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Microwave radars can be used to monitor the internal structure of the snowpack, delivering real-time and non-destructive measurements. Recently, the working principle of an innovative radar architecture able to identify some of the most important snowpack parameters, without external aids, has been demonstrated. A key point of this new architecture is the use of two independent receiving antennas, and one transmitting antenna. This paper presents a comparison between two different implementations, either based on one physical antenna miming two receiving antennas, or based directly on two physical receiving antennas. The different advantages and disadvantages of both solutions are discussed, highlighting the superior accuracy achieved by the implementation based on two physical receiving antennas. Then, this paper also presents the field results achieved by this type of radar architecture, on the grounds of a 5-day experimental campaign that took place in winter 2019 in the Italian Alps on dry snow. The comparison between the radar measurements and the ground truth (manual snowpit analysis, in terms of snowpack depth, dielectric constant, bulk density, and snow water equivalent) is provided. Overall, a root mean square error of around 3.5 cm, 0.05, 27 kg/m3, and 2.5 cm is achieved, respectively.
This chapter contains a broad overview of the technical and environmental issues to be addressed in the construction of onshore wind energy projects. The former include ecological considerations, including birds and mammals; the requirements of typical pre-construction ornithological surveys are described with an example. Public safety and acceptance is discussed in the context of catastrophic damage to wind turbines, visual impact, shadow flicker, and noise nuisance. In the last case, equations and simple rules for noise assessment are given in the context of typical planning guidelines. Sound power levels for a range of commercial wind turbines are compared, and empirical relationships are given relating noise to rated output, rotor size, and tip speed. Risks to aviation are discussed, covering aircraft collision and interference to radar systems, including both primary and secondary surveillance radars. The concept of ‘stealthy’ wind turbine blades is discussed and described in outline. Other siting criteria include avoidance of RF and microwave communications beams and television interference. Rules are given to avoid interference, while minimising required separation distances.
Russian (former Soviet) systematic studies of Antarctica by radio-echo sounding (RES) and ground-penetrating radar technique (GPR) were commenced in 1964. Since that time airborne RES surveys have covered about 5.5 × 106 km2 of the icy continent discovering remarkable geographic objects such as Subglacial Gamburtsev Mountains, and allowed studies of Filchner-Ronne Ice Shelf, Amery Ice Shelf and Lambert Glacier. Ground-based investigations during the 1990s and 2000s revealed the structure of the Lake Vostok area and surveyed along the Mirny to Vostok and Progress to Vostok traverse routes. GPR studies during the 2010s were to select the site for a new snow-runway at Mirny Station, with the resumption of the aviation after a 25 year hiatus.
Recent speleological surveys of meltwater drainage systems in cold and polythermal glaciers have documented dynamic englacial and in some cases subglacial conduits formed by the ‘cut-and-closure’ mechanism. Investigations of the spatial distribution of such conduits often require a combination of different methods. Here, we studied the englacial drainage system in the cold glacier Longyearbreen, Svalbard by combining speleological exploration of a 478 m long meltwater conduit with a high-resolution ground penetrating radar (GPR) survey with two different centre-frequencies (25 and 100 MHz). The results yielded a 3-D documentation of the present englacial drainage system. The study shows that the overall form of englacial conduits can be detected from velocity−depth converted GPR data, and that the 3-D model can facilitate a method to pinpoint the reflections in a radargram corresponding with the englacial drainage system, although fine detail cannot be resolved. Visible reflections approximately parallel to the mapped englacial water drainage system likely result from sediment incorporated in the ice or from abandoned parts of the englacial drainage system.
Recent geophysical remote sensing, including ground-penetrating radar and magnetometry, has been used to investigate three areas within Chaco Canyon, New Mexico, predicted to contain prehispanic agricultural fields. These localities include a well-known but enigmatic area of large grid patterns near the Chetro Ketl great house, which are visible from the air but not at ground level. The gridded area has been interpreted by many researchers as an agricultural field system, and this perspective has in turn been utilized to model agricultural land use throughout the canyon, particularly intensification associated with emergent social complexity. The geophysical surveys revealed evidence of buried features at all three study areas, but the patterns expressed by these features do not clearly conform to the pattern predicted in the gridded agricultural field model. We argue that the surficial grid pattern seen at the Chetro Ketl field is an unusual example of land modification in the canyon and thus unlikely to represent typical Chacoan agricultural field systems. Instead, canyon residents employed a diverse range of agricultural techniques suited to the variable and patchy nature of canyon hydrology and soils.
The accumulation region of Fedchenko Glacier represents an extensive snow reservoir in the Pamir Mountains feeding the longest glacier in Central Asia. Observed elevation changes indicate a continuous ice loss in the ablation region of Fedchenko Glacier since 1928, while the mass balance of the accumulation region is largely unknown. In this study, we show that accumulation varies considerably in the main accumulation basin, with accumulation rates up to 2400 mm w.e. a−1 in the West, decreasing to <1000 mm w.e. a−1 in the center, although the elevation difference is <200 m. The combination of snow/firn samples and ground-penetrating radar profiles suggests that this accumulation pattern is persistent during the recent past. The recent accumulation history is reconstructed from internal radar reflectors using a firn densification model and shows strong interannual variations, but near constant mean values since 2002. Modeling of trajectories, based on accumulation and glacier geometry, results in an estimate of the depth/age relation close to the main divide. This region provides one of the most suitable locations for retrieving climate information with temporal high resolution for the last millennium, with a potential to cover most of the Holocene in less detail.
Ground-penetrating radar data acquired in the 2016/17 austral summer on Sørsdal Glacier, East Antarctica, provide evidence for meltwater lenses within porous surface ice that are conceptually similar to firn aquifers observed on the Greenland Ice Sheet and the Arctic and Alpine glaciers. These englacial water bodies are associated with a dry relict surface basin and consistent with perennial drainage into an interconnected englacial drainage system, which may explain a large englacial outburst flood observed in satellite imagery in the early 2016/17 melt season. Our observations indicate the rarely-documented presence of an englacial hydrological system in Antarctica, with implications for the storage and routing of surface meltwater. Future work should ascertain the spatial prevalence of such systems around the Antarctic coastline, and identify the degree of surface runoff redistribution and storage in the near surface, to quantify their impact on surface mass balance.
In this chapter, a conservation of mass approach is used to develop a broad picture of the flow field in a glacier or ice sheet. Vertical velocities are shown to be downward in the accumulation area and upward in the ablation area, and horizontal velocities to increase with distance from the head of the glacier, reaching a maximum just below the equilibrium line. Conservation of momentum is then used to calculate the variation, with depth of horizontal and vertical velocity. Effects of valley sides and laterally non-uniform basal boundary conditions on the flow field are explored. Next patterns of internal reflectors imaged by radar are shown to reflect variations in effective strain rate and ice fabric. The reflectors can also be used to measure vertical strain rates and sub-ice shelf melt rates, and to document changes in the flow field over millennial time scales. Drifting snow also affects the flow field in polar environments, leading to development of narrow accumulation zones along the margin, and thus to formation of ice-cored moraines somewhat upglacier from the margin. Finally, inhomogeneous bed conditions beneath ice sheets can lead to streaming flow.
This study presents the first subglacial topography and ice thickness models of the largest ice caps of the Argentine Islands, Wilhelm Archipelago, West Antarctica. During this study, ground-penetrating radar was used to map the thickness and inner structure of the ice caps. Digital surface models of all studied islands were created from aerial images obtained with a small-sized unmanned aerial vehicle and used for the construction of subglacial topography models. Ice caps of the Argentine Islands cover ~50% of the land surface of the islands on average. The maximum thickness of only two islands (Galindez and Skua) exceeds 30 m, while the average thickness of all islands is only ~5 m. The maximum ice thickness reaches 35.3 m on Galindez Island. The ice thickness and glacier distribution are mainly governed by prevailing wind direction from the north. This has created the prominent narrow ice ridges on Uruguay and Irizar islands, which are not supported by topographic obstacles, as well as the elongated shape of other ice caps. The subglacial topography of the ice caps is undulated and mainly dependent on the geological structure and composition of magmatic rocks.
This chapter reviews key findings from analyses of spectral reflectance measurements of Mercury taken by the MESSENGER mission. Mercury’s crust lacks the 1-µm crystal field absorption due to ferrous iron that is common on other silicate bodies, yet is unusually low in reflectance. The most likely darkening phase is carbon as graphite. Variations in reflectance and color reveal that volcanic plains averaging >5 km in thickness overlie graphite-rich low-reflectance material, which may have originated as a graphite flotation crust from a magma ocean. The one unambiguous absorption due to an oxidized transition metal, an ultraviolet oxygen–metal charge transfer band in bright, pyroclastic deposits, may originate by oxidation of carbon and sulfides, reducing 0.3–1 wt.% ferrous iron in silicates to a metallic state, unsaturating the very strong oxygen–metal charge transfer band.
The advent of multiple orbital and in situ missions to planetary bodies beyond Earth has enabled characterization of extraterrestrial shallow crustal processes. We describe examples of interpreting geochemical, isotopic, and radar properties from multiple remote datasets, supplemented with in situ observations from rovers and landers, meteorites, and lunar samples. Given the availability of distinct data types and the relevance to bulk-silicate bodies in the Solar System, we present five case studies for the Moon and Mars. The first involves lunar magmatic processes in relation to TiO2 and radargram-derived physical properties. Next, O and Fe isotope variations relative to the Mg number provide insight into the degree of fractional crystallization in lunar lava flows. Physical mixing of endmembers and chemical weathering processes in Gusev crater soil on Mars are discussed. Effective use of the Chemical Index of Alteration (CIA) is also considered by comparing mineralogic observations across Mars with terrestrial references. Lastly, the nature of bulk soil hydration on Mars is described by assessing chemical variations with Principal Component Analysis (PCA). This chapter describes in situ analyses and mapping across local and regional scales. Data synthesis also involves contrasting depth scales from tens of microns to multiple kilometers.
Radar has proven to be a powerful tool in planetary exploration. Most of the major solid bodies of the Solar System have been observed with radar, either from Earth or from spacecraft. Planetary radar studies are reviewed in this chapter, with information on the various techniques of radar remote sensing provided along with key results. Recent radar results are emphasized. Concluding remarks are provided on future directions in planetary radar remote sensing.
Imaging radars are all-weather instruments that can image planetary surfaces regardless of local atmospheric or solar illumination conditions. Radar images provide information about surfaces that are complementary to the chemistry usually inferred from visible and infrared images. Instead, radar images are strongly influenced by surface roughness and geomorphology, and to a lesser extent by the bulk electrical properties of the surface. This chapter describes the basic principles of high-resolution synthetic aperture radars (SARs), as well as advanced SAR implementations. Radar polarimetry provides information about surface roughness and electrical properties, while radar interferometry allows the measurement of surface topography and surface deformation following events such as earthquakes or volcanic inflation. Radar imagers have returned spectacular information about the surfaces of both Venus and Titan, bodies with dense, opaque atmospheres that are difficult to image using traditional camera systems. Examples of both planetary and Earth observations with SAR are discussed to illustrate the utility of these images.
Mount Achernar moraine is a terrestrial sediment archive that preserves a record of ice-sheet dynamics and climate over multiple glacial cycles. Similar records exist in other blue ice moraines elsewhere on the continent, but an understanding of how these moraines form is limited. We propose a model to explain the formation of extensive, coherent blue ice moraine sequences based on the integration of ground-penetrating radar (GPR) data with ice velocity and surface exposure ages. GPR transects (100 and 25 MHz) both perpendicular and parallel to moraine ridges at Mount Achernar reveal an internal structure defined by alternating relatively clean ice and steeply dipping debris bands extending to depth, and where visible, to the underlying bedrock surface. Sediment is carried to the surface from depth along these debris bands, and sublimates out of the ice, accumulating over time (>300 ka). The internal pattern of dipping reflectors, combined with increasing surface exposure ages, suggest sequential exposure of the sediment where ice and debris accretes laterally to form the moraine. Subsurface structure varies across the moraine and can be linked to changes in basal entrainment conditions. We speculate that higher concentrations of debris may have been entrained in the ice during colder glacial periods or entrained more proximal to the moraine sequence.
This paper presents a comparative cyber security resilience estimation of shipboard radars that are implemented on two oil/chemical tankers certified as SOLAS ships. The estimated radars were chosen from the same manufacturer, but belonged to different generations. The estimation was conducted by means of ships' crew interviews and computational testing of the radars using a widely deployed vulnerability scanning software tool. The identified cyber threats were analysed qualitatively in order to gain a holistic understanding of cyber risks threatening shipboard radar systems. The results obtained experimentally indicate that potential cyber threats mainly relate to maintenance of the radars' underlying operating system, suggesting the need for regulatory standardisation of periodic cyber security testing of radar systems.
How landscapes respond to, and evolve from, large jökulhlaups (glacial outburst floods) is poorly constrained due to limited observations and detailed monitoring. We investigate how melt of glacier ice transported and deposited by multiple jökulhlaups during the 2010 eruption of Eyjafjallajökull, Iceland, modified the volume and surface elevation of jökulhlaup deposits. Jökulhlaups generated by the eruption deposited large volumes of sediment and ice, causing significant geomorphic change in the Gígjökull proglacial basin over a 4-week period. Observation of these events enabled robust constraints on the physical properties of the floods which informs our understanding of the deposits. Using ground-based LiDAR, GPS observations and the satellite-image-derived ArcticDEMs, we quantify the post-depositional response of the 60 m-thick Gígjökull sediment package to the meltout of buried ice and other geomorphic processes. Between 2010 and 2016, total deposit volume reduced by −0.95 × 106 m3 a−1, with significant surface lowering of up to 1.88 m a−1. Surface lowering and volumetric loss of the deposits is attributed to three factors: (i) meltout of ice deposited by the jökulhlaups; (ii) rapid melting of the buried Gígjökull glacier snout; and (iii) incision of the proglacial meltwater system into the jökulhlaup deposits.
While large-scale observations of intensified fracture and rifting can be observed through remote-sensing observations, understanding crevasse initiation may best be achieved with small-scale observations in which crevasses can be directly observed. Here we investigate the kinematic drivers of crevasse initiation in the McMurdo Shear Zone (MSZ), Antarctica. We delineated 420 crevasses from ~95 km of 400 MHz frequency ground-penetrating radar data and compared these data with kinematic outputs derived from remotely-sensed ice surface velocities to develop a statistical method to estimate crevasse initiation threshold strain rate values. We found the MSZ to be dominated by simple shear and that surface shear strain rates proved best for predicting crevasse features, with regions of higher shear strain rate more likely to have a greater number of crevasses. In the surveyed portion of our study region, values of shear strain rate and vorticity rate derived from the MEaSUREs2 velocity dataset range between 0.005–0.020 and 0.006–0.022 a−1, respectively, with crevasses located at ≥0.011 and ≥0.013 a−1. While threshold values from this study cannot be directly applied to other glacial environments, the method described here should allow for the study of shear margin evolution and assessment of localized damage and weakening processes in other locations where in situ data are available.