Function Of Ice Thickness Research Articles

Planar antenna sensor with thermal stability for detection of ice formation

The microstrip patch antenna (MPA) with frequency stability versus temperature is proposed as the ice sensor for de-icing of aerodynamic systems. The operation principle is based on the fact that the formation of ice layer is set to disturb the near fields, thus shifting the resonant frequency. To mitigate the uncertain temperature effect, a thermal stability (TS) strategy is implemented, making the sensor only susceptible to the ice loading effect and enabling stable performance within a large temperature range from − 40∘C to + 80∘C. The proposed ice sensor is in turn interrogated wirelessly by a transmitting (Tx) antenna. Due to the frequency shift, the received signal strength (RSS) is modulated as a function of ice-thickness, allowing for remote ice detection and quantification. Two common types of ices, namely rime and clear ices, are investigated. The ice samples were generated and characterized under different weather conditions in our cold chamber and wind tunnel at Anti-icing Materials International Laboratory (AMIL) with the University of Quebec at Chicoutimi (UQAC). Experimental results show the feasibility of the proposed approach for different real-world scenarios. In particular, the sensor demonstrates the best measurement capability in the case of clear ice with full coverage, achieving the sensitivity of 75 mV/mm.

Studies of Sea-Ice Thickness and Salinity Retrieval Using 0.5–2 GHz Microwave Radiometry

Arctic sea-ice thickness and salinity retrievals are simulated to explore the performance of nadir-observing microwave radiometry operating with up to 16 frequency channels in the 0.5–2-GHz frequency range. A radiative transfer model is used to create lookup tables of the circularly polarized thermal emissions of first-year (FY) and multiyear (MY) sea ice, and the performance of two distinct retrieval methods is examined. The first method retrieves only sea-ice thicknesses, while the second retrieves both ice thickness and ice salinity. Retrieval errors are simulated for both FY and MY sea ice as a function of ice thickness, salinity, and temperature to investigate the impact of radiometric uncertainty, the frequency channels used, and any errors in ancillary information. To gain further insight into Arctic scale retrieval performance, a simulated brightness temperature dataset is produced for Arctic sea ice for the period October 2020–March 2021 using sea-ice thicknesses from the SMOS-CryoSat-2 algorithm. Compared to existing sea-ice thickness retrievals obtained from 1.4-GHz microwave radiometers, the results demonstrate that 0.5–2-GHz radiometry can achieve higher sensitivity to a sea-ice thickness within the range 0.5–1.5 m for FY sea ice and enable the retrieval of multiple sea-ice parameters (thickness and salinity) simultaneously.

A two layer model for wave dissipation in sea ice

Sea ice is highly complex due to the inhomogeneity of the physical properties (e.g. temperature and salinity) as well as the permeability and mixture of water and a matrix of sea ice and/or sea ice crystals. Such complexity has proven itself to be difficult to parameterize in operational wave models. Instead, we assume that there exists a self-similarity scaling law which captures the first order properties. Using dimensional analysis, an equation for the kinematic viscosity is derived, which is proportional to the wave frequency and the ice thickness squared. In addition, the model allows for a two-layer structure where the oscillating pressure gradient due to wave propagation only exists in a fraction of the total ice thickness. These two assumptions lead to a spatial dissipation rate that is a function of ice thickness and wavenumber. The derived dissipation rate compares favourably with available field and laboratory observations.

Wave attenuation and dispersion due to floating ice covers

Experiments investigating the attenuation and dispersion of surface waves in a variety of ice covers are performed using a refrigerated wave flume. The ice conditions tested in the experiments cover naturally occurring combinations of continuous, fragmented, pancake and grease ice. Attenuation rates are shown to be a function of ice thickness, wave frequency, and the general rigidity of the ice cover. Dispersion changes were minor except for large wavelength increases when continuous covers were tested. Results are verified and compared with existing literature to show the extended range of investigation in terms of incident wave frequency and ice conditions.

The feasibility of imaging subglacial hydrology beneath ice streams with ground-based electromagnetics

ABSTRACTSubglacial hydrologic systems in Antarctica and Greenland play a fundamental role in ice-sheet dynamics, yet critical aspects of these systems remain poorly understood due to a lack of observations. Ground-based electromagnetic (EM) geophysical methods are established for mapping groundwater in many environments, but have never been applied to imaging lakes beneath ice sheets. Here, we study the feasibility of passive- and active-source EM imaging for quantifying the nature of subglacial water systems beneath ice streams, with an emphasis on the interfaces between ice and basal meltwater, as well as deeper groundwater in the underlying sediments. We describe a suite of model studies that exam the data sensitivity as a function of ice thickness, water conductivity and hydrologic system geometry for models representative of a subglacial lake and a grounding zone estuary. We show that EM data are directly sensitive to groundwater and can image its lateral and depth extent. By combining the conductivity obtained from EM data with ice thickness and geological structure from conventional geophysical techniques, such as ground-penetrating radar and active seismic surveying, EM data have the potential to provide new insights on the interaction between ice, rock and water at critical ice-sheet boundaries.

Infrared spectra and band strengths of amorphous and crystalline N2O.

Infrared transmission spectra from 4000 to 400 cm-1, and associated band strengths and absorption coefficients, are presented for the first time for both amorphous and crystalline N2O. Changes in the spectra as a function of ice thickness and ice temperature are shown. New measurements of density, refractive index, and specific refraction are reported for amorphous and crystalline N2O. Comparisons are made to published results, and the most-likely reason for some recent disagreements in the literature is discussed. As with CO2, its isoelectronic congener, the formation of amorphous N2O is found to require greater care than the formation of amorphous solids from more-polar molecules.

Predicting ice-induced load amplitudes on ship bow conditional on ice thickness and ship speed in the Baltic Sea

Transportation in ice prone waters is a timely topic due to the pursuit for arctic natural resources and sea routes. One important safety aspect in designing ships that enter ice prone waters is to determine the ice-induced loads on ships. However, ice is a particularly inconsistent material; therefore it is difficult to predict the occurring loads when the ship hull breaks the ice. We propose a novel probabilistic, Bayesian, method for modeling and predicting ice load distributions in different ice and operational conditions. We assume the ice loads to be generated from a random process whose parameters change as a function of ice thickness and ship speed. We test four alternative hierarchical Gaussian Process models. The best model shows good performance in predictive validation tests. According to the results the probability of high ice loads increases with increasing ice thickness and increasing speed. The model can be used to predict continuously ice loads in different ice thickness and speed conditions and, with further development, has potential to be utilized in determining the safe way to operate ships in different conditions.

Probabilistic fracture mechanics analysis of spalling during edge indentation in ice

The design of marine structures for ice environments requires ice load estimates, which are greatly influenced by fracture and associated scale effects. During edge indentation of natural ice, fracture processes are highly influenced by variability associated with flaw structure and contact conditions. A probabilistic framework is the most appropriate for modeling such interactions. In the present analysis, a probabilistic fracture mechanics model has been developed to model localized fracture events for ice specimens with ice edge taper angles ranging from 0° to 45°. Crack instability criteria have been formulated for compressive and tensile states of stress. This approach varies from traditional probabilistic failure models which assume that zones of compressive stress have zero failure probability and include only tensile zones in the calculation of failure probability. For compressive edge loading, experimental results indicate that local edge fractures (spalls) are most likely to emanate from regions of the ice where cracks would be subjected to axial compression and lateral tension. Compressive contact loads required to propagate fractures from zones of bi-axial tension or bi-axial compression were found to be considerably higher and are much less probable. Estimates of the mean pressure required to trigger a fracture event as a function of ice thickness were generated for thicknesses in the range of 0.2–2.0m. These results demonstrate that observed scale effects in ice pressure data can be explained by probabilistic aspects of fracture. Simulations of fracture probabilities as a function of loading eccentricity confirmed that extreme loads of interest in engineering design are most likely to correspond to high pressure zones located near the center of thickness of the ice sheet. Results indicate that fractures occur more readily for flat ice edges and higher pressures are required to propagate fractures for edges with more highly tapered edges. This result provides a theoretical basis to explore the interplay between fracture and crushing, both of which occur during compressive ice failure: fractures create tapered edges that localize contact in manner that supports crushing; crushing, over several cycles, flattens the ice edge in a manner that in turn promotes fracture. While the application presented here is focused on ice mechanics, the analysis methodology could readily be applied to other brittle materials.

Marine ice sheet stability

AbstractWe examine the stability of two-dimensional marine ice sheets in steady state. The dynamics of marine ice sheets is described by a viscous thin-film model with two Stefan-type boundary conditions at the moving boundary or ‘grounding line’ that marks the transition from grounded to floating ice. One of these boundary conditions constrains ice thickness to be at a local critical value for flotation, which depends on depth to bedrock at the grounding line. The other condition sets ice flux as a function of ice thickness at the grounding line. Depending on the shape of the bedrock, multiple equilibria may be possible. Using a linear stability analysis, we confirm a long-standing heuristic argument that asserts that the stability of these equilibria is determined by a simple mass balance consideration. If an advance in the grounding line away from its steady-state position leads to a net mass gain, the steady state is unstable, and stable otherwise. This also confirms that grounding lines can only be stable in positions where bedrock slopes downwards sufficiently steeply.

A preliminary investigation of the influence of basal and surface topography on supraglacial lake distribution near Jakobshavn Isbrae, western Greenland

AbstractThe spatial distribution of supraglacial lakes has been hypothesized to be dominantly controlled by the component of surface roughness influenced by basal topography. Basal topography and surface roughness profiles within the Jakobshavn Isbrae drainage basin in western Greenland, acquired from an ice‐penetrating radar echo sounder, were analysed through fourier and wavelet decompositions. Spectral analyses of basal‐to‐surface transfer under a range of ice thickness were compared with spatial distribution of lakes mapped from high‐resolution Landsat imagery. Fourier analysis identifies dominant signals in both the basal and surface profiles to be ranging between wavelengths of 1·25–12·5 km. The strongest peaks of transfer of basal signals to the surface were identified at wavelengths ∼11∼5 km. Wavelet analysis identifies these peaks with thicker (1200–1400 m) and thinner (500–700 m) ice respectively and also identifies surface frequencies not present in the basal signal indicating some influence from other factors. Spatial autocorrelation analysis of supraglacial lake distribution indentifies high correlations at 1·9, 5·6, 11, 24, and 30 km lags. Lags at 5·6 and 11 km correspond to dominant frequencies present in the basal and surface profiles over thinner and thicker ice respectively. These ∼5 and ∼11 km frequency components present in the basal topography, surface roughness, and lake distribution are within the theoretical transfer window of basal‐to‐surface transfer as a function of ice thickness. The transect analysed in this study does not contain wavelengths in the surface structure that are less than the ice thickness, even though there are relatively higher frequencies present in the surface profile between 0 and 15 km that have less power in the basal profile. Copyright © 2011 John Wiley & Sons, Ltd.

Investigating the stability of subglacial lakes with a full Stokes ice-sheet model

AbstractDespite the large amount of subglacial lakes present underneath the East Antarctic ice sheet and the melt processes involved, the hydrology beneath the ice sheet is poorly understood. Changes in subglacial potential gradients may lead to subglacial lake outbursts, discharging excess water through a subglacial drainage system underneath the ice sheet. Such processes can eventually lead to an increase in ice flow. In this paper, a full Stokes numerical ice-sheet model was employed which takes into account the ice flow over subglacial water bodies in hydrostatic equilibrium with the overlying ice. Sensitivity experiments were carried out for small perturbations in ice flow and basal melt rate as a function of ice thickness, general surface slope, ice viscosity and lake size, in order to investigate their influence on the subglacial potential gradient and the impact on subglacial lake drainage. Experiments clearly demonstrate that small changes in surface slope are sufficient to start and sustain episodic subglacial drainage events. Lake drainage can therefore be regarded as a common feature of the subglacial hydrological system and may influence, to a large extent, the present and future behavior of large ice sheets.

Cenozoic climatic change in Antarctica recorded by volcanic activity and landscape evolution

A long-lasting Cenozoic record (∼50 m.y.) of alkaline igneous rocks characterizes northern Victoria Land, Antarctica. Landscape analysis allows distinction between older volcanic and intrusive rocks with well-developed alpine topography sculptured by wet-based glaciers, and younger volcanic cones lacking these features. Many K-Ar and Rb-Sr dates testify that the erosion that formed the alpine landscape ceased between ca. 8.2 and 7.5 Ma. Since ca. 8 Ma, morphological evolution has been driven by cold-based glaciers; warm-based glaciers were no longer active. That this change affected a 300-km-long coastal area suggests a persistent cause of global significance. Glacier dynamics control landscape shaping as a function of ice thickness and temperature, which are driven by climatic conditions. In this view, a significant climatic change occurred in northern Victoria Land between 8.2 and 7.5 Ma. The perfectly preserved serrated alpine ridges, with their delicate spires, testify that no warm-based ice sheets overrode the region after 7.5 Ma and that polar conditions held sway in the Pliocene and Pleistocene Epochs.

Hydrostatic Pressure Loading due to Ice Formation in Manholes

The magnitude of the hydrostatic pressure that results from the growth of an ice layer at the top of a water‐filled manhole is determined using both analytical (for a thin ice layer) and finite‐element methods (for a thick ice layer). The ice‐layer freeze/fracture cycle during the growth of the ice layer is predicted analytically and subsequently verified experimentally. A general expression for the hydrostatic pressure as a function of ice thickness and cross‐sectional area (l2i/a2) for a square cross section is developed. Experimental results for an ice layer of a circular cross section show that up to l2i/r2≃0.5 the trend in pressure versus ice thickness results is predicted by the finite‐element method although in some cases the actual experimental values are approximately twice the predicted values, probably due to thickening of the ice disk around the periphery. For the l2i/r2≃0.5 case, hydrostatic pressures resulting from ice formation at the top of the manhole can be two orders of magnitude greater than the pressure due to the static head in a water‐filled manhole.

The detectability of Arctic leads using thermal imagery under varying atmospheric conditions

Arctic leads (open or refrozen fractures in sea ice) provide for the exchange of heat between the ice/ocean surface and the atmosphere. Their influence on the energy budget is not easy to quantify, however, because little is known about their spatial and temporal distributions due to the difficulty in detecting and mapping leads using remote sensing techniques. The way in which thermal contrast between leads of varying widths and thicknesses can be distinguished from the background multiyear ice surface under varying atmospheric conditions is examined. The normalized brightness temperature difference between image pixels that include lead fractions and of the background ice is used in an attempt to determine thresholds of detection accounting for sensor field‐of‐view and various atmospheric phenomena that influence the Arctic radiation balance during winter. Brightness temperatures are derived from modeled top‐of‐the‐atmosphere radiances for three thermal channels (3, 4 and 5) of the Advanced Very High Resolution Radiometer. Surface temperatures are prescribed as a function of ice thickness and the effects of the intervening atmosphere are simulated by varying the optical depths of hypothetical cloud or haze layers varying in microphysical characteristics. Results indicate that the limits of lead detection may be determined as a function of pixel lead fraction and atmospheric optical depth if suitable values of normalized contrast are used as detection criteria. For example, given a pixel resolution of 1.0 km and the presence of a layer of ice crystals having a visible optical depth of 0.6 just above the surface, the minimum detectable lead width is estimated to be between 400 m and 750 m depending on what threshold criteria are used which, in turn, depends on the homogeneity of the multiyear ice surface. For the same conditions and range of threshold criteria but assuming a layer optical depth of 0.3, the minimum detectable lead width decreases to between 290 m and 560 m. Minimum detectable lead widths are also found to depend on the microphysical and physical properties of any intervening atmospheric layer. Our simulations indicate that narrower leads are detectable when hazy conditions exist than when stratiform water or ice clouds are present for any given layer optical depth.

Quantitative energy-filtered electron microscopy of biological molecules in ice

The theoretical and experimental bases for quantitative electron microscopy of frozen-hydrated specimens are described, with special considerations of energy filtration to improve the images. The elastic and inelastic scattering from molecules in vacuum and in ice are calculated, and simple methods to approximate scattering are introduced. Multiple scattering calculations are used to describe the scattering from vitreous ice and to predict the characteristics of images of frozen-hydrated molecules as a function of ice thickness and accelerating voltage. Energy filtration is predicted to improve image contrast and signal-to-noise ratio. Experimental values for the inelastic scattering of ice, the energy spectrum of thick ice, and the contrast of biological specimens are determined. The principles of compensation for the contrast transfer function are presented. Tobacco mosaic virus is used to quantify the accuracy of interpreting image intensities to derive the absolute mass, mass per unit length, and internal mass densities of biological molecules. It is shown that compensation for the contrast transfer function is necessary and sufficient to convert the images into accurate representations of molecular density. At a resolution of 2 nm, the radial density reconstructions of tobacco mosaic virus are in quantitative agreement with the atomic model derived from X-ray results.

Wave propagation in the marginal ice zone: Model predictions and comparisons with buoy and synthetic aperture radar data

In this paper the ocean wave dispersion relation and viscous attenuation by a sea ice cover are studied for waves propagating into the marginal ice zone (MIZ). The derivation of the dispersion relation and the viscous attenuation by an ice sheet are discussed for waves under flexure and pack compression. In the MIZ, the flexure effect is important for short waves. For a fixed wave period the changes in wavelength and group velocity as a function of ice thickness are significant. In turn, the exponential wave attenuation rate shows a rollover at short wave periods, whereby the rapid increase in wave attenuation rate with decreasing wave period slows down or even turns into a decrease. The Labrador Ice Margin Experiment (LIMEX), conducted on the MIZ off the east coast of Newfoundland, Canada, in March 1987, provides us with aircraft synthetic aperture radar (SAR) imagery, wave buoy, and ice property data. On the basis of the wave number spectrum from the SAR data and the concurrent wave frequency spectrum from the ocean buoy data and accelerometer data on the ice during LIMEX '87, the dispersion relation has been estimated and compared with a model. Wave energy attenuation rates are estimated from SAR data and the ice motion package data which were deployed at the ice edge and into the ice pack, and compared with the model. The model‐data comparisons are reasonably good for the ice conditions observed during LIMEX '87. Some previously reported data of wave attenuation in the MIZ are revisited for model comparison.

Passive Microwave Spectral Emission from Saline Ice at C-Band During the Growth Phase

This paper focusses on microwave radiometer measurements of the emission from saline ice as a function of ice thickness. The instrument used is a C-band stepped-frequency microwave radiometer (SFMR) that can be tuned to operate at any center frequency from 4 to 8 GHz at a bandwidth of 100 MHz. The measurements were undertaken at a facility constructed by the U. S. Army Cold Regions Research and Engineering Laboratory, which was specifically designed to satisfy remote-sensing requirements. In addition to presenting the data, a simple theory is developed to explain the experimental results in terms of the relevant electromagnetic parameters; namely, the complex dielectric constant and thickness of the ice.

A Numerical Investigation of The Large Scale Dynamics of Sea Ice

Abstract Several numerical simulations of the Arctic ice cover over a seasonal cycle are carried out. Two different types of constitutive laws are examined: rigid plastic and linear viscous. In both cases, the strength of the ice interaction is taken as a function of ice thickness and compactness. The thickness and compactness, in turn, evolve according to continuity equations which include thermodynamic source and sink terms. The simulations with the rigid-plastic law reproduce reasonable geographical ice-thickness variations, ice outflow, and ice-velocity characteristics. The viscous simulations (especially the Newtonian viscous case) produce less satisfactory geographical ice thickness variations, and near-shore velocity characteristics. In addition the Newtonian-viscous simulation produces highly unrealistic ice-edge effects in summer. The results are discussed in terms of the relative magnitudes of the shear and compressive strengths, and in terms of the non-linear versus linear dependence on deformation in the ice rheology. The portion of this study employing a plastic constitutive law is published in full in Journal of Physical Oceanography, Vol. 9, No. 4, 1979, p. 815–46.

A Numerical Investigation of The Large Scale Dynamics of Sea Ice

AbstractSeveral numerical simulations of the Arctic ice cover over a seasonal cycle are carried out. Two different types of constitutive laws are examined: rigid plastic and linear viscous. In both cases, the strength of the ice interaction is taken as a function of ice thickness and compactness. The thickness and compactness, in turn, evolve according to continuity equations which include thermodynamic source and sink terms. The simulations with the rigid-plastic law reproduce reasonable geographical ice-thickness variations, ice outflow, and ice-velocity characteristics. The viscous simulations (especially the Newtonian viscous case) produce less satisfactory geographical ice thickness variations, and near-shore velocity characteristics. In addition the Newtonian-viscous simulation produces highly unrealistic ice-edge effects in summer. The results are discussed in terms of the relative magnitudes of the shear and compressive strengths, and in terms of the non-linear versus linear dependence on deformation in the ice rheology. The portion of this study employing a plastic constitutive law is published in full in Journal of Physical Oceanography, Vol. 9, No. 4, 1979, p. 815–46.