Knowledge of the texture of polar firn is necessary for interpretation of remotely sensed data. We find that dry polar firn is an irregularly stratified, anisotropic medium. Grains in firn may be approximated as prolate spheroids with average axial ratios as high as 1.2 or greater and with a preferred orientation of long axes clustered around the vertical. Such elongate grains are preferentially bonded near their ends into vertical columns, so that grain bonds show a preferred horizontal orientation. The grain-size distribution is similar in most firn and the normalized distribution is stationary in time, but the distribution is somewhat different in depth hoar. Fluctuations of firn properties are large near any depth, but decrease with increasing depth. With increasing depth, anisotropy of surfaces decreases, bond size relative to grain size decreases slightly, and number of bonds per grain and fraction of total grain surface in bonds increase. Grain size increases linearly with age below 2 to 5 m, but increases more rapidly in shallower firn.

A single pronounced internal reflecting horizon has been observed on radio echo-sounding from over 30 glaciers in Spitsbergen. They are often present along the entire length of the glacier, remaining at a fairly constant depth (100–200 m) below the ice surface. Echo-strength data from radio echo-sounding have been used to obtain reflection coefficients, for these horizons, of between -15 and -25 dB. Combined with results of ice-core studies, the possible causes of this internal layer are investigated. The presence of water is found to be the most likely explanation, indicating the existence, at depth, of a layer of temperate ice.

Numerous examples of synthetic aperture radar (SAR) imagery of ice sheets are shown and prominent features of glaciological importance which appear in the images are discussed. Features which can be identified include surface undulations, ice-flow lines, crevasses, icebergs, lakes, and streams (even lakes and streams which are inactive or covered by snow), and possibly, the extent of the ablation and wet snow zones. SAR images presented here include both L-band data from the Seasat satellite and X-band data from an airborne radar. These two data sets overlap at a part of eastern Greenland where a direct comparison can be made between two images. Comparison is also made between SAR and Landsat images in western Greenland. It is concluded that SAR and Landsat are highly complementary instruments; Landsat images contain minimal distortion while SAR’s all-weather, day/night capability plus its ability to penetrate snow provide glaciologists with an additional and very powerful tool for research.

In the first few seasons of the Antarctic Siple Coast project, the University of Wisconsin has concentrated on radar and seismic studies. Highlights of the results to date include the delineation of ice streams A, B, and C and the ridges in between, determination of the surface elevations over the area, discovery of a much more advanced grounding line than previously recognized and recognition of a broad, flat, barely grounded “ice plain” just inside the grounding line. Complex zones between and adjoining some of the ice streams, characterized by an interspersal of undisturbed ice and crevassed patches, give the impression of being transformed from sheet flow into stream flow in a process of ice stream expansion. An indicated negative mass balance for ice stream B could be the result of this “activation” process. Ice stream C, currently stagnant, exhibits terraces and reversals of surface slope, associated with zones of strong, steady basal radar reflections. These features suggest that subglacial water has been trapped by reversals in the hydraulic pressure gradient.

Low seismic P-wave and S-wave velocities in a meters-thick layer immediately below the ice strongly indicate a saturated sediment of such high porosity (~40%) and low effective (differential) pressure (~50 kPa, or 0.5% of the glaciostatic pressure) that it must be too weak not to be deforming. We presume this deforming layer to be a dilated till. Its base exhibits ridges and troughs parallel to the flow direction that resemble glacial megaflutes. We believe that at our site on the upper part of ice stream B the ice stream moves principally by deforming its bed. Analysis of seismographic recordings of micro-earthquakes that occur at the glacier bed shows that the micro-earthquakes are both small in energy and infrequent. This implies that virtually none of the energy of ice stream motion is dissipated by brittle fracture at the bed. If our models are correct, the subgiacial deforming till becomes increasingly soft down-glacier, and/or the ice becomes decoupled from the till by intervening water, until on the “ice plain” basal drag is less important than longitudinal stresses in the dynamic balance. Our models also imply that the “ice plains” rest on “till deltas” that have been formed by the deposition of till carried along beneath the ice streams, and that the till deltas, and the grounding lines that bound them, are currently advancing in front of the active ice streams.

A new seismographic array with a band width of 500 Hz per channel and a dynamic range of 96 dB was developed for detecting natural events on glaciers. It was first deployed on ice stream B during the 1985–86 austral summer. The network consists of nine solar-powered seismographs, each monitoring three components of ground motion. Each of the seismographs is connected by up to 4 km of fiber-optic cable to a central node where seismic events are both detected and recorded. During 85 h of passive seismic monitoring on ice stream B, 25 microearthquakes were observed. Sixteen of these events were associated with shallow crevassing, mostly near the margins, although not within the zones of extreme shearing that bound the ice streams. Nine microearthquakes were associated with low-angle thrusting near the base of the ice stream. The principal initial result of these passive seismic studies is the demonstration that virtually none of the energy dissipated beneath ice stream B takes place through brittle fracture near the base. Nevertheless, fracture associated with microearthquakes may play a significant role in sub-glacial erosion.

A total of 400 soundings along 15 profiles were obtained on White Glacier, Axel Heiberg Island, N.W.T. with a monopulse radar equipment that was rebuilt according to a model of the US Geological Survey. The resulting data allowed maps to be compiled of the ice thickness for the glacier tongue, The radio echo-sounding data and englacial temperature measurements give some indication of the existence of stagnant ice in depressions of the glacier bed in the accumulation zone of White Glacier.

Snow covers about 40 million km2 of the land area of the Northern Hemisphere during the winter season. The accumulation and depletion of snow is dynamically coupled with global hydrological and climatological processes. Snow covered area and snow water equivalent are two essential measurements. Snow cover maps are produced routinely by the National Environmental Satellite Data and Information Service of the National Oceanic and Atmospheric Administration (NOAA/NESDIS) and by the US Air Force Global Weather Center (USAFGWC). The snow covered area reported by these two groups sometimes differs by several million km2, Preliminary analysis is performed to evaluate the accuracy of these products.

Microwave radiation penetrating through clouds and snowpacks could provide depth and water equivalent information about snow fields. Based on theoretical calculations, snow covered area and snow water equivalent retrieval algorithms have been developed. Snow cover maps for the Northern Hemisphere have been derived from Nimbus-7 SMMR data for a period of six years (1978–1984). Intercomparisons of SMMR, NOAA/NESDIS and USAFGWC snow maps have been conducted to evaluate and assess the accuracy of SMMR derived snow maps. The total snow covered area derived from SMMR is usually about 10% less than the other two products. This is because passive microwave sensors cannot detect shallow, dry snow which is less than 5 cm in depth. The major geographic regions in which the differences among these three products are the greatest are in central Asia and western China. Future study is required to determine the absolute accuracy of each product.

Preliminary snow water equivalent maps have also been produced. Comparisons are made between retrieved snow water equivalent over large area and available snow depth measurements. The results of the comparisons are good for uniform snow covered areas, such as the Canadian high plains and the Russian steppes. Heavily forested and mountainous areas tend to mask out the microwave snow signatures and thus comparisons with measured water equivalent are poorer in those areas.

Remote-sensing research in glacial and pro-glacial environments raises several methodological problems relating to the handling of ground and satellite radiometric data. An evaluation is undertaken of the use of ground radiometry to elucidate properties of relevant surface types in order to interpret satellite imagery. It identifies the influence that geometric correction and re-sampling have on the radiometric purity of the resulting data set. Methodological problems inherent in deriving catchment terrain characteristics are discussed with reference to currently glacierized and pro-glacial zones of south-western Switzerland.

As more data are recorded in digital form the importance of automatically extracting parameters of glaciological significance increases. This paper addresses the problem, with particular reference to tracking bedrock or internal reflectors in digitally recorded Radio Echo Sounding (RES) data. It has been found that the simplest solution to this problem is a “supervised” system, where operator decisions may be added interactively, either on operator command or upon loss of track. Increasing internal decision making within the program may reduce the number of operator interventions required, but is unlikely to eliminate them completely.

Algorithms are presented and discussed for determining the position of the interface, for predicting the position of the interface in successive records, for determining the loss of track condition, and for re-acquiring track after loss of track.

The word “lake” in the context of Antarctica has been used to describe both surface features (10–12 km in size) and areas of liquid water on the bedrock beneath the ice sheet (typically a few kilometres in size and at a depth of over 3000 m), There has been however only limited evidence for a relationship between the two phenomena.

This paper reports an analysis of Seasat altimeter observations of an extremely flat area on the surface of the East Antarctic ice sheet, approximately 30 km in extent, centred at 68.6°S 136.0°E and close to the edge of the sub-glacial Astrolabe Basin. It has a regional slope of between zero and 0.01° , and non-random variations in height along track of about ± 1m on the scale of a few kilometres. The average radar backscatter coefficient is 5±2 dB in the region of the Astrolabe Basin, compared to a more usual value of about 10 dB for other areas of the ice sheet. A computer enhanced Landsat image of the region clearly shows the rougher steeper terrain to the North, with the surface in and around the flat area appearing totally smooth and featureless.

NSF/SPRI/TUD radio echo-sounding data from the region, although limited in extent, shows a relatively strong signal (indicative of ice at the pressure melting point) over a large region. The signal under the flat area, however, is particularly strong and smooth, confirming the association between the surface feature and a bedrock lake 3800 m below.

Data collected over Svalbard on 28 June 1984 by a 13.81 GHz airborne radar altimeter enabled analysis of signals returned from two relatively large ice masses. Wave forms received over the ice caps of Austfonna and Vestfonna are analysed with the aid of existing aerial photography, radio echo-sounding data, and Landsat MSS images acquired close to the date of the altimeter flight. Results indicate that altimeter wave forms are controlled mainly by surface roughness and scattering characteristics. Wet snow surfaces have narrow 3 dB back-scatter half-angles and cause high-amplitude signals, in contrast to relatively dry snow surfaces with lower-amplitude diffuse signals. Metre-scale surface roughness primarily affects wave-form amplitude and leading-edge slope, this becoming apparent over ice streams on Vestfonna.

A method to estimate open pack ice thickness drifting in a marginal ice zone (MIZ) is presented, The estimates are obtained from two-day sequences of sidelapping Landsat-1 MSS images and two-day sequences of wind field data by four steps: estimating the surface wind speed, estimating the angle of sea ice deflection, estimating three ratios between ice parameters and estimating the lower and upper limits of pack ice thickness. The method has been applied to six groups of open pack ice floes drifting in the MIZ of the Beaufort Sea during 1973–1975. In the absence of simultaneous in-situ observation, the results have not been tested, The method presented may be applied to any MIZ. Rather than using Landsat-1 MSS images, data from a high resolution active microwave remote sensing system should be employed in the future as its data will be independent of sun illumination and cloud cover.

The surface conditions of the inland ice sheet in east Dronning Maud Land, Antarctica, are derived from the NOAA-7 AVHRR data received at Syowa Station and then compared with the ground observations which were collected in November 1984 along a 243 km long traverse route at altitudes ranging from 2700 to 3400 m a.s.l. The variations in the AVHRR data are well related to the distribution of glazed surfaces. The areas with lower albedo, higher surface temperature, lower ratio of channel 2/channel 1, and lower T4-T5 coincide with the areas where a glazed surface has developed. This result is attributed to the fact that the glazed surface is composed of a multi-layered ice crust and that its radiative and thermal properties are closer to ice than to snow. The present study shows that the NOAA AVHRR data are useful for distinguishing bare ice, glazed surfaces, and snow surfaces of the Antarctic ice sheet.

A certain snow-covered area determined from air photographs in different years can contain different volumes of snow. The pattern recognition of snow fields reveals whether the snow reserves are relatively high or low for the given snow coverage. It also signals a short terra increase of the snow-covered area by summer snowfall.

The Scott Polar Research Institute (SPRI) Mk IV 60 MHz radio echo-sounding (RES) system has proven itself to be a most effective and versatile tool in glaciology. During the last 15 years, it has been used from a variety of platforms, both surface and airborne, and over a range of ice thicknesses from 4000 m to 100 m. However, the photographic recording methods used during this period were felt to be increasingly outdated in the context of modern data handling procedures. Accordingly, in late 1982 the Mk IV system was modified to incorporate fast digitizing of the RES receiver output, with microcomputer-controlled magnetic-tape recording of both the radar data and navigational inputs (Drewry and Liestøl 1985). The new system will be described, along with the improvements in data processing which have resulted from its use.

A cruise to Antarctic waters from late October to mid December 1985 provided the opportunity to study characteristics of the seasonal sea ice from a time close to that of maximum extent through early spring decay. The area covered by the observations extends from the northern ice limit to the Antarctic coast between long. 50 °E and 80 E. Shipboard observations included ice extent, type and thickness, and snow depth. Ice cores were drilled at several sites, providing data on salinity and structure.

The observations verify the highly dynamic and divergent nature of the Antarctic seasonal sea-ice 2one. Floe size and thickness varied greatly at all locations, although generally increasing from north to south. A high percentage of the total ice mass exhibited a frazil crystal structure, indicative of the existence of open water in the vicinity.

The ground based observations are compared with observations from satellite sensors. The remote sensing data include the visual channel imagery from NOAA 6, NOAA 9, and Meteor 11. Comparisons are made with the operational ice charts produced (mainly from satellite data) by the Joint Ice Center, and with the analyses available by facsimile from Molodezhnaya.

The synthetic aperture radar (SAR) data have been used to study sea ice with respect to its motion and formation/deformation. With the prospect of the Alaska SAR Facility development in the near future, there is a great need for robust and efficient sea-ice analysis techniques. This paper presents a sea-ice motion analysis technique that can be used for (1) local motion analysis of a selected ice patch and (2) a global ice motion over the entire image area. Though there are several sea-ice motion tracking techniques, they do not provide the required operational speed or robustness. In order to meet the operational speed requirement (over fifty images per day), we have developed a sea-ice motion analysis technique which requires very little human interaction and much simplified computation. The proposed technique uses a subset of easily distinguishable features to predict global motion characteristics and apply template matching over a predicted search area. We applied the developed technique to two pairs of SEASAT SAR images, one pair with a minor motion of “ice pack” and another with a larger and discontinuous motion of “fast ice”. The two major achievements of the new approach are: first, development of a set of computer-aided tools for feature selection and registration and, secondly, implementation of an optimal search strategy for automatic template matching via a motion prediction model.

Use of satellite multi-spectral remote-sensing data to map snow and estimate snow characteristics over remote and inaccessible areas requires that we distinguish snow from other surface cover and from clouds, and compensate for the effects of the atmosphere and rugged terrain. Because our space-borne radiometers typically measure reflectance in a few wavelength bands, for climate modeling we must use inferences of snow grain-size and contaminant amount to estimate snow albedo throughout the solar spectrum. Although digital elevation data may be used to simulate typical conditions for a satellite image, precise registration of an elevation data set with satellite data is usually impossible. Instead, an atmospheric model simulates combinations of Thematic Mapper (TM) band radiances for snow of various grain-sizes and contaminant amounts. These can be recognized in TM images and snow can automatically be distinguished from other surfaces and classified into clean new snow, older metamorphosed snow, or snow mixed with vegetation.

Landsat Thematic Mapper (TM) data have been analyzed to study the reflectivity characteristics of three glaciers: the Grossglockner mountain group of glaciers in Austria and the McCall and Meares Glaciers in Alaska, USA. The ratio of TM band 4 (0.76–0.90 μm) to TM band 5 (1.55–1.75 μm) was found to be useful for enhancing reflectivity differences on the glaciers. Using this ratio, distinct zones of similar reflectivity were noted on the Grossglockner mountain group of glaciers and on the Meares Glacier; no distinct zones were observed on the McCall Glacier. On the TM subscene containing the Grossglockner mountain group of glaciers, 28.2% of the glacierized area was determined to be in the zone corresponding most closely to the ablation area, and 71.8% with the location of the accumulation area. Using these measurements, the glacier system has an accumulation area ratio (AAR) of approximately 0.72. Within the accumulation area, two zones of different reflectivity were delineated. Radiometric surface temperatures were measured using TM band 6 (10.4–12.5 μm) on the Grossglockner mountain group of glaciers and on the Meares Glacier. The average radiometric surface temperature of the Grossglockner mountain group of glaciers decreased from 0.9 ± 0.34 °C in the ablation area, to −0.9 ± 0.83 C in the accumulation area.

Digitally enhanced Landsat Thematic Mapper (TM) images of Antarctica reveal snow and ice features to a detail never seen before in satellite images. The six TM reflective spectral bands have a nominal spatial resolution of 30 m, compared to 80 m for the Multispectral Scanner (MSS). TM bands 2–4 are similar to the MSS bands. TM infra-red bands 5 and 7 discriminate better between clouds and snow than MSS or the lower TM bands. They also reveal snow features related to grain-size and possibly other snow properties. These features are not observed in the visible wavelengths. Large features such as flow lines show best in the MSS and lower TM bands. Their visibility is due to photometric effects on slopes. TM thermal band 6 has a resolution of 120 m. It shows ground radiation temperatures and may serve to detect liquid water and to discriminate between features having similar reflectivities in the other bands, such as blue ice.

Repeated Landsat images can be used for sophisticated glaciological studies. By comparing images from 1975 and 1985, flow rates averaging 0.72 km a−1, and mean longitudinal and transverse strains of respectively 1.3 × 10 −4 a −1 and 130 × 10−4 a−1 have been measured for Jutulstraumen, Dronning Maud Land.