bluuebunny/crossref_metadata_2025 huggingface dataset:
Avalanche modelling and integration of expert knowledge in the ELSA system
Authors: Buisson Laurent , Charlier Claude
Published: September 2017

The choice of the best protection system against avalanches on a particular path requires an accurate description, or image, of these avalanches. In order to get this image, avalanche consultants can use several numerical models which are often difficult to handle. Moreover, these models deal only with a part of the phenomena involved in avalanches and ignore the others. As a result, the consultants must use their experience and knowledge to imagine the avalanches on any particular path.

This paper presents ELSA (Etude et Limites de Sites Avalancheux), a computer system dedicated to the modelling of the knowledge of avalanche experts and to the integration of the new symbolic computer models with the classical numerical models. The basic aim of integration is to build a unique computer system incorporating all these models.

After a description of the terrain representation, we present the different scenarios that ELSA takes into account. Then, the methods which deal with some phenomena occurring in avalanches are described. The problems involved in the integration of these methods close this paper.
Numerical study on snow transport and drift formation
Authors: Uematsu Takahiko
Published: September 2017

A three-dimensional, numerical simulation model for snow transport and drift formation is proposed in which saltation as well as suspension are considered as dynamic behavioral factors of moving snow particles. The procedure for simulation is as follows: (1) Air flow field is simulated solving the Reynolds equations and the continuity equation. (2) Using the result of the air field flow simulation, the blown-snow density field is simulated using the diffusion equations in which the fall velocity of blown snow particles is considered. In the boundary conditions, the particle movement of saltation is taken into consideration. (3) Finally, the snowdrift rate is computed based on the amount of snow particles not transported by saltation. This model was quantitatively tested for the phenomenon of snowdrift development. The computed results showed good agreement with observations.
Field test of a new snow-particle counter (SPC) system
Authors: Sato Takeshi , Kimura Tadashi , Ishimaru Taminoe , Maruyama Toshisuke
Published: September 2017

The optical system of the snow-particle counter (SPC), which was developed by Schmidt in 1977, has been improved. A laser diode is used as a light source, achieving uniform sensitivity to a blowing snow particle regardless of the location of particle trajectory within a sampling volume. The light entering a slit, which may be affected by a blowing snow particle, is perfectly detected by use of a piano-cylindrical lens and a dual-type photodiode. A signal processor has been developed to get output voltage proportional to the mass flux of blowing snow.

From the estimates based on blowing snow characteristics and wind speed profile, the new SPC system can accurately detect all the particles of effective sizes at least at a height above 0.1 m when the wind speed at a height of 1 m is less than 15 m s−1.

Considering the Fraunhofer diffraction by both the wire and the particle, the relation between a particle diameter and sensor output of the new SPC system is derived from the calibration with spinning wires.

Mass flux obtained with the new SPC system was found to be close to that with a snow trap. The system was operated continuously for at least nine days using two 35 A h lead batteries.
Crystal growth rates in polar firn
Authors: Shoji Hitoshi , Mitani Atau , Horita Kohji , Langway Chester C.
Published: September 2017

Continuous crystal-size measurements made on the G6 Antarctic ice core (100m deep) show enhanced growth rates above a depth of 30 m (Zone 1) and in the interval between 70 and 80 m (Zone 2). Crystal growth in Zone 1 most probably takes place by a process of sublimation and condensation. The higher growth rate in Zone 2 is most probably related to the pore close-off transformation process in which a non-uniform strain field is created to form air bubbles by plastic deformation and “cannibalization” of individual ice crystals.
Flow, flow transition and runout distances of flowing avalanches
Authors: Salm B.
Published: September 2017

A simple quasi one-dimensional model of flowing avalanches is presented. It is a further development of that used in the Swiss Guidelines for practitioners. It is shown that shearing in avalanche movement is concentrated near the ground and that, due to the geometrical roughness of the ground, a flow resistance proportional to the square of velocity must be taken into account in addition to dry friction. For the change of flow on changing slope angles it is demonstrated that under certain conditions for internal friction a “normal” flow on a flat lower part can no longer be attained; the avalanche behaves like a rigid body. The runout distance is in fair agreement with the Guidelines if a larger internal friction is used. The main differences lie in much smaller deposition depths and smaller velocities during runout.
Chemical characteristics of snow in the region along the Sea of Japan
Authors: Satow Kazuhide
Published: September 2017

The amount of acidity in precipitation has been measured in heavy-snowfall regions facing the Sea of Japan. The average pH value of precipitation measured throughout the year at Nagaoka was 4.80 during 4.5 years, 1987–92. During winter the pH value is lower and electric conductivity higher. The spatial distribution of chemical components in new-fallen snow was studied along a 55 km-long sampling route. Results from four surveys showed that acidic snows have average pH values of 4.63–4.90. From the distribution of anion and cation concentration in new-fallen snow, it is concluded that strong northwest monsoons during winter bring an abundance of snow with salt components and many non-salt components from the Sea of Japan and also, possibly, from the Asian continent.
A theoretical prediction of the effects of electrostatic forces on saltating snow particles
Authors: Schmidt Scott , Dent J.D.
Published: September 2017

Electrification of snow particles during blizzards creates forces that may strongly effect their trajectories in saltation along a charged surface. This paper shows the results of adding such forces to the equations of motion for saltation. Evaluating these equations requires knowledge of the electric-field strength very near the surface, and a review shows that such measurements are lacking. However, extrapolation of reported measurements from greater heights agrees with the electric field computed for a bed of spherical particles. In this hypothetical field, the equations of motion predict large changes in saltation length that might occur as particles pass over surfaces with positive and negative sign. Such changes apparently coincide with surface erosion and deposition.
Structure and wind transport of seasonal snow on the Arctic slope of Alaska
Authors: Benson Carl S. , Sturm Matthew
Published: September 2017

The winter snow on the Arctic slope of Alaska lasts for nine months each year, yet little is known about it from a scientific point of view. Its quantity has been seriously underestimated (by a factor of three) in the weather service records, and the directions and magnitudes of wind-transported snow were unknown before the studies reported here. Our measurements of snow on the tundra indicate two major types which differ in depth, density, overall structure, and thermal characteristics: the veneer facies, lying on and interacting with the tundra, and the drift facies which forms in certain topographic settings. The flux of windblown snow has been determined by repeated measurements on three carefully selected “drift traps”, such as river banks, which are large enough so they do not fill during the winter. The measurements span 30 years to show year-to-year variability. The largest transport of snow is from the prevailing easterly winds; about half as much is transported by storm winds from the west. The lowest amount is transported by katabatic drainage winds which flow from the south out of the Brooks Range; they extend a variable, and largely unknown, distance northward onto the Arctic slope before they yield to the stronger easterly and westerly winds.
Shear frame stability parameters for large-scale avalanche forecasting
Authors: Jamieson J.B. , Johnston C.D.
Published: September 2017

During the winters of 1990, 1991 and 1992, a field study of stability parameters for forecasting slab avalanches was conducted in the Cariboo and Monashee mountains of western Canada. In a level study plot at 1900 m and on nearby slopes, the shear strength of the weak snowpack layer judged most likely to cause slab avalanches was measured with a 0.025 m2 shear frame and a force gauge. Based on the ratio of shear strength to stress due to the snow load overlying the weak layer, a simple stability parameter and a more theoretically based stability index which corrects the strength for normal load were calculated. These stability parameters are compared with avalanche activity reported for the same day within approximately 30 km of the study plot. Each stability parameter is assessed on the basis of the number of days that it successfully predicted one or more potentially harmful avalanches and the number of days that it successfully predicted no potentially harmful avalanches. Both parameters predicted correctly on at least 75% of the 70 days they were evaluated. The simpler empirical stability parameter worked as well as the one that corrects strength for normal load. For large-scale forecasting of dry-snow slab avalanches, shear frame stability parameters appear to be a useful addition to meteorological data, snowpack observations and slope tests.
Greatest Holocene advance of Glaciar Pio XI, Chilean Patagonia: possible causes
Authors: Warren Charles R. , Rivera Andrés , Post Austin
Published: September 2017

Glaciar Pio XI (or Glaciar Brüggen) may be the only glacier in the world currently at its Neoglacial maximum. During the 20th century, most glaciers in Patagonia have consistently retreated, whereas Glaciar Pio XI has advanced almost 10 km, most recently at rates of ≤ 1.5 m d−1. This advance cannot be explained with reference to climate alone. An explanatory model combining calving dynamics, sediment budget and fjord topography explains the main features of recent behaviour. This case-study exemplifies the climatically out-of-phase behaviour so typical of calving glaciers, and illustrates the spatial and temporal scale over which they may behave asynchronously in the southern Andes.
The rate of chemical weathering beneath a quiescent, surge-type, polythermal-based glacier, southern Spitsbergen, Svalbard
Authors: Wadham J. L. , Hodson A. J. , Tranter M. , Dowdeswell J. A.
Published: September 2017

Glacierized basins in the high Arctic are believed to be regions of low chemical weathering rates, despite the lack of pertinent data, because it is believed that water does not flow in significant quantities through subglacial drainage systems. We have calculated chemical weathering rates at Finsterwalderbreen, a polythermal, surge-type glacier in Svalbard. Rates of 320 and 150 meq Σ+ m−1 year−1 were measured in 1994 and 1995, respectively. The corresponding water fluxes were 4.1 × 107 and 1.7 × 107 m3. We estimate that we have measured ~72% of the total annual discharge, hence the true annual chemical weathering rates are ~440 and 210 meq Σ+ m−2 year−1, respectively This gives a mean annual chemical weathering rate of 330 meq Σ+ m−2 year−1, which approximates the continental average of 390 meq Σ+ m−2 year−1 and is intermediate between chemical weathering rates measured on cold-based glaciers (~110–160 meq Σ+ m−2 year−1) and temperate glaciers (450–1000 meq Σ+ m−2 year−1). This suggests that there may be a direct link between chemical weathering rates and thermal regime, and that glacierized basins in the high Arctic cannot necessarily be considered as regions of low chemical weathering and CO2 drawdown.
Large-scale rheology of the Ross Ice Shelf, Antarctica, computed by a control method
Authors: Rommelaere Vincent , MacAyeal Douglas R.
Published: September 2017

Measurements made during the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS, 1973–78) are used to determine the large-scale rheological conditions of the Ross Ice Shelf, Antarctica. Our method includes a numerical ice-shelf model based on the stress-equilibrium equations and control theory. We additionally perform a few tests on simplified geometries to investigate the precision of our method. Our results consist of a map of the depth-averaged viscosity of the central part of the Ross Ice Shelf to within an uncertainty of 20%. We find that the viscosity variations are consistent with Glen’s flow law. Application of a more realistic flow law in our study provides little enhancement of ice-shelf model accuracy until uncertainties associated with basal melting conditions and with temperature profiles at inflow boundaries are addressed. Finally, our results suggest a strong viscosity anomaly in the west-central part of the ice shelf, which is interpreted to be associated with changes in the dynamics of Ice Stream A or B at least 1000 years ago. This feature conforms to the prevailing notion that the West Antarctic ice streams are unsteady.
Investigation of a possible crevasse near the main airstrip on McMurdo Ice Shelf, Antarctica
Authors: Whillans I. M. , Merry C. J. , Hamilton G. S.
Published: September 2017

A dark line appears on a recent satellite image of McMurdo Ice Shelf, Antarctica. It is parallel to the calving front. Initial thoughts were that the line marks an opening crevasse associated with an impending major calving event. The feature was studied by means of a strain and surface-elevation grid that was surveyed twice, 25 d apart, using global positioning system (GPS) techniques. Results show that the dark line is not due to an opening crevasse. The feature is probably the surface expression of firn collapse over sea water soaking horizontally into the ice shelf.
Glacial lake drainage: a stability analysis
Authors: Szilder Krzysztof , Lozowski Edward P. , Sharp Martin J.
Published: September 2017

A model has been formulated to determine the stability regimes for water flow in a Subglacial conduit draining from a reservoir. The physics of the water flow is described with a set of differential equations expressing conservation of mass, momentum and energy. Non-steady flow of water in the conduit is considered, the conduit being simultaneously enlarged by frictional heating and compressed by plastic deformation in response to the pressure difference across the tunnel wall. With the aid of simplifying assumptions, a mathematical model has been constructed from two time-dependent, non-linear, ordinary differential equations, which describe the time evolution of the conduit cross-sectional area and the water depth in the reservoir. The model has been used to study the influence of conduit area and reservoir levels on the stability of the water flow for various glacier and ice-sheet configurations. The region of the parameter space where the system can achieve equilibrium has been identified. However, in the majority of cases the equilibrium is unstable, and an initial perturbation from equilibrium may lead to a catastrophic outburst of water which empties the reservoir.
Seasonal variation in the apparent height of the East Antarctic ice sheet
Authors: Yi D. , Bentley C. R. , Stenoien M. D.
Published: September 2017

A satellite radar altimeter can be used to monitor surface elevation change over polar ice sheets. Thirty-five months of Geosat Exact Repeat Mission (ERM) data from November 1986 to September 1989 over a section of East Antarctica (69–72.1 ∘S, 80–140∘ E) have been used in this study. A model that considers both surface and volume scattering was used to retrack the altimeter waveforms. Surface elevations for each month after the first three were compared to the average elevations for the first 3 months through a crossover method. The averaged crossover elevation difference changed with time in a way that suggests a yearly cycle in surface elevation. The average amplitude of the cycle is about 0.6 m. We have been unable to find any satisfactory explanation for the observed changes, in terms of either sources of error or contributors to real surface-height changes. We strongly suspect that orbit error plays a major role in producing the variations, although we know of no quantitatively satisfactory source of a quasi-seasonal variation in orbit error. Other possible contributors include a real seasonal variation in accumulation rate, seasonal changes in the delay of the radar signal as it propagates through the atmosphere, unmodeled variations in the depth of penetration of the radar pulse into the firn, changes in the thickness of the ice and the firn zone in response to seasonal variations in pressure and temperature, and the inverted barometer effect. Even though we do not know the cause of the variations, the results show the importance of comparing elevations at the same time of year for observations that are not continuous, while at the same time showing that even annually spaced measurements may not be free of substantial errors associated with interannual variability. The quasi-periodic variations obscure any evidence of a moderate secular change in surface height, if there is one, but a dramatic lowering at rates approaching 1 ma–1, such as are known elsewhere in Antarctica, can definitely be ruled out.
Numerical modelling of the historic front variation and the future behaviour of the Pasterze glacier, Austria
Authors: Zuo Z. , Oerlemans J.
Published: September 2017

An ice-flow model is used to simulate the front variations of the Pasterze glacier, Austria. The model deals explicitly with the ice flux from sub-streams and tributaries to the main ice stream. The dynamic calibration method adopted successfully calibrates the ice-flow model under a non-steady-state condition. Despite the complexity of the glacier geometry, the ice dynamics of the Pasterze are adequately simulated.

Results of the sensitivity experiments suggest that the Pasterze glacier has been in a non-steady state most of the time and has a response time of 34–50 years.

Projections of the behaviour of the Pasterze in the next 100 years are made under various climate scenarios. Results suggest that the Pasterze will undergo a substantial retreat if there is future warming. The glacier is likely to retreat 2–5 km by the year 2100. The ice volume could be reduced by 24–63% by the end of the 21st century.
Visible and near-infrared digital images for determination of ice velocities and surface elevation during a surge on Osbornebreen, a tidewater glacier in Svalbard
Authors: Rolstad Cecilie , Amlien Jostein , Hagen Jon-Ove , Lundén Bengt
Published: September 2017

A field of vectors showing the average velocity of the surging glacier Osbornebreen, Svalbard, was determined by comparing sequential SPOT (Système pour l’Observation de la Terre) and Landsat thematic mapper images. Crevasses which developed during the initial phase of the surge in the winter of 1986–87 were tracked using a fast Fourier chip cross-correlation technique. A digital elevation model (DEM) was developed using digital photogrammetry on aerial photographs from 1990. This new DEM was compared with a map drawn in 1966. The velocity field could be almost entirely determined with 1 month separation of the images, but only partly determined with images 1 year apart, due to changes of the crevasse pattern. The velocity field is similar to that found for Kronebreen, a continuously fast-moving tidewater glacier. No distinct zones of compressive flow were present and the data gave no evidence of a compression zone/surge front traveling downstream. The velocity field, the rapid advance of the terminus and the development of transverse crevasses in the upper accumulation area within a 6 month period may indicate that the surge developed as a zone of extension starting near the terminus and propagating quickly upstream. The crevasse pattern in the images is therefore interpreted to be the result of the extension zone traveling upstream, and, as the whole glacier starts to slide, the crevasse pattern alters according to the bedrock topography.
Dynamic behavior of Glaciar Perito Moreno, southern Patagonia
Authors: Skvarca Pedro , Naruse Renji
Published: September 2017

Frontal oscillations since the beginning of the 20th century are known at Glaciar Perito Moreno, an eastward outlet glacier of Hielo Patagónico Sur (southern Patagonia ice field). In 1900, the calving front was located about 1 km from the opposite bank. From 1935 to 1988, ruptures of ice-dams occurred at intervals of 1–5 years. Although this glacier has thus oscillated, it can be regarded as having been in a rather stable condition during the last half-century. Ice thickness in the ablation area has also remained unchanged from 1990 to 1996. The near-steady behavior of Glaciar Perito Moreno may be attributed to a regulating effect of the calving rate, namely, a decrease in the ablation amount due to calving with a retreat of the glacier.

Using 12 m long ablation poles, ice-flow velocities at the ablation area were measured several times in 1993 and 1994. The velocity in the early summer (November) was found to be slightly larger than the annual mean. It is concluded that basal sliding is significant throughout the year at this temperate glacier, with large fluctuations within a short period.
The effect of continentality on glacier response and mass balance
Authors: Holmlund Per , Schneider Thomas
Published: September 2017

The continentality index is a good measure of the nature of the climate in a region, as it reflects not only the temperature but also the large-scale circulation. It correlates well with glacier mass-balance parameters. The climate along the west–east transect slightly north of the Arctic Circle across the Scandinavian Caledonides is governed by the prevailing westerlies; however, during winter the eastern part of the Caledonides is influenced by weather systems from the southeast. The differences in continentality meant by temperature and precipitation have a major impact on the response times of glaciers. The climatic change in this area has been dominated by increased summer mean temperatures (1910–20) and increased maritime influence since the 1980s. The slower-reacting glaciers on the Swedish side of the mountains are still adapting to the temperature increase at the beginning of the 20th century, and the increase in maritime influence gradually becomes less important towards the west. Thus, differences in the behaviour of glacier fronts along the west–east transect mirror differences in continentality.
100 years of ice dynamics of Hintereisferner, Central Alps, Austria, 1894–1994
Authors: Span N. , Kuhn M. H. , Schneider H.
Published: September 2017

Velocity measurements carried out on Hintereisferner, Central Alps, Austria, provide the unique opportunity to study 100 years of ice dynamics of this glacier. During this time, three periods of accelerated flow occurred, around 1920, in 1940 and in the 1970s; but only around 1920 did the acceleration actually lead to an advance of about 60 m. The velocity increased from 30 m year−1 in 1914 to more than 120 m year−1 in 1919, and doubled during the accelerations of 1940 and 1980. In the course of the third event, the velocity increase spread over a period of more than a decade (1965–79) with a comparatively low maximum. These velocity changes cannot be explained by increased deformation velocity due to increased ice thickness alone.

Time series of the velocities at various locations along the glacier are given for the entire period, and an attempt was made to construct a time series of the velocity at a point 2 km from the strongly retreating front. The flow divergence was about 0.1 per year in the lowest 2 km, and emergence velocities reached 5 myear−1.
Mathematical modeling of temporal changes in snow-firn properties in the cold season
Authors: Guseva-Lozinski Elena
Published: September 2017

The paper describes a non-linear dynamic thermomechanical model of the snow–firn development in the high mountain environment during the cold season. The model allows the estimation of the thermal and mechanical development of snow in an inhomogeneous stratified snowpack and in the upper part of the firn layer, the development of the snow–firn structure and transformation of snow into firn. The non-linear mathematical model consists of a heat problem, water-vapor diffusion problem, densification of the snow–firn layer, structural equations and strength conditions of the metamorphosed snow–firn depending on its temperature, structural parameters, density and rate of sublimation. The model includes conditions of snow transformation into firn and its structural changes. These equations are non-linear and coupled. The iterative finite-difference numerical method was used for the calculations and involved a full mathematical model. Numerical experiments were implemented using the complete model as well as real. The numerical computations were made for various meteorological data, temperature gradients and in the wide range of structural parameters. The calculation results were found to be in good agreement with the results of observations.
Fluctuations of unstable mountain glaciers: scale and character
Authors: Kotlyakov V. M. , Osipova G. B. , Tsvetkov D. G.
Published: September 2017

The paper describes the characteristics and behavior of unstable glaciers in the Pamirs, central Asia, over the last 30 years. These glaciers are divided into three groups: glaciers with registered surges; glaciers with signs of current instability; glaciers with signs of instability in the recent past. Examples are given to illustrate the nature of glacier fluctuations at a time of general glacier retreat in the Pamirs. A description is given of the evolution of Medvezhiy surging glacier, which was the subject of detailed annual observation from 1963 to 1991. Comparative characteristics of two building-up stages of this glacier, 1964–72 and 1974–88, are produced. On the basis of aerotopographic monitoring and with the aid of computer analysis, the kinematics of the glacier surface during the 1988–89 surge are traced in detail and the role of microsurges in the course of glacier build-up and the glacier surge is established.
Changes of the equilibrium-line altitude in the tropical Cordillera Blanca, Peru, 1930–50, and their spatial variations
Authors: Kaser Georg , Georges Christian
Published: September 2017

As on all Peruvian Cordilleras, the glaciers on the eastern slopes of the Cordillera Blanca extend to generally lower elevations than those on the western slopes. The mountain range of Santa Cruz–Pucahirca possesses the largest east–west extension within the Cordillera Blanca. A significant retreat of the glaciers between two quasi-stationary situations around 1930 and 1950 was reconstructed from air photographs. The derived ELAs as well as the ∆ELA1930–50 show spatial diversities. The pattern of the ELAs is caused by differences in both accumulation and effective global radiation. The change in ELAs1930–50 is partly due to a spatially uniform increase in air temperature. The remaining rise of the equilibrium line, which varies within different parts of the investigation area, has to be related to changes in precipitation and effective global radiation. Both correspond to changes in air humidity which is suggested to be an important factor for tropical glacier fluctuations. A model of superposed typical tropical circulation patterns of different scales and ELA–climate model-based approaches is presented.
Stick–slip sliding behaviour at the base of a glacier
Authors: Fischer Urs H. , Clarke G. K. C.
Published: September 2017

Measurement of basal sliding is an important component in studying the mechanical and hydrological coupling between a glacier and its bed. During the 1992 summer field season we used a “drag spool” to measure sliding at the ice/bed interface of Trapridge Glacier, a small surge-type glacier in the St Elias Mountains, Yukon Territory, Canada. Measured diurnal variations in sliding appear to be correlated to subglacial water pressure fluctuations. In contrast to other observations where peak subglacial water pressure and glacier motion appear to coincide, our data imply that maximum sliding rates coincide with rises in water pressure. If the growth of water-filled cavities at the glacier bed is associated with these pressure increases, then our observations may correspond to numerical results by Iken (1981) which indicate that the largest sliding velocity occurs during cavity growth and not when the steady-state size of cavitation is attained. However, our data suggest the idea that a localized stick–slip relaxation process is at work. As the water pressure rises, a local strain build-up in the ice is released, resulting in a momentary increase in sliding rate; once the finite relaxation has occurred, further rises in water pressure do not produce additional enhancement of basal sliding, and the stick–slip cycle begins again by accumulation of elastic strain. We have developed a theoretical model for the sliding motion of ice over a surface having a basal drag that varies temporally in response to changes in subglacial water pressure. Our model results support the proposed stick–slip sliding process at the glacier base, whereby accumulated elastic strain in the ice is released as the rising water pressure decouples the ice from the bed.
Topography and dynamics of Austfonna, Nordaustlandet, Svalbard, from SAR interferometry
Authors: Unwin Beverley , Wingham Duncan
Published: September 2017

The ice caps of Nordaustlandet, Svalbard, represent one of the largest glaciated areas outside of Antarctica and Greenland. They demonstrate a variety of different flow regimes within a comparatively compact area. We report on the first interferometrically derived elevation models and velocity visualisations of Austfonna. This initial investigation had three purposes: to determine whether the coherence and velocity characteristics of the region permitted interferometric survey; to determine the accuracy of derived elevations; and to assess the possibility of investigating time-variant flow of the more dynamic ice bodies using differential interferometry. A trio of coherent synthetic aperture radar images from ERS-1 ’s First Ice Phase was identified. The images were combined to separate the topographic and velocity components of the resultant interferograms. The topographic phase difference was used to produce a digital elevation model of Austfonna. Its accuracy relative to radio-echo-sounding derived tie-points is 8 m and its resolution 40 m. We also present synoptic views of the velocity field of three of Austfonna’s drainage basins, and comment on the extraction of useful velocity information.
Snow and ice applications of AVHRR in polar regions: report of a workshop held in Boulder, Colorado, 20 May 1992
Authors: Steffen K. , Bindschadler R. , Casassa G. , Comiso J. , Eppler D. , Fetterer F. , Hawkins J. , Key J. , Rothrock D. , Thomas R. , Weaver R. , Welch R.
Published: September 2017

The third symposium on Remote Sensing of Snow and Ice, organized by the International Glaciological Society, took place in Boulder, Colorado, 17–22 May 1992. As part of this meeting a total of 21 papers was presented on snow and ice applications of Advanced Very High Resolution Radiometer (AVHRR) satellite data in polar regions. Also during this meeting a NASA sponsored Workshop was held to review the status of polar surface measurements from AVHRR. In the following we have summarized the ideas and recommendations from the workshop, and the conclusions of relevant papers given during the regular symposium sessions. The seven topics discussed include cloud masking, ice surface temperature, narrow-band albedo, ice concentration, lead statistics, sea-ice motion and ice-sheet studies with specifics on applications, algorithms and accuracy, following recommendations for future improvements. In general, we can affirm the strong potential of AVHRR for studying sea ice and snow covered surfaces, and we highly recommend this satellite data set for long-term monitoring of polar process studies. However, progress is needed to reduce the uncertainty of the retrieved parameters for all of the above mentioned topics to make this data set useful for direct climate applications such as heat balance studies and others. Further, the acquisition and processing of polar AVHRR data must become better coordinated between receiving stations, data centers and funding agencies to guarantee a long-term commitment to the collection and distribution of high quality data.
Measurements of snow- and glacier-covered areas with single-polarization SAR
Authors: Shi Jiancheng , Dozier Jeff
Published: September 2017

Climatological and hydrological investigations in mountainous regions frequently require delineation of the areas covered by snow and glacial ice. Active microwave sensors can discriminate snow and glacier from other targets, are effective under all weather conditions, and have a spatial resolution compatible with the topographic variation in alpine regions. Using data acquired with the NASA AIRSAR, which operates at three frequencies and four combinations of polarization, we examine the usage of synthetic aperture radar (SAR) to map snow- and glacier-covered areas. In order to assess the available SARs that operate from satellites, we analyze single-frequency, single-polarization data, and we compare our results with images from the Landsat Thematic Mapper obtained under clear conditions only a few days after the SAR flight. Single polarization, C-band (5.3 GHz) SAR data can discriminate between areas covered by wet snow from those that are ice-free, but do not easily separate glacier ice from snow and rock. L-band SAR (1.25 GHz) data cannot discriminate between snow and glacier ice. The accuracy (74%) of SAR is high enough to justify its use as the data source in areas that are too cloud-covered to obtain reliable data from the thematic mapper.
Mapping alpine snow using a spectral mixture modeling technique
Authors: Nolin Anne W. , Dozier Jeff , Mertes Leal A. K.
Published: September 2017

Remote sensing has provided a means of obtaining estimates of snow-covered area, yet traditional methods have had difficulty mapping snow in shaded and vegetated areas. Spectral mixture analysis is a linear mixture modeling technique that shows promise for mapping land surface covers, particularly when imaging spectrometer data are used. Applying this technique to AVIRIS data collected over the Sierra Nevada, California, we have estimated the fraction of snow cover in each pixel, even in areas that are shaded or forested. This modeling technique enables us to map snow cover at the sub-pixel level and provides a means of estimating the errors associated with the calculation.
Multi-temporal microwave satellite observation of snowpacks
Authors: Wankiewicz Anthony
Published: September 2017

Microwave brightness temperatures from snowpacks are simulated with a multiple-scattering model using observed hydrometeorological variables at three target areas on the Canadian plains. Comparison of model microwave emissions with those observed from the Nimbus 7 satellite allows the derivation of the snowpack properties of grain-size and microwave absorption. A simulated time series of microwave brightness temperature is produced for the winter season of 1884—85, for assessing the utility of multi-temporal satellite observations for snowpack monitoring.
Photogrammetric analysis of 1984–89 surface altitude change of the partially debris-covered Eliot Glacier, Mount Hood, Oregon, U.S.A.
Authors: Lundstrom S.C. , McCafferty A.E. , Coe J.A.
Published: September 2017

Photogrammetric analysis of Eliot Glacier, Mount Hood, Oregon indicates an average thinning of the ablation area of 4.2 m during 1984–89. Thinning is generally more marked near the equilibrium line, where debris cover is absent, than on the lowest part of the glacier, where superglacial debris thickness is greater than 1.0 m. The pattern of glacier thickness change is partly related to the reduction of ablation with increasing debris thickness, though flow kinematics must also be important to charge in ice thickness.
Complex ice stream flow revealed by sequential satellite imagery
Authors: Scambos Ted A. , Bindschadler Robert
Published: September 2017

The velocity field of the confluence area of two large ice stream tributaries forming Ice Stream D in West Antarctica is studied using sequential Landsat images. Sequential satellite image analysis allows for a very high density of velocity measurements, based on computer-measured displacements of features such as crevasses, crevasse scars, and ice mounds recognizable in both images. Automated displacement measurement of these features results in a detailed map of surface velocities from which surface-horizontal strain-rate fields can be calculated. Correlations between the surface morphology, the velocity field, and the strain-rate field of Ice Stream D reveal a number of important characteristics of ice stream flow:

• the characteristic flowband appearance of streaming ice is present at velocities from below 100 m a−1 to above 350 m a−1;

• in the upstream areas, there appears to be no sharp transition between “sheet” flow, typical of the surrounding ice sheet, and “streaming” flow;

• the fastest moving portions of the ice stream are nearly devoid of surface topography undulations;

• the confluence area is characterized by acceleration of the ice in the slower tributary as it impinges on faster-moving ice, and by highly convergent flow. Velocity in the faster-moving tributary changes little, and there is no persistent evidence of the shear margins of the joined tributaries downstream of the confluence.

This study demonstrates that sequential satellite image analysis, coupled with computer-determined displacement measurements, can provide accurate velocity and strain-rate information on a regional scale rapidly and cost-effectively. Such data sets are required for modelling ice sheet evolution, and for monitoring any changes in ice flow within the ice streams.
The response of lead patterns in the Beaufort Sea to storm-scale wind forcing
Authors: Walter Bernard A. , Overland James E.
Published: September 2017

With the use of time series of AVHRR imagery we examine a non-typical case of ice motion and lead pattern formation in the Beaufort Sea during a period of persistent southwesterly to southerly winds during 31 March-14 April 1991. Our goal is to suggest sea-ice rheologies through the use of satellite imagery. Ice motions were estimated by making a negative of the first image in a time sequence and combining it with a second image using a logical AND operation. Thus leads for the first day are white and those for the second day are black. For the period 31 March-5 April with westerly winds there was a slip line oriented southwest-northeast across the central Beaufort Sea and another slip line parallel to it 150 km to the north. Relative motion was 0.015 m s−1 across the slip lines. With southerly winds during 9-14 April the entire field of leads was advected to the north. Lead patterns are organized on a hierarchy of scales and the scales are a result of the particular magnitude of forcing by the atmosphere. Angles between diamond-shaped lead features with spacings of both 150 km and 10-20 km are approximately 30°, which as Erlingsson showed corresponds to an angle of internal friction of 15°. We provide an argument for the scale-invariant nature of the lead patterns and suggest that it may be possible to parameterize small-scale (less than tens of km) lead patterns.
Velocity measurements and changes in position of Thwaites Glacier/iceberg tongue from aerial photography, Landsat images and NOAA AVHRR data
Authors: Ferrigno J.G. , Lucchitta B.K. , Mullins K.F. , Allison A.L. , Allen R.J. , Gould W.G.
Published: September 2017

The Thwaites Glacier/iceberg tongue complex has been a significant feature of the Antarctic coastline for at least 50 years. In 1986, major changes began to occur in this area. Fast ice melted and several icebergs calved from the base of the iceberg tongue and the terminus of Thwaites Glacier. The iceberg tongue rotated to an east-west orientation and drifted westward. Between 1986 and 1992, a total of 140 km of drift has occurred.

Remote digital velocity measurements were made on Thwaites Glacier using sequential Landsat images to try to determine if changes in velocity had occurred in conjunction with the changes in ice position. Measurements on Landsat images from 1972 and 1984 revealed an average annual velocity of 2.62 km a−1 during that time period, and measurements on images from 1984 and 1990 an average annual velocity of 2.84kma−1, an increase of more than 8%. Estimates made on Thwaites Glacier by others using earlier data contained enough uncertainty that it was impossible to determine a velocity profile over a longer period of time. Examination of the morphology of the glacier/iceberg tongue showed no evidence of surge activity.
Texture-based classification of cloud and ice-cap surface features
Authors: Rees W.G. , Lin I-I
Published: September 2017

It is well known that the interpretation of high resolution (<100 m) visible and near infrared (e.g. Landsat) imagery of large ice masses is hindered by the uniform reflectivity of snow, ice and cloud surfaces. Such interpretation is at present largely performed manually, but there is a good prospect that it could be automated by the incorporation of image texture. This paper describes preliminary work towards the identification of the most appropriate texture technique, or combination of techniques, and assesses the likely performance of such methods.

Different textures are identified with different types of surface cover, and the use of these differences to classify images is investigated. Specifically, we compare a traditional texture measure, the Grey Level Co-occurrence Matrix (GLCM), with a modification of a relatively new technique, fractional Brownian motion (FBM). These two methods are applied to three Landsat MSS images of the Nordaustlandet ice cap, Svalbard. The classification accuracy, computation time and memory required, advantages and limitations of the two methods are compared. The GLCM technique appears to be able to distinguish three groups of image classes, namely dry snow, wet snow, and melt features, ablation areas or cloud cover. The FBM technique is computationally more efficient, and though it performs in general less well than the GLCM technique it gives better discrimination of cloud cover.
Detection of coastal polynyas with passive microwave data
Authors: Markus Thorsten , Burns Barbara A.
Published: September 2017

A method to detect sub-pixel-scale polynyas with passive microwave data has been developed. Models for the brightness temperature transition from sea ice to shelf ice, with and without a coastal polynya, are generated by simulating the satellite overflight across the coast. The models are compared with image data along transects across the coast; correlation coefficients are used to determine the best-fit model and thereby detect the influence of open water. Polynya areas derived from a single SSM/I overpass compare well with coincident AVHRR data showing a mean difference of 156 km2. A longer time series based on daily averaged SSM/I data over a study area adjacent to research station Halley indicates that the opening and closing of polynyas are highly correlated with station wind data.
Antarctic glacier-tongue velocities from Landsat images: first results
Authors: Lucchitta B.K. , Mullins Κ.F. , Allison A.L. , Ferrigno J.G.
Published: September 2017

We measured the velocities of six glacier tongues and a few tongues within ice shelves distributed around the Antarctic coastline by determining the displacement of crevasse patterns seen on sequential Landsat images. The velocities range from less than 0.2 km a−1 for East Antarctic ice-shelf tongues to more than 2.5 km a−1 for the Thwaites Glacier Tongue. All glacier tongues show increases in velocity toward their distal margins. In general, the tongues of glaciers draining the West Antarctic ice sheet have moved significantly faster than those in East Antarctica. This observation may be significant in light of the hypothesized possible disintegration of the West Antarctic ice sheet.
Comparison and integration of ice-pack temperatures derived from AVHRR and passive microwave imagery
Authors: Maslanik J. , Key J.
Published: September 2017

Co-located sets of AVHRR and SSM/I passive microwave imagery are used to estimate ice surface temperatures and to infer cloud cover in the Arctic. Physical temperatures are determined from the AVHRR data by modeling atmospheric and surface conditions. The resulting field-of-view temperatures are converted to ice surface skin temperatures by adjusting for ice concentration calculated using the SSM/I data. By selecting AVHRR-derived temperatures for clear sky conditions, “effective” emissivities of first-year and multi-year ice are calculated. Given these emissivities, microwave brightness temperatures, and proportions of first-year and multi-year ice as estimated using the NASA Team Algorithm, physical temperatures of the sea ice/snow surface are calculated that are, in theory, relatively independent of cloud conditions. The resulting ice temperatures are used to delineate a portion of the cloud cover in the AVHRR data. The advantages of this approach are that only a fairly small amount of AVHRR data are needed to calibrate the SSM/I imagery that can then be used to calculate a time-series of temperatures on a large scale.
Sea-ice tracking on the east coast of Canada using NOAA AVHRR imagery
Authors: Heacock T. , Hirose T. , Lee F. , Manore M. , Ramsay B.
Published: September 2017

An Ice Tracking System (ITS) is under development which will automatically extract ice kinematic information from time sequential imagery over Canadian waterways. NOAA AVHRR data are routinely collected at the Ice Centre Environment Canada (ICEC) and are a valuable data source for operational ice analysis and forecasting. For this study AVHRR data were collected between January and February 1992 over the Grand Banks of Newfoundland. The requirement for cloud-free data limited its use. Multiple images over short time intervals were available for a one to two day period, however these were followed by gaps of three to four days. On days when imagery was available synoptic conditions were always similar favouring a southeasterly ice drift. The east coast of Canada is a very difficult ice environment in which to extract accurate ice motion. The ice regime consists mainly of young ice types exhibiting very dynamic behaviour. To the NOAA sensor the ice cover can appear viscous and featureless. The inaccuracies in the extracted ice kinematic information was attributed to positional errors with the input data and the inability of the tracking algorithm to identify correctly the same features on time sequential images. Geocoding inaccuracies, a result of the systematic geocoding process, had an average error of 2.7 km. Algorithm inaccuracies, a result of incorrect matching, had an average error of 2.45 km.