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11.
通过迭代CFAR算法，本文发展了一种针对分块SAR图像的冰山检测方法。考虑到滑动窗口运算负担大、计算效率低，首先对SAR图像进行分块，以提取分块内的亮目标冰山。利用高斯模型表征后向散射系数的统计分布，冰山检测阈值可简单地表达为均值和方差的线性组合，将分块内像素逐个比对阈值以检测冰山。考虑到同一场景中尺寸变化大的冰山影响检测精度，以识别的冰山像素做种子执行区域生长，从而提取大尺寸的冰山。针对单个分块迭代上述处理，以降低高斯模型表征分块统计分布的误差，提高冰山检测精度。利用2013年11月22日和29日获取自极地海域的两景RADARSAT-2图像开展验证试验。结果表明，数量多、尺寸变化大并嵌入在海冰等极地常见情形下的冰山，能被文中方法有效识别，选取区域内正确率高达85%以上，且具有良好的运行效率。 相似文献
12.
随着全球气候变暖,冰架崩解事件的发生愈益频繁.冰架崩解产生的冰山是南极冰盖-冰架-海洋系统中活跃的组成部分,冰山的运动特征和时空分布对南大洋洋流循环、海洋生态以及水文系统有着非常重要的影响.因此利用卫星遥感监测冰山运动与变化信息,探究冰山崩解和消融过程,研究南极冰山分布,以及冰山和周围海洋环境之间的相互作用机制,是理解南极冰山变化与全球气候变化之间关系的关键.本文利用覆盖全南极海岸线的ENVISAT ASAR影像,基于简译软件的面向对象的多尺度图像分割算法实现了全南极近岸海域冰山对象的提取.利用2006年8月63期ENVISAT ASAR影像提取了32 267座面积大于0.06 km2的冰山,统计了冰山空间分布特征,研究发现南极小型冰山在全南极淡水输入中扮演着重要的作用. 相似文献
13.
利用欧洲环境卫星(EnviSat)所携带的先进合成孔径雷达(ASAR)数据高时间、高空间分辨率的特点,实现了全南极范围内冰架年崩解面积的高精度估算和崩解类型的解译。利用40期重复覆盖全南极海岸线的EnviSatASAR数据探测了冰架崩解的位置、类型和发生时间,统计分析了2005年8月到2011年8月连续6年南极冰架崩解频率和面积的时空变化。结果显示:(1)2005年—2011年平均崩解面积为2969.7km2,年崩解面积变化幅度较大,年崩解频率略呈下降的趋势;(2)南极冰架崩解主要发生1—3月,其中2月崩解最频繁;(3)东南极威尔克斯地区域是当前南极冰架崩解最活跃的区域,冰架罗斯、龙尼-菲尔希纳及埃默里等3大冰架很稳定且鲜有崩解发生,东南极毛德皇后地区域冰架相对稳定;(4)空间尺度小于100km2的崩解频率占到总频率的94.1%,忽略它们将导致南极年崩解面积低估20.7%—92.9%;(5)以内部冰川应力为主要驱动力的开裂型(Rift-opening)崩解较以外部大气和海洋因素为主要驱动力的融水型(Melt-related)崩解发生更为频繁,但是两者在量上的差异不大(约10%)。 相似文献
14.
Clare M. Robertson Martin S. Brook Kat A. Holt Ian C. Fuller Douglas I. Benn 《New Zealand geographer》2013,69(1):14-25
Hooker Glacier in the central Southern Alps of New Zealand has undergone significant downwasting and recession (～2.14 km) during the last two centuries. High retreat rates (51 m a?1 1986–2001, 43 m a?1 2001–2011) have produced a large (1.22 km2) proglacial lake. We present a retreat scenario for Hooker Glacier. A retreat scenario predicts that the glacier terminus will stabilise >3 km up‐valley of the current lake outlet after 2028 when ice velocity equals calving rate. 相似文献
15.
There has been increasing attention over the last decade to the potential effects of glacier retreat on downstream discharge and aquatic habitat. This study focused on streamflow variability downstream of Bridge Glacier in the southern Coast Mountains of BC between 1979 and 2014, prior to and during a period in which the glacier experienced enhanced calving and rapid retreat across a lake‐filled basin. Here we combined empirical trend detection and a conceptual‐parametric hydrological model to address the following hypotheses: (1) streamflow trends in late summer and early autumn should reflect the opposing influences of climatic warming (which would tend to increase unit‐area meltwater production) and the reduction in glacier area (which would tend to reduce the total volume of meltwater generated), and (2) winter streamflow should increase because of displacement of lake water as ice flows past the grounding line and calves into the lake basin. In relation to the first hypothesis, we found no significant trends in monthly discharge during summer. However, applying regression analysis to account for air temperature and precipitation variations, weak but statistically significant negative trends were detected for August and melt season discharge. The HBV‐EC model was applied using time‐varying glacier cover, as derived from Landsat imagery. Relative to simulations based on constant glacier extent, model results indicated that glacier recession caused a decline in mean monthly streamflow of 9% in August and 11% in September. These declines in late‐summer streamflow are consistent with the results from our empirical analysis. The second hypothesis is supported by the finding of positive trends for December, January, and February discharge. Despite the modelled declines in late‐summer mean monthly streamflow, recorded discharge data exhibited neither positive nor negative trends during the melt season, suggesting that Bridge Glacier may currently be at or close to the point of peak water. Further analysis of the impact of lake‐terminating glaciers on downstream discharge is needed to refine the peak water model. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
16.
The Tasman Glacier is the largest glacier in New Zealand. Although 20th century warming caused down-wastage, it remained at its Little Ice Age terminus until the late 20th century. Since then, rapid calving retreat (Ur) has occurred, allowing a large (5.96 × 106 m2) proglacial lake to form (maximum depth ∼240 m). From sequential satellite image analysis and echo sounding of Tasman Lake, we document (Ur) from 2000 to 2008. Ur varies temporally, with mean Ur of 54 m/a from 2000 to 2006 and a mean Ur of 144 m/a from 2007 to 2008. Consistent with global data sets, calving rate appears closely associated with lake depth at the calving terminus. 相似文献
17.
Late Pleistocene ice export events into the Arctic Ocean from the M'Clure Strait Ice Stream, Canadian Arctic Archipelago 总被引：3，自引：1，他引：2
Chris R. Stokes Chris D. Clark Dennis A. Darby Douglas A. Hodgson 《Global and Planetary Change》2005,49(3-4):139-162
Rapidly-flowing sectors of an ice sheet (ice streams) can play an important role in abrupt climate change through the delivery of icebergs and meltwater and the subsequent disruption of ocean thermohaline circulation (e.g., the North Atlantic's Heinrich events). Recently, several cores have been raised from the Arctic Ocean which document the existence of massive ice export events during the Late Pleistocene and whose provenance has been linked to source regions in the Canadian Arctic Archipelago. In this paper, satellite imagery is used to map glacial geomorphology in the vicinity of Victoria Island, Banks Island and Prince of Wales Island (Canadian Arctic) in order to reconstruct ice flow patterns in the highly complex glacial landscape. A total of 88 discrete flow-sets are mapped and of these, 13 exhibit the characteristic geomorphology of palaeo-ice streams (i.e., parallel patterns of large, highly elongated mega-scale glacial lineations forming a convergent flow pattern with abrupt lateral margins). Previous studies by other workers and cross-cutting relationships indicate that the majority of these ice streams are relatively young and operated during or immediately prior to deglaciation. Our new mapping, however, documents a large (> 700 km long; 110 km wide) and relatively old ice stream imprint centred in M'Clintock Channel and converging into Viscount Melville Sound. A trough mouth fan located on the continental shelf suggests that it extended along M'Clure Strait and was grounded at the shelf edge. The location of the M'Clure Strait Ice Stream exactly matches the source area of 4 (possibly 5) major ice export events recorded in core PS1230 raised from Fram Strait, the major ice exit for the Arctic Ocean. These ice export events occur at 12.9, 15.6, 22 and 29.8 ka (14C yr BP) and we argue that they record vigorous episodes of activity of the M'Clure Strait Ice Stream. The timing of these events is remarkably similar to the North Atlantic's Heinrich events and we take this as evidence that the M'Clure Strait Ice Stream was also activated around the same time. This may hold important implications for the cause of the North Atlantic's Heinrich events and hints at the possibility of a pan-ice sheet response. 相似文献
18.
The precipitation fields of a palaeoatmospheric general circulation model are used to derive estimates of the geographical distribution, and flux, of icebergs from the Laurentide, Fennoscandinavian and eastern Siberian ice‐sheets at the Last Glacial Maximum (LGM). The atmospheric model fields from LGM simulations using CLIMAP or Peltier (ICE‐4G) ice orography were studied, to test the sensitivity of the predicted flux. The estimated Northern Hemispheric LGM iceberg flux is 3500–4000 km3 yr?1, of which about 60% issued directly into the North Atlantic. The iceberg flux from the St Lawrence area is of similar significance to that issuing from Hudson Strait in all estimates. Both the North Pacific and the Arctic received substantial iceberg fluxes (ca. 700 km3 yr?1), with relatively minor differences occurring between the two ice‐sheet reconstructions. Apparent discrepancies between Arctic deep‐sea core samples of ice‐rafted debris and our estimates of mean glacial iceberg flux may be ascribed to coastal trapping of bergs, the existence of floating ice tongues or a rapid exit of icebergs from the Arctic basin into the Greenland Sea through the Fram Strait. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
19.
Anthony Raphael Davidson William Rayment Steve M Dawson Trudi Webster Elisabeth Slooten 《新西兰海洋与淡水研究杂志》2018,52(3):372-382
Southern right whales (Eubalaena australis) were widespread in New Zealand waters before commercial whaling in the nineteenth century caused drastic declines in their abundance and distribution. Following the cessation of whaling, the population has been recovering and is now slowly recolonising its former range. Estimates of population demographics, including reproductive output, are essential for predicting the trajectory of this population. We gathered photo-identification data on female southern right whales during annual field trips to the Auckland Islands, the principal calving area in New Zealand waters. Forty-five calving intervals were observed between 2006 and 2013 (mean interval?=?3.31 years, 95% CI?=?3.06–3.57). Incorporating the effects of possible missed calving events produced a plausible range of mean calving intervals from 3.17 to 3.31 years. Our results suggest that the calving interval of New Zealand southern right whales is similar to that found in populations elsewhere. 相似文献
20.
For ship structural design and good maneuverability in an ice-covered sea, the local and global load of ice cover on ships should be well understood. This paper reviews the extensive work done on ice loads on ships, including： （a） Ice pressure and local load determination based on field and model tests; （b） Global ice loads on ships from full-scale field observations, model tests and numerical models under different ice conditions （level ice and pack ice） and ship operations （maneuvering and mooring）. Spe- cial attention is paid to the discrete element simulation of global ice loads on ships; and （c） Analytical solutions and numerical models of impact loads of icebergs on ships for polar navigation. Finally, research potential in these areas is discussed. 相似文献