Deliverables A ridge field model Summary: Ice ridges are major obstacles for ship traffic and induce the largest loads against offshore structures. Ridges are elongated piles of ice blocks with roughly triangular cross-section. Their total thickness ranges from 5 to 20 m in the Baltic and from 10 to 40 m in the Arctic. Ridges are created by ice cover stresses induced by wind and currents. The generation of ridgess into the ice cover creates ridges fields and the description of the ridge fields is of importance for navigation and offshore design. The ridge field can be parameterised by the size of ridges and by the density of ridge occurrence. These parameters change in time trough the season and this change can be associated with the strains observed in the ice cover or predicted by ice forecast models. Ice monitoring by satellite data Summary: Satellite observations of sea ice is an essential method in the studies of local ice cover deformation and mesoscale ice dynamics, which are the main research problems in the ICE STATE project. This study presents results of the first analysis of satellite images used in the ICE STATE field experiment, ZIP-97, in the Bothniam Bay in March 1997. This experiment offered the first opportunity to study RADARSAT SAR images of sea ice in this region, both ScarSAR images covering the whole Bothnian Bay and Fine-resolution images of the experimental area. RADARSAT images, in combination with ERS-2 SAR images, were used to investigate ice dynamics including ridge formation, lead generation and the basinwide ice velocity field. Drifting ice buoys with GPS positioning system were used for comparison with the SAR-derived ice rift vectors. Also optical images with medium and high resolution and aircraft photographs data were used for validation of the SAR images. The satellite data can be used for ice type classification, ridge mapping, identification of floes, leads, shear zones, drifting ice and fast ice. Satellites can make synoptic maps of large ice areas at a resolution of 100m. Microwave data from SAR can be used independent of weather and light condition, while optical instruments require cloud free conditions and daylight. Generation of statistical properties associated with ice crushing and cracking. Summary: The morphological properties of ice cover are generated in processes that are analogical to fragmentation processes. These include the generation of cracks, fragmentation of floes, formation of pressure ridges and mechanical thickness increase. These processes are inherently similar through a range of scales, from ice specimens to ice fields hundreds of kilometers in diameter. The mechanical properties and dynamical behaviour of ice is dependent on its morphological properties so the description of ice morphological processes is a key issues in ice physical modelling. As these are theoretically analogous to fragmentation process, fragmentation-coagulation equations can be adopted to serve as a unified basis for ice morphological evolution. Methodology to produce ice rigs in laboratory. Summary: The mechanical deformation of the ice cover in northern seas takes place through ridging and rafting. Ridges are the piles of ice rubble which criss-cross the ice pack. The study of the energetics and mechanics of ridging is important because the energy expended in deformation determines the large-scale strength of the ice pack and because the horizontal stresses an ice cover and the strength and thickness of pressure ridges are important in the design and operation of Arctic vessels and offshore structures. However, because it is difficult to observe a ridge built-up process in the field, the ice deformations and failure mechanisms active in ridging are not fully known. In order to study ridging in laboratory conditions, an in that way gain insight that would focus research efforts in the studies of ridging, a methodology to produce ice ridges in an ice model basin has been developed. By using this novel test set up, ridges were formed in laboratory conditions for the first time by driving two ice sheets against each other. In addition to relevance in ridging studies, the new test method is applicable to studies on ice loads on offshore structures and to research on local ice deformations in general Mesoscale ice modelling Summary: A sea ice model is implemented based on the assumption that ice maybe considered as a granular medium. A theoretical framework is presented for the model based on the work by Erlingsson (1993) and Tremblay and Mysak (1997). The sea-ice cover is represented by an ice thickness distribution function, a snow cover and a lead parametrization. The ice thickness distribution function is discretized giving conservation equation for each thickness class. The ice model has been coupled and validated with a version of MICON which is set up for the Baltic Sea. A few experiments have been run where the model results have been intercompared and validated against results from a tradtional Hibler type ice model. As an example it is now possible to extract information about the percentage of a grid cell coverd by ridges of different thicknesses. From simulations in the Baltic sea it is not clear whether the granular ice dynamics provides an improvment or not compared to the Hibler type rheolgy. More extensive simulations are needed for these where also multiyear ice is included for the Arctic Ocean. A ridging model Summary: The mechanical deformation of the ice cover in northern seas takes place through ridging and rafting. Ridges are the piles of ice rubble which criss-cross the ice pack. The study of the energetics and mechanics of ridging is important because the energy expended in deformation determines the large-scale strength of the ice pack and because the horizontal stresses in ice cover and the strength and thickness of pressure ridges are important in the design and operation of Arctic vessels and offshore structures. Based on laboratory experiments and computer simulation, a simple model for ridging has been formulated. The purpose ridging model gives a description of the ridging process and also a description of the ridging force. The model applies to the case where two similar ice sheets are pushed together as occurs in the Baltic. In the Arctic, ridges often form when thin sheets of lead are pushed against thicker multiyear floes. Exploitable results Sea ice deformation data set The data set consists of the four following main sections: ice deformation data from Zooming in Ice Physics field experiment, ZIP-97, ice-thickness measurements from the sdame experiment, observations of ice temperature from ZIP-97, and ice local deformation data from Sea Ice Mechanic Initiative field experiment, SIMI-93. The SIMI expermemnt was carried out from September 1993 to August 1994 in Beaufort Sea in the region 74-77 degrees North and 138-162 degrees West. There data from the Fall/Winter of 1993 was used for the project.ZIP-97 field campaign took place in Bay of Bothnia, Northern Baltic, March 1997. We performed measurements at 7 observational sites during SIMI experiment and at four sites during ZIP-97. the deformation of an ice-floe was collected as time series with the help of BP-delta strainmeters and CRREL bi-axial stress guages. Allsensors have have a high resolution and were able to detect very small variations in the stressed state of ice floe. Besides the long period variability of the deformation was observed because of the long monitoring period.This allowed us to study the wide range of the temporal scales and elaborate the down-scaling hypothesis. The evolution of vertical ice temperatures profiles was monitored using the thermistor chains, accelerometers and "bubble-liquid" tiltmeters were engaged in the wave observations. These measurements revealed for the first time the presence of the horizontal shear high frequency resonant waves in the spectra of ice motion and also oscillations with the variation in the frequency. On the basis of the observations models describing these type of oscillations were developed. Concurrent measurements of the ice stresses and deformations gave us the stress-strain relationships for the scale of the ice-floe; the result never gained before. For both the field experiments mesoscale observations and satellite remote sensing commplemented the local scale measurements. Searching for OpenAIRE data... There was an error trying to search data from OpenAIRE No results available
