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.     

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.     

Routine Monitoring of Changes in the Columbia Glacier, Alaska, with Synthetic Aperture Radar

This study focuses on the use of spaceborne Synthetic Aperture Radar (SAR) from the European Remote Sensing Satellite (ERS-1) and the Canadian RADARSAT satellite to monitor retreating glaciers, specifically the Columbia Glacier, and the hazards caused by their recession on a routine basis. The Columbia Glacier is an important tidewater glacier to monitor because of its present rapid retreat, its generation of icebergs, and its vicinity to oil-tanker traffic in and out of the Port of Valdez, Alaska. We have established routine monitoring of the Prince William Sound area using SAR aboard the Canadian RADARSAT on a semi-weekly basis. To demonstrate the use of this data, four ERS-1 and seven RADARSAT SAR images from 1992 to 1998 are used in this study to monitor the long-term retreat of the Columbia Glacier. A loss of 17.7±0.2 square kilometers is measured from 1992 to 1997, with 38.4% of this change occurring from 1993 to 1994. Also, hazards such as icebergs are monitored in near real-time. SAR is an efficient and cost-effective means of monitoring glaciers, where cloud cover and logistical costs and difficulties hamper other data-collection efforts. These data are available to U.S. Government users and would be of benefit to the Prince William Sound region if used operationally.     

Perito Moreno Glacier (Argentina) flow estimation by COSMO SkyMed sequence of high-resolution SAR-X imagery

The Perito Moreno Glacier (Los Glaciares National Park, Patagonia, Argentina) ice stream has been investigated using X-band SAR amplitude images collected from February to December 2009 (excluding June) at time intervals of 8 and 16 days by the COSMO SkyMed satellites. The high spatial resolution dataset (10 × 10 km swath, 1 m per pixel) reveals many details of the glacier surface and the ice velocity fields extracted from sequential image pairs by the maximum cross-correlation method cover most of the glacier area. The efficiency of the cross-correlation method improves with high spatial resolution imagery and the co-registration error of the image pair also reduces. The glacier motion detected in the period shows variability on the time scale considered, evidencing the areas of higher dynamics under different speed regimes.     

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.     

Glacier changes in Glacier Bay,Alaska, during 2000–2012

This article presents measurements of glacier surface areas, mean snow line altitude (MSLA) values, mean snow accumulation area ratio (MAAR) values, and elevation changes in the Glacier Bay, Alaska, using Landsat Thematic Mapper (TM)/Landsat Enhanced Thematic Mapper Plus (ETM+) images and digital elevation models (DEMs) from Shuttle Radar Topography Mission (SRTM) and interferometric synthetic aperture radar (IFSAR) data during 2000–2012. Glacier area estimation results showed that Desolation glacier and Fairweather glacier have lost 2.6% and 2.2% of the glacier area, respectively. Only minor surface area changes were seen in Cascade glacier, Crillon glacier, and Lituya glacier during the study period. The results of MSLA and MAAR showed that the MSLA of Fairweather glacier, Lituya glacier, and Desolation glacier increased by about 120–289 m and the MAAR of Fairweather glacier, Lituya glacier, and Desolation glacier decreased by about 3–6%. In contrast, MSLA and MAAR of Crillon glacier decreased by about 70 m and increased by about 1%, respectively. Glacier elevation change results showed that 7.7 m, 4.6 m and 1.5 m of mean thinning change were observed, respectively, on Fairweather glacier, Lituya glacier, and Desolation glacier. However, 7 m and 0.65 m of mean thickening were, respectively, experienced on Cascade glacier and Crillon glacier in the same period. Results from the study indicated that glacier retreat (Fairweather glacier, Lituya glacier, and Desolation glacier) affected by higher temperatures probably dominates with over-increased precipitation. However, increasing debris cover on the glacier surface can also modify the glacier dynamic, resulting in a different response to global warming.     

Wind resource assessment from C-band SAR

Using accurate inputs of wind speed is crucial in wind resource assessment, as predicted power is proportional to the wind speed cubed. First, wind speeds retrieved from a series of 91 ERS-2 SAR and Envisat ASAR images, at moderate wind speeds (2-15 m s^− 1), were validated against in situ measurements from an offshore mast in the North Sea. The wind direction input, necessary for SAR wind speed retrievals, was obtained from the meteorological mast and from a local gradient analysis of wind streaks in the SAR images. A wind speed standard deviation of ∼ 1.1 m s^− 1 was found when in situ wind directions were used. The use of local gradient wind directions yielded a standard deviation of ∼ 1.3 m s^− 1. Wind speeds retrieved from three geophysical model functions (CMOD-IFR2, CMOD4, and CMOD5) were compared. The best approximation to the in situ measurements of wind speed was found for CMOD-IFR2, despite a bias on the order of − 0.3 m s^− 1. CMOD4 retrievals also underestimated the wind speed, whereas the bias on CMOD5 retrievals was negligible. Then, wind resource assessments were made from the SAR-based wind observations to show how errors in wind speed from the different SAR wind retrievals were reflected in the wind statistics. The mean wind speed, obtained for all of the 91 SAR scenes, was linked closely to the bias of SAR wind retrievals. Agreement to ± 15% of the in situ measurements was found for all the wind retrieval methods tested. The accuracy of power density estimates for the entire data set was evaluated by the standard deviation of SAR wind retrievals relative to the in situ measurements. SAR wind fields retrieved with CMOD-IFR2, using in situ wind direction inputs, exactly yielded the power density predicted from in situ measurements alone. The SAR-based wind resource assessment also corresponded well to predictions from longer time series of in situ measurements. This indicates that a reliable wind resource assessment may be achieved from a series of randomly selected SAR images. The findings presented here could be useful in future wind resource assessment based on SAR images.     

Estimation and validation of glacier surface motion in the northwestern Himalayas using high-resolution SAR intensity tracking

We estimate two-dimensional (2D) glacier surface motion using synthetic aperture radar (SAR) X-band intensity tracking. It has been observed that the viability of SAR interferometry (InSAR) is often limited by coherence loss over glaciers in landlocked regions using SAR data pairs of more than 1 day temporal baseline. An alternative to InSAR is the intensity-tracking approach, which relies on intensity cross-correlation for the estimation of subpixel surface motion in range and azimuth direction. In this work, we apply this approach for 2D glacier surface motion estimation in the north-western (NW) Himalayas, using TerraSAR-X (TS-X) spotlight mode high-resolution data pairs of 11, 22, and 33 day temporal separation. The results are in good agreement with total station surveying measurements synchronous with the satellite data acquisition period. The technique is found to be highly appropriate for monitoring the flow rate of glaciers in the Himalayas on a multitemporal basis.     

Glacier Mapper – a new method designed to assess change in mountain glaciers

This study proposes a new method designed to assess quantitative changes in mountain glaciers. The Glacier Mapper–Change Detector method has a four-step algorithm: (i) image ratioing on two time-comparable satellite images; (ii) digitization of glacier outlines from ratio images using a threshold value; (iii) change detection using the position of glacier outlines at two different moments in time; and (iv) derivation of the future evolution model by using relief-related parameters of glacier changes. The method was calibrated and verified for the Elbrus (Greater Caucasus) glacier over the period 1985–2007 using Landsat TM images. The Glacier Mapper–Change Detector results indicated altitude as the most important relief control for glacial retreat. The most probable future glacial area losses modelled reflect the 1985–2007 glacial retreat patterns.     

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。     

Subglacial controls on dynamic thinning at Trinity-Wykeham Glacier,Prince of Wales Ice Field,Canadian Arctic

ABSTRACT

Mass loss from glaciers and ice caps represents the largest terrestrial component of current sea level rise. However, our understanding of how the processes governing mass loss will respond to climate warming remains incomplete. This study explores the relationship between surface elevation changes (dh/dt), glacier velocity changes (du/dt), and bedrock topography at the Trinity-Wykeham Glacier system (TWG), Canadian High Arctic, using a range of satellite and airborne datasets. We use measurements of dh/dt from ICESat (2003–2009) and CryoSat-2 (2010–2016) repeat observations to show that rates of surface lowering increased from 4 m yr^?1 to 6 m yr^?1 across the lowermost 10 km of the TWG. We show that surface flow rates at both Trinity Glacier and Wykeham Glacier doubled over 16 years, during which time the ice front retreated 4.45 km. The combination of thinning, acceleration and retreat of the TWG suggests that a dynamic thinning mechanism is responsible for the observed changes, and we suggest that both glaciers have transitioned from fully grounded to partially floating. Furthermore, by comparing the separate glacier troughs we suggest that the dynamic changes are modulated by both lateral friction from the valley sides and the complex geometry of the bed. Further, the presence of bedrock ridges induces crevassing on the surface and provides a direct link for surface meltwater to reach the bed. We observe supraglacial lakes that drain at the end of summer and are concurrent with a reduction in glacier velocity, suggesting hydrological connections between the surface and the bed significantly impact ice flow. The bedrock topography thus has a primary influence on the nature of the changes in ice dynamics observed over the last decade.     

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.     

Validation of ERS-2 SAR offshore wind-speed maps in the North Sea

Wind maps are retrieved from ERS-2 Synthetic Aperture Radar (SAR) scenes by the CMOD-IFR2 and CMOD4 algorithms for 61 cases at the Horns Rev site in the North Sea and compared to meteorological in situ observations from a mast located 14?km offshore. The in situ data are corrected for flow distortion and sea-level changes prior to validating the SAR wind maps. The SAR wind maps are area-averaged by a simple footprint method assuming neutral stability and with three nonlinear weighting footprint methods including correction for stability. From a physical point of view, the latter is more correct. However, between in situ and SAR-derived wind-speed estimates comparison results of the nonlinear footprint values are statistically less correlated (R ²=0.73–0.77) and the standard error (SE) is larger (>1.5?m?s^?1) than results from the simple footprint (R ²=0.78–0.80 and SE=1.3?m?s^?1). The results are found with wind direction determined from wind streaks in the SAR images by Fast Fourier Transform. Using in situ wind direction as input to the CMOD-IFR2 and CMOD4 algorithms yields even better linear regression results, e.g. for the simple footprint method R ²=0.88 and SE=0.9?m?s^?1. SAR wind maps may be useful for mapping of future offshore wind resources.     

Find the firn line! The suitability of ERS-1 and ERS-2 SAR data for the analysis of glacier facies on Icelandic icecaps

Icelandic Icecaps are sensitive indicators of climatic fluctuations. Glacier facies boundaries can be identified using remote sensing techniques; SAR data represents the first real opportunity to monitor glacier facies, without cloud attenuation at regular or inter-annual intervals. This study assesses the overall suitability of the data for the monitoring of glacier facies and in particular the firn line altitude (FLA) on Icelandic Icecaps. The results show that the firn line can be identified and located to within +/- 20-40m (vertically). These results were validated using aerial photograph and ground data. RAIDS (Rapid Information Dissemination System) processed data were found to compare favourably with other satellite data for this type of application.     

Internal wave study in the South China Sea using Synthetic Aperture Radar (SAR)

Internal wave distribution maps have been compiled from more than one hundred ERS-1/2, RADARSAT and Space Shuttle SAR images in the South China Sea (SCS) from 1993 to 2000. Based on these distribution maps, most of the internal waves in the north-east part of the SCS were propagating westward. The wave crest can be as long as 200?km with an amplitude of 100?m, due to strong current from the Kuroshio branching out into the SCS. In a recent SCS internal wave study, moorings were deployed in April 1999 and 2000. Simultaneous SAR coverage from ERS-2 and RADARSAT were also collected. The ERS-2 high-resolution SAR images collected from the Taiwan ground station were processed in near real-time to coordinate the field test. SAR data are then used to compare with mooring data. SAR data and Acoustic Doppler Current Profiler (ADCP) data show internal solitons induced by the semi-diurnal tides with a wave speed of 2.4?m?s^?1.     

The effect of sinusoidal rolling ground motion on lifting biomechanics

The objective of this study was to quantify the effects of ground surface motion on the biomechanical responses of a person performing a lifting task. A boat motion simulator (BMS) was built to provide a sinusoidal ground motion (simultaneous vertical linear translation and a roll angular displacement) that simulates the deck motion on a small fishing boat. Sixteen participants performed lifting, lowering and static holding tasks under conditions of two levels of mass (5 and 10 kg) and five ground moving conditions. Each ground moving condition was specified by its ground angular displacement and instantaneous vertical acceleration: A): +6°, −0.54 m/s²; B): +3°, −0.27 m/s²; C): 0°, 0 m/s²; D): −3°, 0.27 m/s²; and E): −6°, 0.54 m/s². As they performed these tasks, trunk kinematics were captured using the lumbar motion monitor and trunk muscle activities were evaluated through surface electromyography. The results showed that peak sagittal plane angular acceleration was significantly higher in Condition A than in Conditions C, D and E (698°/s² vs. 612–617°/s²) while peak sagittal plane angular deceleration during lowering was significantly higher in moving conditions (conditions A and E) than in the stationary condition C (538–542°/s² vs. 487°/s²). The EMG results indicate that the boat motions tend to amplify the effects of the slant of the lifting surface and the external oblique musculature plays an important role in stabilizing the torso during these dynamic lifting tasks.     

Radar imaging of Kelvin arms of ship wakes

The wave pattern generated by a moving ship is formed by two dominant features: the turbulent wake and a 'V'-shaped pattern trailing the ship, consisting of the two Kelvin arms. In this paper we investigate the radar imaging mechanism of Kelvin arms, which are formed by the cusp waves. A composite surface model for the radar backscattering at the ocean surface is used. The radar signatures of Kelvin arms can be attributed to tilt and hydrodynamic modulation of Bragg waves by the cusp waves. The proposed model allows the computation of the normalized radar backscattering cross-section (NRCS) as a function of radar frequency, polarization, incidence angle, wind speed and direction, and wavelength, direction, and slope of the cusp waves. By using this imaging model, radar signatures of cusp waves are calculated for several spaceborne Synthetic Aperture Radars (SARs): (1) the SEASAT L-band HH-polarized SAR, (2) the ERS-1/-2 VV-polarized SAR, (3) the RADARSAT C-band HH-polarized SAR, and (4) the X-, C- and L-band multipolarization SARs of the Space Radar Laboratory flown on the space shuttle during the SIRC/X-SAR mission in 1994. The results of the simulations are compared with SEASAT and SIR-C/X-SAR imagery of ship wake patterns. It is shown that the dependence of the observed radar signatures of Kelvin arms on radar look direction is consistent with the proposed imaging theory and that the measured relative mean NRCS values induced by Kelvin arms can be fairly well reproduced by the proposed model. The simulations indicate that ship wake signatures should be more clearly visible on SEASAT L-band SAR than on ERS-1/-2 or RADARSAT C-band SAR images. The radar signatures of Kelvin arms are strongest at low wind speeds and are not very sensitive to wind direction.     

Assessment of C-band synthetic aperture radar data for mapping and monitoring Coastal Plain forested wetlands in the Mid-Atlantic Region,U.S.A.

Multi-temporal C-band SAR data (C-HH and C-VV), collected by ERS-2 and ENVISAT satellite systems, are compared with field observations of hydrology (i.e., inundation and soil moisture) and National Wetland Inventory maps (U.S. Fish and Wildlife Service) of a large forested wetland complex adjacent to the Patuxent and Middle Patuxent Rivers, tributaries of the Chesapeake Bay. Multi-temporal C-band SAR data were shown to be capable of mapping forested wetlands and monitoring hydroperiod (i.e., temporal fluctuations in inundation and soil moisture) at the study site, and the discrimination of wetland from upland was improved with 10 m digital elevation data. Principal component analysis was used to summarize the multi-temporal SAR data sets and to isolate the dominant temporal trend in inundation and soil moisture (i.e., relative hydroperiod). Significant positive, linear correlations were found between the first principal component and percent area flooded and soil moisture. The correlation (r²) between the first principal component (PC1) of multi-temporal C-HH SAR data and average soil moisture was 0.88 (p = < .0001) during the leaf-off season and 0.87 (p = < .0001) during the leaf-on season, while the correlation between PC1 and average percent area inundated was 0.82 (p = < .0001) and 0.47 (p = .0016) during the leaf-off and leaf-on seasons, respectively. When compared to field data, the SAR forested wetland maps identified areas that were flooded for 25% of the time with 63–96% agreement and areas flooded for 5% of the time with 44–89% agreement, depending on polarization and time of year. The results are encouraging and justify further studies to attempt to quantify the relative SAR-derived hydroperiod classes in terms of physical variables and also to test the application of SAR data to more diverse landscapes at a broader scale. The present evidence suggests that the SAR data will significantly improve routine wooded wetland mapping.     

Evaluating ERS-1 SAR data for the discrimination of tropical forest from other tropical vegetation types in Papua New Guinea

ERS-1 Synthetic Aperture Radar (SAR) data over a study area located in Papua New Guinea, where there is a high probability of cloud cover, are evaluated on their information content for mapping tropical forest ecosystems. The feasibility of forest/non-forest discrimination using mono- and multi-temporal ERS-1 SAR data at 100m pixel size is investigated using two different classification methodologies. An assessment of the optimal acquisition period and number of acquisitions is undertaken. The automatic classification results are compared quantitatively with the aid of field observations in a comparative accuracy assessment methodology, and a comparison is made with Landsat Thematic Mapper (TM) data. Finally, the potential of ERS-1 SAR data for the discrimination of tropical forest types is investigated. The results showed that multi-temporal ERS-1 SAR data acquired at the appropriate times were found to have a high potential for forest/nonforest discrimination and achieved similar classification accuracies to the TM data. The discrimination of forest types proved difficult. However, discrimination was possible between dense and open forest types having different canopy structures.     

Mapping ice sheet margins from ERS-1 SAR and SPOT imagery

We demonstrate a new technique to automatically map the margin of ice sheets using ERS-1 SAR and SPOT imagery. The technique relies on a series of image processing techniques including edge enhancement, dynamic thresholding, region growing, edge detection, and edge following. The mapping technique is used to measure temporal displacement of the ice sheet margin north and south of the Jakobshavn Glacier in Greenland. During the 4 year interval between 1988 and 1992 we find ice sheet margin advance/retreat rates of about +/- 12m/year, consistent with independent observation. We combine the 1988 and 1992 data to assign an average ice margin location for the observation interval assuming a constant displacement rate. The resulting snapshot of the ice sheet margin can be used as a benchmark for future change detection studies. In both cases the uncertainties are better than 200m.