Global Land Ice Measurements From Space Research Articles

The First Rock Glacier Inventory for the Greater Caucasus

Rock glaciers are an integral part of the periglacial environment. At the regional scale in the Greater Caucasus, there have been no comprehensive systematic efforts to assess the distribution of rock glaciers, although some individual parts of ranges have been mapped before. In this study we produce the first inventory of rock glaciers from the entire Greater Caucasus region—Russia, Georgia, and Azerbaijan. A remote sensing survey was conducted using Geo-Information System (GIS) and Google Earth Pro software based on high-resolution satellite imagery—SPOT, Worldview, QuickBird, and IKONOS, based on data obtained during the period 2004–2021. Sentinel-2 imagery from the year 2020 was also used as a supplementary source. The ASTER GDEM (2011) was used to determine location, elevation, and slope for all rock glaciers. Using a manual approach to digitize rock glaciers, we discovered that the mountain range contains 1461 rock glaciers with a total area of 297.8 ± 23.0 km2. Visual inspection of the morphology suggests that 1018 rock glaciers with a total area of 199.6 ± 15.9 km2 (67% of the total rock glacier area) are active, while the remaining rock glaciers appear to be relict. The average maximum altitude of all rock glaciers is found at 3152 ± 96 m above sea level (a.s.l.) while the mean and minimum altitude are 3009 ± 91 m and 2882 ± 87 m a.s.l., respectively. We find that the average minimum altitude of active rock glaciers is higher (2955 ± 98 m a.s.l.) than in relict rock glaciers (2716 ± 83 m a.s.l.). No clear difference is discernible between the surface slope of active (41.4 ± 3°) and relict (38.8 ± 4°) rock glaciers in the entire mountain region. This inventory provides a database for understanding the extent of permafrost in the Greater Caucasus and is an important basis for further research of geomorphology and palaeoglaciology in this region. The inventory will be submitted to the Global Land Ice Measurements from Space (GLIMS) database and can be used for future studies.

Особенности формирования базы данных ледников плато Путорана и хребта Мунку-Сардык

The state of mountain glaciers is closely related to the provision of water resources, tracking climate change, transforming the landscape, etc. Therefore, conducting regular inventories of glaciation areas is a fundamental task of geographical research. The results of the glacier inventory are recorded in special catalogs, currently in digital databases. Such a catalog existed for the glaciers of the USSR, which is presented and expanded in digital form as a database (DB) of glaciers in Russia. The current state of the world’s glaciers is reflected in the database through the Global Land Ice Measurements from Space (GLIMS) service, which is supplemented by data from Randolph Glacier Inventory (RGI) and GAMDAM (Glacier Area Mapping for Discharge from the Asian Mountains). The database was created at the Institute of Geography of the Russian Academy of Sciences, also included in the GLIMS database. However, these databases do not reflect the dynamics of glaciers with a certain periodicity. There are also features of mountain ranges that make it difficult to decrypt glaciers. Such an area includes the Putorana plateau. The trapway structure of the relief, which contributes to the formation of perennial snowflakes, and the presence of many rivers and lakes on which ice forms, requires additional information to compile a database of glaciers. The representation of the characteristics of glaciers for several main parameters (area, length, exposure, elevation of the bottom and top of the glacier, etc.) in a mountain range including 10–20 glaciers is not difficult. However, the glaciers of the Putorana plateau are distinguished by their abundance and peculiarity of configuration, determined by the features of the relief. Only according to the initial data (topographic maps), about two hundred nival-glacial objects were identified, recorded as glaciers. Therefore, it is advisable to consider this database as a database of nival-glacial formations, which are to be classified according to the type of object. Presenting the dynamics of glaciers in the database, under the condition of climate warming, leading mainly to the reduction and disappearance of glaciers, it is also necessary to take into account the disintegration of once large glaciers. The latter is characteristic of the glaciers of the Putorana plateau. The created database reflects the state of glaciers in 1960, 1979, 1987. In this paper, a comparison is made with the glaciers of the Munku-Sardyk ridge, as characteristic and most studied representatives of the glaciation of the southern part of Siberia. The features of the presentation of the characteristics of these glaciers in international databases are noted.

Strong acceleration of glacier area loss in the Greater Caucasus between 2000 and 2020

Abstract. An updated glacier inventory is important for understanding glacier behaviour given the accelerating glacier retreat observed around the world. Here, we present data from a new glacier inventory for two points in time (2000, 2020) covering the entire Greater Caucasus (Georgia, Russia, and Azerbaijan). Satellite imagery (Landsat, Sentinel, SPOT) was used to conduct a remote-sensing survey of glacier change. The 30 m resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM; 17 November 2011) was used to determine aspect, slope, and elevations, for all glaciers. Glacier margins were mapped manually and reveal that in 2000 the mountain range contained 2186 glaciers with a total glacier area of 1381.5 ± 58.2 km2. By 2020, the area had decreased to 1060.9 ± 33.6 km2 a reduction of 23.2 ± 3.8 % (320.6 ± 45.9 km2) or −1.16 % yr−1 over the last 20 years in the Greater Caucasus. Of the 2223 glaciers, 14 have an area > 10 km2, resulting in the 221.9 km2 or 20.9 % of total glacier area in 2020. The Bezengi Glacier with an area of 39.4 ± 0.9 km2 was the largest glacier mapped in the 2020 database. Glaciers between 1.0 and 5.0 km2 accounted for 478.1 km2 or 34.6 % in total area in 2000, while they accounted for 354.0 km2 or 33.4 % in total area in 2020. The rates of area shrinkage and mean elevation vary between the northern and southern and between the western, central, and eastern Greater Caucasus. Area shrinkage is significantly stronger in the eastern Greater Caucasus (−1.82 % yr−1), where most glaciers are very small. The observed increased summer temperatures and decreased winter precipitation along with increased Saharan dust deposition might be responsible for the predominantly negative mass balances of Djankuat and Garabashi glaciers with long-term measurements. Both glacier inventories are available from the Global Land Ice Measurements from Space (GLIMS) database and can be used for future studies.

A NEW DRAINAGE BASIN DELINEATION FOR THE SOUTHERN PATAGONIAN ICE FIELD BASED ON TERRASAR-X VELOCITIES AND TANDEM-X ELEVATIONS

Abstract. The drainage basins or catchments for the Patagonian Ice Field are part of glacier inventories like the Randolph Glacier Inventory (RGI) or the Global Land Ice Measurements from Space (GLIMS). These catchments are used in many glaciological studies for integrating remote sensing measurements over the area of a single glacier. An accurate basin boundary delineation is therefore important for applications like mass balance measurements for individual glaciers in Patagonia. Here we investigate existing catchment delineations of the Southern Patagonian Ice Field (SPI) with a modified watershed algorithm that is capable of including ice velocity measurements from SAR offset tracking during the delineation process. The classical watershed delineation is performed using only a DEM. We show that apart from the basins of Bernardo, Greve, Tempano and Occidental there is no dependence of the basin boundary on the measured ice velocity direction and that the glaciers of SPI flow in the direction of the steepest surface slope of modern high resolution DEMs like the TDM global DEM or SRTM. Additionally, a map of basin probabilities has been produced, which highlights several locations on the ice field where the delineation of the exact basin boundary is difficult.

GlacierNet: A Deep-Learning Approach for Debris-Covered Glacier Mapping

Rising global temperatures over the past decades is directly affecting glacier dynamics. To understand glacier fluctuations and document regional glacier-state trends, glacier-boundary detection is necessary. Debris-covered glacier (DCG) mapping, however, is notoriously difficult using conventional geospatial technology methods. Therefore, in this research for automated DCG mapping, we evaluate the utility of a convolutional neural network (CNN), which is a deep learning feed-forward neural network. The CNN inputs include Landsat satellite images, an Advanced Land Observation Satellite (ALOS) digital elevation model (DEM) and DEM-derived land-surface parameters. Our CNN based deep-learning approach named GlacierNet was designed by appropriately choosing the type, number and size of layers and filters, and encoder depth based on the properties of the input data, CNN segmentation process and empirical results. The GlacierNet was then trained using input data and corresponding glacier boundaries from the Global Land Ice Measurements from Space (GLIMS) database, and tested on glaciers in the Karakoram and Nepal Himalaya. Our results show proof-of-concept that GlacierNet reasonably identifies the boundaries of DCGs with a relatively high degree of accuracy, and that morphometric parameters improves boundary detection.

A consistent glacier inventory for Karakoram and Pamir derived from Landsat data: distribution of debris cover and mapping challenges

Abstract. Knowledge about the coverage and characteristics of glaciers in High Mountain Asia (HMA) is still incomplete and heterogeneous. However, several applications, such as modelling of past or future glacier development, run-off, or glacier volume, rely on the existence and accessibility of complete datasets. In particular, precise outlines of glacier extent are required to spatially constrain glacier-specific calculations such as length, area, and volume changes or flow velocities. As a contribution to the Randolph Glacier Inventory (RGI) and the Global Land Ice Measurements from Space (GLIMS) glacier database, we have produced a homogeneous inventory of the Pamir and the Karakoram mountain ranges using 28 Landsat TM and ETM+ scenes acquired around the year 2000. We applied a standardized method of automated digital glacier mapping and manual correction using coherence images from the Advanced Land Observing Satellite 1 (ALOS-1) Phased Array type L-band Synthetic Aperture Radar 1 (PALSAR-1) as an additional source of information; we then (i) separated the glacier complexes into individual glaciers using drainage divides derived by watershed analysis from the ASTER global digital elevation model version 2 (GDEM2) and (ii) separately delineated all debris-covered areas. Assessment of uncertainties was performed for debris-covered and clean-ice glacier parts using the buffer method and independent multiple digitizing of three glaciers representing key challenges such as shadows and debris cover. Indeed, along with seasonal snow at high elevations, shadow and debris cover represent the largest uncertainties in our final dataset. In total, we mapped more than 27 800 glaciers >0.02 km2 covering an area of 35 520±1948 km2 and an elevation range from 2260 to 8600 m. Regional median glacier elevations vary from 4150 m (Pamir Alai) to almost 5400 m (Karakoram), which is largely due to differences in temperature and precipitation. Supraglacial debris covers an area of 3587±662 km2, i.e. 10 % of the total glacierized area. Larger glaciers have a higher share in debris-covered area (up to >20 %), making it an important factor to be considered in subsequent applications (https://doi.org/10.1594/PANGAEA.894707).

Topography-Related Glacier Area Changes in Central Tianshan from 1989 to 2015 Derived from Landsat Images and ASTER GDEM Data

Studies have investigated the glacier projected area (2D Area) on a horizontal plane, which is much smaller than the glacier topographic surface extent (3D Area) in steep terrains. This study maps the glacier outline in Central Tianshan using Landsat images from four periods, i.e., 1989, 2002, 2007 and 2015, by an object-based classification approach, and analyzes the glacier 2D and 3D area changes related to topographic factors based on Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global DEM data. This approach shows an accuracy of 90.8% for clean ice mapping. The derived clean ice outlines are in good agreement with the 2nd Chinese Glacier Inventory (CGI2) and the Global Land Ice Measurements from Space (GLIMS). The fields with a northern aspect receive the least surface solar radiation, leading to dominant existing glaciers. Glaciers are near evenly distributed in slope zones of 0° to 50° and have a mean slope angle of 28.8°, resulting in a 30.3% larger 3D area than the 2D area in 2015 in Central Tianshan. The glacier 2D area decreased by 404 km2 (−8.1%) between 1989 and 2015, while the 3D area declined by 516 km2 (−7.9%). The glacier 2D area showed a reduction of −1.8% between 1989 and 2002, −3.8% between 2002 and 2007, and −2.7% between 2007 and 2015, and these retreating rates closely responded to the variations of regional mean air temperature and precipitation. Topographically, most reductions occurred in elevation bands of 3000–4000 m and in slope zones of 10–20° and 40–50°, and in the eastern aspect fields. The northern Tekes River catchment had the largest shrinking rate of −17.0% (2D area), followed by the southern Karasu River (−14.2%) and Muzart River (−7.7%) catchments. In contrast, glaciers in the Kumerik/Aksu and Tailan River catchments in the Tuomuer region showed little change (−2%).

The Greater Caucasus Glacier Inventory (Russia, Georgia and Azerbaijan)

Abstract. There have been numerous studies of glaciers in the Greater Caucasus, but none that have generated a modern glacier database across the whole mountain range. Here, we present an updated and expanded glacier inventory at three time periods (1960, 1986, 2014) covering the entire Greater Caucasus. Large-scale topographic maps and satellite imagery (Corona, Landsat 5, Landsat 8 and ASTER) were used to conduct a remote-sensing survey of glacier change, and the 30 m resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM; 17 November 2011) was used to determine the aspect, slope and height distribution of glaciers. Glacier margins were mapped manually and reveal that in 1960 the mountains contained 2349 glaciers with a total glacier surface area of 1674.9 ± 70.4 km2. By 1986, glacier surface area had decreased to 1482.1 ± 64.4 km2 (2209 glaciers), and by 2014 to 1193.2 ± 54.0 km2 (2020 glaciers). This represents a 28.8 ± 4.4 % (481 ± 21.2 km2) or 0.53 % yr−1 reduction in total glacier surface area between 1960 and 2014 and an increase in the rate of area loss since 1986 (0.69 % yr−1) compared to 1960–1986 (0.44 % yr−1). Glacier mean size decreased from 0.70 km2 in 1960 to 0.66 km2 in 1986 and to 0.57 km2 in 2014. This new glacier inventory has been submitted to the Global Land Ice Measurements from Space (GLIMS) database and can be used as a basis data set for future studies.

Glacier recession in the Altai Mountains of Mongolia in 1990–2016

ABSTRACTRelatively little is known about glaciers in the continental climates of North Asia and even less is known about the glaciers of the Mongolian Altai. In an attempt to fill this knowledge gap, we present a new satellite-derived glacier inventory for the Altai Mountains of Mongolia, using the recently launched Landat-8 OLI and Sentinel-2A MSI sensors to monitor glacier change from 1990 to 2016. We examine changes in climatic trends and glacier topomorphological parameters in conjunction with glacier fluctuations to determine governing controls over glacier recession in the Altai Mountains. Our glacier mapping results produced 627 debris-free glaciers with an area of 334.0 ± 42.3 km2 as of 2016. These data were made available for download through the Global Land Ice Measurements from Space (GLIMS) initiative. A subsample of 206 glaciers that were mapped in 1990, 2000, 2010, and 2016 revealed that from 1990 to 2016, glacier area reduced by 43% at 6.4 ± 0.4 km2 yr−1. Glacier recession was greatest from 1990 to 2000 at a rate of 10.9 ± 0.8 km2 yr−1, followed by 2010–2016 at 4.4 ± 0.3 km2 yr−1. Rates of glacier recession were significantly correlated with intrinsic glacier parameters, including mean, minimum and range elevations, mean slope and aspect. Furthermore, climate records indicated the warmest summer temperatures occurred during periods of high glacier recession.

A complete glacier inventory of the Antarctic Peninsula based on Landsat 7 images from 2000 to 2002 and other preexisting data sets

Abstract. The glaciers on the Antarctic Peninsula (AP) potentially make a large contribution to sea level rise. However, this contribution has been difficult to estimate since no complete glacier inventory (outlines, attributes, separation from the ice sheet) is available. This work fills the gap and presents a new glacier inventory of the AP north of 70° S, based on digitally combining preexisting data sets with geographic information system (GIS) techniques. Rock outcrops have been removed from the glacier basin outlines of Cook et al. (2014) by intersection with the latest layer of the Antarctic Digital Database (Burton-Johnson et al., 2016). Glacier-specific topographic parameters (e.g., mean elevation, slope and aspect) as well as hypsometry have been calculated from the DEM of Cook et al. (2012). We also assigned connectivity levels to all glaciers following the concept by Rastner et al. (2012). Moreover, the bedrock data set of Huss and Farinotti (2014) enabled us to add ice thickness and volume for each glacier. The new inventory is available from the Global Land Ice Measurements from Space (GLIMS) database (doi:10.7265/N5V98602) and consists of 1589 glaciers covering an area of 95 273 km2, slightly more than the 89 720 km2 covered by glaciers surrounding the Greenland Ice Sheet. Hence, compared to the preexisting data set of Cook et al. (2014), this data set covers a smaller area and one glacier less due to the intersection with the rock outcrop data set. The total estimated ice volume is 34 590 km3, of which one-third is below sea level. The hypsometric curve has a bimodal shape due to the unique topography of the AP, which consists mainly of ice caps with outlet glaciers. Most of the glacierized area is located at 200–500 m a.s.l., with a secondary maximum at 1500–1900 m. Approximately 63 % of the area is drained by marine-terminating glaciers, and ice-shelf tributary glaciers cover 35 % of the area. This combination indicates a high sensitivity of the glaciers to climate change for several reasons: (1) only slightly rising equilibrium-line altitudes would expose huge additional areas to ablation, (2) rising ocean temperatures increase melting of marine terminating glaciers, and (3) ice shelves have a buttressing effect on their feeding glaciers and their collapse would alter glacier dynamics and strongly enhance ice loss (Rott et al., 2011). The new inventory should facilitate modeling of the related effects using approaches tailored to glaciers for a more accurate determination of their future evolution and contribution to sea level rise.

Monitoring glacial thickness changes in the Tibetan Plateau derived from ICESat data

Monitoring glacier changes is essential for estimating the water mass balance of the Tibetan Plateau. Recent research indicates that glaciers at individual regions on the Tibetan Plateau and surroundings are shrinking and thinning during the last decades. Studies considering large regions often ignored however the impact of locally varying weather conditions and terrain characteristics on glacial evolution, i.e. the impact of orographic precipitation and variation in solar radiation. Our hypothesis is therefore that adjacent glaciers of opposite orientation change in a different way. In this study, we exploit Ice Cloud and land Elevation Satellite (ICESat)/ Geoscience Laser Altimetry System (GLAS) data in combination with the NASA Shuttle Radar Topographic Mission (SRTM) digital elevation model (DEM) and the Global Land Ice Measurements from Space (GLIMS) glacier mask to estimate glacial thickness change trends between 2003 and 2009 on the whole Tibetan Plateau. The results show that 90 glacial areas could be distinguished. Most of observed glacial areas on the Tibetan Plateau are thinning, except for some glaciers in the Northwest. In general, glacial elevations on the whole Tibetan Plateau decreased at an average rate of -0.17 ± 0.47 meters per year (m a-1) between 2003 and 2009, taking together glaciers of any size, distribution, and location of the observed glacial area. Moreover, the results show that glacial elevation changes indeed strongly depend on the relative position in a mountain range.

Inventory of glaciers in mongolia, derived from landsat imagery from 1989 to 2011

Glaciers in the Altai Mountains of Mongolia provide an estimated 11% of the total water resources within the country. Yet, their number and area in inconsistent. Using satellite imagery acquired from Landsat 4, 5, and 7, and SRTM digital elevation model (DEM) data, we present here an intuitive, robust, and inexpensive methodology to map the exposed ice of glaciers in the Altai Mountains for the period 1989 to 2011. The total glacierized area was 515 km2 in 1989/1991, 428 km2 in 1998/2001, and 372 km2 in 2010/2011; it decreased by 17% from 1989/1991 to 1998/2001, 13% from 1998/2001 to 2010/2011, and 28% for the entire period 1989/1991 to 2010/2011. In analyzing a sub‐sample of 260 glaciers, 6% advanced, 11% were stable, and 83% receded from 1989 to 2011. The glacier dataset is available to the public free of charge at the Global Land Ice Measurements from Space (GLIMS) website.

Hydrologic vulnerability to climate change of the Mandrone glacier (Adamello-Presanella group, Italian Alps)

In order to assess the annual mass balance of the Mandrone glacier in the Central Alps an energy-balance model was applied, supported by snowpack, meteorological and glaciological observations, together with satellite measurements of snow covered areas and albedo. The Physically based Distributed Snow Land and Ice Model (PDSLIM), a distributed multi-layer model for temperate glaciers, which was previously tested on both basin and point scales, was applied.Verification was performed with a network of ablation stakes over two summer periods. Satellite images processed within the Global Land Ice Measurements from Space (GLIMS) project were used to estimate the ice albedo and to verify the position of the simulated transient snowline on specific dates. The energy balance was estimated for the Mandrone and Presena glaciers in the Central Italian Alps. Their modeled balances (−1439 and −1503mmw.e.year−1, respectively), estimated over a 15year period, are in good agreement with those obtained with the glaciological method for the Caresèr glacier, a WGMS (World Glacier Monitoring Service) reference located in the nearby Ortles-Cevedale group.Projections according to the regional climate model COSMO-CLM (standing for COnsortium for Small-scale MOdeling model in CLimate Mode) indicate that the Mandrone glacier might not survive the current century and might be halved in size by 2050.

Automated mapping of Earth's annual minimum exposed snow and ice with MODIS

Global snow and ice have been diminishing during the Anthropocene but we still lack a complete mapping of annual minimum exposed snow and ice with a consistent, repeatable algorithm. The Global Land Ice Measurements from Space (GLIMS) project has compiled digital glacier outlines and related metadata for the majority of the world's glaciers but inconsistency among product algorithms and time periods represented precludes the production of a consistently derived global data set. Here we present the MODIS Persistent Ice (MODICE) algorithm that leverages the time series of fractional snow and ice cover from the MODIS Snow Covered Area and Grain size (MODSCAG) algorithm. The end product of MODICE is a consistently derived map of annual minimum exposed snow and ice. Comparisons of MODICE with GLIMS glacier outlines derived from SPOT, ASTER, and Landsat Thematic Mapper show strong agreement with the higher resolution outlines subject to uncertainties with spatial resolution, deep mountain shadows, and GLIMS interpretation errors.

A new glacier inventory for the Jostedalsbreen region, Norway, from Landsat TM scenes of 2006 and changes since 1966

AbstractPronounced changes in glacier mass and length were observed for the monitored glaciers in the Jostedalsbreen region, Norway, since the last glacier inventories were compiled in the 1960s and 1980s. However, the current overall extent of the glaciers in the region is not well known. To obtain this information, we have compiled a new inventory from two mosaicked Landsat Thematic Mapper (TM) scenes acquired in 2006 that have excellent snow conditions for glacier mapping, the first suitable scenes for this purpose after 22 years of imaging with TM. Drainage divides and topographic inventory parameters were derived from a 25 m national digital elevation model for 1450 glaciers. By digitizing glacier outlines from 1 : 50 000 scale topographic maps of 1966, we calculated changes in glacier area for ~300 glaciers. Cumulative length changes for the 1997–2006 period were derived from an additional TM scene and compared with field measurements for nine glaciers. Overall, we find a 9% area loss since 1966, with a clear dependence on glacier size; however, seasonal snow in 1966 in some regions made area determination challenging. The satellite-derived length changes confirmed the observed high spatial variability and were in good agreement with field data (±1 pixel), apart from glacier tongues in cast shadow. The new inventory will be freely available from the Global Land Ice Measurements from Space (GLIMS) glacier database.

Towards a global glacier inventory from satellite data

Abstract. There is a major need for a complete and detailed global glacier inventory that is freely available in a digital format (vector outlines with attribute data) for all kinds of glaciological assessments, e.g. sea level rise, hydro-power, run-off and natural hazards. However, such an inventory is not yet available and the uncertainties due to the missing data for related calculations are large. While the existing World Glacier Inventory offers tabular data that were compiled from aerial photography and maps during the 1960s to 1970s for about 72'000 glaciers, current efforts are being exerted within the framework of the Global Land Ice Measurements from Space (GLIMS) initiative to compile vector outlines from satellite data and combine them with digital elevation models (DEMs). At this point, inventory data from about 100'000 of the estimated 160'000 glaciers are available in the GLIMS database. Due to the now free availability of satellite data from the United States Geological Survey's archive and near global DEMs with appropriate spatial resolution, a globally complete and detailed glacier inventory appears viable. This contribution provides an overview of past and ongoing activities related to the creation of glacier inventory data from satellite sensors, along with the methods employed and the challenges encountered in different parts of the world.

Using L-band SAR coherence to delineate glacier extent

Significant retreat has been seen in many glaciers worldwide. With increasing concern about the impact of global warming, there has been a concerted effort to monitor ongoing change. Projects such as Global Land Ice Measurements from Space (GLIMS) rely on the contributions of institutions worldwide to update a global database of digital glacier outlines. To a great extent, this effort relies on the manual extraction of glacier area from satellite optical instruments, such as the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Unfortunately, dependence on optical imagery poses two significant challenges. First, clouds preclude the viewing of many glaciers, making periodic measurements impossible. Second, many alpine glaciers have significant debris cover, additionally complicating delineation of glacier extent from optical data. The sensitivity of synthetic aperture radar (SAR) coherence to motion offers a method for detecting glacial extent that is independent of weather and allows for the discrimination of active glaciers, with and without debris cover. In this paper, we describe an automated method for delineating the surface area of two glaciers in Alaska, one with and one without a debris-covered terminus. We use the periodic global observations of the Advanced Land Observing Satellite (ALOS) Phased Array L-band SAR (PALSAR) instrument to generate coherence images. Low coherence serves as our primary indicator of glacial extent. However, coherence can be degraded by dense vegetation and the topography of mountainous areas. Hence we develop a decision tree that also considers phase gradients and mountain slope to identify glacier boundaries. The result is a robust technique for generating digital glacier outlines. Coupled with the comprehensive global acquisitions of ALOS, it suggests a new method for measuring glacier extents around the world.

Space-based assessment of glacier fluctuations in the Wakhan Pamir, Afghanistan

Alpine glaciers directly and indirectly respond to climate and play a significant role in mountain geodynamics. Many glaciers around the world have been found to be retreating and downwasting, although these patterns are highly variable due to variations in local topography, regional climate and ice-flow dynamics. Unfortunately, limited information is available on glacier fluctuations in the Wakhan Pamir of Afghanistan, and no data exist from there in the World Glacier Monitoring Services (WGMS) database. Our general circulation model (GCM) climate simulations represent a double carbon-dioxide-loading scenario, and results suggest that glaciers in this region should be downwasting and retreating. Therefore, as part of the Global Land Ice Measurements from Space (GLIMS) project, we evaluated ASTER and Landsat MSS data to assess glacier fluctuations from 1976–2003, in the Wakhan Corridor of Afghanistan. We sampled 30 alpine valley, compound alpine valley or cirque-type glaciers of varying size and orientation. Results indicate that 28 glacier-terminus positions have retreated, and the largest average retreat rate was 36 m year − 1. Satellite image analysis reveals non-vegetated glacier forefields formed prior to 1976, as well as geomorphological evidence for apparent glacier-surface downwasting after 1976. Climatic conditions and glacier retreat have resulted in disconnection of tributary glaciers to their main trunk, the formation of high-altitude lakes, and an increased frequency and size of proglacial lakes. Collectively, these results suggest increased hazard potential in some basins and a negative regional mass balance.

Challenges and recommendations in mapping of glacier parameters from space: results of the 2008 Global Land Ice Measurements from Space (GLIMS) workshop, Boulder, Colorado, USA

AbstractOn 16–18 June 2008 the US National Snow and Ice Data Center held a GLIMS workshop in Boulder, CO, USA, focusing on formulating procedures and best practices for operational glacier mapping using satellite imagery. Despite the progress made in recent years, there still remain many cases where automatic delineation of glacier boundaries in satellite imagery is difficult, error prone or time-consuming. This workshop identified six themes for consideration by focus groups: (1) mapping clean ice and lakes; (2) mapping ice divides; (3) mapping debris-covered glaciers; (4) assessing changes in glacier area and elevation through comparisons with older data; (5) digital elevation model (DEM) generation from satellite stereo pairs; and (6) accuracy and error analysis. Talks presented examples and work in progress for each of these topics, and focus groups worked on compiling a summary of available algorithms and procedures to address and avoid identified hurdles. Special emphasis was given to establishing standard protocols for glacier delineation and analysis, creating illustrated tutorials and providing source code for available methods. This paper summarizes the major results of the 2008 GLIMS workshop, with an emphasis on definitions, methods and recommendations for satellite data processing. While the list of proposed methods and recommendations is not comprehensive and is still a work in progress, our goal here is to provide a starting point for the GLIMS regional centers as well as for the wider glaciological community in terms of documentation on possible pitfalls along with potential solutions.

Completing the World Glacier Inventory

AbstractAn inventory of the surface area and volume of the world’s glaciers, outside Greenland and Antarctica, was part of the International Hydrological Decade (1965–74). It was considered essential to an understanding of the role played by glaciers in the hydrological cycle and was to be repeated every 50 years to detect change. To date, 46% of the estimated total glacier area has been inventoried and made available through the World Glacier Monitoring Service and the US National Snow and Ice Data Center. As the original inventory method was too time-consuming and inapplicable for some areas, a simplified method was developed in the early 1980s using satellite images. The Global Land Ice Measurements from Space (GLIMS) project now covers 34% of the estimated glacierized area outside Greenland and Antarctica. Both inventory efforts have made good progress and contributed substantially to our knowledge of glaciology and its related sciences, but global coverage is still incomplete. If both inventories are combined, 46% of the world’s glacierized area is still missing; 26% is covered by both methods, which allows the quality of the satellite-based and semi-automatic inventories to be assessed by comparison. About 95 000 glaciers remain to be inventoried, of which about half are in the Canadian Cordillera, South America and the Canadian Arctic Islands. As the cryosphere is changing rapidly, it is of the utmost importance to complete the global glacier inventory as soon as possible, and identify an appropriate repeat cycle.