Consideration of the errors inherent in mapping historical glacier positions in Austria from the ground and space (1893-2001)

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.     

多时相遥感影像监测南极冰川流速

测定南极冰川的流速，对于研究南极冰雪物质平衡、南极环境变化及其对全球环境的影响和极区航行有重大意义。本论述了利用多时相卫星遥感影像监测冰川变化的原理和方法，通过对英格里特一克里斯泰森海岸不同时期的遥感影像进行几何纠正和配准及叠加处理，测量和计算出极记录冰川的平均流速，并对它们的变化特点进行了初步的分析和评价。     

A story about distributions of dimensions and locations of boulders

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.     

天山一号冰川产果胶酶酵母菌的筛选及其系统发育分析

从前期天山冰川冻土及融水中分离到68株可培养酵母菌中,通过筛选性培养基筛选产低温果胶酶的菌株。选择培养基显示菌株C2、C9、L1和L13可产低温果胶酶。对4株酵母菌最适生长温度进行测定,16 ℃条件下4株酵母菌均能生长,属耐冷菌范畴。通过26S rDNA基因序列分析确定产果胶酶菌种的系统进化地位,在系统发育上,4株产酶菌分别与Cryptococcus macerans DQ377662、Cryptococcus sp. DQ377668、Rhodotorula laryngis JQ768911、Rhodotorula sp. JX124722的同源性最高。     

基于Landsat数据的郭扎错北面冰川近20年来面积动态变化遥感研究

冰川能够敏感地反映区域环境变化,是研究全球变化的重要因素之一。昆仑山地区冰川集中,是研究冰川动态变化的理想区域。根据郭扎错北面1991~2009年Landsat TM与ETM+遥感影像,研究了该地区冰川近20 a来的变化情况。结果发现,该地区冰川变化显著,并得出以下结论：① 郭扎错北面冰川面积在1991~2009年间具有先增加后减少的波动规律;② 该区域内存在东部冰川比西部变化量大和变化率快的差异性;③ 该地区中峰冰川在2001~2004年间面积大幅增加,可能与2001年11月14日发生在昆仑山口以西的8.1级强烈地震有关;④ 该研究区内冰川面积变化主要受年均温度和年累积降水量的综合影响。     

基于SAR数据的山地冰川表面运动速度分析

合成孔径雷达(SAR)因其可全天时、全天候工作且不受云、雨的影响而成为遥感应用的前沿领域。SAR干涉测量(Inteferometry)利用SAR数据的相位信息可获得大地表面厘米级的形变而成为冰川表面流速监测广泛使用的手段;SAR图像相关方法(SRFT)能克服干涉测量方法因失相干严重而难以产生清晰的干涉条纹以及可见光图像质量由于云遮、雪盖限制的不足而成为目前山地冰川表面流速遥感监测的首选方式。为深入探讨SAR图像相关方法的适用性,以天山科契卡尔巴西冰川为研究区域,分析使用不同时间基线的ALOS PALSAR数据与ENVISat ASAR C-band 的图像相关方法估计冰川的表面流速,并使用实地测杆的DGPS(Differential GPS)测量流速进行对比验证,发现在冰川表碛覆盖区域使用图像相关方法测量的值与实测值有很好的一致性,而在裸露冰区域或坡度较大区域,误差比较大。比较长时间基线的SAR数据对特征识别的结果发现：时间基线为1 a的冬季获取的数据对估计值与实测值在表碛覆盖区域比较一致,这可能是由于前后两次获取图像时天气或地面状况比较接近。比较ALOS PALSAR 数据与ENVISat ASAR数据发现：波长较长的L-band(23.5 cm) 比C-band (5.7 cm)SAR数据更适合山地冰川的表面流速估计;另外在运用SAR数据特征匹配方法时也可能是极化方式的差异使得ALOS PALSAR (HH极化)数据比ENVISat ASAR(VV极化)数据更适合冰川研究。     

SPOT5-HRS digital elevation models and the monitoring of glacier elevation changes in North-West Canada and South-East Alaska

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 Orthoengine^SE 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.     

高分辨率SAR影像提取冰川面积与冰面河

冰川面积变化是冰川积累与消融的直接体现,与气候变化密切相关。遥感的方法可以为冰川的轮廓及面积监测提供可靠手段,但常用的光学遥感容易受到冰川区多变气象条件的影响。合成孔径雷达（SAR）不受天气影响,尤其是高分辨率SAR影像能够提供冰川表面丰富的细节特征,更好地监测冰川变化。应用相位一致性方法和快速行进法相结合的方法提取冰川轮廓和表面纹理。依据提取的冰川轮廓计算的冰川面积误差在5%以下,表明该方法能够准确地提取冰川面积。同时,在高分辨率SAR图像上,利用提取的冰川表面纹理信息可以有效监测到光学图像上难以识别的冰面河,而冰面河与冰川中长期消融密切相关,提取的冰面河信息将为冰川监测提供一种新的视角。     

Remote sensing estimates of glacier mass balances in the Himachal Pradesh (Western Himalaya, India)

Although they correspond to an important fraction of the total area of mountain glaciers (33,000 km² out of 546,000 km²), Himalayan glaciers and their mass balance are poorly sampled. For example, between 1977 and 1999, the average area surveyed each year on the field was 6.8 km² only. No direct mass balance measurement is available after 1999. To contribute to fill this gap, we use remote sensing data to monitor glacier elevation changes and mass balances in the Spiti/Lahaul region (32.2°N, 77.6°E, Himachal Pradesh, Western Himalaya, India). Our measurements are obtained by comparing a 2004 digital elevation model (DEM) to the 2000 SRTM (Shuttle Radar Topographic Mission) topography.The 2004 DEM is derived from two SPOT5 satellite optical images without any ground control points. This is achieved thanks to the good on-board geolocation of SPOT5 scenes and using SRTM elevations as a reference on the ice free zones. Before comparison on glaciers, the two DEMs are analyzed on the stable areas surrounding the glaciers where no elevation change is expected. Two different biases are detected. A long wavelength bias affects the SPOT5 DEM and is correlated to an anomaly in the roll of the SPOT5 satellite. A bias is also observed as a function of altitude and is attributed to the SRTM dataset. Both biases are modeled and removed to permit unbiased comparison of the two DEM on the 915 km² ice-covered area digitized from an ASTER image.On most glaciers, a clear thinning is measured at low elevations, even on debris-covered tongues. Between 1999 and 2004, we obtain an overall specific mass balance of − 0.7 to − 0.85 m/a (water equivalent) depending on the density we use for the lost (or gained) material in the accumulation zone. This rate of ice loss is twice higher than the long-term (1977 to 1999) mass balance record for Himalaya indicating an increase in the pace of glacier wastage. To assess whether these ice losses are size-dependant, all glaciers were classified into three samples according to their areal extent. All three samples show ice loss, the loss being higher for glaciers larger than 30 km². In the case of the benchmark Chhota Shigri glacier, a good agreement is found between our satellite observations and the mass balances measured on the field during hydrological years 2002-2003 and 2003-2004. Future studies using a similar methodology could determine whether similar ice losses have occurred in other parts of the Himalaya and may allow evaluation of the contribution of this mountain range to ongoing sea level rise.