Ice Surface Research Articles

Microwave Observations of Ganymede's Sub‐Surface Ice: I. Ice Temperature and Structure

AbstractOn 7 June 2021, Juno flew within 1,000 km of Ganymede's surface, partially mapping its ice shell at six frequencies ranging from 0.6 to 22 GHz. The radiance at these frequencies originates from successively deeper layers of the sub‐surface and may reach depths of 24 km at 0.6 GHz. The MWR observations cover a latitude range from 20°S to 60°N and a longitude range from 120°W to 60°E. We present brightness temperature and derived reflectivity maps of Ganymede with a spatial resolution of up to ∼140 km. The microwave brightness temperature at all MWR wavelengths is anti‐correlated with the visible brightness of the terrain. Normalizing the MWR brightness temperatures using a thermal model for the ice shell reveals that the brightest regions are significantly more reflective in the microwave than the dark regions and that all terrain types are more reflective than is expected from a solid ice surface. We suggest that multiple reflections of the colder sky background at sub‐surface interfaces (e.g., fractures) explain the depressed brightness temperatures observed in brighter terrain types. A thin silicate or salt contaminant surface layer, which is significantly more reflective than ice in the microwave, could explain the microwave reflectivity in the dark regions with little to no contribution from sub‐surface fractures. The observed 0.6–1.2 GHz brightness temperature difference suggests an upper bound on the ice shell conducting layer depth of 150 km in the observation area.

Atmospheric controls on the Terra Nova Bay polynya occurrence in Antarctica

Polynyas, or ice-free regions within the sea ice pack, are a common occurrence around Antarctica. A recurrent and often large polynya is the Terra Nova Bay Polynya (TNBP), located on the western side of the Ross Sea just off Victoria Land. In this study, we investigate the atmospheric conditions leading to the occurrence of the TNBP and its spatial variability, as estimated using satellite-derived ice surface temperature and sea ice concentration data. A cluster analysis revealed that katabatic winds descending the Transantarctic Mountains, account for about 45% of the days when the TNBP exceeded its 2010–2017 mean extent plus one standard deviation. Warmer and more moist air intrusions from lower-latitudes from the Pacific Ocean, which are favoured in the negative phase of the Southern Annular Mode, play a role in its expansion in the remaining days. This is more frequent in the transition seasons, when such events are more likely to reach Antarctica and contribute to the occurrence and the widening of the polynya. In-situ weather data confirmed the effects of the mid-latitude air intrusions, while sea ice drifts of up to 25 km day−1 cleared the ice offshore and promoted the widening of the polynya starting from the coastal areas. Knowing the atmospheric factors involved in the occurrence of coastal polynyas around Antarctica is essential as it helps in improving their representation and predictability in climate models and hence advance the models’ capabilities in projecting Antarctic sea ice variability.

Ice recrystallization inhibition effect of cellulose nanocrystals at constant and cycling temperatures

Understanding the effects of ice recrystallization inhibitors at varying temperatures is critical for evaluating their applications. We studied the ice recrystallization inhibition (IRI) effects of cellulose nanocrystals (CNCs) at constant and cycling temperatures. A splat assay using a 3.0 % sucrose solution showed that the IRI effect of 0.2 % CNCs decreased with increasing temperatures from −10 °C to −2 °C; the IRI effects of 0.5 % and 1.0 % CNCs remained unchanged for an increase in temperature from −10 °C to −4 °C but decreased at the temperature of −2 °C. A sandwich assay using a 25.0 % sucrose solution revealed that IRI effects increased with increasing temperatures, except in the presence of 0.2 % and 0.5 % CNCs at −5 °C and − 4 °C. A sandwich assay using a 35.0 % sucrose solution revealed that better IRI effects were observed at higher temperatures at all CNCs concentrations. At cycling temperatures, CNCs were inactive for storage times for ≤2 h, regardless of the rate, holding time, and amplitude of temperature fluctuation, but were active for storage times of 2 and 10 days. The IRI effects of CNCs at different temperatures may be related to the coverage of CNCs on ice surface, diffusion rate of CNCs to ice surface, and types of ice recrystallization.

Автоматизация работы спредера при обработке крупнотоннажных контейнеров в условиях крена и дифферента судна

Current development of IT technologies makes it possible to automate production processes in the transport industry. Introducing the automated systems helps reduce the downtime of vehicles under loading and unloading operations. Handling various loads or specializing in a certain cargo flow, the terminal operator selects lifting and transport equipment and the degree of its automation. Automation of lifting and transport equipment has been most developed at container terminals, because the container as a cargo unit has certain dimensions, the metal surface of the container reflects the signals of the distance sensors mounted on the cargo handling device (spreader). During the experiments, it was found out that the signal of ultrasonic sensors is reflected from the surface of ice, which can form on the container in winter, laser sensors show the distance to the surface of the container. Installation of laser sensors helps to reduce the working cycle time of lifting and transport equipment, reduce the likelihood of damage to the container. Loading and unloading operations on ships have their own specifics. In case of roll and /or trim, it is difficult to point the spreader at the container, which leads to an increase in the working cycle, therefore, the idle time of the vessel under processing. To solve the problem of reducing the working cycle time of lifting and transport equipment when unloading a vessel with a roll or trim of the vessel, a laboratory sample of the mechanism for stabilizing the spreader relative to the surface of the container has been developed. The stabilization mechanism operates according to the following algorithm: the signal from the laser sensors goes to the microcontroller, which compares the signals and then transmits the signal to the actuator, which stabilizes the spreader parallel to the surface of the container. The proposed device will increase the productivity of lifting and transport equipment when handling ships with roll and trim.

Cohesive collisions of particles in liquid media studied by CFD-DEM, video tracking, and Positron Emission Particle Tracking

This paper investigates the cohesive collision of ice in an oil phase at temperatures ranging from −15.7 °C to −0.3 °C. The new information on the coefficient of restitution (COR) was obtained using three different velocity measurement methods: high-speed experimental video recording, Positron Emission Particle Tracking (PEPT), and numerical simulations. A new type of PEPT tracer was developed for the experiments. The COR values were in the interval 0.57...0.82, with a maximum at around −10 °C. The CFD-DEM coupled approach was applied to reproduce experiments with an ice particle drop and its collision with an inclined ice surface in a decane. The particle–wall interaction is modeled using commercial software, considering particle cohesion, particle size, and shape. CFD-DEM predicted the COR with an average deviation ∼10% from the experimental data. The numerical model’s results agree with the experiments, demonstrating that the CFD-DEM method is suitable for describing multiphase cohesive interactions.

A Computational Investigation into the Hydrogenation of NO on Water Ice Surfaces to Rationalize the NO:HNO:NOH Disparity in Space

Molecules possessing NO bonds are important precursors in biology; however, in the interstellar medium (ISM), such bonds are observed in relatively low abundance. NO and HNO are two species detected concurrently within the ISM that contain this bond in its simplest form. However, NO is observed to be approximately 200 times more abundant than HNO, which is curious due to the ubiquity of hydrogenated species in the ISM. In the present work, we use computational techniques to determine whether (i) HNO can be formed from NO on cold dust grain surfaces and (ii) if formed, HNO is able to desorb from the surface. Dust grains, which at low (10 K) temperature are primarily coated in water ice, are modeled using both hexagonal and amorphous ice models. A strong thermodynamic driving force is calculated for NO hydrogenation to HNO on the water ice surfaces, suggesting facile formation of HNO. Interestingly, the formation of NOH is also a thermodynamic possibility. Investigation into the reaction kinetics showed no barrier to hydrogenation in either scenario on the hexagonal ice surface; however, on the more astronomically relevant amorphous ice, barriers of 0.53 eV (51 kJ mol–1) and 0.77 eV (74 kJ mol–1) are observed for the formation of HNO and NOH, respectively. Comparison of the adsorption energies showed NO to bind to the surface the weakest (< –0.2 eV/–19 kJ mol–1), followed by HNO (< –0.6 eV/–58 kJ mol–1), and then NOH (< –1.50 eV/–144 kJ mol–1). This suggests that, once formed, HNO is likely to remain adsorbed to the surface, thus accounting for the lower gas phase abundance observed compared to NO. NOH, if formed, will be even less likely to desorb in appreciable amounts and hence remains undetected. Combined, the results suggest that hydrogenated species are possible to be formed from NO on ice surfaces and are likely to remain bound to the surface, supporting the experimental observations.

Meltwater layer dynamics in a central Arctic lead: Effects of lead width, re-freezing, and mixing during late summer

Leads play an important role in the exchange of heat, gases, vapour, and particles between seawater and the atmosphere in ice-covered polar oceans. In summer, these processes can be modified significantly by the formation of a meltwater layer at the surface, yet we know little about the dynamics of meltwater layer formation and persistence. During the drift campaign of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC), we examined how variation in lead width, re-freezing, and mixing events affected the vertical structure of lead waters during late summer in the central Arctic. At the beginning of the 4-week survey period, a meltwater layer occupied the surface 0.8 m of the lead, and temperature and salinity showed strong vertical gradients. Stable oxygen isotopes indicate that the meltwater consisted mainly of sea ice meltwater rather than snow meltwater. During the first half of the survey period (before freezing), the meltwater layer thickness decreased rapidly as lead width increased and stretched the layer horizontally. During the latter half of the survey period (after freezing of the lead surface), stratification weakened and the meltwater layer became thinner before disappearing completely due to surface ice formation and mixing processes. Removal of meltwater during surface ice formation explained about 43% of the reduction in thickness of the meltwater layer. The remaining approximate 57% could be explained by mixing within the water column initiated by disturbance of the lower boundary of the meltwater layer through wind-induced ice floe drift. These results indicate that rapid, dynamic changes to lead water structure can have potentially significant effects on the exchange of physical and biogeochemical components throughout the atmosphere–lead–underlying seawater system.

The first cultivation of the glacier ice alga Ancylonema alaskanum (Zygnematophyceae, Streptophyta): differences in morphology and photophysiology of field vs laboratory strain cells

AbstractMelting glacier surfaces are unique ecosystems for specialized microbes, frequently harbouring blooms of microalgae with pigments contributing to the darkening of ice surfaces, reducing albedo and enhancing melt rates. The main cause of this phenomenon is algae of the genus Ancylonema. Prior investigation depended on field-collected material because these algae resisted cultivation. To enhance research on how these algae dominate melting ice, we established a strain of Ancylonema alaskanum from an alpine glacier and exposed to temperatures around the freezing point at irradiations of ~10% of full sunlight. The morphology of the culture changed, with the cells becoming longer and turning green by losing their brownish pigmentation, indicating that these dark phenols are crucial for survival in the cryosphere. Photophysiological comparisons of strain and glacial material showed adaptation of the photosynthetic apparatus to prevailing conditions. This laboratorial strain opens possibilities for a wide range of comparative ‘omics’ research.

Reconfigurable wheel-crawler-integrated walking mechanism design and kinetic analysis

PurposeThis study aims to the complex and unpredictable terrain environment of the Qinghai-Tibet Plateau scientific research station, such as cement road, wetland, gravel desert, snowfield, ice surface, grassland, slimy ground, steep slope, step, etc., a reconfigurable walking mechanism based on two movement modes of wheel and triangular crawler was proposed.Design/methodology/approachBy analyzing the deformation mechanism of the walking mechanism, a reconfigurable wheel-crawler-integrated walking mechanism and the configuration scheme are designed. The analysis of the kinematics and mechanical properties of the swing arm system and the deformation mechanism of the walking mechanism.FindingsThe reconfigurable wheel-crawler-integrated walking mechanism can be switched between the wheel and triangular crawler modes by driving the deformation mechanism. Through the numerical simulation of its movement process, and the trial production and experiment of the prototype, indicates the validity of the reconfigurable wheel-crawler-integrated walking mechanism design.Originality/valueThe work of this paper provides a reconfigurable wheel-crawler-integrated-walking mechanism, which can be used by robots in the Qinghai-Tibet Plateau scientific research station. It has excellent reconfigurability and can effectively improve the robot’s adaptability to complex terrain.

Martian cloud map retrievals for 2006–2008 from MRO CRISM multi-spectral data

As the state of Mars Climate modeling advances, there will be a growing need to provide observational results to act as comparisons or even as assimilation products to the next generation of models. This is especially true for atmospheric aerosols that are hard to model as they either have unspecified and/or ubiquitous sources (dust clouds) or form faster than the model time-steps can efficiently use (ice clouds). To that end, we present here our technique to recover ice and dust cloud optical depth maps from Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) multi-spectral mapping mode data. We use a multi-step, boot-strapping technique that does not make any a priori assumptions about the aerosols or surface reflectance at any point other than assuming the surface, at any time, can be constructed from a linear combination of a finite number of spectral endmembers. It uses singular value decomposition (SVD) and target transformation (TT) to define a candidate endmember space then uses N-FINDR and Hyperplane-based Craig Simplex Identification (HyperCSI) to locate the spectral endmembers. Radiative transfer models are then used to recover the ice and dust optical depth and surface reflectance that best fits the CRISM spectrum. Our resulting optical depth maps are shown to be in gross agreement with ultraviolet (UV), visible wavelength (VIS), and thermal infrared (TIR) results covering the same time periods. Retrieved optical depth values are, on average, within about 50% of those previously reported (Wolff et al., 2019; Montabone et al., 2015), although specific locations can vary by about a factor of 2 indicating some refinements to our retrievals will be needed before we can go into production mode on the remaining CRISM data.

Perturbation of Hydrogen Bonding Network Plays an Important Role in Determining Antifreeze Activity

In order to develop new antifreeze agents, it is crucial to understand the antifreeze activity. The adsorption-inhibition mechanism has been widely accepted, and most previous studies focus on ice-binding affinity of additive molecules but rarely discuss their influence on the hydrogen bonding network of ice. Herein, we investigate the ice recrystallization inhibition (IRI) activity of two structurally similar molecules, histidine (His) and phenylalanine (Phe). It is verified by experiment that Phe has excellent IRI activity, while His does not. Molecular dynamics simulation is conducted to study the process of ice growth with amino acids and to explore the origin of the difference between His and Phe. We find that His is prone to be swallowed up by ice and thus no longer hinders its growth, whereas Phe can remain unswallowed on the ice surface for a long period, which is attributed to their different abilities to perturb the hydrogen bonding network. Based on a statistical analysis of oxygen–hydrogen bond orientations, we propose a method to evaluate the order of the hydrogen bonding network. With this method, the IRI activity of His and Phe can be well interpreted, and the influence of different groups on the hydrogen bonding network can be quantified. This study takes the structural integrity of ice into consideration and provides a possibility to investigate the influence of different additive molecules on hydrogen bonding network, which is expected to improve the understanding of antifreeze mechanism.

Similarity in phytoplankton photophysiology among under-ice, marginal ice, and open water environments of Baffin Bay (Arctic Ocean)

As sea ice is declining rapidly in the Arctic, phytoplankton are being exposed to very different light regimes. Here we investigated how phytoplankton photoacclimate in three different irradiance regimes: under the ice, in the marginal ice zone, and in open water. We sampled from these three regimes in spring–summer 2016 during the Green Edge cruise in Baffin Bay. We also conducted experiments to investigate the impact of short-term surface light exposure on phytoplankton photophysiology, focusing on processes related to photoprotection and photodamage. These experiments were designed to simulate phytoplankton mixing to the surface or sea ice rapidly disappearing. Despite differences in hydrography, nutrient concentrations, light conditions, and phytoplankton biomass in each regime, the phytoplankton community was similar in terms of photophysiological state. Photoprotective pigments (including the xanthophyll cycle) were high in all three regimes sampled. As with the in situ measurements, ice conditions and light history had little impact on how phytoplankton responded to high light exposure, leading us to conclude that phytoplankton are largely prepared for a high light transition, even when originating from low light environments under sea ice.

Seismic Constraints on Damage Growth Within an Unstable Hanging Glacier

AbstractForecasting hanging glacier instabilities remain challenging as sensing technology focusing on the ice surface fails to detect englacial damage leading to large‐scale failure. Here, we combine icequake cluster analysis with coda wave interferometry constraining damage growth on Switzerland's Eiger hanging glacier before a 15,000 m3 break‐off event. The method focuses on icequake migration within clusters rather than previously proposed “event counting.” Results show that one cluster originated from the glacier front and migrated by 13.9(±1.2) m within 5 weeks before the break‐off event. The corresponding crevasse extension separates unstable and stable ice masses. We use the measured source displacement for damage parametrization and find a 90% agreement between an analytical model based on damage mechanics and frontal flow velocities measured with an interferometric radar. Our analysis provides observational constraints for damage growth, which to date is primarily a theoretical concept for modeling englacial fractures.

Cyclic Steps Created by Flowing Water on Ice Surface

The interface between ice and fluid can become unstable and devolve into cyclic steps bounded by hydraulic jumps. These steps are created by flowing water or wind over the ice surface. This study presents an analytical model to reproduce cyclic steps created by water over the ice surface. We apply four governing equations: the momentum equation, the continuity equation, the heat transfer equation in water, and the energy balance equation (the Stefan equation). After calculation, we can generate the variations in the depth-averaged water temperature, the depth-averaged velocity, and the ice elevation over one step wavelength. We can also understand the cyclic step formation process and how the heat transfer capacity of air and water, and the Froude number in the normal flow condition influence the wavelength. The results of the obtained steps in the analysis are compared with experimental observations to validate our model.

Gas dynamics within landfast sea ice of an Arctic fjord (NE Greenland) during the spring–summer transition

Sea ice is an active component of the Earth’s climate system, interacting with both the atmosphere and the ocean. Arctic sea ice is commonly covered by melt ponds during late spring and summer, strongly affecting sea ice physical and optical properties. How melt pond formation affects sea ice gas dynamics and exchanges between sea ice and the atmosphere, with potential feedbacks on climate, is not well known. Here we measured concentrations of N2, O2, and Ar, total alkalinity, and dissolved inorganic carbon within sea ice of Young Sound, NE Greenland, to examine how melt pond formation and meltwater drainage through the ice affect its physical properties and gas composition, including impacts on CO2 exchange with the atmosphere. Sea ice gas composition was controlled mainly by physical processes, with most of the gas initially in gaseous form in the upper ice layer. A minor contribution from biological processes was associated with positive estimates of net community production (up to 2.6 µmol Lice−1 d−1), indicating that the ice was net autotrophic. As the sea ice warmed, the upper ice gas concentrations decreased, suggesting a release of gas bubbles to the atmosphere. However, as melt ponds formed, the ice surface became strongly depleted in gases. Due to melt pond development, meltwater permeated through the ice, resulting in the formation of an underwater ice layer also depleted in gases. Sea ice, including brine, slush, and melt ponds, was undersaturated in CO2 compared to the atmosphere, supporting an uptake of up to −4.26 mmol m−2 d−1 of atmospheric CO2. As melt pond formation progressed, however, this uptake weakened in the strongly altered remaining ice surface (the “white ice”), averaging −0.04 mmol m−2 d−1. This study reveals the importance of melt pond formation and dynamics for sea ice gas composition.

Pulsed plasma discharge effects on efficiency and rate of penetration of melt probes in ice

Current melt probe designs increase their rate of penetration by shooting hot water jets towards the ice surface in addition to passively melting surrounding ice. In this paper pulsed plasma discharges taking place at the nose of the melt probe were investigated as a low power, less mechanically complex, alternative to water jetting systems. A prototype plasma melt probe was constructed and tested on solid ice in a low temperature, −17 °C, laboratory environment. The rate of penetration was determined for both passive heating and heating coupled with plasma discharges at 4.5 cm/h and 11 cm/h respectively. The 140% increase in the penetration rate occurred with a <5% increase in required power when compared to the passive melting mode. This is potentially due to microcracking and convection induced by the plasma discharges. The rate of penetration of the pulsed plasma melt probe is low compared to water jetting melt probes, but this is due to the low total power of around 40 W compared to 0.5 to 5 kW. The efficiency of the plasma augmented melt probe of about 40%, and the yield of 1.33 cm3/kJ is approaching the performance of more refined concepts and is achieved with no mechanical moving parts. If the pulsed plasma melt probe can be configured to safely operate with onboard scientific equipment it may become a promising option for drilling on Mars or Europa where power is a scarce resource.

Numerical simulations of heat exchange and vapor flow in ice fractures on Enceladus

Cassini spacecraft observed plume of water vapor and ice particles above the south polar terrain (SPT) of Saturn's moon Enceladus in 2005. The area of the SPT is marked by four prominent linear depressions in the ice dubbed “tigers stripes” (TS) that appear to be the source of the plume. The area around TS is also the source of anomalously high heat flux. The current consensus based on analysis of Cassini observations and modeling suggests that TS are fractures in the ice that penetrate to warm sub-ice ocean. Escaping vapor laden with ice particles forms the visible plume and latent heat of condensing vapor serves as the source of the surface thermal anomaly. In the present work previously developed numerical model of vapor flow and heat exchange inside TS fractures is refined and used to explain Cassini observations. Model improvements include consideration of a possible snow layer on the surface and inclusion of surface ice sublimation into energy balance model. Results of the simulations with improved model suggest that Cassini observations of vapor mass flow and endogenic heat flux can be explained if the width of the ice fractures is in the range 0.05–0.1 m, similar to previously published results. Wider fractures are possible if only a small portion of TS total length produces vapor plume, but the whole ~500 km length of TS fractures still contributes to the surface thermal anomaly. Alternatively, wider fractures are also possible in fractures with high effective friction due to wall roughness or channel tortuosity. Simulated heat output of fractures with different widths and depths in the range of 1.5–3 km is ~2.5–3.0 GW and is only weakly dependent on fracture width. A 2-m-thick surface snow layer covering the fracture can significantly lower outgoing heat flux to 0.9–1.9 GW and reduce surface temperatures by 20–40 K. The total heat flow from different fractures (including conduction from the water-filled portion) is remarkably similar - it is ~3.3 GW and 2.3 GW for fractures without and with a surface snow layer, respectively. The simulated heat flow is lower than the observed heat flow, suggesting that each TS depression may host 2 to 6 narrow ice fractures. The long-standing puzzle of the large difference between the observed heat flow from near TS (~4.2 GW) and from the whole SPT (~15.8 GW) is explained by conduction of ~11 GW of heat from the ocean through the ~5 km-thick ice shell underlying the SPT. Predicted high surface temperatures near fracture exit result in high rates of ice sublimation, which may produce a secondary source of water vapor feeding the observed plume. Fracture outlet likely evolves into a cone-like cross-section widening towards the surface on timescales from 1 to 100 years.

Microphone recording of flexural waves for estimation of lake ice thickness

In this study we took an intentionally low-tech approach, aiming to estimate key physical parameters of lake ice using a single, inexpensive microphone. We consider this approach highly relevant to the issue of transport safety and the relatively high number of accidents involving breakthrough failure of thin ice underlines the importance of this topic. We conducted a range of experiments on three frozen lakes in the Tromsø region of Northern Norway and found that the monochromatic air-coupled flexural wave was a robust feature of impulsively excited frozen lakes. Ice thickness was estimated via a closed form solution that only depends on the measured monochromatic frequency of the air-coupled flexural wave and a set of assumed physical parameters for the ice, air and water. We discuss the impact of uncertainty in the assumed parameters on estimated ice thickness and bearing capacity, finding the uncertainty to be quite small, particularly when physical observation of ice type or drilled thickness are available to constrain the assumed Young's modulus of the ice. Ice thicknesses estimated from air-coupled flexural waves were typically within 5–10% of ice thickness measured in holes drilled in the vicinity of the microphone for both artificial sources including hammer strikes, jumping and tapping with ice skates and natural ice quakes. The thickness estimates were also similarly accurate whether the microphone was resting on the ice, placed on land along the shoreline or handheld. We also showed that it is possible to record the dispersive ice flexural wave using a microphone, particularly when it was resting on the ice surface. Since thickness was constrained by the air-coupled flexural wave, we were able to estimate the propagation distance, corresponding to the horizontal offset between source and microphone, by inversion of the time dispersed arrival of the chirp signal corresponding to the ice flexural wave. We also demonstrated that a microphone can record inharmonic monochromatic overtones of the air-coupled flexural wave, that were linked to the geometry and boundary conditions of the frozen lakes using finite element modal analysis. This study leads us to conclude that a simple microphone can be a powerful tool giving a surprising amount of information on the lake-ice system. Using a microphone to record air-coupled flexural waves appears to be a promising additional tool for evaluation of ice conditions, convenient enough that it could substantially increase the availability of timely and accurate information on ice thickness and thereby contribute to safer travel on floating ice.

On the turbulent heat fluxes: A comparison among satellite-based estimates, atmospheric reanalyses, and in-situ observations during the winter climate over Arctic sea ice

The surface energy budget is crucial for Arctic sea ice mass balance calculation and climate systems, among which turbulent heat fluxes significantly affect the air–sea exchanges of heat and moisture in the atmospheric boundary layer. Satellite observations (e.g. CERES and APP-X) and atmospheric reanalyses (e.g., ERA5) are often used to represent components of the energy budget at regional and pan-Arctic scales. However, the uncertainties of the satellite-based turbulent heat fluxes are largely unknown, and cross-comparisons with reanalysis data and in-situ observations are limited. In this study, satellite-based turbulent heat fluxes were assessed against in-situ observations from the N-ICE2015 drifting ice station (north of Svalbard, January–June 2015) and ERA5 reanalysis. The turbulent heat fluxes were calculated by two approaches using the satellite-based ice surface temperature and radiative fluxes, surface atmospheric parameters from ERA5, and snow/sea ice thickness from the pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS). We found that the bulk-aerodynamic formula based results could better capture the variations of turbulent heat fluxes, while the maximum entropy production based estimates are comparable with ERA5 in terms of root-mean-square error (RMSE). CERES-based estimates outperform the APP-X-based ones but ERA5 performs the best in all seasons (RMSE of 18 and 7 W m−2 for sensible and latent heat flux, respectively). The air–ice temperature/humidity differences and the surface radiation budget were found the primary driving factors in the bulk-formula method and maximum entropy production (MEP) method, respectively. Furthermore, errors in the surface and near-surface temperature and humidity explain almost 50% of the uncertainties in the estimates based on the bulk-formula, whereas errors in the net radiative fluxes explain more than 50% of the uncertainties in the MEP-based results.

InSARTrac Field Tests—Combining Computer Vision and Terrestrial InSAR for 3D Displacement Monitoring

InSARTrac is an innovative method for 3D displacement monitoring that combines terrestrial interferometric synthetic aperture radar (InSAR) and computer vision-based feature tracking. The 3D measurements obtained are considered far superior to 1D or 2D data and facilitate evaluations concerning the mechanisms controlling kinematics. This study presents the results of InSARTrac measurements at the Mölltal Glacier in Carinthia, Austria. The duration of glacier monitoring was four weeks and involved two instrument setup positions to obtain comparative measurements of supraglacial rock debris from different angles without utilizing retroreflectors. The mean displacement rate of the resultant vector is 22 mm/day and includes ~11 mm/day in the downgradient ice surface direction and 6 to 18 mm/day vertically downward. Additionally, the entire glacier surface was measured three times using a LIDAR-equipped UAV, revealing mean vertical displacements of 16 mm/day. The measurements indicate an InSARTrac accuracy of 4.2 ppm, which is 27% lower than in the initial controlled tests utilizing retroreflectors. The field test demonstrates the capability of InSARTrac to provide meaningful 3D displacement measurements of supraglacial rock debris. The material monitored has texture and reflectivity similar to certain classes of landslides, rock glaciers, and other alpine processes, indicating that InSARTrac has promising applications for monitoring a variety of geologic phenomena.