The Salinity Distribution in Young Sea-Ice

When undertaking a study of the lateral variation of the salinity of sea-ice it is necessary to select an area of ice with a known history. The field measurements reported here were made in North Star Bay, Thule, northwestern Greenland .... The sampling for the sheet ice grid was started at 1100 on November 6 and by 2100 the 2-, 4-, 8- and 16-foot grids were completed. The 32-, 64- and 128-foot grids were completed the following morning. ... Sampling of the pancake ice was started at 0900 on November 9 and completed by the evening of the same day. ... the standard deviation of the salinity values from closely spaced cored samples in sheet ice is always equal to or greater than ±0.3 per mil. In pancake ice, the standard deviation is usually ±1.0 per mil. ... this uncertainty will produce a standard deviation of approx. ±4 to 6 per cent of the total brine volume in the sheet ice and ±11 to 19 per cent of the total brine volume in pancake ice. This then accounts for a considerable proportion of the scatter observed in studying the strength properties of sea-ice

The Polar Oceans Program of the Alaska SAR Facility

The science plan for the Alaska SAR Facility (ASF) focuses on earth surface characteristics that are of interest within the overall concept of global change and that show significant regional, seasonal and interannual variations resulting in changes in the strength of their radar returns. The polar oceans, with the continuous motion and deformation of the pack ice and the changes in the surface state of the surrounding open seas, offer excellent opportunities for such research. Because such studies require both frequent and detailed analysis of Synthetic Aperture Radar (SAR) data, a Geophysical Processor System (GPS) has been developed to speed the extraction of useful geophysical information from SAR data sets. The system will initially produce three main types of products: (a) sets of ice motion vectors obtained by automated computer tracking of identifiable ice floes on sequential images, (b) the areal extent and location of several different ice types and open water and (c) a characterization of the wave state in ice-free regions as well as within the ice in the marginal ice zone at locations where significant wave penetration occurs. Details of these analysis procedures are described. Initially the GPS is planned to process 10 image pairs/day for ice motion, 20 images/day for ice type variations and 1 image/day for wave information, with a total estimated processing time of 13 hours. A variety of projects plan to utilize the SAR data stream in studies of ice, lead and polynya dynamics and thermodynamics. A common feature of these research programs will be attempts to provide, via the coupling of the SAR data with ice property and ice dynamics models, improved estimates of the heat and mass fluxes into both the atmosphere and the ocean as affected by the characteristics of the ice cover.Key words: SAR, radar, sea ice, image analysis, remote sensingMots clés: RAAS, radar, glace de mer, analyse d’images, télédétectio

Structure of a Multi-Year Pressure Ridge

Three transverse profiles across a large pressure ridge located in the Beaufort Sea are presented. The ridge sail extended 4m. above sea level and the ridge keel 13 m. below. The cross-sections of the ridge keel can be described as roughly semi-circular. This suggests that form drag coefficients for flow transverse to the long axes of multi-year ridges may be as high as 0.8. Examination of several salinity, temperature and brine-volume profiles shows that much of the ice in the ridge has a very low salinity and is quite strong. All the inter-block voids that initially existed in the ridge at the time of its formation have been completely filled with ice. These observations, coupled with icebreaking experience indicate that multi-year ridges are, indeed, significant obstacles to even the largest icebreaking ship and should be avoided if possible. A very large first year ridge with a sail height of 12.8 m. is also described. This is the largest free-floating ridge yet measured

The Effective Solute Distribution Coefficient During the Freezing of NaCl Solutions

International Conference on Low Temperature Science. I. Conference on Physics of Snow and Ice, II. Conference on Cryobiology. (August, 14-19, 1966, Sapporo, Japan

Insulator Tests in A High Performance, Square-Bore Railgun

The Center for Electromechanics at The University of Texas at Austin (CEM-UT) has developed a 1 m long, 1.27 cm square-bore railgun for testing different rail, insulator, and projectile materials. This railgun incorporates a unique frame assembly which allows the gun to be assembled and then pressed into the containment vessel with little pressure. After it is pressed together, an external clamp is assembled around it in order to provide the necessary preload to activate the bore seals. The unique feature of the gun assembly allows stock geometry, 2.54 cm x 0.635 cm (1 in. x % in.) cross section, insulating materials to be installed and tested with minimal down time between shots. To date the 1-m long, 1.27 cm square-bore railgun has been used to test the following insulator materials: float glass, polycarbonate, 40% glass filled polycarbonate, G-7 laminate, and quartz glass. The best results have been obtained with quartz glass and glass-filled polycarbonate. Copper and molybdenum flame-sprayed copper have been tried as rail materials with the latter showing greatest success. Currently molybdenum flame sprayed copper rails and glass filled polycarbonate insulators have been repetitively fired at 350 kA levels while maintaining a rail-to-rail resistance of greater than a megohm. During the experiments performed at CEM-UT, much effort was invested in producing a consistent, high-quality bore finish. The indication is that candidate materials to be tested cannot be accurately evaluated if the bore finish is not accurate and smooth.Center for Electromechanic

Plasma Armature Railgun Launcher Simulations

The Center for Electromechanics at the University of Texas (CEM- UT) at Austin has developed a velocity dependent friction model which accurately predicts the losses associated with a plasma armature railgun while performing research associated with several Defense Advanced Research Projects Agency (DARPA) contracts. Test results from CEM-UT's 1 m long, 1.27 cm square bore, plasma-armature railgun have been used to determine the validity of the model. Deviation between calculated and measured performance is typically less than 5% at railgun currents below 500 kA, however, at currents greater than 500 kA, the deviation increases. Experimental evidence suggests that the rail gun' s lack of stiffness and subsequent venting of driving pressure rather than the electromechanical model is primarily responsible for the divergence between predicted and measured results. To test this theory a railgun was built using external preloading rings (Ringfeder®) to increase its stiffness. On the first test of the Ringfeder® railgun, 700 kA was discharged into the gun and the projectile was accelerated to 5.9 km/s. Test data indicates that the projectile accelerated through the entire length of the railgun and that a minimum amount of plasma leakage had occurred during the test. An analysis of the 700-kA test was done to compare the results of CEM-UT's frictional loss model to ablation and viscous drag loss models.Center for Electromechanic

Electromagnetic Railgun Launcher Model Testing Simulation

The Center for Electromechanics at the University of Texas (CEM-UT) at Austin has developed two simulations for predicting railgun performance while performing research associated with several Defense Advanced Research Projects Agency (DARPA) contracts. The first predicts the electrical performance of the power supply and the electromechanical performance of the railgun. It is capable of modeling a switched homopolar generator (HPG) charged inductive supply, capacitor storage bank pulse forming network supply (PFN), or a combination of the two power supplies. The s1~cond calculates the railgun's electromechanical performance using the experimentally measured railgun current. Test results from CEM-UT's 1-m long, 1.27 cm square-bore,plasma armature railgun have been used to determine the validity of the aforementioned simulations. Deviation between calculated performance and measured performance is typically less than 5% at railgun current levels lower than 500 kA, however at higher currents the deviation increases. Experimental evidence suggests that the railgun's lack of stiffness and subsequent venting of driving pressure rather than the electromechanical model is primarily responsible for the divergence between predicted and measured results. Additional testing and comparisons are currently being performed with stiffer railgun structures.Center for Electromechanic