Investigations of the Upper Snow Pack at Summit, Greenland. Report of the July 2004 Field Season

Three detailed snow-pit studies were completed around the Summit Camp in central Greenland during July 2004. At each site the temperature of the snow pack was measured with a digital thermometer and the thickness of different layers. the snow stratigraphy and the snow crystal size were documented. Snow samples were taken at 5 cm intervals with a tube of known volume and a steel box of known volume, the contents of which were later weighed on a scale in order to determine the density of the snow. Also oxygen isotope samples were taken from one pit for analysis to get an estimate of the age of the snow. Three shallow cores were extracted and snow samples were taken in 10 cm intervals for isotope analysis and density measurements. The melt water samples were brought back to the laboratory at BPRC (OSU) for isotope analysis. This report is a summary of the findings and preliminary results of this field investigation

Variations in Radar Backscatter Across the Great Ice Sheets

Radar backscatter over the great ice sheets is modulated by the near surface properties of polar firn. These properties (grain size, density, stratigraphy, wetness) change in time and from region to region. Information was compiled on the spatial variation in backscatter across selected parts of Antarctica and Greenland from ERS-l SAR data. This SAR-derived backscatter information is compared to similar data, collected in situ and from the ERS-l scatterometer, obtained from literature. These results will be used to refine processing schemes for the Radarsat Antarctic Mapping Project

Graphical Ice Sheet Analyzer

During the past decade, long time series of passive microwave data sets have become available over the polar regions. These data sets can be used to study important glacial, atmospheric and oceanic processes. However, the data volume is large and the data area is extensive, requiring researchers to develop methods that enable easy manipulation and visualization of these data sets. Further more, a key attribute of these data sets is their sequential format, which can be used to develop unique intuitions about changes in the dynamical processes with time. To inspect the data over Greenland and Antarctica, and to retain the basic temporal information provided by the passive microwave data, a tool was developed to create images of consecutive days of data and combine them to form animations. To help visualize the glaciologic aspects of the data, the images in the animations consist of two distinctive data sets; a Digital Elevation Model and Passive Microwave Data, which are co-registered to provide a 3D image. Initially, Special Sensor Microwave / Imager 37v brightness temperatures were used to create the animations. These SSM/I brightness temperatures have allowed researchers to identify four polar processes in the animations; surface melting, sea ice coverage, temperature variances, and weather fronts and patterns. Analyzing these processes is aided by the animations because they allow researchers to see spacial and temporal interactions. The weather patterns, in particular, influence the surface melting on the ice sheets. The seasonal ebb and flow of the sea ice is a dramatic event that can span millions of square kilometers in only a few months. The imagery data sets are not solely limited to SSM/I data. Any data in standard byte image format can be viewed. Several secondary programs have been created along with the main software package that allow for conversion of data to this format

RHEOLOGY OF GLACIER ICE

The constitutive relation for glacier ice remains an issue in glaciology. This is evidenced by the recent appearance of several articles in the literature that report on interpretations of existing data and which draw conclusions ranging from newtonian viscous to power law creep for polycrystalline ice. In this paper we describe the results of a new analysis based on the height of bottom crevasses found in floating ice shelves. The analysis relates the effective stress in the glacier to the height of the crevasse. The power of this approach is that the computed stress takes into account all factors influencing the deformation of the ice shelf including ice rises and shear along the boundaries of the ice shelf. By comparing calculated stresses to measured surface strain rates, we are able to estimate the exponent in the flow law and the flow law constant. We find that strain rate increases as the third power of the deviatoric stress with a constant of proportionality equal to 2.3 x 10-25

C‐band SAR backscatter characteristics of Arctic sea and land ice during winter

Synthetic Aperture Radar (SAR) data has become an important tool for studies of polar regions, due to high spatial resolution even during the polar night and under cloudy skies. We have studied the temporal variation of sea and land ice backscatter of twenty-four SAR images from the European Remote Sensing satellite (ERS-1) covering an area in Lady Ann Strait and Jones Sound, Nunavut, from January to March 1992. The presence of fast ice in Jones Sound and glaciers and ice caps on the surrounding islands provides an ideal setting for temporal backscatter studies of ice surfaces. Sample regions for eight different ice types were selected and the temporal backscatter variation was studied. The observed backscatter values for each ice type characterize the radar signatures of the ice surfaces. This time series of twenty-four SAR images over a 3-month period provides new insights into the degree of temporal variability of each surface. Ice caps exhibit the highest backscatter value of -3.9 dB with high temporal variability. Valley glacier ice backscatter values decrease with decreasing altitude, and are temporally the most stable, with standard deviations of 0.08–0.10 dB over the 90-day period. First-year ice and lead ice show a negative trend in backscatter values in time and a positive correlation of up to 0.59 with air temperature over the 90-day period. For first-year ice and lead ice, episodes of large temperature fluctuations (±12°C) are associated with rapid changes in backscatter values (±2 dB). We attribute the backscatter increase to a temperature-induced increase in brine volume at the base of the snow pack. Multi-year ice, conglomerate ice and shore ice are relatively stable over the 3-month period, with a backscatter variation of only a few dBs. An observed lag time of up to three days between backscatter increase/decrease and air temperature can be attributed to the insulation effect of the snow cover over sea ice. The net range of the backscatter values observed on the most temporally stable surface, valley glacier ice, of about 0.30 dB indicates that the ERS-1 SAR instrument exceeds the 1 dB calibration accuracy specified for the Alaska SAR Facility processor for the three winter months