The potential of synthetic aperture radar interferometry for assessing meltwater lake dynamics on Antarctic ice shelves

Surface meltwater drains on several Antarctic ice shelves, resulting in surface and sub-surface lakes that are potentially critical for the ice shelf collapse. Despite these phenomena, our understanding and assessment of the drainage and refreezing of these lakes is limited, mainly due to lack of field observations and to the limitations of optical satellite imagery during polar night and in cloudy conditions. This paper explores the potential of backscatter intensity and of interferometric coherence and phase from synthetic aperture radar (SAR) imagery as an alternative to assess the dynamics of meltwater lakes. In four case study regions over Amery and Roi Baudouin ice shelves, East Antarctica, we examine spatial and temporal variations in SAR backscatter intensity and interferometric (InSAR) coherence and phase over several lakes derived from Sentinel-1A/B C-band SAR imagery. Throughout the year, the lakes are observed in a completely frozen state, in a partially frozen state with a floating ice lid and as open-water lakes. Our analysis reveals that the meltwater lake delineation is challenging during the melting period when the contrast between melting snow and lakes is indistinguishable. Despite this finding, we show using a combination of backscatter and InSAR observations that lake dynamics can be effectively captured during other non-summertime months. Moreover, our findings highlight the utility of InSAR-based observations for discriminating between refrozen ice and sub-surface meltwater and indicate the potential for phase-based detection and monitoring of rapid meltwater drainage events. The potential of this technique to monitor these meltwater change events is, however, strongly determined by the satellite revisit interval and potential changes in scattering properties due to snowfall or melt events.

Heat capacity of dispersed rocks

Protection of automobile roads from negative cryogenic processes is a current issue to which significant attention is devoted in both scientific and engineering communities. In many cases important for practice, the the thermal factor determines the reliability and security of the use of the road in the cryolithic zone. The heat capacity of dispersed rocks is among the most important indicators of the physical properties determining the intensity of thermal processes in the road surfaces and road foundations. The precision of determination of the total heat capacity of the rocks in thawed and frozen state largely determines the precision of the forecast of the thermal regime of roads in the cryolithic zone. A complex assessment of the impact of ice content of the dispersed rocks on the value of total heat capacity was done. 2D and 3D charts which allow to assess the possible range of change in the heat capacity of the dispersed rocks in thawed and frozen state, in both a wide range and in the typical range of values, were produced. Among the main criteria determining the extent of the seasonal freezing and thawing of the soils of the active layer is the Stefan number, a dimensionless criterion. An overall assessment of the impact of ice content on the ground (rock) foundations of the roads and of the air temperature in the warm period of the year on the quantitative values of the Stefan number was done. Charts allowing to determine in both a wide and typical range the changes of values of the Stefan numbers, permitting to assess the possible range of changes of the Stefan number, were made. It was determined, in particular, that for the typical dispersed rocks of the road foundations in the cryolithic zone the range of change in the Stefan numbers is 2.1-6.5.

The potential of InSAR for assessing meltwater lake dynamics on Antarctic ice shelves

Surface meltwater drains on several Antarctic ice shelves, resulting in surface and sub-surface lakes that are potentially critical for the ice shelf collapse. Yet, our understanding and assessment of the drainage or refreezing of these lakes is limited, mainly due to lack of field observations and to the limitations of optical satellite imagery. Therefore, this paper explores the potential of backscatter intensity and of interferometric coherence and phase from C-band synthetic aperture radar (SAR) imagery as an alternative to assess the dynamics of meltwater lakes. In two case studies over Amery and Roi Baudouin ice shelves, we analyse i) the spatial and ii) the temporal variations of SAR backscatter intensity with iii) coherence and iv) interferogram phase (InSAR) patterns detected by Sentinel-1 data over multiple meltwater lakes. Throughout the year the lakes are observed in completely frozen state, in partially frozen state with a floating ice lid, and as open water lakes. The analysis reveals that the meltwater lake delineation is challenging during the melting period when the contrast between melting snow and lakes is confounded. On the other hand, it shows that the lake dynamics can be effectively captured during the refreezing process and the winter season by combining backscatter and InSAR information. In particular, the InSAR coherence and interferogram phase information are deemed essential throughout this whole period to distinguish between refrozen ice and subsurface meltwater. Additionally, the results provide significant evidence on the potential of the interferogram fringe patterns to detect and characterise instant events, such as lake drainage events over ice shelves. The potential of this technique to monitor these meltwater change events is however strongly determined by the satellite revisit interval and potential changes in scattering properties due to snowfall or melt events.

INVESTIGATION OF THE THERMAL CONDUCTIVITY OF AUTOCLAVED AER ATED CONCRETE

The results of measuring the thermal conductivity coefficients of autoclaved aerated concrete grades D450 and D600 in the dry, water-saturated and frozen state are presented.

Modern methods of cooling permafrost ground beds of multi-storey residential buildings

Introduction. The bearing capacity of soil in the frozen state is much higher than its bearing capacity at positive temperatures. Therefore, it makes sense to use frozen soil as the footing of a building in permafrost regions. However, the preservation of soil in the frozen state in a built-up area is a challenging engineering problem despite low average annual air temperatures (below –4 °C). Materials and methods. The co-authors employed numerical methods to study the temperature regime of the footing using TEMRA software. This software was developed at MISI – MGSU (State Registration Certificate 2016618937); it solves non-stationary thermophysical problems by the enthalpy method with regard for the phase transitions of the bound moisture in the temperature range. Results. Two approaches are used to preserve building footings in the frozen state: natural seasonal surface cooling and deep cooling, on the one hand, and reducing the thermal effect produced by the building on footing soils, on the other hand. In the first case, the surface under the building is cooled with air in the winter season using the cold ventilated space under the building, the so-called “ventilated basement”. Deep cooling is carried out using Seasonal Cooling Devices (SCD) that employs air-soil heat exchange with the help of pipes, filled with the heat transfer agent during the winter period. A change in the average annual air temperature inside the ventilated basement and seasonal insulation of its walls or the ground bed can reduce the thermal effect, produced by the building. Conclusions. The most effective way to keep ground beds of multi-storey residential buildings frozen is the thermal insulation of the footing surface in combination with deep liquid cooling devices.

A systematic assessment of the diamond trap method for measuring fluid compositions in high-pressure experiments

A variety of experimental techniques have been proposed to measure the composition of aqueous fluids in high-pressure experiments. In particular, the “diamond trap method,” where the fluid is sampled in the pore space of diamond powder and analyzed by laser-ablation ICP-MS after the experiment, has become a popular tool. Here, we carried out several tests to assess the reliability of this method. (1) We prepared several capsules loaded with fluid of known composition and analyzed the fluid by laser-ablation ICP-MS, either (a) after drying the diamond trap at ambient condition; (b) after freezing and subsequent freeze-drying; and (c) after freezing and by analyzing a frozen state. Of these methods, the analysis in the frozen state (c) was most accurate, while the results from the other two methods were poorly reproducible, and the averages sometimes deviated from the expected composition by more than a factor of 2. (2) We tested the reliability of the diamond trap method by using it to measure mineral solubilities in some well-studied systems at high pressure and high temperature in piston-cylinder runs. In the systems quartz-H2O, forsterite-enstatite-H2O, and albite-H2O, the results from analyzing the diamond trap in a frozen state by laser-ablation ICP-MS generally agreed well with the expected compositions according to literature data. However, in the systems corundum-H2O and rutile-H2O, the data from the analysis of the diamond trap were poorly reproducible and appeared to indicate much higher solubilities than expected. We attribute this not to some unreliability of the analytical method, but instead to the fact that in these systems, minor temperature gradients along the capsule may induce the dissolution and re-precipitation of material during the run, which causes a contamination of the diamond trap by solid phases. (3) We carried out several tests on the reliability of the diamond trap to measure fluid compositions and trace element partition coefficients in the eclogite-fluid system at 4 GPa and 800 °C using piston-cylinder experiments. The good agreement between “forward” and “reversed” experiments—with trace elements initially either doped in the solid starting material or the fluid—as well as the independence of partition coefficients on bulk concentrations suggests that the data obtained are reliable in most cases. We also show that the rate of quenching/cooling has little effect on the analytical results, that temperature oscillations during the run can be used to enhance grain growth, and that well-equilibrated samples can be obtained in conventional piston-cylinder runs. Overall, our results suggest that the diamond trap method combined with laser-ablation ICP-MS in frozen state yields reliable results accurate within a factor of two in most cases; however, the precipitation of accessory minerals in the diamond trap during the run may severely affect the data in some systems and may lead to a gross overestimation of fluid concentrations.

EFFECT OF FREEZING ON THE MILK QUALITY OF COWS

Due to the fact that milk has a short shelf life, the issue of its freezing and long-term storage in the frozen state is relevant. A study was conducted on the effect of freezing on the milk quality after its defrosting of cows-mothers and cows-daughters of Red-Motley breed. As a result, it was established how milk quality indicators to change after five months of storage in a frozen state in cows of two age groups. A high correlation was established between quality indicators before and after freezing. The influence of the “freezing” factor on milk quality indicators was recognized statistically significant, the “generation” factor – not significant.

Evaluation of storage methods of beef by microbiological and chemical indicators

Meat and meat products are a major part of a person's ration. However, due to their high nutritional value, they are a favorable environment for the development of microorganisms and require refrigerated storage. The purpose of this work was to evaluate the storage methods for refrigerated and frozen beef by microbiological and chemical parameters and to suggest criteria for evaluating beef by the content of psychrotrophic microorganisms. It was found out that the storage of beef meat with an initial mesophilic bacterial content of about 4.88 log CFU.cm-2 of surface and psychrotrophic bacteria 3.79 log CFU.cm-2 at temperature 0 °C is only possible for 8 days, further, the microbiological indices exceed the acceptable standards. Investigation of the dynamics of microflora reproduction during the storage of beef in the frozen state at temperature -2 to -3 °C for 20 days established a decrease in 1.3 times the number of mesophilic bacteria in 10 days of storage. At the same time, the number of psychrotrophic microorganisms during this storage time was increased in 4.5 times, and 20 days in 7.9 times and amounted to 5.3 log CFU.cm-2 of surface area. This indicates that the storage of meat in the frozen state inhibits or completely stops the development of mesophilic microorganisms for 20 days. It was found out that storing of beef in the cooled state at a temperature of 0 ±0.5 °C for more than eight days is impractical, as its biochemical indices are worsening and signs of spoilage are appearing. At the same time, storing of beef in the frozen state at a temperature of -2 to -3 °C for 20 days does not cause such significant biochemical changes as in beef stored in the cooled state at a temperature of 0 ±0.5 °C for 16 days. Therefore, we have experimentally substantiated the quantitative indicators of the content of psychrotrophic microorganisms on the surface of beef intended for storage in a cooled or frozen state. The proposed microbiological criteria will improve the safety of beef.