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During the concluding phase of the NASA Operation IceBridge (OIB), we successfully completed two airborne measurement campaigns (in 2018 and 2021, respectively) using a compact S and C band radar installed on a Single Otter aircraft and collected data over Alaskan mountains, ice fields, and glaciers. This paper reports seasonal snow depths derived from radar data. We found large variations in seasonal radar-inferred depths with multi-modal distributions assuming a constant relative permittivity for snow equal to 1.89. About 34 % of the snow depths observed in 2018 were between 3.2 and 4.2 m, and close to 30 % of the snow depths observed in 2021 were between 2.5 and 3.5 m. We observed snow strata in ice facies, combined percolation and wet-snow facies, and dry-snow facies from radar data and identified the transition areas from wet-snow facies to ice facies for multiple glaciers based on the snow strata and radar backscattering characteristics. Our analysis focuses on the measured strata of multiple years at the caldera of Mount Wrangell (K'elt'aeni) to estimate the local snow accumulation rate. We developed a method for using our radar readings of multi-year strata to constrain the uncertain parameters of interpretation models with the assumption that most of the snow layers detected by the radar at the caldera are annual accumulation layers. At a 2004 ice core and 2005 temperature sensor tower site, the locally estimated average snow accumulation rate is ∼2.89 m w.e. a−1 between the years 2003 and 2021. Our estimate of the snow accumulation rate between 2005 and 2006 is 2.82 m w.e. a−1, which matches closely to the 2.75 m w.e. a−1 inferred from independent ground-truth measurements made the same year. The snow accumulation rate between the years 2003 and 2021 also showed a linear increasing trend of 0.011 m w.e. a−2. This trend is corroborated by comparisons with the surface mass balance (SMB) derived for the same period from the regional atmospheric climate model MAR (Modèle Atmosphérique Régional). According to MAR data, which show an increase of 0.86 ∘C in this area for the period of 2003–2021, the linear upward trend is associated with the increase in snowfall and rainfall events, which may be attributed to elevated global temperatures. The findings of this study confirmed the viability of our methodology, as well as its underlying assumptions and interpretation models.

During the concluding phase of the NASA Operation IceBridge (OIB), we successfully completed two airborne measurement campaigns (in 2018 and 2021, respectively) using a compact S/C band radar installed on a Single Otter aircraft and collected data over Alaskan mountains, ice fields, and glaciers. We observed snow strata in ice facies, wet-snow/percolation facies and dry snow facies from radar data. This paper reports seasonal snow depths derived from our observations. We found large variations in seasonal radar-inferred depths assuming a constant relative permittivity for snow equal to 1.89. The majority of the seasonal depths observed in 2018 were between 3.2 m and 4.2 m, and around 3 m in 2021. We also identified the transition areas from wet-snow facies to ice facies for multiple glaciers based on the snow strata and radar backscattering characteristics. Our analysis focuses on the measured strata of multiple years at the caldera of Mount Wrangell to estimate the local snow accumulation rate. We developed a method for using our radar readings of multi-year strata to constrain the uncertain parameters of interpretation models with the assumption that most of the snow layers detected by the radar at the caldera are annual accumulation layers. At a 2004 ice core and 2005 temperature sensor tower site, the locally estimated average snow accumulation rate is ~2.89 m w. e. a-1 between the years 2002 and 2021. Our estimate of the snow accumulation rate between 2005 and 2006 is 2.82 m w. e. a-1, which matches closely to the 2.75 m w. e. a-1 inferred from independent ground-truth measurements made the same year. We also found a linear increasing trend of 0.011 m w. e. a-1 per year between the years 2002 and 2021. With this trend, we extrapolated the snow accumulation back to 1992 and obtained an average accumulation rate of 2.74 w. e. a-1 between the years 1992 and 2004, which agrees well with the value of 2.66 w. e. a-1 for the same period determined from the ice core data retrieved at the caldera in 2004. The results reported here verified the efficacy of our method, its assumption, and the interpretation models.

In this article, we introduce a pH-responsive charge-reversible and photo-crosslinkable polymer nanoparticle. It is prepared via typical self-assembly from a block copolymer poly((7-(4-viny...

Tree heights are important input for many inventory and ecosystem models. While optical and infrared sensors such as LiDAR are widely used in forest surveys, microwave radar has the unique advantage of being able to operate in bad weather or poor visibility conditions. In this work, we employed a LiDAR combined with a compact ultra-wideband frequency modulated continuous wave (FMCW) radar onboard a Single Otter aircraft to collect data over forested areas in Alaska. While the primary focus of the mission was to map the surface elevation and snow thickness of Alaskan glaciers as a part of NASA Operation IceBridge (OIB), we recorded LiDAR and radar returns during the transit flights to analyze backscattering signatures from tree-covered areas, thereby assessing the potential application of our radar to forest and vegetation remote sensing. We analyzed these measurements and estimated the tree heights along the flight trajectory. The very good agreement between the tree height profiles from the two instruments shows promising results for wide area forestry studies using microwave radar.

This paper provides an update and overview of the Center for Remote Sensing of Ice Sheets (CReSIS) radars and platforms, including representative results from these systems. CReSIS radar systems operate over a frequency range of 14–38 GHz. Each radar system's specific frequency band is driven by the required depth of signal penetration, measurement resolution, allocated frequency spectra, and antenna operating frequencies (often influenced by aircraft integration). We also highlight recent system advancements and future work, including (1) increasing system bandwidth; (2) miniaturizing radar hardware; and (3) increasing sensitivity. For platform development, we are developing smaller, easier to operate and less expensive unmanned aerial systems. Next-generation platforms will further expand accessibility to scientists with vertical takeoff and landing capabilities.

The service performances of asphalt pavement, especially rutting, will be inevitably affected by climate change. However, existing studies have generally focused on the rutting depth and rutting life, and thus became insufficient for comprehensively evaluating the influence of climate change on rutting over the service life. A resilience assessment method for asphalt pavement rutting is developed to solve the above problem. First, the original resilience method is extended to fit the system whose performance level continues to decline. Then, the calculation formulas of rutting resilience are derived by combining the rutting prediction model and the level assessment model. Subsequently, the influence degrees of climate change in representative cities on rutting resilience are studied. The results suggest that neglecting climate change in rutting design of asphalt pavement will lead to insufficient resilience, especially in northern China. Furthermore, the predicted temperature under RCP8.5 should be employed for asphalt pavement design.

We developed a portable ultra-wideband radar system capable of reconfigurable operation in multiple frequency bands (separate or simultaneous) spanning from microwaves through millimeter waves. The instrument provides a compact solution for fine-resolution measurements of elevation changes and superficial snow/firn thickness from low-altitude, mid-sized airborne platforms. In this article, we provide an overview of the radar system design and its performance during laboratory testing. We demonstrate its application in aerial surveys of snow layer thickness at S/C bands, dual-band airborne altimetry at Ku-/Ka-bands, and present first-order comparisons with coincident airborne lidar data.

We designed a Ka-band prototype radar altimeter operated at a center frequency of 35 GHz with a 6 GHz bandwidth. The instrument was intended for fine-resolution verification and validation of space borne altimetry datasets. We installed it onboard the NASA C-130 aircraft in conjunction with two other wideband microwave instruments and collected airborne altimetry data over Greenland land ice and arctic sea ice during the 2015 NASA Operation IceBridge arctic campaign. Apart from the major application of verification and calibration of satellite-based measurements, data from this instrument can be used to derive snow grain size because of the dominant effect of volume scattering in radar signatures. In this paper, we briefly describe the system design and the installation on the NASA C-130, discuss the observed penetration depths of Ka-band signals into the snowpack, present sample results of optical-equivalent snow grain size estimates from radar measurements over the dry snow zone using a simplified snowpack model. We show that the observed penetration depths and the snow grain size estimates from the airborne Ka-band radar retrievals agree well with the model and in-situ snow-pit measurements.

We developed an airborne radar system capable of simultaneous operation at Ku- and Ka- bands. The system is compact and lightweight, and supports coincident altimetry measurements in both bands with ultra-wide bandwidth (up to 6 GHz). Wide-band data can be used to obtain fine vertical resolution or sub-banded to match the operational parameters of orbital instruments. We installed the system onboard a Twin Otter aircraft and collected data over the East Greenland ice sheet margin and on Arctic marine ice during a test field campaign conducted in the summer of 2019. The work was carried as an international collaboration to support the validation of ESA's CryoSat-2 and NASA's ICESat-2 measurements. In this paper, we present an overview of the instrument and its airborne test configuration and field operation; provide initial results from field trials; and outline the potential application of dual-band airborne radar data for the validation of satellite instruments.

The path optimization problem with capacity constraints has always been a combinatorial optimization problem, and the quantum evolution algorithm has excellent performance in solving combinatorial optimization problems. Firstly, after analyzing the traditional path optimization problem and the path optimization problem with capacity constraints, the distribution center is numbered 0 based on the customer-based decimal coding method, and the quantum evolution algorithm is improved according to the capacity constraint method. Fixed quantum rotation angle to dynamic rotation angle. The improved algorithm is then applied to vehicle path optimization problems with capacity constraints. Finally, through the MATLAB and LINGO methods to verify the comparison, it can be concluded that the improved quantum evolution algorithm can accurately solve the vehicle path optimization problem, and the improved quantum evolution algorithm has a good influence on the path optimization problem.

In this paper, we present a brief overview of the state of the art in radar systems for ice and snow measurements. Emphasis is given to the instrumentation developed at the University of Kansas for multi-band data retrieval at frequencies ranging from 14 MHz to 38 GHz, which is operated onboard manned and unmanned aircraft. The information collected with these systems is used to estimate parameters such as ice thickness, ice surface and bedrock topography, snow cover thickness on sea ice, and annual snow accumulation. We give a summary of recent field programs (including operations out of Punta Arenas, Chile), present sample results, and discuss recent collaborations with Chilean institutions.

In this work, novel mesoporous silica spheres were prepared by calcination of golf-shaped silica microspheres, which were fabricated via a typical sol-gel method by using synthetic amphiphilic block copolymer poly(acrylate isobutyl polyhedral oligomeric silsesquioxane)-b-poly(dimethylaminoethyl methacrylate co-styrene)) (PAPOSS-b-(PDMAEMA-co-PSt) and anionic surfactant sodium dodecyl sulfate (SDS) as dual-template. Firstly, three different POSS-based block copolymers were synthesized through subsequent homopolymerization of acrylate isobutyl POSS and chain extension of dimethylaminoethyl methacrylate (DMAEMA) and styrene with various feed ratios via reversible transfer radical polymerization (RAFT). These amphiphilic block polymers and SDS were utilized as cooperative template to golf-shaped silica microspheres. The electrostatic interaction between protonated PDMAEMA segments and anion surfactant as well as the strong interaction between PAPOSS segments and silicon source plays the dominant role in forming golf-shaped silica spheres. Moreover, the surface morphology of silica spheres can be tuned by varying molar ratio of PDMAEMA/PAPOSS. The resulting golf-shaped silica microspheres were further calcined to give mesoporous silica spheres which exhibited a BET surface area of 1031 m2 g−1, a total pore volume of 0.826 cm3 g−1, and a narrow pore size distribution centered at 3.20 nm.

We present a new digital elevation model (DEM) of the bed, with a 1 km gridding, of the Weddell Sea (WS) sector of the West Antarctic Ice Sheet (WAIS). The DEM has a total area of ∼ 125 000 km2 covering the Institute, Möller and Foundation ice streams, as well as the Bungenstock ice rise. In comparison with the Bedmap2 product, our DEM includes new aerogeophysical datasets acquired by the Center for Remote Sensing of Ice Sheets (CReSIS) through the NASA Operation IceBridge (OIB) program in 2012, 2014 and 2016. We also improve bed elevation information from the single largest existing dataset in the region, collected by the British Antarctic Survey (BAS) Polarimetric radar Airborne Science Instrument (PASIN) in 2010–2011, from the relatively crude measurements determined in the field for quality control purposes used in Bedmap2. While the gross form of the new DEM is similar to Bedmap2, there are some notable differences. For example, the position and size of a deep subglacial trough (∼ 2 km below sea level) between the ice-sheet interior and the grounding line of the Foundation Ice Stream have been redefined. From the revised DEM, we are able to better derive the expected routing of basal water and, by comparison with that calculated using Bedmap2, we are able to assess regions where hydraulic flow is sensitive to change. Given the potential vulnerability of this sector to ocean-induced melting at the grounding line, especially in light of the improved definition of the Foundation Ice Stream trough, our revised DEM will be of value to ice-sheet modelling in efforts to quantify future glaciological changes in the region and, from this, the potential impact on global sea level. The new 1 km bed elevation product of the WS sector can be found at https://doi.org/10.5281/zenodo.1035488.

Climate change is extensively affecting ice sheets resulting in accelerating mass loss in recent decades. Assessment of this reduction and its causes is required to project future ice mass loss. Annual snow accumulation is an important component of the surface mass balance of ice sheets. While in situ snow accumulation measurements are temporally and spatially limited due to their high cost, airborne radar sounders can achieve ice sheet wide coverage by capturing and tracking annual snow layers in the radar images or echograms. In this paper, we use deep learning to uniquely identify the position of each annual snow layer in the Snow Radar echograms taken across different regions over the Greenland ice sheet. We train with more than 15,000 images generated from radar echograms and estimate the thickness of each snow layer within a mean absolute error of 0.54 to 7.28 pixels, depending on dataset. A highly precise snow layer thickness can help improve weather models and, thus, support glaciological studies. Such a well-trained deep learning model can be used with ever-growing datasets to aid in the accurate assessment of snow accumulation on the dynamically changing ice sheets.

A novel halogen-free 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-containing co-curing agent, 6,6′-(1,4-phenylenebis(((4-(phenylamino)phenyl)amino)methylene))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (DPN) was synthesized via a simple 1-pot or 2-step procedure with yield of 86.2% and 70.8%, respectively. The molecular structures of 4,4′-((1,4-phenylenebis(methanylylidene))bis(azanylylidene))bis(N-phenylaniline) (DPN intermediate) and DPN are characterized by FTIR, NMR, and MS. TGA tests show that the char yield of DPN/EP composites raises to 30.9% when the molar ratio of DPN to 4,4-diaminodiphenyl methane(DDM) is 20:80. Tg values of DPN/EP composites tested by DSC and DMA are similar to neat epoxy resin (EP), which is due to the secondary amine in DPN that participates in the cross-linking reaction of epoxy resin. The storage modulus in the rubber stage (E′-190 °C) of flame-retardant epoxy resin is close to that of neat EP, while their tanδ's are lower, which indicates the similarity of samples' cross-linking density due to the participation of DPN in the cross-linking reaction. The results show that when the molar ratio of DPN and DDM is 5:95, the epoxy has a higher Tg value and better mechanical properties than other samples. The introduction of DPN efficiently improves the flame-retardant properties of epoxy resin with V-0 rating of UL-94 vertical burning test, non-dripping, 41% of limit oxygen index (LOI) value, low peak heat release rate (PHRR), and total heat release (THR).

Frequency-modulated-continuous-wave (FM-CW) radar has been used extensively for the airborne measurement of snow thickness over sea ice and the mapping of annual accumulation over land ice. In contrast to conventional in situ measurements, FM-CW radar, when operated onboard an airborne platform, can be a useful tool for widearea surveys of snow deposition. Since the early 2000s, the Center for Remote Sensing of Ice Sheets (CReSIS) at the University of Kansas (KU) has designed, developed, and deployed airborne ultrawide-band (UWB) FM-CW radars, called Snow Radars, on National Science Foundation (NSF)-, NASA-, Naval Research Laboratory (NRL)-, and Alfred Wegener Institute (AWI)-provided aircraft in both Arctic and Antarctic regions and generated a large amount of snow data products. In addition to the significant standalone value of the snow-thickness measurements, these data are being used in estimating Arctic sea ice thickness, which is a key variable in the study of atmosphere-ocean-ice interactions. This article provides a review of snow remote sensing techniques with airborne FM-CW radars to document the operating principle, design, and evolution of CReSIS' UWB FM-CW radars and discuss and promote understanding of the advantages and limitations associated with these systems.

Ice crystal orientation fabric (COF) records information about past ice-sheet deformation and influences the present-day flow of ice. Polarimetric radar sounding provides a means to infer anisotropic COF patterns due to the associated birefringence of polar ice. Here, we develop a polarimetric coherence (phase-based) method to determine horizontal properties of the COF. The method utilizes the azimuth and depth dependence of the vertical gradient of the hhvv coherence phase to infer the dielectric principal axes and birefringence, which are then related to the second-order fabric orientation tensor. Specifically, under the assumption that one of the orientational eigenvectors is vertical, we can determine the horizontal eigenvectors and the difference between the horizontal eigenvalues (a measure of horizontal fabric asymmetry). The method exploits single-polarized data acquired with varying antenna orientation. It applies to ground-based ``multi-polarization'' surveys and is demonstrated using data acquired by Center for Remote Sensing of Ice Sheets (CReSIS) using Multi-Channel Coherent Radar Depth Sounder (MCRDS) from the North Greenland Eemian Ice Drilling (NEEM) ice core region in Greenland. The analysis is validated using a combination of polarimetric matrix backscatter simulations and comparison with COF data from the NEEM ice core. The results are consistent with a conventional model of ice deformation at an ice divide where a lateral tension component is present, with minor horizontal COF asymmetry and the greatest horizontal concentration of crystallographic axes orientated near parallel to the ice divide.

Snow in mountainous areas provides freshwater resources for lower basins and coastal areas. Snow layering at mountain summits contains information about local seasonal snow accumulation and climate history. Knowledge of snow depths is required to estimate the snow water equivalent. However, monitoring spatial distribution and temporal changes in snow depth and accumulation over remote mountains and glaciers in wide areas is challenging because of limited accessibility for in-situ measurements. As a part of NASA Operation IceBridge missions, we took airborne radar measurements of snow over Alaskan mountains, icefields and glaciers in late May of 2018, with a compact frequency-modulated continuous wave radar system, operating from 2 GHz to 8 GHz and installed on a Single Otter aircraft. In this paper, we describe the radar instrument, its installation onto the platform, the data collection and processing activities, and report the major results from these surveys. We observed seasonal snow depth between ~0.3 m to ~15 m for elevations above sea level from ~1726 m to ~3624 m. We successfully mapped snow accumulation layers to depths exceeding ~85 m below the surface at high-elevation summits of Mount Wrangell and Bona. The traced snow depth profiles over glaciers and accumulation layers at mountain summits point to the utility of these data to the study of water resource management, hydrology modelling, and regional climate change.

In Rodriguez-Morales et al., 2021, Fig. 1 appeared with some flaws related to a production error. For the sake of clarity, here we list the inconsistencies we identified and provide a revised version of the figure. This erratum does not affect any of the claims, results, discussions, or conclusions in the original manuscript.

In Rodriguez-Morales et al. , 2021, Fig. 1 appeared with some flaws related to a production error. For the sake of clarity, here we list the inconsistencies we identified and provide a revised version of the figure. This erratum does not affect any of the claims, results, discussions, or conclusions in the original manuscript.

We developed a multichannel wideband synthetic aperture radar (SAR) that operates over a frequency range of 190–450 MHz for measurements over the ice sheets in Antarctica and Greenland. The antenna-array, which consists of eight elements housed in a certified external structure for a BASLER aircraft, was used for measurements during the 2013–2014 Antarctic field season. We performed measurements with this system in conjunction with two ultra-wideband radars operating over a frequency range of 2–8 GHz and 12–18 GHz on Siple Coast ice streams in West Antarctica during December 2013 and January 2014. We sounded ice thicker than 2 km with a signal-to-noise ratio (SNR) of more than 20 dB in an area with two-way ice loss of about 27 dB/km. The same system also simultaneously mapped near-surface internal layers with submeter resolution from the ice-surface to a depth of about 1100 for 1200 m thick ice. In this paper, we provide a detailed overview of the radar instrumentation and signal processing algorithms and present a few sample results. The radar will be operated over a frequency range of 150–550 MHz with a 24-element antenna-array for wide-ranging measurements over the Greenland and Antarctic ice sheets, starting around August 2015.

The first-order control of ice thickness and height above sea level is linked to the decreasing strength of ice-bed coupling alone flowlines from an interior ice divide to the calving front of an ice shelf. Uncoupling progresses as a frozen bed progressively thaws for sheet flow, as a thawed bed is progressively drowned for stream flow, and as lateral and/or local grounding vanish for shelf flow. This can reduce ice thicknesses by 90 % and ice elevations by 99 % along flowlines. Original work presented here includes (1) replacing flow and sliding laws for sheet flow with upper and lower yield stresses for creep in cold overlying ice and basal ice sliding over deforming till, respectively, (2) replacing integrating the Navier–Stokes equations for stream flow with geometrical solutions to the force balance, and (3) including resistance to shelf flow caused by lateral confinement in a fjord and local grounding at ice rumples and ice rises. A comparison is made between our approach and two approaches based on continuum mechanics. Applications are made to Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland.

Characterizing the clogging process of permeable asphalt mixtures helps clarify the permeability of permeable pavements. This study aimed to determine the clogging characteristics of permeable asphalt mixtures. By analyzing the particle size of pavement surface sediment, the size of clogging particle was determined in the range from 0.15 to 2.36 mm. Five types of permeable asphalt mixtures were synthesized, and the clogging characteristics test was performed with the independently developed multidirectional permeability test instrument. The variation of the permeability in the clogging process was explored. Subsequently, the internal void of permeable asphalt mixtures was characterized by computerized tomography. As suggested from the results, the void evolution at different depths of specimen varied with the rise in the number of clogging particles. It was reported that the clogging process of permeable asphalt mixtures consisted of four stages, i.e., fast clogging, clogging recovery, gradual clogging and clogging acceleration. Under the clogging effect, the permeability of permeable asphalt mixtures could vary from non-Darcy to Darcy permeability, and the variation speed of the transverse permeability was faster than that of the vertical one. Lastly, the effects of water head height, the gradation type of permeable asphalt mixtures and clogging particles on the clogging characteristics were analyzed.

The premise of elucidating the clogging mechanism of permeable asphalt mixtures refers to the determination of the distributing behaviors of clogging particles. This study aimed to determine the distributing behaviors of clogging particles in permeable asphalt mixtures from the microstructure perspective. By collecting pavement sediment and conducting particle size analysis, the size range of clogging particles was determined in the range from 0.15 to 2.36 mm. Three types of permeable asphalt mixtures were synthesized, and the tomographic images of asphalt mixtures were captured with the computed tomography. To determine the optimal parameters of image registration, mutual information and the calculated time were adopted. On that basis, the algorithm to identify clogging particles in permeable asphalt mixtures was developed, and the spatial distributing behaviors of clogging particles were explored. As suggested from the results, the clogging particles were primarily deposited deeply in the structure under the action of fluid carrying, and the particles near the periphery exhibited larger content than the center of the structure. With the clogging process, the deposition positions of clogging particles were from deep to shallow, and the particle distribution varied from the centralized distribution to uniform distribution. The particle deposition area experienced three stages (i.e., the emergence, expansion and stability of particle deposition). Lastly, the effect of gradation type of asphalt mixture and the size of clogging particles on particle distributing behaviors were analyzed.

The design and application of bitumen rheological property is an essential part of road engineering, which is strongly associated with colloidal structure form by millions of molecules. Our work aims at developing a transferable CGMD model for the bitumen molecular system to explore the microstructure in the Mesoscopic scale. In the present study, we focus on the mapping site construction and the validation of the modified MARTINI forcefield based on Flory-Huggins theory. On this basis, the CGMD model owned 126,692 molecules were built to research the influencing factors of bitumen aggregation, the dynamic evolution process of a three-dimensional periodic layer structure was observed. The result shows that the diffusion coefficient order of asphaltene, resin, oil, and model average is resin > model average > oil > asphaltene, and the order does not vary with temperature. At different character temperatures, the diffusion coefficients value has changed in orders of magnitude, which is correspond to viscoelasticity studies. Meanwhile, the molecular relative concentration at different temperatures has revealed the aggregation behavior of asphaltene in the bitumen, when the temperature is high enough, all the asphaltene molecules are separate to a certain distance and keep stable. With the temperature decreasing, some asphaltene molecules tend to move closer and form smaller aggregate.

Rutting has always been considered the main disease in asphalt pavement. Dealing with rutting disease would be benefitted by understanding the formation of rutting and testing the rutting performance of mixtures more reasonably. The objective of this paper is to systematically investigate the rutting mechanism by employing a self-designed rutting tester along with the corresponding numerical simulations. The deformation of different positions of the existing tracking tester was found to be inconsistent, and the loading was not in line with reality. Accordingly, a more practical tester was proposed: the reduced scale circular tracking (RSCT) tester integrates the functions of asphalt mixture fabrication and rutting monitoring. The results demonstrated that the loading of the new tester is closer to the actual situation. In addition, determining the stress and displacement characteristics of particles in the asphalt mixture was found to be difficult due to the limitations of the testing methods. Therefore, a two-dimensional virtual rutting test based on the RSCT was built using PFC2D (Particle Flow Code 2 Dimension) to investigate the mechanism of formation in rutting and to obtain the corresponding guidance. The numerical simulation showed that all particles of the specimen tended to move away from the load location. The main cause of rutting formation was the eddy current flow of asphalt mastic driven by coarse aggregates. The aggregates with diameters ranging from 9.5 to 4.75 mm were observed to have the greatest contribution to rutting deformation. Therefore, the aggregate amount of these spans should be focused on in the design of mixture grading.

This paper presents recent updates to the CReSIS radar sensor package and the platforms supporting these sensors. These sensors cover a wide frequency range (14 MHz to 38 GHz). The specific frequency bands are chosen to balance between bandwidth available and signal penetration. The wide frequency range is also used for measuring different phenomenology. CReSIS has integrated these radar systems, including antennas, on a wide variety of fixed wing crewed aircraft, several UAV platforms, and for ground-based applications. The software for processing the radar data is now open source and an overview of the capabilities and how to access and use the software are presented. Finally, example data products which explore the new capabilities of the sensors and platforms are given.

We present a new bed elevation digital elevation model (DEM), with a 1 km spatial resolution, for the Weddell Sea sector of the West Antarctic Ice Sheet. The DEM has a total area of ~125,000 km2 covering the Institute, Möller and Foundation ice streams and the Bungenstock ice rise. In comparison with the Bedmap2 product, our DEM includes several new aerogeophysical datasets acquired by the Center for Remote Sensing of Ice Sheets (CReSIS) through the NASA Operation IceBridge (OIB) program in 2012, 2014 and 2016. We also update bed elevation information from the single largest existing dataset in the region, collected by the British Antarctic Survey (BAS) Polarimetric Airborne Survey Instrument (PASIN) in 2010-11, as BEDMAP2 included only relatively crude ice thickness measurements determined in the field for quality control purposes. This have resulted in the deep parts of the topography not being visible in the fieldwork non-SAR processed radargrams. While the gross form of the new DEM is similar to Bedmap2, there are some notable differences. For example, the position and size of a deep trough (~ 2 km below sea level) between the ice sheet interior and the grounding line of Foundation ice stream has been redefined. From the revised DEM, we are able to better derive the expected routing of basal water at the ice-bed interface, and by comparison with that calculated using Bedmap2 we are able to assess regions where hydraulic flow is sensitive to change. Given the sensitivity of this sector of the ice sheet to ocean-induced melting at the grounding line, especially in light of improved definition of the Foundation ice stream trough, our revised DEM will be of value to ice-sheet modelling in efforts to quantify future glaciological changes in the region, and therefore the potential impact on global sea level. The new 1 km bed elevation product of the Weddell Sea sector, West Antarctica can be found in the http://doi.org/10.5281/zenodo.1035488.

Understanding the subglacial conditions is crucial in determining the ice dynamics and predicting the stability of ice sheets. Radio echo sounding (RES) surveys have been extensively carried out to map the ice sheets of Greenland and Antarctica. Using RES data, basal conditions of ice sheets can be determined from estimated reflectivity that is affected by ice surface and bed roughness. Roughness is also one of the important parameters to explain ice dynamics. In this paper the ice surface and bed roughness of Petermann Glacier, one of the largest outlet glacier of Greenland, is estimated with the Multi-Channel Coherent Radar Depth Sounder (MCoRDS) data by fitting the echo amplitude distribution to statistical models. The roughness derived from MCoRDS data is compared and verified with the roughness estimations from Airborne Topographic Mapper (ATM) and Ku-band altimeter measurements. It has been observed that Petermann glacier has rougher ice inland and a smoother bed towards the trunk of the glacier.

A series of novel azobenzene-based amphiphilic random copolymers P(POSSMA-co-AZOMA-co-DMAEMA) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. A light and reduction dual-responsive azo group, pH-responsive tertiary amine group and super hydrophobic POSS moiety were incorporated into the polymer chain to generate multi-stimuli-responsiveness. Self-assembly of these amphiphilic copolymers led to the formation of spherical micelles in aqueous solution. The light, pH and reduction responsive properties of the micelles were investigated systematically by DLS, TEM, UV-vis, FTIR and NMR. The azo groups can undergo trans–cis isomerization under UV light irradiation, thus causing a diameter change of the micelles. Owing to the large proportion of tertiary amine groups in amphiphiles, these micelles showed sensitive pH-response behavior. The hydrophobic azo pendant in the polymer chain completely reduced to a more hydrophilic substituted aniline in a reductive environment, resulting in the increase of overall hydrophilicity of amphiphiles and the disassembly of polymeric micelles. Owing to these multi-stimuli–responses, the polymeric micelles showed rapid and efficient release properties of hydrophobic molecules in response to pH and reductive stimuli.

Ice properties inferred from multi-polarization measurements, such as birefringence and crystal orientation fabric (COF), can provide insight into ice strain, viscosity, and ice flow. In 2008, the Center for Remote Sensing of Ice Sheets (CReSIS) used a ground-based VHF (very high frequency) radar to take multi-channel and multi-polarization measurements around the NEEM (North Greenland Eemian Ice Drilling) site. The system operated with 30 MHz bandwidth at a center frequency of 150 MHz. This paper describes the radar system, antenna configurations, data collection, and processing and analysis of this data set. Within the framework derived from uniaxial ice crystal model, we found that ice birefringence dominates the power variation patterns of co-polarization and cross-polarization measurements in the area of 100 km2 around the ice core site. The phase shift between ordinary and extraordinary waves increases nonlinearly with depth. The ice optic axis lies in planes that are close to the vertical plane and perpendicular or parallel to the ice divide depending on depth. The ice optic axis has an average tilt angle of about 11.6° vertically, and its plane may rotate either clockwise or counterclockwise by about 10° across the 100 km2 area, and at a specific location the plane may rotate slightly counterclockwise as depth increases. Comparisons between the radar observations, simulations, and ice core fabric data are in very good agreement. We calculated the effective colatitude at different depths by using azimuth and colatitude measurements of the c axis of ice crystals. We obtained an average effective c axis tilt angle of 9.6° from the vertical axis, very comparable to the average optic axis tilt angle estimated from radar polarization measurements. The comparisons give us confidence in applying this polarimetric radio echo sounding technique to infer profiles of ice fabric in locations where there are no ice core measurements.

The flow of ice is temperature-dependent, but direct measurements of englacial temperature are sparse. The dielectric attenuation of radio waves through ice is also temperature-dependent, and radar sounding of ice sheets is sensitive to this attenuation. Here we estimate depth-averaged radar-attenuation rates within the Greenland Ice Sheet from airborne radar-sounding data and its associated radiostratigraphy. Using existing empirical relationships between temperature, chemistry, and radar attenuation, we then infer the depth-averaged englacial temperature. The dated radiostratigraphy permits a correction for the confounding effect of spatially varying ice chemistry. Where radar transects intersect boreholes, radar-inferred temperature is consistently higher than that measured directly. We attribute this discrepancy to the poorly recognized frequency dependence of the radar-attenuation rate and correct for this effect empirically, resulting in a robust relationship between radar-inferred and borehole-measured depth-averaged temperature. Radar-inferred englacial temperature is often lower than modern surface temperature and that of a steady state ice-sheet model, particularly in southern Greenland. This pattern suggests that past changes in surface boundary conditions (temperature and accumulation rate) affect the ice sheet's present temperature structure over a much larger area than previously recognized. This radar-inferred temperature structure provides a new constraint for thermomechanical models of the Greenland Ice Sheet.

Ice basal conditions determine the ice flow dynamics and are needed for the accurate modeling of ice sheets. In this paper, a large volume of data, collected over Antarctica's Byrd Glacier in 2011–2012 with multichannel radar, is analyzed to infer the basal conditions. The analysis of received radio echo sounding data includes power loss corrections for spherical spreading and roughness of the ice-surface and ice-bed interfaces, and the estimate of relative englacial attenuation and basal reflectivity values. From the estimated relative basal reflectivity values, basal conditions are inferred, and are validated using geophysical features from radar images, abruptness and coherence index values. The identified locations of high basal reflectivity values provide new insights on the subglacial hydrological network of Byrd Glacier.

We present an overview of a set of radar instruments developed at the University of Kansas for multi-spectral measurements of ice and snow properties. The systems operate at different frequency bands ranging from 14 MHz to 38 GHz, onboard manned and unmanned aircraft. The data collected with these systems are used to estimate parameters such as ice thickness, ice surface and bedrock topography, snow cover thickness on sea ice, and annual snow accumulation. We give a summary of recent field programs (including operations out of Punta Arenas, Chile) and discuss current collaborations with Chilean institutions.

Radar research has been synonymous with the University of Kansas (KU) for over half a century. As part of this special session organized to highlight significant radar programs in academia, this paper surveys recent and ongoing work at KU. This work encompasses a wide breadth of sensing applications including the remote sensing of ice sheets, autonomous navigation methods for unmanned aerial vehicles (UAVs), novel laser radar capabilities, detection of highenergy cosmic rays using bistatic radar, different forms of waveform diversity such as MIMO radar and pulse agility, and various radar-embedded communication methods. The results of these efforts impact our understanding of the changing nature of the environment, address the proliferation of unmanned systems in the US airspace, realize new sensing modalities enabled by the joint consideration of electromagnetics and signal processing, and greater facilitate radar operation in an increasingly congested and contested spectrum.

Airborne sounding of ice sheets requires large, wing-mounted antenna arrays to effectively filter and suppress the surface clutter that often masks weak bed echoes. However, when a high-sensitivity antenna array is mounted to the wings of an aircraft, the array is subjected to structural dynamics and subsequent deformation. We measured the response of a scaled wing-mounted array when excited at four different vibration frequencies to characterize the effects of airframe vibration on array beamforming and received radar signals. We determined that phase and amplitude errors caused by the expected vibration from the aircraft do not significantly degrade the radiation pattern when the Chebyshev or minimum-variance distortionless response (MVDR) beamformers are used. In the case of the Chebyshev-weighted array, vibrations did not cause pattern sidelobes to vary by more than 1.5 dB. In the case of the minimum-variance-distortionless-response-weighted array, vibrations did cause pattern nulls to shift and decrease in depth, but these pattern distortions were negligible, and did not significantly degrade clutter suppression. In addition, we were able to identify the frequency of vibration as well as the frequency of local structural modes by taking the FFT of the signal's phase.

This paper presents a radar sensor package specifically developed for wide-coverage sounding and imaging of polar ice sheets from a variety of aircraft. Our instruments address the need for a reliable remote sensing solution well-suited for extensive surveys at low and high altitudes and capable of making measurements with fine spatial and temporal resolution. The sensor package that we are presenting consists of four primary instruments and ancillary systems with all the associated antennas integrated into the aircraft to maintain aerodynamic performance. The instruments operate simultaneously over different frequency bands within the 160 MHz-18 GHz range. The sensor package has allowed us to sound the most challenging areas of the polar ice sheets, ice sheet margins, and outlet glaciers; to map near-surface internal layers with fine resolution; and to detect the snow-air and snow-ice interfaces of snow cover over sea ice to generate estimates of snow thickness. In this paper, we provide a succinct description of each radar and associated antenna structures and present sample results to document their performance. We also give a brief overview of our field measurement programs and demonstrate the unique capability of the sensor package to perform multifrequency coincidental measurements from a single airborne platform. Finally, we illustrate the relevance of using multispectral radar data as a tool to characterize the entire ice column and to reveal important subglacial features.

This paper presents the bed topography of Jakobshavn Isbræ, Greenland, and Byrd Glacier, Antarctica, derived from sounding these glaciers with high-sensitivity radars. To understand the processes causing the speed-up and retreat of outlet glaciers, and to enable the development of next-generation ice-sheet models, we need information on bed topography and basal conditions. To this end, we performed measurements with the progressively improved Multichannel Coherent Radar Depth Sounder/Imager (MCoRDS/I). We processed the data from each antenna-array element using synthetic aperture radar algorithms to improve radar sensitivity and reduce along-track surface clutter. We then applied array and image-processing algorithms to extract the weak bed echoes buried in off-vertical scatter (cross-track surface clutter). At Jakobshavn Isbræ, we observed 2.7 km thick ice ~30 km upstream of the calving front and ~850 m thick ice at the calving front. We also observed echoes from multiple interfaces near the bed. We applied the MUSIC algorithm to the data to derive the direction of arrival of the signals. This analysis revealed that clutter is dominated by the ice surface at Jakobshavn Isbræ. At Byrd Glacier, we found ~3.62 km thick ice, as well as a subglacial trench ~3.05 km below sea level. We used ice thickness information derived from radar data in conjunction with surface elevation data to generate bed maps for these two critical glaciers. The performance of current radars must be improved further by ~15 dB to fully sound the deepest part of Byrd Glacier. Unmanned aerial systems equipped with radars that can be flown over lines spaced as close as 5 m apart in the cross-track direction to synthesize a two-dimensional aperture would be ideal for collecting fine-resolution data over glaciers like Jakobshavn near their grounding lines.

In the asphalt&ndash, aggregate system, the aggregate-bitumen interface cohesive and adhesive bond determine the mechanical properties of asphalt pavement. The presence of moisture leading to adhesive failure at the binder-aggregate interface and/or cohesive failure within the binder or binder-filler mastic is the main mechanisms of moisture damage in the spring-thaw season. In order to evaluate the effect of nano hydrophobic silane silica (NHSS) on aggregate-bitumen interface bond strength in the spring-thaw season, an aggregate-bitumen interface bond strength test was proposed to quantify the interface bond strength of base asphalt and NHSS modified asphalt. Then, the effect of temperature, freeze-thawing cycles and moisture on aggregate-bitumen interface shear strength of base asphalt and NHSS modified asphalt was also discussed. The results illustrated that the shear failure dominated the aggregate-bitumen interface bonding failure in the spring-thaw season, and temperature and moisture had a significant effect on interface shear strength of modified and unmodified asphalt. Moreover, the addition of NHSS could increase the aggregate-bitumen interface shear strength under any working conditions. Furthermore, the moisture damage model of aggregate-bitumen interface shear strength of base asphalt (BA) and NHSS modified asphalt was established based on a research method combining numerical calculations and laboratory tests.