejecting the null hypothesis of Gaussianity in below 25% of the cases for short periods of time and in over 95% of the cases for long periods of time. The analysis pursued relates to a recent one by the author in which the heights of sea waves are proved to be non-Gaussian. It is similar in that the Gaussianity of the process is studied as a whole and not just of its one-dimensional marginal, as it is common in the literature. It differs, however, in that the analysis of the sea surface elevations is harder from a statistical point of view, as the one-dimensional marginals can be Gaussian, which is observed throughout the study and in that a longitudinal study is performed here.
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Racoviteanu, Adina E., Yves Arnaud, Mark W. Williams, and Julio Ordoñez. "Decadal changes in glacier parameters in the Cordillera Blanca, Peru, derived from remote sensing." Journal of Glaciology 54, no. 186 (2008): 499–510. http://dx.doi.org/10.3189/002214308785836922.
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AbstractWe present spatial patterns of glacier fluctuations from the Cordillera Blanca, Peru, (glacier area, terminus elevations, median elevations and hypsography) at decadal timescales derived from 1970 aerial photography, 2003 SPOT5 satellite data, Geographic Information Systems (GIS) and statistical analyses. We derived new glacier outlines from the 2003 SPOT images, and ingested them in the Global Land and Ice Measurements from Space (GLIMS) glacier database. We examined changes in glacier area on the eastern and western side of the Cordillera in relation to topographic and climate variables (temperature and precipitation). Results include (1) an estimated glacierized area of 569.6 ± 21 km2 in 2003, (2) an overall loss in glacierized area of 22.4% from 1970 to 2003, (3) an average rise in glacier terminus elevations by 113 m and an average rise in the median elevation of glaciers by 66 m, showing a shift of ice to higher elevations, especially on the eastern side of the Cordillera, and (4) an increase in the number of glaciers, which indicates disintegration of ice bodies. Annual air temperature showed a significant upward trend in the last 30 years, with larger temperature increases at lower elevations. There was a slight but not significant decrease in precipitation. Our results are consistent with glacier retreat and warming trends noted in the last three decades in the tropics.
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Babonis, G. S., B. Csatho, and T. Schenk. "MASS BALANCE CHANGES AND ICE DYNAMICS OF GREENLAND AND ANTARCTIC ICE SHEETS FROM LASER ALTIMETRY." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B8 (June 23, 2016): 481–87. http://dx.doi.org/10.5194/isprs-archives-xli-b8-481-2016.
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During the past few decades the Greenland and Antarctic ice sheets have lost ice at accelerating rates, caused by increasing surface temperature. The melting of the two big ice sheets has a big impact on global sea level rise. If the ice sheets would melt down entirely, the sea level would rise more than 60 m. Even a much smaller rise would cause dramatic damage along coastal regions. In this paper we report about a major upgrade of surface elevation changes derived from laser altimetry data, acquired by NASA’s Ice, Cloud and land Elevation Satellite mission (ICESat) and airborne laser campaigns, such as Airborne Topographic Mapper (ATM) and Land, Vegetation and Ice Sensor (LVIS). For detecting changes in ice sheet elevations we have developed the Surface Elevation Reconstruction And Change detection (SERAC) method. It computes elevation changes of small surface patches by keeping the surface shape constant and considering the absolute values as surface elevations. We report about important upgrades of earlier results, for example the inclusion of local ice caps and the temporal extension from 1993 to 2014 for the Greenland Ice Sheet and for a comprehensive reconstruction of ice thickness and mass changes for the Antarctic Ice Sheets.
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Babonis, G. S., B. Csatho, and T. Schenk. "MASS BALANCE CHANGES AND ICE DYNAMICS OF GREENLAND AND ANTARCTIC ICE SHEETS FROM LASER ALTIMETRY." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B8 (June 23, 2016): 481–87. http://dx.doi.org/10.5194/isprsarchives-xli-b8-481-2016.
Full textAbstract:
During the past few decades the Greenland and Antarctic ice sheets have lost ice at accelerating rates, caused by increasing surface temperature. The melting of the two big ice sheets has a big impact on global sea level rise. If the ice sheets would melt down entirely, the sea level would rise more than 60 m. Even a much smaller rise would cause dramatic damage along coastal regions. In this paper we report about a major upgrade of surface elevation changes derived from laser altimetry data, acquired by NASA’s Ice, Cloud and land Elevation Satellite mission (ICESat) and airborne laser campaigns, such as Airborne Topographic Mapper (ATM) and Land, Vegetation and Ice Sensor (LVIS). For detecting changes in ice sheet elevations we have developed the Surface Elevation Reconstruction And Change detection (SERAC) method. It computes elevation changes of small surface patches by keeping the surface shape constant and considering the absolute values as surface elevations. We report about important upgrades of earlier results, for example the inclusion of local ice caps and the temporal extension from 1993 to 2014 for the Greenland Ice Sheet and for a comprehensive reconstruction of ice thickness and mass changes for the Antarctic Ice Sheets.
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Fuentes, Padarian, van Ogtrop, and Vervoort. "Comparison of Surface Water Volume Estimation Methodologies that Couple Surface Reflectance Data and Digital Terrain Models." Water 11, no. 4 (April 15, 2019): 780. http://dx.doi.org/10.3390/w11040780.
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Uncertainty about global change requires alternatives to quantify the availability of water resources and their dynamics. A methodology based on different satellite imagery and surface elevation models to estimate surface water volumes would be useful to monitor flood events and reservoir storages. In this study, reservoirs with associated digital terrain models (DTM) and continuously monitored volumes were selected. The inundated extent was based on a supervised classification using surface reflectance in Landsat 5 images. To estimate associated water volumes, the DTMs were sampled at the perimeter of inundated areas and an inverse distance weighting interpolation was used to populate the water elevation inside the flooded polygons. The developed methodology (IDW) was compared against different published methodologies to estimate water volumes from digital elevation models, which assume either a flat water surface using the maximum elevation of inundated areas (Max), and a flat water surface using the median elevation of the perimeter of inundated areas (Median), or a tilted surface, where water elevations are based on an iterative focal maximum statistic with increasing window sizes (FwDET), and finally a tilted water surface obtained by replacing the focal maximum statistic from the FwDET methodology with a focal mean statistic (FwDET_mean). Volume estimates depend strongly on both water detection and the terrain model. The Max and the FwDET methodologies are highly affected by the water detection step, and the FwDET_mean methodology leads to lower volume estimates due to the iterative smoothing of elevations, which also tends to be computationally expensive for big areas. The Median and IDW methodologies outperform the rest of the methods, and IDW can be used for both reservoir and flood volume monitoring. Different sources of error can be observed, being systematic errors associated with the DTM acquisition time and the reported volumes, which for example fail to consider dynamic sedimentation processes taking place in reservoirs. Resolution effects account for a fraction of errors, being mainly caused by terrain curvature.
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Lee, W. L., Y. Gu, K. N. Liou, L. R. Leung, and H. H. Hsu. "A global model simulation for 3-D radiative transfer impact on surface hydrology over the Sierra Nevada and Rocky Mountains." Atmospheric Chemistry and Physics 15, no. 10 (May 19, 2015): 5405–13. http://dx.doi.org/10.5194/acp-15-5405-2015.
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Abstract. We investigate 3-D mountain effects on solar flux distributions and their impact on surface hydrology over the western United States, specifically the Rocky Mountains and the Sierra Nevada, using the global CCSM4 (Community Climate System Model version 4; Community Atmosphere Model/Community Land Model – CAM4/CLM4) with a 0.23° × 0.31° resolution for simulations over 6 years. In a 3-D radiative transfer parameterization, we have updated surface topography data from a resolution of 1 km to 90 m to improve parameterization accuracy. In addition, we have also modified the upward-flux deviation (3-D–PP (plane-parallel)) adjustment to ensure that the energy balance at the surface is conserved in global climate simulations based on 3-D radiation parameterization. We show that deviations in the net surface fluxes are not only affected by 3-D mountains but also influenced by feedbacks of cloud and snow in association with the long-term simulations. Deviations in sensible heat and surface temperature generally follow the patterns of net surface solar flux. The monthly snow water equivalent (SWE) deviations show an increase in lower elevations due to reduced snowmelt, leading to a reduction in cumulative runoff. Over higher-elevation areas, negative SWE deviations are found because of increased solar radiation available at the surface. Simulated precipitation increases for lower elevations, while it decreases for higher elevations, with a minimum in April. Liquid runoff significantly decreases at higher elevations after April due to reduced SWE and precipitation.
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Bindschadler, R. A., and H. J. Zwally. "Surface Topography of the Greenland Ice Sheet by Satellite Radar Altimetry (Abstract)." Annals of Glaciology 8 (1986): 196. http://dx.doi.org/10.3189/s0260305500001452.
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A map of the surface elevation for the southern half of the Greenland ice sheet has been produced from data gathered by the radar altimeter on board the SEASAT satellite. From June 1978 until September 1978, useful data were collected during most passes over the ice sheet, but data was not collected continuously along each pass. Over 85 000 separate ranges were obtained from the satellite to the surface at points spaced 662 m apart along each orbital pass.Techniques required for the reduction of the recorded return waveforms to surface elevations have previously been described in a series of papers (Martin and others, 1983; Brenner and others, 1983; and Zwally and others, 1983). Once all corrections have been applied to the range data due to atmospheric effects, ocean and earth tides, and orbital perturbations, the set of ranges at orbital crossing points (where ascending orbits crossed descending orbits) had a mean relative error of 2.9 m, with a standard deviation of ±2.9 m. Elevations over the flatter and smoother portions of the ice sheet have a precision as small as ±0.25 m, while data over sloping and rough areas are of lower quality. Along each orbital track, the data are corrected for the slope-induced error.The reduced set of surface elevations has been interpolated to assigned elevation values at the nodal points of a regular grid with a 10 km spacing (polar stereographic projection). This grid was then contoured at intervals of 50 m above 2400 m altitude and 100 m at lower elevations. Similar grids of slope-induced error corrections were contoured to provide some measure of its effect on the data. Ancillary plots of parameters of the fitting and gridding process are included to help in estimating the quality of the derived surface topography in different regions.The surface elevation contour map shows the existence of distinct drainage basins within the ice sheet — most notably in the southern and eastern areas. This detail will prove most useful in the delineation of these basins for hydrological or glaciological studies. In combination with ice-thickness data, these elevation data permit a more accurate measurement of the bedrock elevation. The corrected altimeter data in orbital-pass and map format have been provided to the National Space Science Data Center at Goddard Space Flight Center and to the World Data Center-A, Glaciology, as a source of information to be used by other scientific investigators. These data have already been used to produce detailed maps of the topography in more localized areas (e.g. Figure 2, from Zwally and others, 1983 and Figure 2 of Bindschadler, 1984).
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Bindschadler, R. A., and H. J. Zwally. "Surface Topography of the Greenland Ice Sheet by Satellite Radar Altimetry (Abstract)." Annals of Glaciology 8 (1986): 196. http://dx.doi.org/10.1017/s0260305500001452.
Full textAbstract:
A map of the surface elevation for the southern half of the Greenland ice sheet has been produced from data gathered by the radar altimeter on board the SEASAT satellite. From June 1978 until September 1978, useful data were collected during most passes over the ice sheet, but data was not collected continuously along each pass. Over 85 000 separate ranges were obtained from the satellite to the surface at points spaced 662 m apart along each orbital pass. Techniques required for the reduction of the recorded return waveforms to surface elevations have previously been described in a series of papers (Martin and others, 1983; Brenner and others, 1983; and Zwally and others, 1983). Once all corrections have been applied to the range data due to atmospheric effects, ocean and earth tides, and orbital perturbations, the set of ranges at orbital crossing points (where ascending orbits crossed descending orbits) had a mean relative error of 2.9 m, with a standard deviation of ±2.9 m. Elevations over the flatter and smoother portions of the ice sheet have a precision as small as ±0.25 m, while data over sloping and rough areas are of lower quality. Along each orbital track, the data are corrected for the slope-induced error. The reduced set of surface elevations has been interpolated to assigned elevation values at the nodal points of a regular grid with a 10 km spacing (polar stereographic projection). This grid was then contoured at intervals of 50 m above 2400 m altitude and 100 m at lower elevations. Similar grids of slope-induced error corrections were contoured to provide some measure of its effect on the data. Ancillary plots of parameters of the fitting and gridding process are included to help in estimating the quality of the derived surface topography in different regions. The surface elevation contour map shows the existence of distinct drainage basins within the ice sheet — most notably in the southern and eastern areas. This detail will prove most useful in the delineation of these basins for hydrological or glaciological studies. In combination with ice-thickness data, these elevation data permit a more accurate measurement of the bedrock elevation. The corrected altimeter data in orbital-pass and map format have been provided to the National Space Science Data Center at Goddard Space Flight Center and to the World Data Center-A, Glaciology, as a source of information to be used by other scientific investigators. These data have already been used to produce detailed maps of the topography in more localized areas (e.g. Figure 2, from Zwally and others, 1983 and Figure 2 of Bindschadler, 1984).
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Muskett, Reginald R., Craig S. Lingle, Jeanne M. Sauber, Austin S. Post, Wendell V. Tangborn, Bernhard T. Rabus, and Keith A. Echelmeyer. "Airborne and spaceborne DEM- and laser altimetry-derived surface elevation and volume changes of the Bering Glacier system, Alaska, USA, and Yukon, Canada, 1972–2006." Journal of Glaciology 55, no. 190 (2009): 316–26. http://dx.doi.org/10.3189/002214309788608750.
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AbstractUsing airborne and spaceborne high-resolution digital elevation models and laser altimetry, we present estimates of interannual and multi-decadal surface elevation changes on the Bering Glacier system, Alaska, USA, and Yukon, Canada, from 1972 to 2006. We find: (1) the rate of lowering during 1972–95 was 0.9 ± 0.1 m a−1; (2) this rate accelerated to 3.0 ± 0.7 m a−1 during 1995–2000; and (3) during 2000–03 the lowering rate was 1.5 ± 0.4 m a−1. From 1972 to 2003, 70% of the area of the system experienced a volume loss of 191 ± 17 km3, which was an area-average surface elevation lowering of 1.7 ± 0.2 m a−1. From November 2004 to November 2006, surface elevations across Bering Glacier, from McIntosh Peak on the south to Waxell Ridge on the north, rose as much as 53 m. Up-glacier on Bagley Ice Valley about 10 km east of Juniper Island nunatak, surface elevations lowered as much as 28 m from October 2003 to October 2006. NASA Terra/MODIS observations from May to September 2006 indicated muddy outburst floods from the Bering terminus into Vitus Lake. This suggests basal–englacial hydrologic storage changes were a contributing factor in the surface elevation changes in the fall of 2006.
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Horton, S., M. Schirmer, and B. Jamieson. "Meteorological, elevation, and slope effects on surface hoar formation." Cryosphere Discussions 9, no. 2 (March 23, 2015): 1857–85. http://dx.doi.org/10.5194/tcd-9-1857-2015.
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Abstract. Failure in layers of buried surface hoar crystals (frost) can cause hazardous snow slab avalanches. Surface hoar crystals form on the snow surface and are sensitive to micro-meteorological conditions. In this study, the role of meteorological and terrain factors were investigated for three surface hoar layers in the Columbia Mountains of Canada. The distribution of crystals was observed over different elevations and aspects during 20 days of field observations. The same layers were modelled on a 2.5 km horizontal grid by forcing the snow cover model SNOWPACK with forecast weather data from a numerical weather prediction model. The moisture content of the air (i.e. absolute humidity) had the largest impact on modelled surface hoar growth, with warm and moist air being favourable. Surface hoar was most developed at certain elevation bands, usually corresponding to elevations with warm humid air, light winds, and cold surface temperatures. SNOWPACK simulations on virtual slopes systematically predicted smaller surface hoar on south-facing slopes. In the field, a complex combination of surface hoar and sun crusts were observed, suggesting the model did not adequately resolve the surface energy balance on slopes. Overall, a coupled weather–snow cover model could benefit avalanche forecasters by predicting surface hoar layers on a regional scale over different elevation bands.
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Grice, J. R., P. H. Taylor, and R. Eatock Taylor. "Second-order statistics and ‘designer’ waves for violent free-surface motion around multi-column structures." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, no. 2033 (January 28, 2015): 20140113. http://dx.doi.org/10.1098/rsta.2014.0113.
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Extreme wave–structure interactions are investigated using second-order diffraction theory. The statistics of surface elevation around a multi-column structure are collected using Monte Carlo-type simulations for severe sea states. Within the footprint of a realistic four-column structure, we find that the presence of the structure can give rise to extreme crest elevations greater than twice those at the same return period in the incident wave field. Much of this extra elevation is associated with the excitation of second-order near-trapped modes. A ‘designer’ incident wave can be defined at each point around the structure for a given sea state as the average input wave to produce extreme crest elevations at a given return period, and we show that this wave can be simply vertically scaled to estimate the response at other return periods.
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Neves, Diogo R. C. B., Moisés Brito, António Alberto Pires-Silva, Conceição Juana Fortes, and Jorge Matos. "Experimental Investigation of Air Bubble Curtain Effects on Water Wave Field." Defect and Diffusion Forum 415 (April 27, 2022): 81–99. http://dx.doi.org/10.4028/p-9jm010.
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This paper studies the effects of an air bubble curtain on surface water waves. Water particle velocities and free surface elevations were measured simultaneously at two cross-shore locations downstream of the air bubble curtain. Measurements were carried out for regular waves using different air bubble curtain configurations. Free surface elevations were measured using resistive gauges and the instantaneous velocities were acquired using an Acoustic Doppler Velocimeter (ADV). The characteristics of the free surface elevation time series, velocity field and turbulence are analyzed and discussed. The free surface elevation was found to be attenuated by the air bubble curtains. The phase averaged velocity profiles also depict the effect of the air bubbles in the flow field by generating milder longitudinal velocities (u) and by increasing the transverse component of the velocity (w). The increase in the turbulence intensity and the different energy spectrum produced by the air bubble curtain is also observed. The experimental results indicate that the thickness of the air bubble curtain and the total air flow rate affects the wave field.
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Nilsson, Johan, Alex Gardner, Louise Sandberg Sørensen, and Rene Forsberg. "Improved retrieval of land ice topography from CryoSat-2 data and its impact for volume-change estimation of the Greenland Ice Sheet." Cryosphere 10, no. 6 (December 1, 2016): 2953–69. http://dx.doi.org/10.5194/tc-10-2953-2016.
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Abstract. A new methodology for retrieval of glacier and ice sheet elevations and elevation changes from CryoSat-2 data is presented. Surface elevations and elevation changes determined using this approach show significant improvements over ESA's publicly available CryoSat-2 elevation product (L2 Baseline-B). The results are compared to near-coincident airborne laser altimetry from NASA's Operation IceBridge and seasonal height amplitudes from the Ice, Cloud, and Elevation Satellite (ICESat). Applying this methodology to CryoSat-2 data collected in interferometric synthetic aperture mode (SIN) over the high-relief regions of the Greenland Ice Sheet we find an improvement in the root-mean-square error (RMSE) of 27 and 40 % compared to ESA's L2 product in the derived elevation and elevation changes, respectively. In the interior part of the ice sheet, where CryoSat-2 operates in low-resolution mode (LRM), we find an improvement in the RMSE of 68 and 55 % in the derived elevation and elevation changes, respectively. There is also an 86 % improvement in the magnitude of the seasonal amplitudes when compared to amplitudes derived from ICESat data. These results indicate that the new methodology provides improved tracking of the snow/ice surface with lower sensitivity to changes in near-surface dielectric properties. To demonstrate the utility of the new processing methodology we produce elevations, elevation changes, and total volume changes from CryoSat-2 data for the Greenland Ice Sheet during the period January 2011 to January 2015. We find that the Greenland Ice Sheet decreased in volume at a rate of 289 ± 20 km3a−1, with high interannual variability and spatial heterogeneity in rates of loss. This rate is 65 km3a−1 more negative than rates determined from ESA's L2 product, highlighting the importance of CryoSat-2 processing methodologies.
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POLIDORI, Laurent, Carlos Rodrigo Tanajura CALDEIRA, Maël SMESSAERT, and Mhamad EL HAGE. "Digital elevation modeling through forests: the challenge of the Amazon." Acta Amazonica 52, no. 1 (January 2022): 69–80. http://dx.doi.org/10.1590/1809-4392202103091.
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ABSTRACT Elevation mapping at ground level is challenging in forested areas like the Amazon region, which is mostly covered by dense rainforest. The most common techniques, i.e. photogrammetry and short wavelength radar, provide elevations at canopy level at best, while most applications require ground elevations. Even lidar and P-band radar, which can penetrate foliage and measure elevations at ground level, have some limitations which are analyzed in here. We address three research questions: To what extent can a terrain model be replaced by a more easily available canopy-level surface model for topography-based applications? How can the elevation be obtained at ground level through forest? Can a priori knowledge of general continental relief properties be used to compensate for the limits of measurement methods in the presence of forest?
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Fyfe, John C., and Gregory M. Flato. "Enhanced Climate Change and Its Detection over the Rocky Mountains." Journal of Climate 12, no. 1 (January 1, 1999): 230–43. http://dx.doi.org/10.1175/1520-0442-12.1.230.
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Abstract Results from an ensemble of climate change experiments with increasing greenhouse gas and aerosols using the Canadian Centre for Climate Modelling and Analysis Coupled Climate Model are presented with a focus on surface quantities over the Rocky Mountains. There is a marked elevation dependency of the simulated surface screen temperature increase over the Rocky Mountains in the winter and spring seasons, with more pronounced changes at higher elevations. The elevation signal is linked to a rise in the snow line in the winter and spring seasons, which amplifies the surface warming via the snow-albedo feedback. Analysis of the winter surface energy budget shows that large changes in the solar component of the radiative input are the direct consequence of surface albedo changes caused by decreasing snow cover. Although the warming signal is enhanced at higher elevations, a two-way analysis of variance reveals that the elevation effect has no potential for early climate change detection. In the early stages of surface warming the elevation effect is masked by relatively large noise, so that the signal-to-noise ratio over the Rocky Mountains is no larger than elsewhere. Only after significant continental-scale warming does the local Rocky Mountain signal begin to dominate the pattern of climate change over western North America (and presumably also the surrounding ecosystems and hydrological networks).
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Du, Weibing, Ningke Shi, Linjuan Xu, Shiqiong Zhang, Dandan Ma, and Shuangting Wang. "Monitoring the Spatiotemporal Difference in Glacier Elevation on Bogda Mountain from 2000 to 2017." International Journal of Environmental Research and Public Health 18, no. 12 (June 12, 2021): 6374. http://dx.doi.org/10.3390/ijerph18126374.
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The difference in glacier surface elevation is a sensitive indicator of climate change and is also important for disaster warning and water supply. In this paper, 25 glaciers on Bogda Mountain, in the eastern Tianshan Mountains, are selected as the study object as they are typical of glaciers in arid or semi-arid areas with importance for water supply. The Repeat Orbit Interferometry (ROI) method is used to survey the surface elevation of these glaciers using Sentinel-1A Radar data from 2017. Using data from the Shuttle Radar Topography Mission (SRTM) and a Digital Elevation Model (DEM), the difference in the glacier surface elevation between 2000 and 2017 is obtained. A scheme to evaluate the accuracy of estimated variations in glacier surface elevation is proposed in this article. By considering the surfaces of lakes in the study region as ideal horizontal planes, the average standard deviation (SD) value of the lake elevation is taken as the error caused by the radar sensor and observing conditions. The SD of the lake elevation is used as an index to evaluate the error in the estimated variation of the glacier surface elevation, and the obtained SD values indicate that the result obtained using the ROI method is reliable. Additionally, the glacier surface elevation variation pattern and a Logarithmic Fitting Model (LFM) are used to reduce the error in high-altitude glacial accumulation areas to improve the estimation of the difference in the glacier surface elevation obtained using ROI. The average SD of the elevation of the 12 lakes is ±2.87 m, which shows that the obtained glacier surface elevations are reliable. This article concludes that, between 2000 and 2017, the surface elevation of glaciers on Bogda Mountain decreased by an average of 11.6 ± 1.3 m, corresponding to an average decrease rate of 0.68 m/a, and glaciers volume decreased by an average of 0.504 km3. Meanwhile, the surface elevations of the lakes increased by an average of 8.16 m. The decrease of glacier surface elevation leads to the expansion of glacial lakes. From the north slope clockwise to the south slope, the glacier elevation variation showed a decreasing trend, and the elevation variation gradually increased from the south slope to the north slope. With the increase of glacier altitude, the variation of glacier surface elevation gradually changed from negative to positive. The findings of this article suggest that the rate of glacier retreat on Bogda Mountain increased from 2000 to 2017.
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Zapevalov, A. S. "High-order cumulants of sea surface elevations." Russian Meteorology and Hydrology 36, no. 9 (September 2011): 624–29. http://dx.doi.org/10.3103/s1068373911090081.
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Horton, S., M. Schirmer, and B. Jamieson. "Meteorological, elevation, and slope effects on surface hoar formation." Cryosphere 9, no. 4 (August 7, 2015): 1523–33. http://dx.doi.org/10.5194/tc-9-1523-2015.
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Abstract. Failure in layers of buried surface hoar crystals (frost) can cause hazardous snow slab avalanches. Surface hoar crystals form on the snow surface and are sensitive to micro-meteorological conditions. In this study, the role of meteorological and terrain factors was investigated for three layers of surface hoar in the Columbia Mountains of Canada. The distribution of crystals over different elevations and aspects was observed on 20 days of field observations during a period of high pressure. The same layers were modelled over simplified terrain on a 2.5 km horizontal grid by forcing the snow cover model SNOWPACK with forecast weather data from a numerical weather prediction model. Modelled surface hoar growth was associated with warm air temperatures, high humidity, cold surface temperatures, and low wind speeds. Surface hoar was most developed in regions and elevation bands where these conditions existed, although strong winds at high elevations caused some model discrepancies. SNOWPACK simulations on virtual slopes systematically predicted smaller surface hoar on south-facing slopes. In the field, a complex combination of surface hoar and sun crusts were observed, suggesting the simplified model did not adequately resolve the surface energy balance on slopes. Overall, a coupled weather–snow cover model could benefit avalanche forecasters by predicting surface hoar layers on a regional scale over different elevation bands.
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Emery, Charlotte Marie, Sylvain Biancamaria, Aaron Boone, Sophie Ricci, Mélanie C. Rochoux, Vanessa Pedinotti, and Cédric H. David. "Assimilation of wide-swath altimetry water elevation anomalies to correct large-scale river routing model parameters." Hydrology and Earth System Sciences 24, no. 5 (May 6, 2020): 2207–33. http://dx.doi.org/10.5194/hess-24-2207-2020.
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Abstract. Land surface models combined with river routing models are widely used to study the continental part of the water cycle. They give global estimates of water flows and storages, but they are not without non-negligible uncertainties, among which inexact input parameters play a significant part. The incoming Surface Water and Ocean Topography (SWOT) satellite mission, with a launch scheduled for 2021 and with a required lifetime of at least 3 years, will be dedicated to the measuring of water surface elevations, widths and surface slopes of rivers wider than 100 m, at a global scale. SWOT will provide a significant number of new observations for river hydrology and maybe combined, through data assimilation, with global-scale models in order to correct their input parameters and reduce their associated uncertainty. Comparing simulated water depths with measured water surface elevations remains however a challenge and can introduce within the system large bias. A promising alternative for assimilating water surface elevations consists of assimilating water surface elevation anomalies which do not depend on a reference surface. The objective of this study is to present a data assimilation platform based on the asynchronous ensemble Kalman filter (AEnKF) that can assimilate synthetic SWOT observations of water depths and water elevation anomalies to correct the input parameters of a large-scale hydrologic model over a 21 d time window. The study is applied to the ISBA-CTRIP model over the Amazon basin and focuses on correcting the spatial distribution of the river Manning coefficients. The data assimilation algorithm, tested through a set of observing system simulation experiments (OSSEs), is able to retrieve the true value of the Manning coefficients within one assimilation cycle much of the time (basin-averaged Manning coefficient root mean square error, RMSEn, is reduced from 33 % to [1 %–10 %] after one assimilation cycle) and shows promising perspectives with assimilating water anomalies (basin-averaged Manning coefficient RMSEn is reduced from 33 % to [1 %–2 %] when assimilating water surface elevation anomalies over 1 year), which allows us to overcome the issue of unknown bathymetry.
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Higham, Martin, Mike Craven, Andrew Ruddell, and Ian Allison. "Snow-accumulation distribution in the interior of the Lambert Glacier basin, Antarctica." Annals of Glaciology 25 (1997): 412–17. http://dx.doi.org/10.3189/s0260305500014373.
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A prime input variable to uncoupled ice-sheet models, or for estimating the mass budget of present-day ice sheets, is the distribution of net surface mass balance. In most eases this is extrapolated from relatively few direct measurements over a limited time period, and parameterised in terms of continentality, surface elevation and other broad-scale indicators. Between 1989 and 1995 a series of oversnow traverses around the interior of the Lambert Glacier basin gathered a comprehensive set of data on snow accumulation and surface properties, surface climatology, ice-sheet velocities, elevations and thicknesses. Above the 2000 m level accumulation averages were found to be 76 kg ma−2a−1 (σ = 74), much lower than at similar elevations in Wilkes Land. The traverse route contains three distinct accumulation regimes: a relatively high accumulation zone along the western side despite higher average elevations, a very low accumulation zone in the south due to the effect of inereased continentality and an eastern sector that exhibits a rain-shadow effect in predominantly easterly wind fields. Inter-annual variability is high- with 1993 a colder year, recording only half the longer term average accumulation over the portion of the route that was measured.
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Higham, Martin, Mike Craven, Andrew Ruddell, and Ian Allison. "Snow-accumulation distribution in the interior of the Lambert Glacier basin, Antarctica." Annals of Glaciology 25 (1997): 412–17. http://dx.doi.org/10.1017/s0260305500014373.
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A prime input variable to uncoupled ice-sheet models, or for estimating the mass budget of present-day ice sheets, is the distribution of net surface mass balance. In most eases this is extrapolated from relatively few direct measurements over a limited time period, and parameterised in terms of continentality, surface elevation and other broad-scale indicators. Between 1989 and 1995 a series of oversnow traverses around the interior of the Lambert Glacier basin gathered a comprehensive set of data on snow accumulation and surface properties, surface climatology, ice-sheet velocities, elevations and thicknesses. Above the 2000 m level accumulation averages were found to be 76 kg ma−2a−1(σ= 74), much lower than at similar elevations in Wilkes Land. The traverse route contains three distinct accumulation regimes: a relatively high accumulation zone along the western side despite higher average elevations, a very low accumulation zone in the south due to the effect of inereased continentality and an eastern sector that exhibits a rain-shadow effect in predominantly easterly wind fields. Inter-annual variability is high- with 1993 a colder year, recording only half the longer term average accumulation over the portion of the route that was measured.
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Dyke, Arthur S., Lynda A. Dredge, and Douglas A. Hodgson. "North American Deglacial Marine- and Lake-Limit Surfaces*." Géographie physique et Quaternaire 59, no. 2-3 (April 4, 2007): 155–85. http://dx.doi.org/10.7202/014753ar.
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Abstract The deglacial marine-limit surface is a virtual topography that shows the increase of elevation since deglaciation. The currently available set of marine-limit elevations (n = 929), about three times the number available in the most recent synthesis, allows a fairly detailed rendering of the surface across most of glaciated North America and Greenland. Certain large glacial lake-limit surfaces are analogous to marine-limit surfaces, except that their gradients were not dampened by eustatic sea-level rise. Collectively the surfaces reflect both gross ice-sheet geometry and regional to local rates of ice-marginal recession. As such, they are replication targets for glacioisostatic modelling that are supplementary to and more continuously distributed than relative sea-level curves.
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Khanal, Mandar, Mahamudul Hasan, Nikolaus Sterbentz, Ryen Johnson, and Jesse Weatherly. "Accuracy Comparison of Aerial Lidar, Mobile-Terrestrial Lidar, and UAV Photogrammetric Capture Data Elevations over Different Terrain Types." Infrastructures 5, no. 8 (July 31, 2020): 65. http://dx.doi.org/10.3390/infrastructures5080065.
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Lidar and other remotely sensed data such as UAV photogrammetric data capture are being collected and utilized for roadway design on an increasing basis. These methods are desirable over conventional survey due to their efficiency and cost-effectiveness over large areas. A high degree of relative accuracy is achievable through the establishment of survey control. In this case study, elevations (z-values) derived from mobile-terrestrial lidar, aerial lidar, and UAV photogrammetric capture collected with survey control were statistically compared to conventionally surveyed elevations. A cost comparison of the methods is also included. Each set of z-values corresponds to a discrete horizontal point originally part of the conventional survey, collected as cross-sections. These cross-sections were surveyed at three approximate tenth-mile sample locations along US-30 near Georgetown, Idaho. The cross-sections were collected as elevational accuracy verification, and each sample location was selected as an area where the mobile-terrestrial lidar in particular was expected to have more difficulty achieving accuracy off the road surface. Processing and analysis were performed in Esri ArcMap 10.6, and all data were obtained from the Idaho Transportation Department, District 5. Overall, the aerial lidar elevations were found to be closest to conventionally surveyed elevations; on road surface and level terrain, mobile-terrestrial and UAV photogrammetric capture elevations were closer to the conventionally measured elevations.
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Vincent, Christian, Adrien Gilbert, Bruno Jourdain, Luc Piard, Patrick Ginot, Vladimir Mikhalenko, Philippe Possenti, Emmanuel Le Meur, Olivier Laarman, and Delphine Six. "Strong changes in englacial temperatures despite insignificant changes in ice thickness at Dôme du Goûter glacier (Mont Blanc area)." Cryosphere 14, no. 3 (March 12, 2020): 925–34. http://dx.doi.org/10.5194/tc-14-925-2020.
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Abstract. The response of very-high-elevation glaciated areas on Mont Blanc to climate change has been analysed using observations and numerical modelling over the last 2 decades. Unlike the changes at low elevations, we observe very low glacier thickness changes, of about −2.6 m on average since 1993. The slight changes in horizontal ice flow velocities and submergence velocities suggest a decrease of about 10 % in ice flux and surface mass balance. This is due to less snow accumulation and is consistent with the precipitation decrease observed in meteorological data. Conversely, measurements performed in deep boreholes since 1994 reveal strong changes in englacial temperature reaching a 1.5 ∘C increase at a depth of 50 m. We conclude that at such very high elevations, current changes in climate do not lead to visible changes in glacier thickness but cause invisible changes within the glacier in terms of englacial temperatures. Our analysis from numerical modelling shows that glacier near-surface temperature warming is enhanced by increasing melt frequency at high elevations although the impact on surface mass balance is low. This results in a non-linear response of englacial temperature to currently rising air temperatures. In addition, borehole temperature inversion including a new dataset confirms previous findings of similar air temperature changes at high and low elevations in the Alps.
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Abolins, Mark, and Albert Ogden. "Application of the global SRTM and AW3D30 digital elevation models to mapping folds at cave sites." International Journal of Speleology 50, no. 1 (January 2021): 75–89. http://dx.doi.org/10.5038/1827-806x.50.1.2338.
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A novel method to map and quantitatively describe very gentle folds (limb dip <5°) at cratonic cave sites was evaluated at Snail Shell and Nanna caves, central Tennessee, USA. Elevations from the global SRTM digital terrain model (DTM) were assigned to points on late Ordovician geologic contacts, and the elevations of the points were used to interpolate 28 m cell size natural neighbor digital elevation models (DEM’s) of the contacts. The global Forest Canopy Height Dataset was subtracted from the global 28 m cell size AW3D30 digital surface model (DSM) to create a DTM, and that DTM was applied in the same way. Comparison of mean and modal strikes of the interpolated surfaces with mean and modal cave passage trend shows that many passages are sub-parallel to the trend of an anticline. WithiSn 500 m of the caves, the SRTM- and AW3D30-based interpolated surfaces have mean strikes within 8° of the mean strike of an interpolated reference surface created with a high resolution (~0.76 m cell size and 10 cm RMSE) Tennessee, USA LiDAR DTM. This evaluation shows that the SRTM- and AW3D30-based method has the potential to reveal a relationship between the trend of a fold, on one hand, and cave passages, on the other, at sites where a geologic contact varies in elevation by >35 m within an area of <12.4 km2 and the mean dip of bedding is >0.9°.
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Osama, Nahed, Bisheng Yang, Yue Ma, and Mohamed Freeshah. "A Digital Terrain Modeling Method in Urban Areas by the ICESat-2 (Generating precise terrain surface profiles from photon-counting technology)." Photogrammetric Engineering & Remote Sensing 87, no. 4 (April 1, 2021): 237–48. http://dx.doi.org/10.14358/pers.87.4.237.
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The ICE, Cloud and land Elevation Satellite-2 (ICES at-2) can provide new measurements of the Earth's elevations through photon-counting technology. Most research has focused on extracting the ground and the canopy photons in vegetated areas. Yet the extraction of the ground photons from urban areas, where the vegetation is mixed with artificial constructions, has not been fully investigated. This article proposes a new method to estimate the ground surface elevations in urban areas. The ICES at-2 signal photons were detected by the improved Density-Based Spatial Clustering of Applications with Noise algorithm and the Advanced Topographic Laser Altimeter System algorithm. The Advanced Land Observing Satellite-1 PALSAR –derived digital surface model has been utilized to separate the terrain surface from the ICES at-2 data. A set of ground-truth data was used to evaluate the accuracy of these two methods, and the achieved accuracy was up to 2.7 cm, which makes our method effective and accurate in determining the ground elevation in urban scenes.
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Bindschadler, R., H. Choi, A. Wichlacz, R. Bingham, J. Bohlander, K. Brunt, H. Corr, et al. "Getting around Antarctica: new high-resolution mappings of the grounded and freely-floating boundaries of the Antarctic ice sheet created for the International Polar Year." Cryosphere 5, no. 3 (July 18, 2011): 569–88. http://dx.doi.org/10.5194/tc-5-569-2011.
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Abstract. Two ice-dynamic transitions of the Antarctic ice sheet – the boundary of grounded ice features and the freely-floating boundary – are mapped at 15-m resolution by participants of the International Polar Year project ASAID using customized software combining Landsat-7 imagery and ICESat/GLAS laser altimetry. The grounded ice boundary is 53 610 km long; 74 % abuts to floating ice shelves or outlet glaciers, 19 % is adjacent to open or sea-ice covered ocean, and 7 % of the boundary ice terminates on land. The freely-floating boundary, called here the hydrostatic line, is the most landward position on ice shelves that expresses the full amplitude of oscillating ocean tides. It extends 27 521 km and is discontinuous. Positional (one-sigma) accuracies of the grounded ice boundary vary an order of magnitude ranging from ±52 m for the land and open-ocean terminating segments to ±502 m for the outlet glaciers. The hydrostatic line is less well positioned with errors over 2 km. Elevations along each line are selected from 6 candidate digital elevation models based on their agreement with ICESat elevation values and surface shape inferred from the Landsat imagery. Elevations along the hydrostatic line are converted to ice thicknesses by applying a firn-correction factor and a flotation criterion. BEDMAP-compiled data and other airborne data are compared to the ASAID elevations and ice thicknesses to arrive at quantitative (one-sigma) uncertainties of surface elevations of ±3.6, ±9.6, ±11.4, ±30 and ±100 m for five ASAID-assigned confidence levels. Over one-half of the surface elevations along the grounded ice boundary and over one-third of the hydrostatic line elevations are ranked in the highest two confidence categories. A comparison between ASAID-calculated ice shelf thicknesses and BEDMAP-compiled data indicate a thin-ice bias of 41.2 &pm; 71.3 m for the ASAID ice thicknesses. The relationship between the seaward offset of the hydrostatic line from the grounded ice boundary only weakly matches a prediction based on beam theory. The mapped products along with the customized software to generate them and a variety of intermediate products are available from the National Snow and Ice Data Center.
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Howat, Ian M., and Slawek Tulaczyk. "Trends in spring snowpack over a half-century of climate warming in California, USA." Annals of Glaciology 40 (2005): 151–56. http://dx.doi.org/10.3189/172756405781813816.
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AbstractLinear trends in 1 April snow water equivalent (SWE) in California, USA, are determined from a dense network of observations over the period 1950–2002. These trends are compared to concurrent time series of precipitation and temperature and Pacific Ocean climate indices. We find increased winter temperatures have accompanied both decreasing and increasing SWE trends, resulting in a weak overall negative trend in spring SWE. The spatial distribution of SWE trend is dependent on both latitude and elevation. Increases in both precipitation and temperature have led to increases in SWE at high elevations in southern Sierra Nevada and decreases at lower elevations. Increased temperature and decreased precipitation are associated with SWE loss in northern California. Trends in SWE can partially be attributed to shifts in Pacific Ocean climate indices.
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Yi, D., C. R. Bentley, and M. D. Stenoien. "Seasonal variation in the apparent height of the East Antarctic ice sheet." Annals of Glaciology 24 (1997): 191–98. http://dx.doi.org/10.3189/s0260305500012167.
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A satellite radar altimeter can be used to monitor surface elevation change over polar ice sheets. Thirty-five months of Geosat Exact Repeat Mission (ERM) data from November 1986 to September 1989 over a section of East Antarctica (69–72.1 ∘S, 80–140∘ E) have been used in this study. A model that considers both surface and volume scattering was used to retrack the altimeter waveforms. Surface elevations for each month after the first three were compared to the average elevations for the first 3 months through a crossover method. The averaged crossover elevation difference changed with time in a way that suggests a yearly cycle in surface elevation. The average amplitude of the cycle is about 0.6 m. We have been unable to find any satisfactory explanation for the observed changes, in terms of either sources of error or contributors to real surface-height changes. We strongly suspect that orbit error plays a major role in producing the variations, although we know of no quantitatively satisfactory source of a quasi-seasonal variation in orbit error. Other possible contributors include a real seasonal variation in accumulation rate, seasonal changes in the delay of the radar signal as it propagates through the atmosphere, unmodeled variations in the depth of penetration of the radar pulse into the firn, changes in the thickness of the ice and the firn zone in response to seasonal variations in pressure and temperature, and the inverted barometer effect. Even though we do not know the cause of the variations, the results show the importance of comparing elevations at the same time of year for observations that are not continuous, while at the same time showing that even annually spaced measurements may not be free of substantial errors associated with interannual variability. The quasi-periodic variations obscure any evidence of a moderate secular change in surface height, if there is one, but a dramatic lowering at rates approaching 1 ma–1, such as are known elsewhere in Antarctica, can definitely be ruled out.
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Yi, D., C. R. Bentley, and M. D. Stenoien. "Seasonal variation in the apparent height of the East Antarctic ice sheet." Annals of Glaciology 24 (1997): 191–98. http://dx.doi.org/10.1017/s0260305500012167.
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A satellite radar altimeter can be used to monitor surface elevation change over polar ice sheets. Thirty-five months of Geosat Exact Repeat Mission (ERM) data from November 1986 to September 1989 over a section of East Antarctica (69–72.1 ∘S, 80–140∘ E) have been used in this study. A model that considers both surface and volume scattering was used to retrack the altimeter waveforms. Surface elevations for each month after the first three were compared to the average elevations for the first 3 months through a crossover method. The averaged crossover elevation difference changed with time in a way that suggests a yearly cycle in surface elevation. The average amplitude of the cycle is about 0.6 m. We have been unable to find any satisfactory explanation for the observed changes, in terms of either sources of error or contributors to real surface-height changes. We strongly suspect that orbit error plays a major role in producing the variations, although we know of no quantitatively satisfactory source of a quasi-seasonal variation in orbit error. Other possible contributors include a real seasonal variation in accumulation rate, seasonal changes in the delay of the radar signal as it propagates through the atmosphere, unmodeled variations in the depth of penetration of the radar pulse into the firn, changes in the thickness of the ice and the firn zone in response to seasonal variations in pressure and temperature, and the inverted barometer effect. Even though we do not know the cause of the variations, the results show the importance of comparing elevations at the same time of year for observations that are not continuous, while at the same time showing that even annually spaced measurements may not be free of substantial errors associated with interannual variability. The quasi-periodic variations obscure any evidence of a moderate secular change in surface height, if there is one, but a dramatic lowering at rates approaching 1 ma–1, such as are known elsewhere in Antarctica, can definitely be ruled out.
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Salles, Tristan, Patrice Rey, and Enrico Bertuzzo. "Mapping landscape connectivity as a driver of species richness under tectonic and climatic forcing." Earth Surface Dynamics 7, no. 4 (October 1, 2019): 895–910. http://dx.doi.org/10.5194/esurf-7-895-2019.
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Abstract. Species distribution and richness ultimately result from complex interactions between biological, physical, and environmental factors. It has been recently shown for a static natural landscape that the elevational connectivity, which measures the proximity of a site to others with similar habitats, is a key physical driver of local species richness. Here we examine changes in elevational connectivity during mountain building using a landscape evolution model. We find that under uniform tectonic and variable climatic forcing, connectivity peaks at mid-elevations when the landscape reaches its geomorphic steady state and that the orographic effect on geomorphic evolution tends to favour lower connectivity on leeward-facing catchments. Statistical comparisons between connectivity distribution and results from a metacommunity model confirm that to the 1st order, landscape elevation connectivity explains species richness in simulated mountainous regions. Our results also predict that low-connectivity areas which favour isolation, a driver for in situ speciation, are distributed across the entire elevational range for simulated orogenic cycles. Adjustments of catchment morphology after the cessation of tectonic activity should reduce speciation by decreasing the number of isolated regions.
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Spaulding, W. Geoffrey. "Vegetation Dynamics During the Last Deglaciation, Southeastern Great Basin, U.S.A." Quaternary Research 33, no. 2 (March 1990): 188–203. http://dx.doi.org/10.1016/0033-5894(90)90018-g.
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AbstractVegetation changes in the southeastern Great Basin between 17,500 and 8000 yr B.P. can be reconstructed from plant macrofossil assemblages in ancient packrat (Neotoma spp.) middens. Vegetation instability after ca. 16,000 yr B.P. involved a dispoportionate number of local immigrations (arrivals) relative to apparent local extinctions (departures). At a site in modern woodland, less than 50% of the arrivals were of transients, species that subsequently went locally extinct; but at a low-elevation desert site almost all arrivals before 10,000 yr B.P. were transient species. Thus, by the close of the last glacial age, higher elevations supported vegetation that resembled present woodland, while lower elevations supported desertscrub that bore little resemblance to modern thermophilous desertscrub.Differences in the pace of plant community “modernization” in different elevational zones can be attributed to migrational lag. Woodland species survived the last glacial age at low elevations nearby, and began arriving at sites within current woodland before 11,700 yr B.P. Warm-desert plants were displaced far to the south, and began arriving after 9500 yr B.P. Moreover, their staggered arrival times suggest that low winter temperatures did not inhibit their migration during the early Holocene. These data suggest that biotic factors, particularly variable dispersal distances and consequent migrational lag, did affect deglacial vegetation change.
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Gilman, Eric, Joanna Ellison, Ierupaala Sauni, and Solialofi Tuaumu. "Trends in surface elevations of American Samoa mangroves." Wetlands Ecology and Management 15, no. 5 (April 20, 2007): 391–404. http://dx.doi.org/10.1007/s11273-007-9038-6.
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Kennett, Michael, and Trond Eiken. "Airborne measurement of glacier surface elevation by scanning laser altimeter." Annals of Glaciology 24 (1997): 293–96. http://dx.doi.org/10.3189/s0260305500012337.
Full textAbstract:
Airborne scanning laser altimetry is a relatively new technique for remote sensing of ground elevation. A laser ranger is scanned across a swath beneath the aircraft, producing a two-dimensional distribution of elevations when combined with data on aircraft position and orientation. Smooth snow-covered glaciers are ideal surfaces for laser scanning since they are highly reflective. A new prototype laser system is described together with results from Hardangerjökulen, Norway. An analysis of the data shows that noise levels are very low at around 2 cm, and that repeatability between overlapping swaths is approximately ± 10 cm. This is consistent with an absolute accuracy of 15 cm or better from manufacturer’s and other measurements. Swath widths of over 1 km are attainable, at lowing complete coverage of small to medium-sized glaciers using parallel flight tracks. The high accuracy and dense, even coverage (about 20 000 points per km2) gives good-quality derived products such as DEMs and enables reliable measurement of glacier volume change. Scanning laser altimetry has many advantages over photogrammetry, which was previously the only remote-sensing method of measuring elevations over large areas but which performs poorly over snow-covered glaciers.
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Kennett, Michael, and Trond Eiken. "Airborne measurement of glacier surface elevation by scanning laser altimeter." Annals of Glaciology 24 (1997): 293–96. http://dx.doi.org/10.1017/s0260305500012337.
Full textAbstract:
Airborne scanning laser altimetry is a relatively new technique for remote sensing of ground elevation. A laser ranger is scanned across a swath beneath the aircraft, producing a two-dimensional distribution of elevations when combined with data on aircraft position and orientation. Smooth snow-covered glaciers are ideal surfaces for laser scanning since they are highly reflective. A new prototype laser system is described together with results from Hardangerjökulen, Norway. An analysis of the data shows that noise levels are very low at around 2 cm, and that repeatability between overlapping swaths is approximately ± 10 cm. This is consistent with an absolute accuracy of 15 cm or better from manufacturer’s and other measurements. Swath widths of over 1 km are attainable, at lowing complete coverage of small to medium-sized glaciers using parallel flight tracks. The high accuracy and dense, even coverage (about 20 000 points per km2) gives good-quality derived products such as DEMs and enables reliable measurement of glacier volume change. Scanning laser altimetry has many advantages over photogrammetry, which was previously the only remote-sensing method of measuring elevations over large areas but which performs poorly over snow-covered glaciers.
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Thyssen, F., and K. Grosfeld. "Ekström Ice Shelf, Antarctica." Annals of Glaciology 11 (1988): 180–83. http://dx.doi.org/10.3189/s0260305500006510.
Full textAbstract:
In 1980–81, 1983–84 and 1985–86 airborne surveys with an electromagnetic reflection (EMR) system were made of Ekström Ice Shelf, Antarctica. The EMR data were supplemented by measurements of surface elevation with radar altimetry during flights at a constant pressure altitude. The accurate measurement of ice thickness in areas with clearly developed bottom reflectors was used to generate a plot of surface elevation against ice thickness. The effect of changing barometric pressure during the flights could be reduced by this means. Elevations were calibrated over the open sea at the beginning and end of each flight.On the basis of these data, the surface elevation, ice thickness and isostatic anomalies have been mapped over the ice shelf.
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Thyssen, F., and K. Grosfeld. "Ekström Ice Shelf, Antarctica." Annals of Glaciology 11 (1988): 180–83. http://dx.doi.org/10.1017/s0260305500006510.
Full textAbstract:
In 1980–81, 1983–84 and 1985–86 airborne surveys with an electromagnetic reflection (EMR) system were made of Ekström Ice Shelf, Antarctica. The EMR data were supplemented by measurements of surface elevation with radar altimetry during flights at a constant pressure altitude. The accurate measurement of ice thickness in areas with clearly developed bottom reflectors was used to generate a plot of surface elevation against ice thickness. The effect of changing barometric pressure during the flights could be reduced by this means. Elevations were calibrated over the open sea at the beginning and end of each flight. On the basis of these data, the surface elevation, ice thickness and isostatic anomalies have been mapped over the ice shelf.
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Fastook, James L., Henry H. Brecher, and Terence J. Hughes. "Derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: Jakobshavns Isbræ, Greenland." Journal of Glaciology 41, no. 137 (1995): 161–73. http://dx.doi.org/10.1017/s0022143000017858.
Full textAbstract:
AbstractJakobshavns Isbræ (69 °10′ N, 49 °59′ W) drains about 6.5% of the Greenland ice sheet and is the fastest ice stream known. The Jakobshavns Isbræ basin of about 10 000 km2was mapped photogrammetrically from four sets of aerial photography, two taken in July 1985 and two in July 1986. Positions and elevations of several hundred natural features on the ice surface were determined for each epoch by photogrammetric block aerial triangulation, and surface velocity vectors were computed from the positions. The two flights in 1985 yielded the best results and provided most common points (716) for velocity determinations and are therefore used in the modeling studies. The data from these irregularly spaced points were used to calculate ice elevations and velocity vectors at uniformly spaced grid points 3 km apart by interpolation. The field of surface strain rates was then calculated from these gridded data and used to compute the field of surface deviatoric stresses, using the flow law of ice, for rectilinear coordinates,X, Ypointing eastward and northward, and curvilinear coordinates.L, Τpointing longitudinally and transversely to the changing ice-flow direction, Ice-surface elevations and slopes were then used to calculate ice thicknesses and the fraction of the ice velocity due to basal sliding. Our calculated ice thicknesses are in fair agreement with an ice-thickness map based on seismic sounding and supplied to us by K. Echelmeyer. Ice thicknesses were subtracted from measured ice-surface elevations to map bed topography. Our calculation shows that basal sliding is significant only in the 10–15 km before Jakobshavns Isbræ becomes afloat in Jakobshavns Isfjord.
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Fastook, James L., Henry H. Brecher, and Terence J. Hughes. "Derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: Jakobshavns Isbræ, Greenland." Journal of Glaciology 41, no. 137 (1995): 161–73. http://dx.doi.org/10.3189/s0022143000017858.
Full textAbstract:
AbstractJakobshavns Isbræ (69 °10′ N, 49 °59′ W) drains about 6.5% of the Greenland ice sheet and is the fastest ice stream known. The Jakobshavns Isbræ basin of about 10 000 km2 was mapped photogrammetrically from four sets of aerial photography, two taken in July 1985 and two in July 1986. Positions and elevations of several hundred natural features on the ice surface were determined for each epoch by photogrammetric block aerial triangulation, and surface velocity vectors were computed from the positions. The two flights in 1985 yielded the best results and provided most common points (716) for velocity determinations and are therefore used in the modeling studies. The data from these irregularly spaced points were used to calculate ice elevations and velocity vectors at uniformly spaced grid points 3 km apart by interpolation. The field of surface strain rates was then calculated from these gridded data and used to compute the field of surface deviatoric stresses, using the flow law of ice, for rectilinear coordinates, X, Y pointing eastward and northward, and curvilinear coordinates. L, Τ pointing longitudinally and transversely to the changing ice-flow direction, Ice-surface elevations and slopes were then used to calculate ice thicknesses and the fraction of the ice velocity due to basal sliding. Our calculated ice thicknesses are in fair agreement with an ice-thickness map based on seismic sounding and supplied to us by K. Echelmeyer. Ice thicknesses were subtracted from measured ice-surface elevations to map bed topography. Our calculation shows that basal sliding is significant only in the 10–15 km before Jakobshavns Isbræ becomes afloat in Jakobshavns Isfjord.
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Sievers, J., C. S. M. Doake, J. Ihde, D. R. Mantripp, V. S. Pozdeev, B. Ritter, H. W. Schenke, F. Thyssen, and D. G. Vaughan. "Validating and improving elevation data of a satellite-image map of Filchner,Ronne Ice Shelf, Antarctica, with Results from ERS-1." Annals of Glaciology 20 (1994): 347–52. http://dx.doi.org/10.3189/1994aog20-1-347-352.
Full textAbstract:
A satellite-image map with surface-elevation contours of Filchner Ronne Ice Shelf has been published previously as a topographic map. The image map was constructed from a mosaic of 69 Landsat Multispectral Scanner (MSS) images and NOAA AVHRR data. The standard deviation in position in the central part of the mosaic is ±125m. Topographic-glaciologic features were taken from Landsat scenes and represent the best coastline of this region. Surface elevations have been calculated from airborne and ground measurements of either ice thickness (by assuming hydrostatic equilibrium) or barometric pressure. Accuracies vary from ±2 to ±7 m, Oversnow trigonometric levelling in the northeastern part of the ice shelf, tied to sea level at the ice front, has given accuracies of ± 1m. Accuracies reduce to about ±20 m in the grounded ice areas,ERS-I radar-altimeter data over the ice shelf have been processed to give ellipsoidal heights elevation above the ellipsoid), Geoidal reductions have been used to convert these to orthometric heights (elevation above sea level). No tidal corrections have been applied. The overall accuracy of the radar-altimeter-derived elevations is estimated to be better than ±5m. There are noticeable differences from the topographic map in the central part where the radar data indicate a lower surface. However, the maps agree to within the stated error figures.
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Sievers, J., C. S. M. Doake, J. Ihde, D. R. Mantripp, V. S. Pozdeev, B. Ritter, H. W. Schenke, F. Thyssen, and D. G. Vaughan. "Validating and improving elevation data of a satellite-image map of Filchner,Ronne Ice Shelf, Antarctica, with Results from ERS-1." Annals of Glaciology 20 (1994): 347–52. http://dx.doi.org/10.1017/s0260305500016670.
Full textAbstract:
A satellite-image map with surface-elevation contours of Filchner Ronne Ice Shelf has been published previously as a topographic map. The image map was constructed from a mosaic of 69 Landsat Multispectral Scanner (MSS) images and NOAA AVHRR data. The standard deviation in position in the central part of the mosaic is ±125m. Topographic-glaciologic features were taken from Landsat scenes and represent the best coastline of this region. Surface elevations have been calculated from airborne and ground measurements of either ice thickness (by assuming hydrostatic equilibrium) or barometric pressure. Accuracies vary from ±2 to ±7 m, Oversnow trigonometric levelling in the northeastern part of the ice shelf, tied to sea level at the ice front, has given accuracies of ± 1m. Accuracies reduce to about ±20 m in the grounded ice areas, ERS-I radar-altimeter data over the ice shelf have been processed to give ellipsoidal heights elevation above the ellipsoid), Geoidal reductions have been used to convert these to orthometric heights (elevation above sea level). No tidal corrections have been applied. The overall accuracy of the radar-altimeter-derived elevations is estimated to be better than ±5m. There are noticeable differences from the topographic map in the central part where the radar data indicate a lower surface. However, the maps agree to within the stated error figures.