With the development of remote sensing techniques, optical images become more efficient compare to field survey. However, the quality of optical images would influenced by cloud. Radar is known to be very sensitive to vegetation physiognomy and biomass. The sensitivity of synthetic aperture radar (SAR) to the structural features of terrain leads to landcover classification into simple and easily interpreted structural classes. In this paper, the potential of using free of charge Sentinel-1 SAR imagery for land cover mapping in the Moravian-Silesian region, is investigated. The images recorded in 2018 were used for a per-pixel and object-based classification of agricultural land. The per-pixel classification was performed by the maximum likelihood algorithm, the object-based classification then using the support vector machine algorithm. The legend was taken from the Land Parcel Identification System (LPIS) and contained the following three classes – grassland, arable land and a class that involves hop fields, vineyards, and orchards. Post processing of the classification results has been done using the confusion matrix (also known as error matrix) and corresponding overall accuracy and Kappa coefficients of all the classification methods have been calculated. Significantly better results were achieved through object-oriented classification. In both areas of interest, the highest processing and user precision was achieved for the arable land class.

With its temporal resolution of 10 days (five days with two satellites, and significantly more at high latitudes), its swath width of 290 km, and its 10 m and 20 m spatial resolution bands from the visible to the shortwave infrared, the European Sentinel-2 satellites have significant potential for glacier remote sensing, in particular mapping of glacier outlines and facies, and velocity measurements. Testing Level 1C commissioning and ramp-up phase data for initial sensor quality experiences, we find a high radiometric performance, but with slight striping effects under certain conditions. Through co-registration of repeat Sentinal-2 data we also find lateral offset patterns and noise on the order of a few metres. Neither of these issues will complicate most typical glaciological applications. Absolute geo-location of the data investigated was on the order of one pixel at the time of writing. The most severe geometric problem stems from vertical errors of the DEM used for ortho-rectifying Sentinel-2 data. These errors propagate into locally varying lateral offsets in the images, up to several pixels with respect to other georeferenced data, or between Sentinel-2 data from different orbits. Finally, we characterize the potential and limitations of tracking glacier flow from repeat Sentinel-2 data using a set of typical glaciers in different environments: Aletsch Glacier, Swiss Alps; Fox Glacier, New Zealand; Jakobshavn Isbree, Greenland; Antarctic Peninsula at the Larsen C ice shelf.

We report on the recent reactivation of a large rift in the Brunt Ice Shelf, East Antarctica, in December 2012, and the formation of a 50-km long new rift in October 2016. Observations from a suite of ground based and remote sensing instruments between January 2000 and July 2017 were used to track progress of both rifts in unprecedented detail. Results reveal a steady accelerating trend in their width, in combination with alternating episodes of fast (> 600 m/day) and slow propagation of the rift tip, controlled by the heterogeneous structure of the ice shelf. A numerical ice-flow model and a simple propagation algorithm 5 based on the stress distribution in the ice shelf were successfully used to hindcast the observed trajectories, and to simulate future rift progression under different assumptions. Results show a high likelihood of ice loss at the McDonald Ice Rumples, the only pinning point of the ice shelf. The nascent iceberg calving and associated reduction in pinning of the Brunt Ice Shelf may provide a uniquely monitored natural experiment of ice shelf variability, and provoke a deeper understanding of similar processes elsewhere in Antarctica. 10

We employ Sentinel-1a C band satellite radar interferometry data in Terrain Observation with Progressive Scans mode to map the grounding line and ice velocity of Pope, Smith, and Kohler glaciers, in West Antarctica, for the years 2014–2016 and compare the results with those obtained using Earth Remote Sensing Satellites (ERS-1/2) in 1992, 1996, and 2011. We observe an ongoing, rapid grounding line retreat of Smith at 2 km/yr (40 km since 1996), an 11 km retreat of Pope (0.5 km/yr), and a 2 km readvance of Kohler since 2011. The variability in glacier retreat is consistent with the distribution of basal slopes, i.e., fast along retrograde beds and slow along prograde beds. We find that several pinning points holding Dotson and Crosson ice shelves disappeared since 1996 due to ice shelf thinning, which signal the ongoing weakening of these ice shelves. Overall, the results indicate that ice shelf and glacier retreat in this sector remain unabated.

We computed circum-Arctic surface velocity maps of glaciers and ice caps over the Canadian Arctic, Svalbard and the Russian Arctic for at least two times between the 1990s and 2017 using satellite SAR data. Our analyses are mainly performed with offset-tracking of ALOS-1 PALSAR-1 (2007–2011) and Sentinel-1 (2015–2017) data. In certain cases JERS-1 SAR (1994–1998), TerraSAR-X (2008–2012), Radarsat-2 (2009–2016) and ALOS-2 PALSAR-2 (2015–2016) data were used to fill-in spatial or temporal gaps. Validation of the latest Sentinel-1 results was accomplished by means of SAR data at higher spatial resolution (Radarsat-2 Wide Ultra Fine) and ground-based measurements. In general, we observe a deceleration of flow velocities for the major tidewater glaciers in the Canadian Arctic and an increase in frontal velocity along with a retreat of frontal positions over Svalbard and the Russian Arctic. However, all regions have strong accelerations for selected glaciers. The latter developments can be well traced based on the very high temporal sampling of Sentinel-1 acquisitions since 2015, revealing new insights in glacier dynamics. For example, surges on Spitsbergen (e.g., Negribreen, Nathorsbreen, Penckbreen and Strongbreen) have a different characteristic and timing than those over Eastern Austfonna and Edgeoya (e.g., Basin 3, Basin 2 and Stonebreen). Events similar to those ongoing on Eastern Austofonna were also observed over the Vavilov Ice Cap on Severnaya Zemlya and possibly Simony Glacier on Franz-Josef Land. Collectively, there seems to be a recently increasing number of glaciers with frontal destabilization over Eastern Svalbard and the Russian Arctic compared to the 1990s.

Various glaciological topics require observations of horizontal velocities over vast areas, e.g., detecting acceleration of glaciers, as well as for estimating basal parameters of ice sheets using inverse modelling approaches. The quality of the velocity is of high importance; hence, methods to remove noisy points in remote sensing derived data are required. We present a three-step filtering process and assess its performance for velocity fields in Greenland and Antarctica. The filtering uses the detection of smooth segments, removal of outliers using the median and constraints on the variability of the flow direction over short distances. The applied filter preserves the structures in the velocity fields well (e.g., shear margins) and removes noisy data points successfully, while keeping 72–96% of the data. In slow flowing regions, which are particularly challenging, the standard deviation is reduced by up to 96%, an improvement that affects vast areas of the ice sheets.

Variations of the ionosphere can significantly disrupt synthetic aperture radar (SAR) acquisitions and interferometric measurements of ground deformation. In this paper, we show how the ionosphere can also strongly modify C-band interferograms despite its smaller influence at higher frequencies. Thus, ionospheric phase screens should not be neglected: their compensation improves the estimation of ground deformation maps. The split-spectrum method is able to estimate the dispersive ionospheric component of the interferometric phase; we describe the implementation of this method for the burst modes TOPS and ScanSAR to estimate and remove ionospheric phase screens. We present Sentinel-1 interferograms of the 2016 Taiwan earthquake and ALOS-2 interferograms of the 2015 Nepal earthquake, which show strong ionospheric phase gradients, and their corrected versions. Finally, to validate the results and better understand the origin of these ionospheric variations, we compare the estimated differential ionosphere with global Total Electron Content maps and local Global Positioning System measurements.

This paper presents the first comprehensive review on the scientific utilization of earth observation data provided by the German TerraSAR-X mission. It considers the different application fields and technical capabilities to identify the key applications and the preferred technical capabilities of this high-resolution SAR satellite system from a scientific point of view. The TerraSAR-X mission is conducted in a close cooperation with industry. Over the past decade, scientists have gained access to data through a proposal submission and evaluation process. For this review, we have considered 1636 data utilization proposals and analyzed 2850 publications. In general, TerraSAR-X data is used in a wide range of geoscientific research areas comprising anthroposphere, biosphere, cryosphere, geosphere, and hydrosphere. Methodological and technical research is a cross-cutting issue that supports all geoscientific fields. Most of the proposals address research questions concerning the geosphere, whereas the majority of the publications focused on research regarding “methods and techniques”. All geoscientific fields involve systematic observations for the establishment of time series in support of monitoring activities. High-resolution SAR data are mainly used for the determination and investigation of surface movements, where SAR interferometry in its different variants is the predominant technology. However, feature tracking techniques also benefit from the high spatial resolution. Researchers make use of polarimetric SAR capabilities, although they are not a key feature of the TerraSAR-X system. The StripMap mode with three meter spatial resolution is the preferred SAR imaging mode, accounting for 60 percent of all scientific data acquisitions. The Spotlight modes with the highest spatial resolution of less than one meter are requested by only approximately 30 percent of the newly acquired TerraSAR-X data.

The velocity of ice flow in the Antarctic is a crucial factor to determine ice discharge and thus future sea level rise. Feature tracking has been widely used in optical and radar imagery with fine resolution to retrieve flow parameters, although the primitive result may be contaminated by noise. In this paper, we present a series of modified post-processing steps, such as SNR thresholding by residual, complex Butterworth filters, and triple standard deviation truncation, to improve the performance of primitive results, and apply it to MODIS-based Mosaic of Antarctica (MOA) datasets. The final velocity field result displays the general flow pattern of the peripheral Antarctic. Seventy-eight out of 97 streamlines starting from seed points are smooth and continuous. The RMSE with 178 manually selected tie points is within 60 m·a−1. The systematic comparison with Making Earth System Data Records for Use in Research Environments (MEaSUREs) datasets in seven drainages shows that the results regarding high magnitude and large-scale ice shelf are highly reliable; absolute mean and median difference are less than 18 m·a−1, while the result of localized drainage suffered from too much tracking error. The relative differences from manually selected and random points are controlled within 8% when speed is beyond 500 m·a−1, but bias and uncertainty are pronounced when speed is lower than that. The result through our accuracy control strategy highlights that coarse remote-sensed images such as Moderate Resolution Imaging Spectrophotometer (MODIS) can still offer the capability for comprehensive and long-term continental ice sheet surface velocity mapping.

The melting of the polar ice caps is considered to be an essential factor for global sea-level rise and has received significant attention. Quantitative research on ice cap mass changes is critical in global climate change. In this study, GRACE JPL RL06 data under the Mascon scheme based on the dynamic method were used. Greenland, which is highly sensitive to climate change, was selected as the study area. Greenland was divided into six sub-research regions, according to its watersheds. The spatial–temporal mass changes were compared to corresponding temperature and precipitation statistics to analyze the relationship between changes in ice sheet mass and climate change. The results show that: (i) From February 2002 to September 2019, the rate of change in the Greenland Ice Sheet mass was about −263 ± 13 Gt yr−1 and the areas with the most substantial ice sheet loss and climate changes were concentrated in the western and southern parts of Greenland. (ii) The mass balance of the Greenland Ice Sheet during the study period was at a loss, and this was closely related to increasing trends in temperature and precipitation. (iii) In the coastal areas of western and southern Greenland, the rate of mass change has accelerated significantly, mainly because of climate change.

The long-term evolution of lakes on the Tibetan Plateau (TP) could be observed from Landsat series of satellite data since the 1970s. However, the seasonal cycles of lakes on the TP have received little attention due to high cloud contamination of the commonly-used optical images. In this study, for the first time, the seasonal cycle of lakes on the TP was detected using Sentinel-1 Synthetic Aperture Radar (SAR) data with a high repeat cycle. A total of approximately 6000 Level-1 scenes were obtained that covered all large lakes (>50 km2) in the study area. The images were extracted from stripmap (SM) and interferometric wide swath (IW) modes that had a pixel spacing of 40 m in the range and azimuth directions. The lake boundaries extracted from Sentinel-1 data using the algorithm developed in this study were in good agreement with in-situ measurements of lake shoreline, lake outlines delineated from the corresponding Landsat images in 2015 and lake levels for Qinghai Lake. Upon analysis, it was found that the seasonal cycles of lakes exhibited drastically different patterns across the TP. For example, large size lakes (>100 km2) reached their peaks in August-September while lakes with areas of 50-100 km2 reached their peaks in early June-July. The peaks of seasonal cycles for endorheic lakes were more pronounced than those for exorheic lakes with flat peaks, and glacier-fed lakes with additional supplies of water exhibited delayed peaks in their seasonal cycles relative to those of non-glacier-fed lakes. Large-scale atmospheric circulation systems, such as the westerlies, Indian summer monsoon, transition in between, and East Asian summer monsoon, were also found to affect the seasonal cycles of lakes. The results of this study suggest that Sentinel-1 SAR data are a powerful tool that can be used to fill gaps in intra-annual lake observations.

The Terrain Observation by Progressive Scans (TOPS) acquisition mode of the Sentinel-1 mission provides a wide coverage per acquisition with resolutions of 5 m in range and 20 m in azimuth, which makes this acquisition mode attractive for glacier velocity monitoring. Here, we retrieve surface velocities from the southern Ellesmere Island ice caps (Canadian Arctic) using both offset tracking and Differential Interferometric Synthetic Aperture Radar (D-InSAR) techniques and combining ascending and descending passes. We optimise the offset tracking technique by omitting the azimuth offsets. By doing so, we are able to improve the final resolution of the velocity product, as Sentinel-1 shows a lower resolution in the azimuth direction. Simultaneously, we avoid the undesired ionospheric effect manifested in the data as azimuth streaks. The D-InSAR technique shows its merits when applied to slow-moving areas, while offset tracking is more suitable for fast-moving areas. This research shows that the methods used here are complementary and the use of both to determine glacier velocities is better than only using one or the other. We observe glacier surface velocities of up to 1200 m year − 1 for the fastest tidewater glaciers. The land-terminating glaciers show typical velocities between 12 and 33 m year − 1 , though with peaks up to 150 m year − 1 in narrowing zones of the confining valleys.

The Sentinel satellite constellation series, developed and operated by the European Space Agency, represents the dedicated space component of the European Copernicus program, committed to long-term operational services in environment, climate and security. We developed, tested and evaluated an algorithm for generating maps of snowmelt area from C-band synthetic aperture radar (SAR) data of the Sentinel-1 mission. For snowmelt classification, a change detection method is applied, using multitemporal dual-polarized SAR data acquired in Interferometric Wide swath (IW) mode, the basic operation mode over land surfaces. Of particular benefit for wet snow retrievals are the high instrument stability, the high spatial resolution across the 250 km wide swath, and the short revisit time. In order to study the impact of polarization, we generated maps of melting snow using data of the VV-polarized channel, the VH-polarized channel and a combined VV- and VH-based channel using a weighting function that accounts for effects of the local incidence angle. Comparisons are performed with snow maps derived from Landsat images over study areas in the Alps and in Iceland. The pixel-by-pixel comparisons show good agreement between the snow products of the two sensors, with the best performance for retrievals based on the combined (VV and VH) channel and a minor decline for the VH-based product. The VV-based snowmelt extent product shows a drop-off in quality over areas with steep terrain because of the decreasing backscatter contrast of snow-covered versus snow-free surfaces on fore-slopes. The investigations demonstrate the excellent capability of the Sentinel-1 mission for operational monitoring of snowmelt areas.

The Greenland ice sheet is a major contributor to sea level rise, adding on average 0.47 ± 0.23 mm year−1 to global mean sea level between 1991 and 2015. The cryosphere as a whole has contributed around 45% of observed global sea level rise since 1993. Understanding the present-day state of the Greenland ice sheet is therefore vital for understanding the processes controlling the modern-day rates of sea level change and for making projections of sea level rise into the future. Here, we provide an overview of the current state of the mass budget of Greenland based on a diverse range of remote sensing observations to produce the essential climate variables (ECVs) of ice velocity, surface elevation change, grounding line location, calving front location, and gravimetric mass balance as well as numerical modelling that together build a consistent picture of a shrinking ice sheet. We also combine these observations with output from a regional climate model and from an ice sheet model to gain insight into existing biases in ice sheet dynamics and surface mass balance processes. Observations show surface lowering across virtually all regions of the ice sheet and at some locations up to −2.65 m year−1 between 1995 and 2017 based on radar altimetry analysis. In addition, calving fronts at 28 study sites, representing a sample of typical glaciers, have retreated all around Greenland since the 1990s and in only two out of 28 study locations have they remained stable. During the same period, two of five floating ice shelves have collapsed while the locations of grounding lines at the remaining three floating ice shelves have remained stable over the observation period. In a detailed case study with a fracture model at Petermann glacier, we demonstrate the potential sensitivity of these floating ice shelves to future warming. GRACE gravimetrically-derived mass balance (GMB) data shows that overall Greenland has lost 255 ± 15 Gt year−1 of ice over the period 2003 to 2016, consistent with that shown by IMBIE and a marked increase compared to a rate of loss of 83 ± 63 Gt year−1 in the 1993–2003 period. Regional climate model and ice sheet model simulations show that surface mass processes dominate the Greenland ice sheet mass budget over most of the interior. However, in areas of high ice velocity there is a significant contribution to mass Remote Sens. 2019, 11, 1407; doi:10.3390/rs11121407 www.mdpi.com/journal/remotesensing Remote Sens. 2019, 11, 1407 2 of 26 loss by ice dynamical processes. Marked differences between models and observations indicate that not all processes are captured accurately within models, indicating areas for future research.

The Greenland Ice Sheet (GrIS) is losing mass in response to recent climatic and oceanic warming. Since the mid-1990s, tidewater outlet glaciers across the ice sheet have thinned, retreated, and accelerated, but recent changes in northern Greenland have been comparatively understudied. Consequently, the dynamic response (i.e. changes in surface elevation and velocity) of these outlet glaciers to changes at their termini, particularly calving from floating ice tongues, is poorly constrained. Here we use satellite imagery and historical maps to produce an unprecedented 68-year record of terminus change across 18 major outlet glaciers and combine this with previously published surface elevation and velocity datasets. Overall, recent (1995–2015) retreat rates were higher than at any time in the previous 47 years (since 1948). Despite increased retreat rates from the 1990s, there was distinct variability in dynamic glacier behaviour depending on whether the terminus was grounded or floating. Grounded glaciers accelerated and thinned in response to retreat over the last 2 decades, while most glaciers terminating in ice tongues appeared dynamically insensitive to recent ice tongue retreat and/or total collapse. We also identify glacier geometry (e.g. fjord width, basal topography, and ice tongue confinement) as an important influence on the dynamic adjustment of glaciers to changes at their termini. Recent grounded outlet glacier retreat and ice tongue loss across northern Greenland suggest that the region is undergoing rapid change and could soon contribute substantially to sea level rise via the loss of grounded ice.

Systematically monitoring Greenland’s outlet glaciers is central to understanding the timescales over which their flow and sea level contributions evolve. In this study we use data from the new Sentinel-1a/b satellite constellation to generate 187 velocity maps, covering four key outlet glaciers in Greenland: Jakobshavn Isbræ, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachariæ Isstrøm. These data provide a new high temporal resolution record (6-day averaged solutions) of each glacier’s evolution since 2014, and resolve recent seasonal speedup periods and inter-annual changes in Greenland outlet glacier speed with an estimated certainty of 10 %. We find that since 2012, Jakobshavn Isbræ has been decelerating, and now flows approximately 1250 m yr−1 (10 %), slower than 5 years previously, thus reversing an increasing trend in ice velocity that has persisted during the last decade. Despite this, we show that seasonal variability in ice velocity remains significant: up to 750 m yr−1 (14 %) at a distance of 12 km inland of the terminus. We also use our new dataset to estimate the duration of speedup periods (80–95 days) and to demonstrate a strong relationship between ice front position and ice flow at Jakobshavn Isbræ, with increases in speed of ∼ 1800 m yr−1 in response to 1 km of retreat. Elsewhere, we record significant seasonal changes in flow of up to 25 % (2015) and 18 % (2016) at Petermann Glacier and Zachariæ Isstrøm, respectively. This study provides a first demonstration of the capacity of a new era of operational radar satellites to provide frequent and timely monitoring of ice sheet flow, and to better resolve the timescales over which glacier dynamics evolve.

Surface‐derived meltwater can access the bed of the Greenland ice sheet, causing seasonal velocity variations. The magnitude, timing, and net impact on annual average ice flow of these seasonal perturbations depend on the hydraulic efficiency of the subglacial drainage system. We examine the relationships between drainage system efficiency and ice velocity, at three contrasting tidewater glaciers in southwest Greenland during 2014–2019, using high‐resolution remotely sensed ice velocities, modeled surface melting, subglacial discharge at the terminus, and results from buoyant plume modeling. All glaciers underwent a seasonal speed‐up, which usually coincided with surface melt onset, and subsequent slow‐down, which usually followed inferred subglacial channelization. The amplitude and timing of these speed variations differed between glaciers, with the speed‐up being larger and more prolonged at our fastest study glacier. At all glaciers, however, the seasonal variations in ice flow are consistent with inferred changes in hydraulic efficiency of the subglacial drainage system and qualitatively indicative of a flow regime in which annually averaged ice velocity is relatively insensitive to interannual variations in meltwater supply—so‐called “ice flow self‐regulation.” These findings suggest that subglacial channel formation may exert a strong control on seasonal ice flow variations, even at fast‐flowing tidewater glaciers.

Supraglacial stream networks incise via thermal erosion of underlying ice, reflecting a balance between localized fluvial incision and dynamic topography from underlying ice flow. We analyze high-resolution digital elevation models of the ice surface and bedrock in the southwest Greenland Ice Sheet from 1000-1600 m elevation to quantify the importance of fluvial erosion. At wavelengths greater than ice thickness, bedrock dominates surface topography so supraglacial drainage basins are fixed spatially. At smaller wavelengths, fluvial erosion significantly affects topography. Stream longitudinal profiles exhibit positive mean curvature and consistent power law scaling between local channel slope and drainage area, suggestive of adjustment toward topographic steady state. We interpret these observations with a model for fluvial thermal erosion on top of a flowing ice substrate that predicts concave up steady state longitudinal profiles, where average concavity is most sensitive to melt rate and the relative magnitudes of ice flow and fluvial erosion.

Supraglacial lakes are an important component of the Greenland Ice Sheet’s mass balance and hydrology, with their drainage affecting ice dynamics. This study uses imagery from the recently launched Sentinel-1A Synthetic Aperture Radar (SAR) satellite to investigate supraglacial lakes in West Greenland. A semi-automated algorithm is developed to detect surface lakes from Sentinel-1 images during the 2015 summer. A combined Landsat-8 and Sentinel-1 dataset, which has a comparable temporal resolution to MODIS (3 days versus daily) but a higher spatial resolution (25-40 m versus 250-500 m), is then used together with a fully-automated lake drainage detection algorithm. Rapid ( 4 days) drainages are investigated for both small (< 0.125 km2, the minimum size detectable by MODIS) and large (≥ 0.125 km2) lakes through the summer. Drainage events of small lakes occur at lower elevations (mean 159 m), and slightly earlier (mean 4.5 days) in the melt season than those of large lakes. The analysis is extended manually into the early winter to calculate the dates and elevations of lake freeze-through more precisely than is possible with optical imagery (mean 30 August; 1270 m mean elevation). Finally, the Sentinel-1 imagery is used to detect subsurface lakes and, for the first time, their dates of appearance and freeze-through (mean 9 August and 7 October, respectively). These subsurface lakes occur at higher elevations than the surface lakes detected in this study (mean 1593 m and 1185 m, respectively). Sentinel-1 imagery therefore provides great potential for tracking melting, water movement and freezing within both the firn zone and ablation area of the Greenland Ice Sheet.

Since many changes are taking place on the surface of the earth for various reasons such as human activities, natural calamities, and environmental changes, the up-to-date regional land information of an area has got lot of importance for local authorities. Though this information can be collected using traditional land surveying methods it suffers from certain issues such as lot of man power involvement, more time consumption, etc. With the advent of technology the satellite data images available from various optical and polarimetric SAR (Synthetic Aperture Radar) sensors can be used for this land use land cover classification purpose. Since the polarimetric SAR (polSAR) data can provide more useful information than optical data it is more preferable for the land use land cover (LULC) classification. PolSAR data available from various airborne sensors and space-borne sensors which are launched into the space during the recent past can be best utilized for LULC classification of any area irrespective of seasonal effects. Though the available classification algorithms are efficient and produce good classification accuracy results they have their own drawbacks for some reasons. The decision tree algorithm developed for LULC classification in the present study is based on Gumbel distribution of nonlinear regression model [1]. Because of the flexibility in the design and other advantages this decision tree algorithm produced consistent classification accuracy results for all the data sets used in the present study [2].