bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Behaviour of Finely Divided Ice
Authors: Paren J. G. , Glen J. W.
Published: September 2017

The electrical behaviour of ice which has been finely ground and compressed was investigated during ageing in air and over a range of temperatures. The dielectric behaviour may be accurately represented as the sum of two elliptical relaxation spectra. The behaviour eventually stabilizes with similar activation energies for the mean relaxation time of each spectrum c. 0.25 eV, and the ratio of the relaxation times is ten in samples of density c. 0.42 Mg m-3. Arguments are presented on whether the higher-frequency dispersion is a consequence of the heterogeneous nature of the samples or is a bulk relaxation process. The similarities between the behaviour of such finely ground ice and of deposited snow and polar glacier ice are discussed. The extent to which the results may be attributed to surface adsorption of CO2 are examined by reference to measurements of the CO2 content of finely divided ice and ice from polar regions.
Inelastic Neutron Scattering from Ice and Other Proton-containing Substances
Authors: Dorner Bruno
Published: September 2017

A brief introduction to neutron scattering is given with special emphasis on the difference between coherent and incoherent contributions. The following report of recent work on ice contains the determination and verification of some phonon dispersion curves, and outlines the state of the art on diffuse scattering due to the proton disorder. Results on “two-dimensional ice” in copper formate tetrahydrate are of great interest as this system exhibits a phase transformation below which the protons are ordered. The study of rotational diffusion and of the tunnel splitting of the rotational ground state of molecules which contain protons is discussed in some detail. These investigations are now possible with very high energy resolution ΔE ≈ 5 × 10-8 eV (4 • 10-4 cm- 1 or 12 MHz).
Thermal Conductivity of Ice in the Temperature Range 0.5 to 5.0 K
Authors: Varrot M. , Rochas G. , Klinger J.
Published: September 2017

A method is described for measuring the thermal conductivity of ice in the temperature range from 0.5 to 5.0 K using a 3He apparatus. The results from our first experiments are not too far from the theoretical law for the low-temperature thermal conductivity of ice . Measurements at still lower temperatures are necessary to confirm our results.
Radiation Damage in Ice at Low Temperatures Studied by Proton Channelling
Authors: Golecki I. , Jaccard C.
Published: September 2017

100 keV protons with fluxes between 3 × 1015 and 3 × 1016 m-2 s-1 and in doses up to 4 × 1020 m-2 have been used in ice between - 191°C and -87°C to create damage and to analyse it. The Rutherford backscattering minimum yield along the c-axis (about 0.05 in good monocrystals) increases up to unity with the dose, according to a function which can be scaled by a critical dose depending mainly on temperature (Arrhenius law with activation enthalpy of 0.17 ± 0.04 eV above -185°C). Higher flux produces more damage above -180°C, but less below. A beam in a random direction is more efficient below - 180°C, but less at higher temperature than an aligned beam. Beam-induced reordering is observed at definite temperatures and doses. The damage is shown to be due to energy loss by electronic excitations, which decay and produce disordered molecule clusters, mainly by incoherent aggregation of vacancies and interstitials.
CO2 in Natural Ice
Authors: Stauffer B. , Berner W.
Published: September 2017

Natural ice contains approximately 100 p.p.m. (by weight) of enclosed air. This air is mainly located in bubbles. Carbon dioxide is an exception. We estimate the fraction of CO2 present in bubbles to be only about 20%. The remaining part is dissolved in the ice. Measurements of the CO2 content of ice samples from temperate and cold glacier ice as well as of freshly fallen snow and of a laboratory-grown single crystal are presented. Glaciological implications are discussed.
Observation of Basal Dislocations in Ice by Etching and Replicating
Authors: Sinha N. K.
Published: September 2017

A method is described for preparing the surface of ice and for forming etch pits on the prismatic surfaces with whisker replicas that correspond to basal dislocations. The technique removes the ambiguity sometimes associated with etch pits and dislocations, and allows direct observation of dislocation glide, pile-up against barriers, and other features in deformed ice.
Studies of Crystal Imperfections in Ice with Reference to the Growth Process by the use of X-Ray Diffraction Topography and Divergent Laue Method
Authors: Mizuno Yukiko
Published: September 2017

This paper presents studies on crystal imperfections including basal and non-basal dislocations, small-angle grain boundaries, stacking faults, and dislocation networks in ice using both X-ray diffraction and Laue techniques; these studies examined the growth process or origin of the ice, i.e. ice from glaciers, ice grown from the melt, or ice formed by sublimation. Several hoar crystals were found to be perfect, dislocation-free crystals, this may be due to their very slow growth rate. Dislocations and Shockley-type stacking faults were observed in some crystals. Dislocation density of a hoar crystal is very large at the point at which it started to grow, but away from this region the density becomes so small that no dislocation can be seen. The arrangement and structure of dislocations around vapour figures were also studied by means of X-ray diffraction topography. It was found that the dislocation density is high along the periphery of the vapour hexagon and that the great majority of dislocations within the hexagon are running from its centre towards the vertices or sides of the hexagon. Long screw dislocations with Burgers vector c <0001> were observed in a tabular ice which was formed artificially at a very slight degree of supercooling. The behaviour of dislocations in ice subjected to a tensile stress was studied by the use of the divergent X-ray technique which gives both enlarged Laue spots and a transmission pattern in the same photograph.
The Creep Activation Energies of Ice
Authors: Homer D. R. , Glen J. W.
Published: September 2017

Monocrystals and bicrystals of ice have been creep tested at temperatures between 4 and — 30°C. The bicrystals had a single grain boundary running parallel to the tensile axis; this configuration inhibited grain-boundary slip between the two grains. The creep tests, which were carried out at constant stress σ and temperature T, yielded data of strain ϵ for time elapsed since the start of the test. These data showed accelerating creep for both monocrystals and bicrystals at all strain levels. Strain-rates were derived at strains of 0.01, 0.05. and 0.10, and these rates were fitted to the expression

k is Boltzmann’s constant and E is the creep activation energy. Derived values of n were 1.9 for monocrystals and 2.9 for bicrystals. The creep activation energy was found to be 78 kJ/mol for monocrystals and 75 kJ/mol for bicrystals. The processes of creep deformation in mono-, bi- and polycrystals are discussed.
Short-Term Rheology of Polycrystalline Ice
Authors: Sinha N. K.
Published: September 2017

Deformation characteristics of polycrystalline ice and their dependence on time, temperature, and stress have been analysed on the basis of a phenomenological relation which describes creep in terms of initial elastic, delayed elastic, and permanent strain. It is shown that the effective modulus of ice observed in the laboratory or in the field can be examined on the basis of this model. The model also provides a basis on which the observed flow law of ice can be examined conveniently. Some apparent inconsistencies in the results of earlier investigations of the mechanical property of ice appear of be reconciled by the model.
The Influence of Ice-Crystal Size on Creep
Authors: Baker Robert W.
Published: September 2017

Uniaxial compression tests were conducted on polycrystalline-ice samples with random c-axis orientation and steady-state creep rates were determined. Experiments were conducted on both inclusion-bearing and inclusion-free ice and were run at constant stress and constant temperature. During freezing, the presence of inclusions in low concentrations inhibits crystal growth; variations in the volume-fraction of inclusions thus result in variations in ice-crystal size. The creep rate of polycrystalline ice at high temperatures and moderate stresses is extremely sensitive to variations in ice-crystal size. Due to an apparent inversion between dislocation-controlled creep and diffusion-controlled creep, the optimum grain size for creep resistance is about 1.0 mm. Increasing or decreasing the average crystal size from this critical value results in an increase in secondary-creep rate.
The Creep of NaCl-Doped Ice Monocrystals
Authors: Riley N. W. , Noll G. , Glen J. W.
Published: September 2017

Monocrystals of ice grown from NaCl solutions (concentration 5 X 10–4 to 10–2 mol/l) have been tested in creep at —10°C by basal glide. The maximum resolved shear stress ranged from 0.6 to 2.5 bar. The resulting creep curves show a deceleration, that is, the creep rate decreases with time. At the highest concentration the creep is essentially transient; the strain tends to a fixed value. This is unlike the behaviour of similarly orientated monocrystals of pure ice or of ice grown from solutions of other dopants so far reported in the literature.

The possible causes for this behaviour are discussed and the implications for the mechanical properties of polycrystalline ice, and in particular sea ice and glacier ice, are described.
Crystallographic Structure of Polycrystalline Ice
Authors: Matsuda M. , Wakahama G.
Published: September 2017

For several types of polycrystalline ice of different origins, the spatial lattice orientation of each crystal was determined by measurements of both the a- and c-axis orientations. Analyses of the orientations of adjoining crystals showed that a great majority of adjoining crystals may be in a twinning relation. With special reference to the multi-maximum c-axis preferred-orientation fabric (the so-called “diamond pattern”), which is expected to occupy the largest part of a glacier ice mass, the crystal boundary structure was estimated. The preferred c-axis orientations of this fabric were explained as being the result of coincident oxygen-oxygen lines (hydrogen-bond lines) between adjoining crystals being concentrated in the orientations where seven oxygen-oxygen lines of one single crystal of ice are distributed. From the above result, it was concluded that the multi-maximum fabric is of the polycrystalline structure closest to the structure of a single crystal of ice among all the fabrics found in large ice masses.

It is found that the occurrence, in glaciers and ice sheets, of a multi-maximum fabric has a bias to the parts which have undergone a strong shear deformation for a long time. It is thus suggested that plastic deformation of ice with this fabric may be attributed to mechanical twinning due to a strong shear stress.
On the Heat Capacity, Entropy, and “Glass Transition” of Vitreous Ice
Authors: Johari G. P.
Published: September 2017

An analysis of the thermal properties of vitreous ice shows that both its heat capacity Cp and its entropy above 100 K are partly configurational in origin. The configurational contribution increases with temperature, and the excess Cp and entropy near the solid-liquid transformation temperature are 36.7 and 2.1 J K-1 mo1-1, respectively. The increase is interpreted as indicating the onset of molecular mobility in vitreous ice. The configurational Cp, of the melt of vitreous ice at 133.6 K, of ≈ 36.7 J K-1 mo1-1, is the same as the configurational Cp, of water at 273 K. Thus, the short-range order in the melt differs little from that in water at 273 K. The maximum calorimetric residual entropy of vitreous ice is 13.4 J K-1 mol-1, which is in fair agreement with the maximum value of 9.2 J K-1 mol-1 anticipated for a tetrahedral random-network model with fully disordered positions of H atoms. Thermodynamic consideration of a glass transition in supercooled liquid water indicates that there is no continuity of state between supercooled water and vitreous ice and, therefore, the structure and thermodynamic properties of a possible glassy state of water should be different from that of vapour-deposited vitreous ice. This paper is published in full in Philosophical Magazine, Eighth Ser., Vol. 35, No. 4, 1977, p. 1077-90.
The Dipolar Correlation Factor of Ice VI
Authors: Johari G. P. , Whalley E.
Published: September 2017

The dipole moment μ of an H2O molecule in the orientationally disordered ices is greater than the moment of an isolated molecule, 1.84 D, due to two factors: (i) the mutual polarization of molecules, and (ii) the short-range average correlation of the dipole vectors, if the molecules are able to reorient. The magnitude of the average enhancement is given by Kirkwood's equation,

1

where ϵ0 and ϵ∞ are respectively the limiting low- and high-frequency relative permittivity of orientational polarization, N is the number density of dipoles, k is the Boltzmann constant and T is the temperature. The dipolar correlation factor g is defined by,

2

where μi and μj are the dipole moments of molecules i and j in a spherical region of radius r immersed in a larger spherical region of radius R and the angular brackets indicate average over all molecules i and all their orientations. In view of the defects, vacancies, imperfections, etc., in ice, it is not certain if the limits in Equation (2) have any experimental significance. However, an approximate value of g can be calculated by taking molecules up to the second co-ordination shell.

The theoretical value of g for polycrystalline ice VI which is fully disordered (within the restrictions of ice rules) has been calculated by taking molecules up to the second nearest neighbours, in both the dendritic and non-dendritic models. The calculations were done for two kinds of molecules, I and II, having multiplicities 2 and 8 respectively, in the tetragonal unit cell in space group P42/nmc, and, through the use of symmetry, keeping to a minimum the number of scalar products.

In both the dendritic and non-dendritic, models, gI is 10%, or more, greater than gII and the appropriately weighted values of g are 2.342 in the former and 2.065 in the latter model. The effect of ring closure is, therefore, to reduce the value of g by 13%. The limiting high temperature experimental value of g from Equation (1), using Onsager's theory for the enhancement of the dipole moment by its own reaction field, is 2.42 (Johari and Whalley, 1976). By analogy with the 10% discrepancy between the theoretical and experimental values of g of ice I, a better estimate of the experimental g of ice VI (using a reaction field other than that given by the Onsager theory) would be about 10% less than this value. Thus the suggested experimental g of ice VI (2.18) is close to the theoretical values obtained from either of the two models and there is little contribution to g from neighbours beyond the second co-ordination shell.
Effect of Hydrostatic Pressure on the Creep of Ice
Authors: Jone Stephen J.
Published: September 2017

Uniaxial compressive creep tests on single crystals and polycrystals of ice at about -10°C under different hydrostatic pressures are described . After creeping under a constant load at atmospheric pressure for some hours, a hydrostatic pressure of the order of 35 MN m-2 was applied and the change in strain-rate was noted. Some hours later the hydrostatic pressure was removed and the test continued at atmospheric pressure. From these changes in strain-rate , an activation volume V was determined from the equation

where R is the gas constant, T is the absolute temperature, P is the hydrostatic pressure and τ is the superimposed uniaxial creep stress. V is negative if E increases with P.

For single crystals, which show an accelerating creep curve, that is the strain-rate increases continuously with time, no sensible activation volume was determined because the strain-rate increased both on the application of the hydrostatic pressure, and on its removal. For polycrystals, application of a hydrostatic pressure caused an increase in strain-rate which gave an activation volume of about - 10 cm3 mol-1. However, on removal of the pressure the strain-rate did not return to its original atmospheric-pressure value implying that steady-state creep had not been reached.

This value of activation volume is in general agreement with two previously published values for creep deformation, but is of opposite sign to the activation volume for dielectric relaxation. Further tests are in progress.
Breaking Strength and Creep Expansion of Deposited Snow
Authors: Watanabe Z.
Published: September 2017

The breaking strengths of snow were measured by a new tester which had been made by the author, and were expressed as functions of density or hardness. One special merit of the apparatus is that they are useable even for new snow, and the strengths were easily measured to several grammes per cm2. The creep expansion of snow was measured by using an optical level, and was expressed as a function of snow density, temperature, internal stress, and lapsed time. One point of the measurement is that the creep expansion rate did not become constant, hut was decreasing with time even several hours from the beginning of the test.
Application of Nucleation Theory to the Process of Droplet Freezing on an Ice Substrate
Authors: Levi L.
Published: September 2017

The probability P that ice embryos, nucleated inside droplets colliding with an ice surface, have crystallographic orientations different from that of the substrate, is correlated with the mean number of droplets which form each crystal in accretions grown in dry regime (substrate temperature Ts < 0°C). The theory of heterogeneous nucleation is applied to represent the ice embryo nucleation rate and the approximate expression is obtained, where ΔGy* is the nucleation energy for randomly oriented critical embryos. Assuming cap-shaped embryos and taking into account the crystal size in accretions grown at Ts = —15°C and air temperatures , it is found that erg

The relationship between the value of ΔGy* and those of the crystal-embryo and crystal-melt interfacial free energies is discussed. Finally the dependence of P0 on the growth conditions and on the ice substrate orientation is analysed, considering the effect of embryo breeding by collision and that of orientation selection, which is responsible for the establishment of preferential orientations in the accretions.
The Morphological Stability of Internal Melting Figures in Ice
Authors: Mae Shinji
Published: September 2017

Wavy perturbations formed on disc-shaped internal melting figures in ice were observed. It was found that a minimum wavelength of the perturbations was approximately 100 μm and a critical thickness of the figures for the formation of the perturbations was 10 μ.m. The critical thickness did not depend on the radius and growth rate of the figures. A minimum wave number of the perturbation was 6 and the axis of its sixfold symmetry was parallel to the <1120> direction, The perturbations with large wave number were formed on the inclined side faces of internal melting figures of which the shape was like a truncated cone. Therefore, it was concluded that the perturbations were nucleated at the sharp edge where the side face and the larger plane of the figures intersected. This conclusion was supported by the observation of internal melting figures at grain boundaries where their periphery was always sharp.
Radio-Echo Sounding: Glaciological Interpretations and Applications
Authors: Robin G. de Q.
Published: September 2017

After a brief review of factors relevant to the propagation of radio waves in ice, problems of profiling the upper and bedrock surfaces of ice sheets are considered. These include deconvolution of echo traces and accurate navigation. Results already available not only provide knowledge of sub-ice geomorphology, but also confirm our general ideas on interaction of temperature and flow in large ice sheets. Difficulties encountered in the study of temperate glaciers appear to be due to irregular dielectric properties of the ice mass, which in turn suggest an irregular distribution of water. In the future, application of radio-echo methods should lead to more detailed knowledge of accumulation and ablation over ice masses, improve our understanding of temperatures at great depths in polar ice sheets, and give data on ice movement from central areas of ice sheets.
Investigation of Sub-Ice Bedrock Characteristics by Radio-Echo Sounding
Authors: Oswald G. K. A.
Published: September 2017

Qualitative inspection of the results of the 1971/72 S.P.R.I.-N.S.F. Antarctic radio-echo sounding programme shows that it is possible to infer some characteristics of the lower face of the ice from the form of received echoes. We confirm the existence of lakes of liquid water beneath the east Antarctic ice by inspection of the top and bottom surface gradients of the ice, and suggest that basal melting occurs over a wide area in this region.

Quantitative studies in Devon Island indicate that small-scale irregularities in the bedrock are characterized by slopes of about 1: 40, with some higher gradients present, possibly indicating the presence of morainal boulders. We deduce that a geological boundary was crossed between 25 and 40 km west of the base camp, the rock to the west of the boundary having lower permittivity, and higher surface slopes than that to the east.

The question of the usefulness of the spatial fading of the echo in deducing surface characteristics is briefly discussed. We conclude that measurements of the fading are indeed useful, especially in the case of echoes with short “tails”.
Advances in geophysical exploration of ice sheets and glaciers
Authors: Bentley Charles R.
Published: September 2017

The techniques of geophysical exploration can be used in a number of ways to investigate the internal characteristics of ice bodies. The application of radio-echo sounding is discussed elsewhere by Robin (1975[a]) so is not considered here except for a few special cases. Anisotropy resulting from non-random ordering of crystal axes produces effects on seismic wave propagation speeds measurable by both refraction and reflection techniques. The effects on shear waves are particularly strong, so the recent development of an effective shear-wave generator should prove very useful. Marked effects on radio-wave polarizations have also been noted, but are not readily interpretable because the anisotropic dielectric characteristics of single-crystal ice in the radio-echo frequency range are not yet known. Elastic internal friction can be determined by careful measurements of seismic-wave amplitudes. Dielectric properties of the ice can be found from VLF propagation experiments and electrical logging in drill holes as well as from the radio-echo sounding techniques discussed by Robin (1975[a]). An activation energy can be estimated from d.c. resistivity measurements where the temperature profile is known. Recent developments have led to much improved methods of determining density-depth variations and long-term mean annual snow accumulation rates from seismic refraction shooting. Internal discontinuities which can be studied include a probable morainal layer detected by seismic reflections, a brine-soaked zone in shelf ice observed from radio-echo. sounding and electrical resistivity surveying, and inverted crevasses penetrating upward from the base of shelf ice, detected by radio echoes. Secular changes in gravity offer a sensitive means of determining long-term changes in surface elevation.
Ultrasonic Properties of Plastically Deformed Ice
Authors: Tatibouet J. , Vassoille R. , Perez J.
Published: September 2017

Many authors have used propagation of ultrasonic waves in ice for glaciological studies. This propagation is characterized by the velocity of sound and by the attenuation of stress waves. In crystalline materials, these two characteristics depend on structural slate. In particular plastic deformation gives velocity and attenuation variations.

We have measured the sound velocity and attenuation of ultrasonic waves in strained specimens of ice (single crystals and polycrystals). These measurements done between 100 and 273 K at a frequency of 5 MHz show that plastic deformation leads to an increase of attenuation arid an increase of velocity. Annealing treatments at 271 K cause recovery of propagation characteristics. The variation in attenuation can be interpreted by the theory of dislocations and this interpretation is supported by our data on the influence of frequency on this increase of attenuation induced by plastic deformation, but the theory of dislocations implies a decrease of modulus, i.e. of velocity, hence we must postulate that an added phenomenon screens the effect of dislocations. That phenomenon could be connected with ageing effects observed on different physical properties of ire and may be due to modification of protonic arrangement or creation of interstitials during plastic deformation. Thus our experiments show that it is necessary to be careful in using results determined from the propagation of ultrasonic waves in ice.
Application of Radar Techniques to Ice and Snow Studies
Authors: Page D. F. , Ramseier R. O.
Published: September 2017

This paper presents an overview of the active microwave tools becoming available to the glaciologist with emphasis on recent radar developments as applied to floating ice. Sufficient theory is presented for the user to understand the techniques. Side-looking radar imagery is discussed using a number of examples resulting from the use of real and synthetic aperture, single and dual polarization. Recent studies of the microwave properties of ice and snow are reviewed, and are shown to be leading to significant advances in high-resolution radar techniques for accurate sounding of these materials. Remote sensing of fresh-water ice thickness is shown to be well established and operational, with similar techniques feasible in the near future for sea ice. It is pointed out that both imaging and probing radars applied to studies of sea ice and snow usually must be used in association with data from other sensors.
Interpretation of Slar Imagery of Sea Ice in Nares Strait and the Arctic Ocean
Authors: Dunbar Moira
Published: September 2017

SLAR imagery of Nares Strait was obtained on three flights carried out in. January, March, and August of 1973 by Canadian Forces Maritime Proving and Evaluation Unit in an Argus aircraft equipped with a Motorola APS-94D SLAR; the March flight also covered two lines in the Arctic Ocean, from Alert 10 the North Pole and from the Pole down the long. 4ºE. meridian to the ice edge at about lat. 80º N. No observations on the ground were possible, but -some back-up was available on all flights from visual observations recorded in the air, and on the March flight from infrared line-scan and vertical photography.

The interpretation of ice features from the SLAR imagery is discussed, and the conclusion reached that in spite of certain ambiguities the technique has great potential which will increase with improving resolution, Extent of coverage per distance flown and independence of light and cloud conditions make it unique among airborne sensors.
Sea-ice Reconnaissance by Radar
Authors: Tabata Tadashi
Published: September 2017

To observe the distribution of pack ice off the coast of the Okhotsk Sea coast of Hokkaido, a radar network consisting of three radar stations was constructed during 1967-69. It covers an area about 70 km wide and 250 km long. The stations are remote-controlled by radio from the Sea Ice Research Laboratory and the information obtained is transmitted back to the laboratory and observed there. Radar has the great advantage of being able to make continuous observations of ice. Usually several special features can be seen on the radar screen, and they are used as markers for the observation of movement. It is ascertained that the average pattern of drift in this area is from north to south-east along the coast line and the ice field undergoes internal deformation during its drift. To get some information on the surface topography of ice from A-scope radar, the intensity of echo signals is classified into 16 steps by computer. To obtain the movement of an ice field from the numerical radar information, a modified two-dimensional cross-correlation method was tested.
Seasonal Effects on Ground-Wave propagation in Cold Regions
Authors: Blomquist Ake
Published: September 2017

The ground-wave is the most important mode of propagation of radio waves in Connection with glaciology. In cold regions, special conditions are often prevalent, involving propagation over non-homogeneous earth, presence of stratified media, and low values of conductivity and dielectric constant in the upper strata.

A radio wave which propagates along the Earth's surface is, however, also influenced by atmospheric refraction. As the frequency is increased, the roughness of the Earth's surface must also be taken into account. Thus seasonal variations are to be expected due to changes in the electrical and topographical properties of the ground as well as the propagation conditions in the atmosphere. It is, however, difficult to separate these various effects, a fact which reduces the possibility of using ground-wave propagation as a loot for obtaining information on the properties of the ground.

Though the propagation of the ground-wave has been dealt with both theoretically and experimentally for almost a century, some of the most valuable information of major importance in cold regions has been obtained during the last ten years. New theoretical papers on propagation over stratified media offer an explanation of the amplitude and phase variations of the ground-wave field, which have been measured, as well as suggesting new methods to be tested as possible aids in solving glaciological problems.

In many practical eases of ground-wave propagation in arctic regions, the formula for the ground-wave field strength can be written in a very simple way. Such a propagation model for frequencies above 30 MHz is presented in which account is taken of the Earth's curvature, the terrain irregularities, and the effect of the tropospheric refraction. This model also includes the recovery effect which occurs in propagation over mixed paths. At the higher frequencies the effect of depolarization becomes very important and sometimes overshadows field-strength variations due to the influence of the electrical properties. Finally some problems will be discussed which remain to be solved or have been given very little attention up to now.
A Submarine Sonar Study of Arctic Pack Ice
Authors: Elizabeth Williams , Charles Swithinbank , Robin G.DE Q.
Published: September 2017

A continuous profile of the Arctic Ocean ice canopy from Spitsbergen to the North Pole was made with 48 kHz echo sounders mourned on a nuclear submarine. A semi-automatic digitizer was used to measure coordinates from the records at a frequency of about 1 000 points per linear kilometre of track. Methods derived for the reconstruction of subglacial relief from 35 MHz radio-echo sounding records were applied to eliminate part of the distortion due to the 20° beam width of the sounders. A corrected profile was used to obtain ice drafts at 2 m intervals. Data were analysed in 10 km sections and figures were summarized for each degree of latitude. The results include: mean ice draft, percentage of ice less than 0.3 m draft, and percentage of level ice. Histograms show the level ice drafts which occur most frequently, and these may indicate the ratio of first-year to older ice. The number of ice keels is listed together with their mean draft and draft distribution. Definitions are found to be of overriding importance in the comparison of data from different areas.
Optical Properties of Salt Ice
Authors: Lane J. W.
Published: September 2017

The dependence of the extinction coefficient on salinity was investigated for both NaCl-ice and salt-ice made from natural sea-water. Specimens were prepared under a variety of conditions and examined over the wavelength range 4 000 to 8 000 Â. The effects of scattering from air bubbles trapped in the ice were examined for ice made from distilled water. It was found that the method of preparing samples markedly affected their structure, but that, when prepared in the same manner, salt-ice made from natural sea-water and NaCl-ice did not show significantly different transmission properties. It was found that, for a wavelength of 6 328 Â, the data could be fit to the relation

within an uncertainty of 26%, where ke is the extinction coefficient, x is the salinity of the ice in g/kg. Within an uncertainty of 10%, there was no variation in transmission for ice at the same temperature and salinity over the wavelength range 4 000 to 8 000 Â. All measurements were made at a temperature of -20° C.
The Use of Erts Photographs to Measure the Movement and Deformation of Sea Ice
Authors: Nye J. F.
Published: September 2017

Is it justified to adopt a two-dimensional continuum model for the movement and large-scale deformation of pack ice? A preliminary study oi’ ERTS-1 photography shows that the details of the ice movement are readily measurable; the problem is not in the accuracy of the remote sensing but in the inherent graininess of the sea ice. There is a spatial variation of ice velocity on a scale of several hundreds of kilometres; smaller-scale variations are superimposed on this, but their amplitude is not enough to obscure the large-scale trend. A continuum model is applicable, but, because of the small-scale variations in the velocity of the sea ice itself, it is not meaningful to specify continuum strain-rates on a scale of, say, 100 km to more than a certain accuracy, If ERTS pictures are available during the AIDJEX main experiment they could provide the necessary strain and displacement measurements for comparison with the predictions of the AIDJEX model.
Radio Depth Sounding on Barnes Ice Cap
Authors: O’Neil R. A. , Jones S. J.
Published: September 2017

In May 1974 two radio depth sounders were used on the Barnes Ice Cap, Baffin Island. One was a S.P.R.I. 35 MHz sounder and the other was a unit operating at 620 MHz. Bottom reflections were observed with both systems at similar depths, indicating no significant velocity change between the two frequencies. Used with a Motorola range positioning system, the 620 MHz unit proved an excellent depth-survey vehicle. Results along the so-called surge profile (Holdsworth, 1973) are presented. Depth and attenuation values are compared with previous data.
Radio-Echo Sounding on South Cascade Glacier, Washington, using A Long-Wavelength, Mono-Pulse Source
Authors: Watts Raymond D. , England Anthony W. , Vickers Roger S. , Meier Mark F.
Published: September 2017

A short-pulse, long-wavelength radio-echo sounder has successfully measured the ice depth on the South Cascade Glacier. Depths up to 250 m were determined with resolution of about 5%. Bottom returns were clear and almost never ambiguous. Their accuracy was confirmed by comparison with hot-point drilling results. The secret for successful sounding in temperate glaciers is the use of a sufficiently low center frequency. Five megahertz was most successful. Tests at 15 MHz indicated an increase in coherent clutter which rendered the bottom return observable only with prior knowledge of its location. The cause of the clutter is probably water-filled voids in the ice which behave as Rayleigh scatterers.

The sounding system consists of an avalanche-transistor transmitter, which delivers a pulse to an acute-angle crossed-wire antenna. The pulse is shaped and given its center-frequency characteristics by the resonant properties of the antenna. The transmitting and receiving antennas are identical, consisting of wires and lumped resistors. The resistors reduce antennas ringing, thereby maintaining as short a pulse as possible. The receiver consists of an oscilloscope and a Polaroid camera. No preamplification is required for depths up to 250 m, but may be necessary for deeper glaciers.
The Study of Fresh-Water Lake Ice using Multiplexed Imaging Radar
Authors: Leonard Bryan M. , Larson R. W.
Published: September 2017

The study of ice in the upper Great Lakes, both from the operational and the scientific points of view, is receiving continued attention. Both quantitative and qualitative field work is being conducted to provide the needed background for accurate interpretation of remotely sensed data. The sensor data under discussion in this paper were obtained by a side-looking multiplexed airborne radar (SLAR). These were supplemented with ground-truth data.

Radar, due to its ability to penetrate adverse weather, is an especially important instrument for monitoring ice in the upper Great Lakes. It has been previously shown that imaging radars can provide maps of ice cover in these areas. However, questions concerning both the nature of the surfaces reflecting radar energy and the interpretation of the radar imagery continually arise.

Our analysis office in Whitefish Bay (Lake Superior) indicated that the combination of the ice/water interface with the ice/air interface is the major contributor to the radar backscatter as seen on the imagery. The ice has a very low dielectric constant (<3.0) and a low loss tangent. Thus, this ice is somewhat transparent to the energy used by the imaging SLAR system. The ice types studied include newly formed black ice, pancake ice, and frozen and consolidated pack and brash ice.

Although ice thickness cannot be measured directly from the received signals, it is suspected that by combining the radar backscatter information with both meteorological and sea-state history of the area and with some basic ground truth, better estimates of the ice thickness may be provided. In addition, certain ice features (e.g. ridges, ice foots, areas of brash ice) may be identified with reasonable confidence. There is a continued need for additional ground work to verify the validity of imaging radars for these types of interpretations.

This paper is being published in full in another issue of the Journal of Glaciology.
An Experiment in Ice Profiling in Nares Strait and the Arctic Ocean
Authors: Lowry R. T.
Published: September 2017

This paper discusses the work being done at the Defence Research Establishment Ottawa (DREO) on profiling of Arctic sea ice using airborne laser profilometers. Data from a flight in March 1973 have been partially analyzed and some results are presented. These include representative ridge counts and power spectra for chosen areas in Nares Strait and the Arctic Ocean. Some work has been done to try to improve the operation of the laser profilometer using real-time data processing. The basic ideas behind this scheme are outlined.
Sea Ice from Below: Sonar Techniques
Authors: Clay C. S. , Kan T. K. , Berkson J. M.
Published: September 2017

Under-ice sonar surveys were carried out in pack-ice fields near Fletcher’s Ice Island and at two sites north of Pt. Barrow, Alaska, U.S.A. A narrow-beam scanning sonar was used to measure the location and relative back-scattering of features on the under surface of Arctic sea ice. The 48 kHz sonar had a 1.5° by 51 ° beam width. Graphic records displaying the range and relative scattering levels were assembled into sonar maps which display location and shape of under-ice features. Two distinct types of back-scattering were found: (1) very high-level back-scattering from well defined under-ice ridges and (2) very low back-scattering from areas between ridges. Higher scattering at ridges was probably due to an increase of roughness and tilting of the average plane of the scattering surface. To measure depths of features, the sonar transducer was adjusted to give a wide horizontal beam and a narrow vertical beam. Polar scans were taken at several depths of the transducer to determine depths of ridges. The tops and bottoms of features were compared and the average ratio of peak elevation to keel depth was about 1:7.

Fuller accounts of some of this work have been published elsewhere (Berkson and others, 1973; Clay and Leong, 1974; Kan and others, 1974}.
The Remote Sensing of Avalanche Victims: Problems and Progress
Authors: Fritzsche Wilfried
Published: September 2017

This paper reviews possible uses of remote-sensing techniques to locate avalanche victims. Until recently probes and dogs were the only methods available, but recently attempts have been made to devise other methods for finding human beings in snow. Ideally such a search should be made possible for other members of the party, as the chance of survival of a victim falls rapidly with increasing time to rescue. For this all members of the party need to have something which the others can locate. The most usual proposal is an electromagnetic transmitter/receiver set. The merits of various possible frequencies are discussed. International agreement on a frequency is urgently required. Magnetic devices might be considered, but the detecting devices are too expensive or heavy to be generally carried. Search parties can of course be equipped with more sophisticated apparatus, and various possibilities are discussed for identifying metal on the victim, for identifying him by radio sounding, for locating him by mapping microwave emission, or for searching for eddy currents induced in him.
Progress in Radio-Echo Sounding Theory
Authors: Rudakov V. N. , Luchininov V. S.
Published: September 2017

The inverse problem of radio-echo sounding consists in the reconstruction of subglacial relief from the known radio-echo profile, and the path, and speed of the aircraft. The present work shows that in the geometrical optical approach the solution of the inverse problem for a homogeneous, two-dimensional object (valley glacier) exists, and there is a unique solution. An algorithm for interpretation of the experimental data is suggested. It may be considered as the generalization of Harrison’s transformations for any surfaces. paths, and speed.

The direct problem of radio-echo sounding consists in the reconstruction of radio-echo profile from the known surface and subsurface relief, path, and aircraft speed. The analysis of traces in the standard radio-echo sounding mode of operation reveals the possibility of introducing a three-index trace classification {K, sign S’(o), K+} where K is the number of real roots characteristic of the equations, K+ the number of positive roots, and S’(o) the position derivative, the argument being equal to zero. The form {o, — o} is optimal for the precision of the calculation of the reflected surface coordinates, as well as for the simplicity of the interpreted picture. By a special choice of the altitude of flight, any form of any surface can be brought to {o, —o}. The decrease in beam width is equivalent to the diminution of roots of the characteristic equations. For a pencil beam the trace degenerates into a point.

The attenuation of the reflected signal depends on the glacier geometry, the dielectric parameters of the medium, the altitude and the course of the aircraft, as well as statistical characteristics of the mutual orientation of the interfaces and aerials. For the description of the energetics of radio-echo sounding, equivalent reflecting surfaces are suggested. These surfaces correspond to the Harrison’s equivalent reflecting surface. Exact formulae for the power of coherent and incoherent components of the reflected signal are obtained. Components of the full attenuation such as absorption, depolarization, and spherical divergence, are investigated with respect to refraction and focusing effects.
Electromagnetic Characteristics of Sea Ice in the Metre and Decimetre Ranges, and its Radio-Echo Sounding
Authors: Bogorodskiy V. V. , Tripolnikov V. P.
Published: September 2017

The paper gives measurements of the velocity of electromagnetic wave propagation in sea ice, the tangent loss, and the specific absorption obtained by means of coaxial-line experiments, assuming sea ice to be the dielectric. Measurements have been made at frequencies of 30, 60, 100, 200 and 400 MHz by pulses of 0.05 and 0.5 ms and video pulses of 0.02 ms at a repetition frequency of 10 kHz, with temperatures from —40° C to —10° C and salinities 17, 8.6, 4.4 and 0.56‰. Data obtained on the values of the tangent loss are in a good agreement with those obtained by Addison. The velocity has been found to be constant (170 m/ms) for radio and video pulses in the ice at any salinity value and temperatures below —22° C. At higher temperatures the velocity decreases being more pronounced with the salinity increase. Data on electrical characteristics of sea ice averaged throughout the ice thickness are presented. These measurements have been made by using long lines, frozen into the ice. Experimental radio-echo soundings of sea ice carried out at the drifting stations SP-19 and SP-21 in 1971-72 and 1972-73 by means of pulsed radar systems in the range 200-100 MHz are also discussed.
An Automatic Snow Depth Meter By An Infrared Technique
Authors: Kimura Tadashi
Published: September 2017

An automatic snow-depth meter was constructed using an infrared beam from a gallium-arsenide photo-emission diode and an infrared detector consisting of a silicon photocell. As the field of view of both photoelectric elements is 30°, high mechanical accuracy is not required. The equipment consists of two poles of the same size, 4.8 m high and 20 cm by 20 cm wide, an operation controller, and a digital recorder. The two poles were set up on the ground facing each other at a distance of 5 m. One pole has the photo-emission diode and the other the infrared detector. In each pole, a long slit 4 cm wide and 4 m long was installed. Through one slit the infrared beam comes out and is received through the other slit. To avoid catching snow or rain in the slits, air was ejected through them.
On the age vs depth and optical clarity of deep ice at the South Pole
Authors:   The Amanda Collaboration
Published: September 2017

The first four strings of phototubes for the AMANDA high-energy neutrino observatory are now frozen in place at a depth of 800-1000 m in ice at the South Pole, During the 1995-96 season, as many as six more strings will be deployed at greater depths. Provided absorption, scattering and refraction of visible light are sufficiently small, the trajectory of a muon into which a neutrino converts can be determined by using the array of phototubes to measure the arrival times of Cherenkov light emitted by the muon. To help in deciding on the depth for implantation of the six new strings, we discuss models of age vs depth for South Pole ice, we estimate mean free paths for scattering from bubbles and dust as a function of depth and we assess distortion of light paths due to refraction at crystal boundaries and interfaces between air-hydrate inclusions and normal ice. We conclude that the interval 1600-2100 m will be suitably transparent for a future 1 km3 observatory except possibly in a region a few tens of meters thick at a depth corresponding to a peak in the dust concentration at 60 k year BP.