Motion patterns of Nabesna Glacier (Alaska) revealed by interferometric SAR techniques

Nabesna Glacier is one of the longest land-terminus mountain glaciers in North America. However, its flow has never been studied. We derived detailed motion patterns of Nabesna Glacier in winter and spring 1994–1996 from the synthetic aperture radar (SAR) images acquired by the European Remote Sensing satellites (ERS-1 and ERS-2) using interferometric SAR (InSAR) techniques. Special effort was made to assess the accuracy of the motion estimates, and remove data points with high uncertainty from the motion profiles, enabling us to obtain reliable glacier flow patterns along the highly curved main course of Nabesna Glacier. The results, covering 80 km of the 87 km main course of the glacier, were used to delineate four distinctive sections in terms of spatial and temporal variability of the glacier speed: (1) the upper section where glacier flow was apparently random both temporally and spatially presumably due to development of crevasses; (2) the upper-middle section with relatively steady flow around 0.27 to 0.4 m/day; (3) the middle section with a stable pattern of acceleration from 0.27–0.3 m/day to the maximum about 0.67–0.73 m/day, followed by a general deceleration to 0.17–0.33 m/day before reaching (4) the lower section where the glacier motion was generally slow yet highly variable although uncertainty in the estimation is high. Occurrence of the flow maximum, as well as many local maxima and minima at consistent locations over different periods suggests that the valley geometry affect the overall flow pattern. On top of this general trend, many small-scale temporal/spatial variations in the glacier flow patterns were observed along the glacier, especially in the lower sections. On average, the flow speeds were in the range of 0.3 to 0.7 m/day; however this lacks any measurements of summer flow speeds which are expected to be significantly higher.     

Movement estimate of the Dongkemadi Glacier on the Qinghai–Tibetan Plateau using L-band and C-band spaceborne SAR data

We measured the complex motion of the Dongkemadi Glacier on Tanggula Mountain, Qinghai–Tibetan Plateau, using two-pass differential synthetic aperture radar interferometry (InSAR) with satellite L-band and C-band SAR data. We derived detailed motion patterns of the Dongkemadi Glacier for the winter seasons of 1996, 2007 and 2008 using a European Remote sensing Satellite-1/2 (ERS-1/2) tandem InSAR pair acquired from descending orbit and a 46-day-separation Advanced Land Observing Satellite (ALOS) InSAR pair acquired from ascending orbit. In this article, we focus on an analysis of the glacier's surface motion features and a validation of the results from the InSAR using Global Positioning System (GPS) survey data. The experimental results show that the glacier flow distribution displays strong spatial variations depending on elevation. The glacier is divided into four clearly defined fast-flowing units in terms of spatial variability of the glacier speed, with evidence from both ERS and ALOS/PALSAR InSAR pairs (palsar – Phased Array type L-band Synthetic Aperture Radar). Among the four fast-flowing units, three are on the Dadongkemadi Glacier (DDG) and one on the Xiaodongkemadi Glacier (XDG). The flow patterns are generally characterized by terrain complexity for both glacier branches. The upper central area of the DDG shows slow movement, maybe due to the convergent and uptaking effect of ice from steep slope areas with opposite flow directions.     

Delineation of glacial zones of Gangotri and other glaciers of Central Himalaya using RISAT-1 C-band dual-pol SAR

The Himalayan glaciers, being unique in nature, need more detailed study over their evolution in the Himalayan glacial zones. A methodology has been developed using two-dimensional signatures from synthetic aperture radar (SAR) C-band dual-polarized data. A linear decision rule-based model has been generated using the signatures and the result further filtered by the use of a digital elevation model (DEM) to delineate glacial zones in the Himalayas. The advantage of using cross-polarized data is the addition of extra information from the volume of the glacial mass. Some important prerequisites for the analysis are SAR image ortho-rectification and calibration, glacier boundary delineation, and the development of sites for collecting SAR backscattering signatures from glaciers along the profile. The study deals with the evolution of glacial snow cover and glacial zones/facies in the Himalayan region under a subtropical humid climate from the ablation to the accumulation season. SAR images from 15 July 2012 to 30 June 2013 over the Gangotri and Mana glaciers were evaluated with the developed model. The identification of a superimposed zone during the ablation season is among the key results. The identified snowlines and other boundaries of glacial facies are studied on a temporal scale. The highest snowline altitude of Mana was recorded at 5768 and 5194 m for the Gangotri glacier in 2012. SAR data are also important in identifying glacial zones buried under winter snow cover. The results obtained are useful in regard to further glaciological studies of the Himalayan glaciers.     

Bara Shigri and Chhota Shigri glacier velocity estimation in western Himalaya using Sentinel-1 SAR data

In this article, we have presented surface velocity estimation of Chhota Shigri (CS) and Bara Shigri (BS) glaciers in the Himalaya using C-band synthetic aperture radar (SAR) data from Sentinel-1 (S-1). Repeat-pass SAR image subpixel offset tracking has been used to generate velocity vectors from yearly and seasonal S-1 data sets. SAR offset tracking on the basis of maximum intensity correlation provided the two-dimensional (2-D) movement of the both CS and BS glaciers of Chandra valley in western Himalaya. Movement of the glacier has been observed in the terminus to ablation zone during 2014–2018. S-1-derived movement is compared with in-situ measurement over CS glacier, and it has shown approximately 25% deviation during 2015–2016 with respect to field measurements from 2009 to 2010. Similar to previous decade observations, S-1 offset tracking movement results of recent three years have shown a decreasing trend.     

Mapping of debris-covered glaciers in the Garhwal Himalayas using ASTER DEMs and thermal data

Mapping of debris-covered glaciers using remote-sensing techniques is recognized as one of the greatest challenges for generating glacier inventories and automated glacier change analysis. The use of visible (VIS) and near-infrared (NIR) bands does not provide sufficient continual information to detect debris-covered ice with remote-sensing data. This article presents a semi-automated mapping method for the debris-covered glaciers of the Garhwal Himalayas based on an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) digital elevation model (DEM) and thermal data. Morphometric parameters such as slope, plan curvature and profile curvature were computed by means of the ASTER DEM and organized in similar surface groups using cluster analysis. A thermal mask was generated from a single band of an ASTER thermal image, while the clean-ice glaciers were identified using a band ratio based on ASTER bands 3 and 4. Vector maps were drawn up from the output of the cluster analysis, the thermal mask and the band ratio mask for the preparation of the final outlines of the debris-covered glaciers using geographic information system (GIS) overlay operations. The semi-automated mapped debris-covered glacier outline of Gangotri Glacier derived from 2006 ASTER data varied by about 5% from the manually outlined debris-covered glacier area of the Cartosat-1 high-resolution image from the same year. By contrast, outlines derived from the method developed using the 2001 ASTER DEM and Landsat thermal data varied by only 0.5% from manually digitized outlines based on Indian Remote Sensing Satellite (IRS)-1C panchromatic (PAN) data. We found that post-depositional sedimentation by debris flow/mass movement was a great hindrance in the fully automated mapping of debris-covered glaciers in the polygenetic environment of the Himalayas. In addition, the resolution of ASTER stereo data and thermal band data limits the automated mapping of small debris-covered glaciers with adjacent end moraine. However, the results obtained for Gangotri Glacier confirm the strong potential of the approach presented.     

Estimating glacier volume loss using remotely sensed images,digital elevation data,and GIS modelling

Glacier retreat has received much attention in the public and scientific community as a sensitive indicator of global warming. Parameters for changes in glacier size include length, area, volume, and mass balance. While measurement of changes in glacier length and area is relatively straightforward using remotely sensed data, estimating changes in volume and mass balance remains a major challenge. The objectives of this research are to (1) develop a new model to describe the nonlinear thinning process of a glacier surface headward from the terminus position and (2) reconstruct historical glacier longitudinal profiles and 3D surfaces based on current glacier longitudinal profile and thinning rate, and estimate glacier volume loss. Using historical terminus positions and Landsat Thematic Mapper (TM), IKONOS, and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) global digital elevation model (GDEM) data for the Gangotri Glacier in the Himalayas, longitudinal profiles and 3D surfaces of the glacier for 1900, 1935, and 1971 were reconstructed, and the amount and rate of volumetric losses during 1900–1935, 1935–1971, and 1971–2005 were derived. The methods can be used for more detailed study on estimating volume loss of the Himalayan glaciers and other glaciers.     

Modelling of Gangotri glacier thickness and volume using an artificial neural network

The volume of glaciers in a glacierized basin is an important characteristic for the existence of the glaciers and their evolution. Knowledge of glacier volume motivates scientific interest for two main reasons. First, the volumes of individual glaciers are monitored to estimate future water and sea level rises. Second, glaciers in the Indian Himalayas have been recognized as important water storage systems for municipal, industrial, and hydroelectric power generation purposes. Therefore, estimation of glacier volume is desired to estimate sea level rise accurately. The problem of deriving volume and glacier ice thickness is solved by developing an artificial neural network (ANN) approach that requires glacier boundaries, central branch lines, width-wise lines, digital elevation model (DEM), and slope information. Two geomorphic assumptions were taken in this investigation after testing, and strong relationships were found between elevation values of the frontal ice-denuded area of the Gangotri glacier and ice thickness derived from an ANN.     

Comparison of annual changes in winter ERS-1 SAR images and glacier mass balance of Slakbreen,Svalbard

The Arctic glaciers are sensitive to climate change, and glacier mass balance is used as an indicator of climate change. However, few mass balance observations are available from the Arctic region. Winter ERS-1 SAR images of the Arctic glacier Slakbreen (78degreesN, 16degrees 30'E) on Svalbard were analysed to investigate a possible relation between SAR backscatter and temporal variations in glacier mass balance. A winter ERS-1 SAR image acquired in 1993 after a summer with large ablation was compared with a winter ERS-1 SAR image acquired after the following summer with low ablation. Changes in mass balance from one year to another were difficult to detect using SAR backscatter data only. Comparison of ground-penetrating radar and SAR data showed that the SAR data contain a signal of the near-surface glacier properties. SAR data were interpreted to reflect variations in accumulation and ablation integrated over several years.     

Extraction of glacier outlines and water-eroded stripes using high-resolution SAR imagery

Glaciers and ice sheets are sensitive indicators of climate change. The changes of outlines and texture features on the glacier surface are useful indicators of glacier change monitoring. The sensitivity of synthetic aperture radar (SAR), which is independent of weather and solar illumination, provides an efficient approach for glacier monitoring and the development of high-resolution SAR makes it possible to study glaciers in more detail. In this article, the decision-tree classification method, the Canny operator, and the phase congruency method are applied and compared to extract glacier outlines and water-eroded stripes using X-band high-resolution SAR imagery of the Dongkemadi glacier area in the Qinghai–Tibet Plateau, collected by the TerraSAR satellites. The experimental results are presented to illustrate the accuracy and efficiency of the phase congruency method as compared to other methods used for the extraction of linear features (outline and stripes) on glaciers. The phase congruency method, which is independent of image illumination and magnification, is used for the first time in glacier outline and stripe extraction. It is shown that, when combined with high-resolution SAR imagery, this method has the potential to provide valuable support for glacier mapping and change monitoring in the future.     

Characteristic of Glaciers’ Movement Along Karakoram Highway

As an international highway，the Karakoram Highway(KKH) is of great importance to China，Pakistan，South-Asian and West-Asian Countries.It crosses the Karakoram Mountains，one of the most glaciers concentrated regions，and is being threatened from glaciers along KKH all the time.Currently，Synthetic Aperture Radar(SAR) have been proved reliably profitable on analyst glaciers’ movement.In this study，we analyzed the characteristics of glaciers’ movement along KKH by using feature-tracking method based on 81 scenes of Sentinel-1A data obtained between Jan.2016 to Jun.2017.And ERS-1 data in 1993 and ALOS PALSAR data in 2006 are taken as comparison for analyzing the trend of glacial surface flow rate.Our results indicated that the glacier flow streamline is basically consistent with the geometric center line of the ice tongue and the velocities increase away from both margins；summer motion was higher than winter motion.The glaciers along the KKH can be divided into three parts：north，central and south，based the boundaries of Tajik Autonomous County in Sinkiang and Khuda Abad，the northern city of Pakistan.The glacier surface velocities of the trunk is lower than 0.15md^-1and relatively stable in the northern.The scale of glaciers in the central region is generally small and far from the KKH.The glaciers in north and central regions may not affect the operation of highways.While parts of the large scale glaciers in the south region had higher velocities，particularly along the section of the highway near Batura Sar.Here，4 glaciers were selected to analyze in detail which are closest to the KKH include Batura，Pasu，Ghulkin and Gulmit in the south region.Seen from all results，the Pasu glacier has rapid motion during the study period，the normal velocity of its trunk is between 1 and 1.5 md^-1，and can reach 3 md^-1 in special place.All these 4 glaciers were flowing faster than other glaciers which reflect the high quantitative mass balance.Accordingly，the safety operation and residents’ life along the Batura Sar may be threatened by these four glaciers advance.     

Estimation of Arctic glacier motion with satellite L-band SAR data

Offset fields between pairs of JERS-1 satellite SAR data acquired in winter with 44 days time interval were employed for the estimation of Arctic glacier motion over Svalbard, Novaya Zemlya and Franz-Josef Land. The displacement maps show that the ice caps are divided into a number of clearly defined fast-flowing units with displacement larger than about 6 m in 44 days (i.e. 50 m/year). The estimated error of the JERS-1 offset tracking derived displacement is on the order of 20 m/year. Occasionally, azimuth streaks related to auroral zone ionospheric disturbances were detected and dedicated processing steps were applied to minimize their influence on the estimated motion pattern. Our analysis demonstrated that offset tracking of L-band SAR images is a robust and direct estimation technique of glacier motion. The method is particularly useful when differential SAR interferometry is limited by loss of coherence, i.e. for rapid and incoherent flow and large acquisition time intervals between the two SAR images. The JERS-1 results, obtained using SAR data acquired by a satellite operated until 1998, raise expectations of L-band SAR data from the ALOS satellite launched in early 2006.     

Quantification of annual glacier surface mass balance for the Chhota Shigri Glacier,Western Himalayas,India using an Equilibrium-Line Altitude (ELA) based approach

ABSTRACT

In line with the increasing scientific interest on the Himalayan glaciers, this study focuses on estimating a long-term annual surface mass balance time series of the Chhota Shigri glacier, a ‘benchmark’ glacier in the western Himalayas. The approach used here is based on the fact that the annual glacier-wide surface mass balance can be deduced from the equilibrium-line altitude (ELA). Depending on the distribution and availability of multiple cloud free remotely sensed images during ablation period, a multi-temporal approach has been used to estimate ELA. When compared with field-based ELA, the results indicate that the multi-temporal approach resulted in better estimates of ELA than the conventional single image approach. Likewise, the annual surface mass balances quantified from this study closely match with field estimates over the common period (2003–2014) and even better than some estimates from earlier studies based on other proxies (meteorological data or glacier surface albedo). A sensitivity analysis shows that the annual surface mass balance quantified from the ELA-based approach is not very sensitive to changes in the mass balance gradient and average mass balance. Hence, the approach has been further applied to reconstruct the long-term annual surface mass balance series of the Chhota Shigri Glacier over the period 1989–2017. Our results show a good agreement between the reconstructed surface mass balance and estimates of other long-term studies. Therefore, this study indicates the great potential for this approach for quantifying the annual surface mass balance for glaciers with no ground data lying in same climatic zone.     

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。     

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。     

Synergistic approach for mapping debris-covered glaciers using optical-thermal remote sensing data with inputs from geomorphometric parameters

Debris cover on glacier boundaries critically impedes the global inventorying of glaciers and confounds most of the techniques developed for semi-automated mapping of glaciers. Debris on the glacier (referred as supraglacial debris) and that occurring outside the glacier boundaries (referred as periglacial debris) being derived from a common source, i.e. the valley rock, tend to have a similar spectral response in the reflection region which renders them mutually indistinguishable. However, there exist temperature differences between them. This aspect has been considered in this remote sensing based study to distinguish between the supraglacial and periglacial debris in a test area in the Chenab basin, Himalayas, by inclusion of thermal infrared (TIR) bands in remote sensing data processing. A synergistic multisensor approach for the delineation of debris-covered glacier boundaries is used here which integrates the inputs from thermal (TERRA-ASTER sensor) and optical (IRS-P6-AWiFS sensor) remote sensing data, multispectral classification techniques and the DEM derived geomorphometric parameters. The results of this study corroborate earlier findings on utilization of temperature differences as one of the parameters in glacial studies. The proposed synergistic approach therefore appears useful in accurate mapping of debris-covered glaciers in the Himalayan region.     

基于时序像素跟踪算法的南伊内里切克冰川运动提取与特征分析

选用Sentinel-1A卫星TOPS模式下获取的8景升轨SAR数据，基于小基线集像素跟踪时序分析技术（Small BAseline Subset Pixel Tracking technique， SBAS-PT），获取了南伊内里切克冰川2018年1月至2018年12月期间不同时段的表面流速分布及其时空变化特征。研究结果表明：2018年南伊内里切克冰川1月到3月整体运动速率较小，从4月起速率明显增加，7月到8月达到最高，9月份起运动速率开始放缓，10月到12月期间冰川表面运动速率较小，全年的平均表面流速约为30cm·d^-1。总体而言，南伊内里切克冰川中上游区域流速明显高于冰川下游，冰川下游冰川物质消融减薄和补给量减少以及表碛物增多等因素致使冰川末端区域逐渐趋于稳定。     

Remote-sensing assessment of glacier fluctuations in the Hindu Raj,Pakistan

Space-based assessments of glaciers across the Himalayas indicate that there is a spatial variation in glacier fluctuations due to variations in local topography, regional climate, and ice-flow dynamics. Unfortunately, limited information is available on glacier fluctuations in northern Pakistan. In this work, we quantify the glacier terminus variations in the Hindu Raj region of Pakistan, where we used Landsat and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) time-series data for 1972, 1989, 1999, and 2007. Eighty-five mountain glaciers of various sizes, orientations, and altitudes were sampled. Our results show that most of the glaciers (70.6%) retreated over the last four decades, although some glaciers advanced (17.6%) or exhibited no detectable change in terminus position (11.8%). Larger glaciers with lower terminus altitudes exhibited greater retreat distances than smaller high-altitude glaciers. Long-term climate data analysis reveals that the recession of glaciers appears to be associated with the rising of summer temperatures in the Hindu Raj. Our results support a spatial trend of an increase in shrinking glaciers towards the western portion of northern Pakistan, with a greater frequency of advancing glaciers towards the east.     

Towards automated mapping and monitoring of potentially dangerous glacial lakes in Bhutan Himalaya using Sentinel-1 Synthetic Aperture Radar data

The majority of glacial lakes around the world are located in remote and hardly accessible regions. The use of remote sensing data is therefore of high importance to identify and assess their potential hazards. However, the persistence of cloud cover, particularly in high mountain areas such as the Himalayas, limits the temporal resolution of optical satellite data with which we can monitor potentially dangerous glacial lakes (PDGLs). The ability of Synthetic Aperture Radar (SAR) satellites to collect data, irrespective of weather and at day or night, facilitates monitoring of PDGLs by without compromising temporal resolution. In this study, we present a semi-automated approach, based on a radar signal intensity threshold between water and non-water feature classes followed by post-processing including elevations, slopes, vegetation and size thresholds, to delineate glacial lakes in Sentinel-1 SAR images in Bhutan Himalaya. We show the capability of our method to be used for delineating and monitoring glacial lakes in Bhutan Himalaya by comparing our results to 10 m resolution Sentinel-2 multispectral data, field survey data, meteorological data, and a time series of monthly images from January to December 2016 of two lakes. Sentinel-1 SAR data can, moreover, be used for detecting lake surface area changes and open water area variations, at temporal resolution of six days, providing substantial advantages over optical satellite data to continuously monitor PDGLs.     

Deformation mapping in three dimensions for underground mining using InSAR – Southern highland coalfield in New South Wales,Australia

This article presents 3D surface deformation mapping results derived from satellite synthetic aperture radar (SAR) data acquired over underground coal mines. Both ENVISAT Advanced Synthetic Aperture Radar (ASAR) and Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) data were used in this study. The quality of the 3D deformation mapping results due to underground mining is mainly limited by two factors. (1) Differential interferometric synthetic aperture radar (DInSAR) is less sensitive to displacement along the north–south direction in the case of the current SAR satellite configurations. (2) The mining-induced displacement is continuous and nonlinear; and the accuracy of the 3D DInSAR measurement is severely affected by the similar but non-identical temporal overlaps of the InSAR pairs. The simulation and real data analyzes have shown that it would be more practical to use DInSAR pairs with the assumption of negligible northing displacement to derive the displacements in the easting and vertical directions. The northing displacement could then be estimated from the residuals. This limitation could be overcome in the future with the launch of more radar satellites, which would provide better viewing geometry.     

一种InSAR相关系数精估计方法

InSAR的相关系数是对SAR干涉图像对相似度的度量,是InSAR技术应用分析的一项基本参数。相关系数的估计是通过比较两幅SAR图像中对应位置的相邻像素值得到的,由于采样点数目的限制及存在由于地形起伏引起的干涉相位,估计结果往往与真实值相差较大。本文提出了一种能够大幅减小相关系数估计误差的方法,首先利用粗精度DEM仿真地形相位以消除地形起伏对相关系数估计的影响,随后采用第二类统计方法进一步提高了相关系数的估计精度。我们用SIR-C/XSAR的Etna火山干涉数据对本文方法进行了验证。