基于合成孔径雷达影像估计慕士塔格峰地区冰川速度场

冰川速度是冰川学研究中的一个重要参数,遥感方法为获取冰川表面速度提供了一种有效的手段。由于慕士塔格峰地区常年有云覆盖,不能为速度提取提供足够多数量的光学影像。但是,基于SAR影像对偏移量的提取算法为该地区冰川流速的测量提供了一个有效的途径。分别获取两幅雷达影像(ALOS/PALSAR)距离向和方位向的偏移,通过信噪比和相关系数选择可信点,然后通过整体拟合的方法去除雷达图像整体偏移,得到与冰川运动相关的偏移信号。首次得到了慕士塔格峰地区冰川表面完整的速度分布情况,依据该地区的速度大小分布特点,对慕士塔格峰四周冰川进行了划分。并进一步分别分析了该地区冰川在距离向和方位向速度大小与地形的关系,表明速度的大小与地形具有直接的相关性。结果表明,基于SAR影像对的偏移量测量为冰川研究提供了一个有效的方法和手段。     

TerraSAR-X几何校正及辐射定标模型

Terra SAR-X图像的几何校正和辐射定标对于获取地面目标高精度地理位置信息和辐射特征具有重要意义。采用距离-多普勒间接定位模型和仿射校正模型进行SAR影像几何校正,同时完成地形辐射校正并对辐射定标精度进行验证。距离向和方位向上达到了约0.3 m和0.4 m的几何定位精度;相对辐射定标精度优于0.3 d B,绝对辐射定标精度为0.22 d B,所以该模型能达到方法较高的精度且简单快捷。     

慕士塔格峰冰川变化遥感研究

以位于新疆维吾尔族自治区西南部的慕士塔格峰冰川为例,利用研究区1965年经航片校对的地形图和2001年5月的ASTER遥感影像为信息源,通过遥感图像处理技术和专家指导下的人工解译得到1965,2001年两期冰川边界图,用GIS统计该地区冰川面积,并分析冰川变化总趋势.结果表明,近36年来,慕士塔格峰冰川整体呈现退缩趋势,冰川面积减少了1.11%,而山峰西侧和南侧的部分冰川有前进的现象.     

适用GEO SAR的改进ωk算法

针对地球同步轨道合成孔径雷达（GEO SAR）"停走"假设失效,回波信号距离和方位二维空变性严重问题,本文引入考虑"停走"假设误差的回波信号模型,提出了一种适用于GEO SAR的改进ωk算法,该算法分别在距离维和方位维采用新的频率轴映射和非均匀快速傅里叶变换（NUFFT）去除了距离向和方位向信号的耦合,实现了适应距离和方位二维空变的方位向压缩.仿真实验验证了所提算法的有效性.      

基于线性预测外推的高分辨率雷达成像

为了提高实验室合成孔径雷达(SAR)成像系统的分辨率,采用自回归(AR)模型,对采集到的数据进行距离向和方位向上的线性预测外推,对外推后的数据进行快速傅里叶变换(FFT)。实验结果表明,相比于传统的快速傅里叶变换成像算法,在同样的硬件条件下,使用该方法可以提高该系统的纵向及横向的分辨率,得到更清晰的雷达图像,或使用较小孔径长度就可以获得相同质量的雷达图像;并且该算法计算速度较快,易于操作,便于在系统上实现实时成像。     

基于模拟影像的山地SAR影像配准方法研究

针对目前常规SAR影像配准方法在困难地区配准可靠性较低的问题,提出了一种基于模拟影像的山地SAR影像配准方法.该方法借助研究区的辅助DEM数据、真实SAR影像的卫星轨道数据和RD模型生成模拟SAR影像,并创建DEM地理坐标相一致的查找表.利用SIFT匹配算法对模拟影像和真实影像进行匹配,间接获取真实SAR影像的特征点,再利用仿射变换通过最小二乘法确定参考影像和待配准影像的变换模型,并进行重采样,最终实现山地SAR影像的配准.采用两种传感器类型的山地SAR影像数据进行了实验验证.结果表明,在地形起伏较大的山地区域,所提方法的配准精度相对于传统配准算法有明显提高,较好地克服了传统SAR影像配准方法对山地SAR影像配准适应性较差、精度较低的缺点,能够有效解决山地SAR影像配准问题.     

基于冰川流速的喀喇昆仑地区典型冰川厚度反演与冰储量估算

文章以青藏高原喀喇昆仑地区却哥隆玛冰川、锡亚琴冰川和巴尔托洛冰川3条规模较大且具代表性的冰川作为研究对象，利用Sentinel-1A卫星雷达影像和像素跟踪算法获取冰川表面流速数据，并基于数字高程模型(digital elevation model, DEM)和冰川表面流速数据，运用层流理论对目标冰川进行厚度反演和冰储量估算；采用全球冰川厚度产品对反演结果进行准确度评价，同时探讨采用层流理论反演冰厚的内在机制及存在的不确定性。结果表明，采用层流理论反演冰川厚度具有较好的可行性。研究结果可为青藏高原冰冻圈动态变化研究提供参考。     

任意构形双基SAR的频域分析与成像

任意构形双基SAR由于其灵活性等特点,成为SAR的重要研究方向之一,一种典型的任意构形双基SAR就是星机混合模式．任意构形双基SAR的斜距历程是发收斜距历程的双根号之和,且具有距离和方位二维空变特性,在建立点目标的频率域模型方面遇到了新的困难．由于发收斜距历程的差异,它们对总的瞬时Doppler频率的贡献是不同的,随距离、方位和Doppler历程而变化．因此,文中在建立任意构形双基SAR点目标频域模型时引入了代表发收雷达对总的瞬时Doppler频率贡献差异的双基参数——瞬时Doppler贡献比,并根据其物理意义求得了它随发收平台运动参数、目标位置和频率变化的近似解,然后利用驻定相位原理和Taylor级数展开法建立了具有任意构形特性的双基SAR点目标的频域模型．并对此频域模型的距离向和方位向的空变性进行了分析,给出了解决任意构形双基SAR成像时二维空变问题的chirp—z频率域成像算法．最后通过机载和星机构形下的仿真验证了此频域模型的准确性和成像方法的有效性．     

基于多光谱冠层成像仪的单株植物冠层体积及总面积指数测量误差分析

基于多光谱冠层成像仪(MCI)测量方法,开展龙眼树冠层体积及总面积指数测量研究,以地面实测数据为基础,重点分析MCI外方位元素(测站三维坐标及三个姿态角)测量、测站距离及测量方案(测站距离、体元及影像分区大小参数组合)三大误差来源及其对测量精度影响.研究发现,测站外方位元素解算精度受控制点成像质量、分布方式、控制点数目等因素影响显著;当体元、影像分区大小固定时,冠层体积及PAI参数测量结果受测站距离、测量方案影响整体较小,且偏差范围均小于8%,但少量方案存在测量结果不稳定性现象,其体积及PAI测量偏差可高达15%.     

基于Sketch Token的异源雷达影像匹配适应性分析

将异源影像间的共性信息提取与描述作为研究重点,提出了一种基于Sketch Token中层特征的异源影像适配性评估方法.该算法利用监督学习策略获取异源雷达影像之间共性特征的先验知识,据此训练Sketch Token特征分类器,并将其作为影像间共性特征的描述子对基准图进行特征提取.利用提取结果的各项统计量训练支持向量机分类器,并以此评估异源影像对中基准图的适配性.利用星载SAR(synthetic aperture radar)影像作为基准图、机载实孔径雷达影像作为实时图进行适配性评估试验,试验结果表明了该算法的有效性.     

Quick ice mass loss and abrupt retreat of the maritime glaciers in the Kangri Karpo Mountains,southeast Tibetan Plateau

The maritime glaciers are sensitive to climate change because of high annual precipitation and high air temperature in the region. A combined comprehensive study was carried out based on glacier mass balance observation, GPS-based glacier terminus position survey, glacier Ground Penetrating Radar, topography maps and RS satellite images in the Kangri Karpo Mountains, Southeast Tibet. The study revealed a strong ice mass loss and quick glacier retreat since the 1970s. Ata Glacier, one glacier from the south slope of the Kangri Karpo Mountains, has formed a 6-km-long terminal moraine zone at the end of the glacier since the 1970s, and the accelerating retreat is largely due to the strong glacier surface melting. Mass balance study on the other four glaciers on the northern side of the Kangri Karpo Mountains shows that they are in large negative mass balance and the glaciers had retreated 15--19 m from May 2006 to May 2007. The in-situ glacier observation also shows that the glacier retreat is more obvious in small glaciers. The enhanced ice mass deficit caused by climate warming and the ongoing extinction of many small glaciers in this region could seriously affect the water resources, environ- ments, local climate and regional sustainable development in the near future.     

Mineral deformation and subglacial processes on ice-bedrock interface of Hailuogou Glacier

Hailuogou Glacier is located in a warm and humid maritime environment. It is large and moves very fast. The bottom of the glacier slides intensively and the temperature at the bottom approaches the pressure melting point. Therefore, there are abundant melting water and debris which act as effective ＂grinding tools＂ for glacial abrasion. Polarizing microscope is used to observe the mineral deformation characteristics on the ice-bedrock interface. It is found that feldspar, quartz, hornblende and biotite are exposed to deformation, fracture and chemical alteration to various extents. Bending deformation is common for biotite, due to their lattice characteristics, and the bending orientations are mostly the same as the glacier flow. Bending deformation also occurs in a few hornblendes. High-angle tension fracture and low-angle shear fracture are common for quartz and feldspar, some of them are totally crushed （mylonizations） due to their rigidity. Thus, all the abrasion, quarrying, subglacial water action and subglacial dissolution processes at the bottom of the glacier are verified at the micro-scale level. Mineral deformation and fracture are the basic subglacial erosion mechanisms. The abrasion thickness is 30-90 μm for each time and the average is 50 μm. Most of the debris are silt produced by glacial abrasion. The extent of mineral deformation and fracture decreases drastically downwards beneath the bedrock surface. The estimated erosion rate is about 2.2-11.4 mm/a, which is similar to that of other maritime alpine glaciers, smaller than that of large-scale piedmont glaciers in Alaska （10-30 mm/a）, and larger than that of continental glaciers （0.1-1.0 mm/a）. The type and size of a glacier are the main factors that influence its erosion rate.     

帕隆藏布流域（波密-然乌段）冰川动态变化遥感分析

帕隆藏布流域位于中国海洋性冰川最为发育的藏东南地区,近年来随着全球温室效应加剧,帕隆藏布流域冰川变化极为显著。采用多期遥感影像,对1994～2015年间帕隆藏布流域波密至然乌段的冰川变化趋势、原因及其影响进行研究。结果表明:(1)20余年间冰川总面积减少了451. 72 km2,各冰川每年大约退缩2. 48%～2. 95%,气温升高以及降雨量减少是导致冰川面积持续退缩的主要原因。(2)由于帕隆藏布江南岸山坡所接收的太阳辐射热量更少,但降水却更加充沛,使得帕隆藏布江南岸冰川分布面积及覆盖率远大于北岸,而冰川退缩速率远小于北岸。(3)冰川的不断退缩使得沟道上游大量冻融松散物源在冰雪融水的外动力条件下,进入沟道形成松散堆积物源,导致流域内大规模发育冰川泥石流。由于帕隆藏布江南岸冰川规模更大,导致帕隆藏布江南岸冰川泥石流更为发育。(4)冰川变化动态监测对冰川泥石流机理分析以及预警研究工作有着重要的参考指导价值。     

Ice-sheet acceleration driven by melt supply variability

Increased ice velocities in Greenland are contributing significantly to eustatic sea level rise. Faster ice flow has been associated with ice-ocean interactions in water-terminating outlet glaciers and with increased surface meltwater supply to the ice-sheet bed inland. Observed correlations between surface melt and ice acceleration have raised the possibility of a positive feedback in which surface melting and accelerated dynamic thinning reinforce one another, suggesting that overall warming could lead to accelerated mass loss. Here I show that it is not simply mean surface melt but an increase in water input variability that drives faster ice flow. Glacier sliding responds to melt indirectly through changes in basal water pressure, with observations showing that water under glaciers drains through channels at low pressure or through interconnected cavities at high pressure. Using a model that captures the dynamic switching between channel and cavity drainage modes, I show that channelization and glacier deceleration rather than acceleration occur above a critical rate of water flow. Higher rates of steady water supply can therefore suppress rather than enhance dynamic thinning, indicating that the melt/dynamic thinning feedback is not universally operational. Short-term increases in water input are, however, accommodated by the drainage system through temporary spikes in water pressure. It is these spikes that lead to ice acceleration, which is therefore driven by strong diurnal melt cycles and an increase in rain and surface lake drainage events rather than an increase in mean melt supply.     

Numerical simulation of Urumqi Glacier No. 1 in the eastern Tianshan, central Asia from 2005 to 2070

Due to climate changes, most of the alpine glaciers have retreated dramatically during the past decades. Thus it is significant to predict the alpine glacier variability in the future for a better understanding of the impact of climate changes on water resource. In this paper, we perform the numerical simulation on Urumqi Glacier No.1 in the eastern Tianshan, central Asia (hereafter Glacier No.1 for short) by considering both the mass balance and ice flow. Given the shape of the Glacier No.1, the velocity of the glacier is obtained by solving a two-dimensional nonlinear Stokes equation and simulated result is in agreement with the observation. In order to predict the variability of Glacier No.1 in the next decades, a climatic scenario is constructed with a temperature rise rate as 0.17°C/10 a and precipitation as constant during the period of 2005-2070. The simulation shows that, the glacier terminus will retreat slowly and the glacier will thin dramatically before 2040, while after year 2040, the glacier terminus retreat will accelerate. This study confirms the increasing retreat rate of alpine glaciers under global warming.     

Large fluctuations in speed on Greenland's Jakobshavn Isbrae glacier

It is important to understand recent changes in the velocity of Greenland glaciers because the mass balance of the Greenland Ice Sheet is partly determined by the flow rates of these outlets. Jakobshavn Isbrae is Greenland's largest outlet glacier, draining about 6.5 per cent of the ice-sheet area, and it has been surveyed repeatedly since 1991 (ref. 2). Here we use remote sensing data to measure the velocity of Jakobshavn Isbrae between 1992 and 2003. We detect large variability of the velocity over time, including a slowing down from 6,700 m yr(-1) in 1985 to 5,700 m yr(-1) in 1992, and a subsequent speeding up to 9,400 m yr(-1) by 2000 and 12,600 m yr(-1) in 2003. These changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter. Our observations indicate that fast-flowing glaciers can significantly alter ice discharge at sub-decadal timescales, with at least a potential to respond rapidly to a changing climate.     

基于遥感与GIS的朋曲流域冰川及冰湖变化研究

由于全球变暖，冰川正逐年退缩，随之引发的冰湖溃决洪水已不容忽视，但静态和孤立地研究冰湖已不能满足人们对冰湖信息的需求．本文基于20世纪70年代的地形图数据和2000年以来的ASTER遥感影像数据，使用GIS手段矢量化朋曲流域20世纪70年代和近期的冰川及冰湖的空间分布，并进行编目．对于获得的空间数据分析结果表明，在过去30年里该区冰川面积减少近9％，冰湖面积则增加了13％，在此基础上比较二者的联系和变化，识别出了24个可能发生溃决的冰湖，这为朋曲流域建立一套冰湖溃决预警系统提供依据；同时，对于研究其他类似地区的冰湖溃决现象也具有指导意义。     

Planetary science: are there active glaciers on Mars?

Head et al. interpret spectacular images from the Mars Express high-resolution stereo camera as evidence of geologically recent rock glaciers in Tharsis and of a piedmont ('hourglass') glacier at the base of a 3-km-high massif east of Hellas. They attribute growth of the low-latitude glaciers to snowfall during periods of increased spin-axis obliquity. The age of the hourglass glacier, considered to be inactive and slowly shrinking beneath a debris cover in the absence of modern snowfall, is estimated to be more than 40 Myr. Although we agree that the maximum glacier extent was climatically controlled, we find evidence in the images to support local augmentation of accumulation from snowfall through a mechanism that does not require climate change on Mars.     

DINSAR measurement of glacier motion in Antarctic Grove Mountain

Grove Mountain is an important nunatak region on East Antarctic Glacier that blocks the ice flow to- ward Lambert Glacier. The existence of nunataks and subglacial mountains leads to complex ice flow patterns, which are difficult to be measured by conventional ground-based methods. In this study, several JERS-1 and ERS-1/2 SAR images covering this area are used for 3-pass and 4-pass differential interferometric processing. The ice flow field of Grove Mountain and the eastern zone are derived and validated with related knowledge. The research shows that DINSAR is an effective method for meas- uring complex ice flow in Antarctic inland glacier. L-band DINSAR is more suitable for mid or fast ice flow than C-band over this region.     

Glacier changes during the last forty years in the Tarim Interior River basin, northwest China

By comparing digitized glacier outlines from the Chinese Glacier Inventory (CGI) during the 1960s–1970s and Landsat Enhance Thematic Mapper (ETM+) images from 1999 to 2001, we investigated changes for about 7665 alpine glaciers among 11665 glaciers in seven sub-basins of the Tarim Interior River basin (TIRB). The results showed that the total glacier area was reduced by 3.3% from the 1960s/ 1970s to 1999/2001 and area losses for 1–5 km2 glaciers accounted for 48.3% of the total glacier area loss in the TIRB. However, the glacier area reductions varied from 0.7% to 7.9% among the seven sub-basins of the TIRB during the study period. The glacier area changing with altitude showed that the maximum contribution of area shrinkage occurred at 4900–5400 m. Data from 25 meteorological stations in the TIRB showed increases in both the annual mean air temperature and annual precipitation during 1960–2000. This indicates that the glacier shrinkage in the TIRB over the last 40 years was largely due to regional climate warming that enhanced glacier ablation and overcame the effects of increased precipitation on the glacier mass balance.