The historical record of in situ measurements of the terminus positions of the Pasterze and Kleines Fleißkees glaciers in the eastern Alps of Austria is used to assess uncertainties in the measurement of decadal scale changes using satellite data. Topographic maps beginning in 1893, and satellite data from 1976 to 2001, were studied in concert with ground measurements to measure glacier changes. Ground measurements show that the tongue of the Pasterze Glacier receded ∼1150 m from 1893 to 2001, while satellite-derived measurements, using August 2001 Landsat Enhanced Thematic Mapper Plus (ETM+) data registered to an 1893 topographic map, show a recession of 1300-1800 m, with an unknown error. The measurement accuracy depends on the registration technique and the pixel resolution of the sensor when two satellite images are used. When using topographic maps, an additional source of error is the accuracy of the glacier position shown on the map. Between 1976 and 2001, Landsat-derived measurements show a recession of the terminus of the Pasterze Glacier of 479±136 m (at an average rate of 19.1 m a−1) while measurements from the ground showed a recession of 428 m (at an average rate of 17.1 m a−1). Four-meter resolution Ikonos satellite images from 2000 and 2001 reveal a shrinkage of 22,096±46 m2 in the Pasterze tongue. The nearby Kleines Fleißkees glacier lost 30% of its area between 1984 and 2001, and the area of exposed ice increased by 0.44±0.0023 km2, according to Landsat satellite measurements. As more recent satellite images are utilized, especially data that are geocoded, the uncertainty associated with measuring glacier changes has decreased. It is not possible to assess the uncertainty when an old topographic map and a satellite image are coregistered. 相似文献
Monitoring the response of land ice to climate change requires accurate and repeatable topographic surveys. The SPOT5-HRS (High Resolution Stereoscopic) instrument covers up to 120 km by 600 km in a single pass and has the potential to accurately map the poorly known topography of most glaciers and ice caps. The acquisition of a large HRS archive over ice-covered regions is planned by the French Space Agency (CNES) and Spotimage, France during the 2007–2008 International Polar Year (IPY). Here, we report on the accuracy and value of HRS digital elevation model (DEM) over ice and snow surfaces.
A DEM is generated by combining tools available from CNES with the PCI OrthoengineSE software, using HRS images acquired in May 2004 over South-East Alaska (USA) and northern British Columbia (Canada). The DEM is evaluated through comparison with shuttle radar topographic mission (SRTM) DEM and ICESAT data, on and around the glaciers. A horizontal shift of 50 m is found between the HRS and SRTM DEMs and is attributed to errors in the SRTM DEM. Over ice-free areas, HRS elevations are 7 m higher than those of SRTM, with a standard deviation of ± 25 m for the difference between the two DEMs. The 7-m difference is partly attributed to the differential penetration of the electromagnetic waves (visible for HRS; microwave for SRTM) in snow and vegetation.
We also report on the application of sequential DEMs (SRTM DEM in February 2000 and HRS DEM in May 2004) for the monitoring of glacier elevation changes. We map the topographic changes induced by a surge of one tributary of Ferris Glacier. Maximum surface lowering of 42 (± 10) m and rising of 77 (± 10) m are observed in the 4 years time interval. Thinning rates up to 10 (± 2.5) m/yr are observed at low altitudes and confirm the ongoing wastage of glaciers in South-East Alaska. 相似文献
Modeling a response over a nonconvex design region is a common problem in diverse areas such as engineering and geophysics. The tools available to model and design for such responses are limited and have received little attention. We propose a new method for selecting design points over nonconvex regions that is based on the application of multidimensional scaling to the geodesic distance. Optimal designs for prediction are described, with special emphasis on Gaussian process models, followed by a simulation study and an application in glaciology. Supplementary materials for this article are available online. 相似文献
The topic concerns the density of occurrence of boulders and the joint distribution of the primary boulder dimensions in the till deposits of the Great Belt region in Denmark. The investigation was made in 1987–1988 on the initiative of A/S Storebæltsforbindelsen in order to prepare the tendering for making a bored tunnel through the till deposit. Geographical universality was discovered through the statistical analysis of observations of boulder coordinates and dimension measures from widespread cliff beach locations. One conclusion is that the joint size distribution up to some degree of modeling approximation has a surprisingly simple structure. In particular, the maximal dimension has an exponential distribution while the ratios between maximal and intermediate dimension and between the intermediate dimension and the smallest dimension are independent and identically distributed according to a beta-distribution. Moreover, these ratios are independent of the maximal dimension.The random point field structure of the boulder coordinates as isolated points or as clusters of points makes Poisson fields reasonable modeling candidates for the fields of both single points and cluster points. The cluster size distributions are well modeled by a Markov chain type of model. Different details of the data and their statistical analysis support several modeling conjectures concerning the glacial history of boulder deposition.In a companion paper, it is described how the results of this beach boulder investigation are used for interpretation of the results from seismic scanning of the till deposits along the planned tunnel line, and for prediction of the density of boulders of maximal dimension above any specified length. 相似文献
The macronutrients in two foods used by indigenous peoples of the British Columbia Plateau region were examined. Yellow Glacier Lily and Balsamroot were commonly harvested, processed and stored in large quantities, up until the last three decades, together with many other plant foods. The macronutrients of the two foods, in which the underground bulbs or roots are utilized, are mainly derived from the carbohydrates. Yellow Glacier Lily bulbs have a high starch content, (770 g kg−1 in fresh bulbs, dry basis), and 57 g kg−1 total dietary fibre. They also contain measurable amounts of simple sugars and fructans before and after cooking. Balsamroot, whose taproots were eaten, is another plant indigenous to the region, but unlike Yellow Glacier Lily it contains negligible amounts of starch. The edible portion of Balsamroot has a high total dietary fibre content (250 g kg−1, dry basis), and high fructan content which is reduced to lower molecular weight sugars after pitcooking. The energy derived from the two foods is very similar on a dry basis ranging from 364 to 395 kcal 100 g−1 in the fresh and pitcooked samples. 相似文献