Current marine navigation radars are capable of high-resolution imagery of marine ice but are not able to classify the marine ice. Classifying marine ice means identifying the ice as first-year ice, multi-year ice or glacier ice. The latter two ice types are as hard as concrete and capable of damaging even ice hardened vessels such as icebreakers. The Canadian Coast Guard has identified the ability of marine navigation radars to classify marine ice as the single greatest improvement to be made in the safety of Arctic navigation. This thesis presents new research that improves our understanding of electromagnetic backscatter from marine ice. The goal of this work was two-fold: to demonstrate the feasibility of using commercial computational electromagnetic modelling software to simulate real-world marine ice targets, and to identify an optimum frequency or range of frequencies at which the marine ice targets can be definitively classified. Engineering models for scattering from electrically large objects made of a highly variable, complex, heterogenous, three-phase mixture of ice, air and brine are developed. To do so, an extensive literature review of the Arctic environment, and the physical and electrical properties of marine ice, is conducted to distill the required geophysical parameters of the three marine ice types of interest in this work. Using well-established dielectric mixing theory, these parameters are applied to homogenize the marine ice and model the target (in the presence of a flat sea halfspace) using a surface integral equation formulation. To reduce the computational resources required to numerically solve the integral equation models using the method of moments, computational electromagnetic modelling studies are conducted to select a suitable seawater halfspace representation and determine if the properties of larger objects can be inferred from scaled down models of the object. A case study is presented for backscatter from marine ice from 6 to 10 GHz, which explores the effects of frequency on the co- and cross-polarized backscatter intensity (and hence the apparent radar cross-section) of the three marine ice types of interest. Good agreement is found between the co- and cross-polarized backscatter intensity responses found from the engineering model computations and some existing experimental data from real-world marine ice targets. This work: (a) proves the feasibility of using computational electromagnetic modelling to simulate real-world marine ice targets, providing a new, cost-effective method for the study of backscatter from marine ice; (b) confirms the viability of using cross-polarization as a method of classification; and (c) identifies 10 to 16 GHz as a potential optimal frequency range for the classification of marine ice using dual-polarization radar.

The use of iceberg-keel ploughmarks as proxy indicators of past and present iceberg morphology, keel depth and drift direction has seldom been approached in the southern hemisphere. Using high-resolution multi-beam swath bathymetry of the mid-shelf Pine Island Trough and outermost Weddell Sea shelf regions of Antarctica, detailed analysis of >13,000 iceberg-keel ploughmarks was undertaken. By considering the draft of icebergs calved from Antarctica today, calculated from detailed satellite altimetric datasets by this work, almost all observed ploughmarks were interpreted to be relict features. In Pine Island Trough, ploughmark planform parameters and cross-sections imply calving of a large number of non-tabular icebergs with v-shaped keels from the palaeo-Pine Island-Thwaites ice stream. Geological evidence of ploughmark form and modern water depth distribution indicates calving-margin thicknesses (949 m) and subaerial ice cliff elevations (102 m) equivalent to the theoretical threshold predicted to trigger ice-cliff structural collapse and calving by marine ice-cliff instability (MICI) processes. Thus, ploughmarks provide the first observational evidence of rapid retreat of the palaeo-Pine Island-Thwaites ice stream, driven by MICI processes commencing ~12.3 cal ka BP. On the Weddell Sea shelf, ploughmark morphologies imply considerable variation in palaeo-iceberg shape and size, most likely reflecting calving from multiple source margins. In turn, an absence of grounded ice on the Weddell Sea shelf and a palaeo-oceanographic regime comparable to today are implied at the time of formation. Analysis of a 3D seismic cube of the Sea Lion Field area of the North Falkland Basin reveals iceberg-keel ploughmarks incised into the modern- and palaeo-seafloor, formed by icebergs of varying shape and size that most-likely calved from the Antarctic Ice Sheet during three past glacial periods (estimated ages ~18 - 26.5 ka BP, ~246 ka BP, ~9.8 Ma BP). Despite illustrating the possibility of iceberg drift into the North Falkland Basin today, the relict ploughmark age implies little risk to any seafloor structures in the area, which might be required for hydrocarbon production. By these analyses, the significance of iceberg-keel ploughmarks as indicators of palaeo-glaciology and palaeo-oceanography at the time of formation is emphasised.

Antarctic ice shelves control the ice flux from the continent to the ocean. As such, they play a major role in the stability of the ice sheet and its potential contribution to sea level rise, especially in the context of global change. Below some of these ice shelves, marine ice can be found which is a product of the Deep Thermohaline Circulation. Due to its specific genetic process, marine ice has intrinsic physical (grain size, ice fabric, bubble content, ) and chemical (impurities, water stable isotopes) properties, that differ from those of 'meteoric ice' formed on the continent through snow metamorphism or 'sea ice' resulting from sea water freezing at the ocean-atmosphere surface. Until now however, the effect of these specific properties on marine ice rheology is still very poorly understood.<p><p>The principal objective being to include realistic mechanical parameters for marine ice in ice shelf flow models, uniaxial compression experiments have been performed on various types of marine ice samples. Technical developments are an important component of this thesis has they were necessary to equip the laboratory with the appropriate tools (pneumatic rig, automatic ice fabric data handling).<p><p>Results from experimental compression on isotropic marine ice show that it represents the higher boundary for meteoric ice viscosity throughout the whole temperature range, thereby validating Cuffey and Paterson's relationship with an enhancement factor equals to 1.<p><p>Marine ice is however often quite anisotropic, showing elongated crystals and wide single maximum fabric, that should impact its mechanical properties. Experiments on pre-oriented marine ice samples have therefore been carried out combining the study of epsilon_{oct} vs. tau_{oct} with a thorough analysis of microstructural data 'before' and 'after' the experiment. <p><p>Depending on the orientation of the sample in the applied stress field and on the intensity of the latter, anisotropic marine ice can be harder or softer than its isotropic counterpart, with n=4 often observed in Glen's flow law. Associating the experimental geometrical settings to potential natural equivalent, results suggest that anisotropic marine ice would strengthen ice shelf flow in most areas (for a same given temperature), apart from suturing areas between individual ice streams as they merge to form the ice shelf, where it could become weaker than meteoric ice in certain circumstances.<p><p>Finally, preliminary sensitivity studies, using a simple ice shelf model with our experimental parameters of Glen's flow law have allowed us to discuss the potential impact of rift location, rift size and thermal regime in the ice shelf behavior. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished