of the scientific community on this type of system increased in the last few years . This is due to the need to answer questions related to the recent climate change and to predict its evolution in the near future. Indeed, an orbital RS can provide important information on the state of Earth polar regions. Moreover, it can probe Earth arid areas from space, thereby giving a new sight on the evolution of such environments and mapping buried aquifers. The main advantages of orbital RSs with respect to airborne and ground-based campaigns is that data acquired from orbit can reveal the subsurface structure of the Earth with unprecedented coverage, sampling and homogeneity. In 2010 we collaborated to the definition of the proposal to ESA of the Glaciers and Icy Environments Sounding mission (GLACIES) . At the time of writing, another mission proposal is the Orbiting Arid Subsurface and Ice Sheet Sounder (OASIS), leaded by the NASA’s Jet Propulsion Laboratory (JPL) in collaboration with the Italian Space Agency (ASI) . All the aforementioned missions, both for planetary exploration and EO, provide/will provide a huge amount of data. This poses the problem of the processing of such data, which in most cases is still carried out according to manual visual inspection. In this context, it is mandatory to develop advanced techniques that can automatically analyze and extract information from the data for properly supporting the scientific community.
Regarding the coverage that can be achieved with a RS instrument, the wave deep penetation capability contributes to building the vertical coverage of the ice subsurface. The motion of the platform that carries the RS instrument contributes to building the ice surface coverage in the horizontal direction. Therefore, the amount of recorded RS data mainly depends on the RS instrument parameters and platform motion. So far, RSs for Earth Observation (EO) have been operated only during dedicated airborne campaigns at the Earth polar regions. Spaceborne RSs have been designed only for the observation of other planetary bodies, e.g., Moon (Lunar Radar Sounder (LRS) ), Mars (SHAllow RADar (SHARAD) , Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) ), Jovian Icy Moons (Radar for Icy Moon Exploration (RIME) , currently under development). Although the design of Earth orbiting RS instruments is very chal- lenging (mainly due to physical constraints and frequency allocation issues), the success of the existing planetary RS instruments have encouraged dedicated studies for defining EO RS missions from space (e.g., Mapping of antarctic Ice and MOnitoring of SubArctic (MIMOSA) , , GLACiers and Icy Environments Sounding (GLACIES) ). Once operative, such EO spacebased RS instruments will acquire data with homogeneous qual- ity and uniform coverage, both spatially and temporally. This is not the case with the existing airborne RS data. Science requirements and technological constraints drive data acquisition strategy plans (e.g., location, coverage) and condition the data quality (e.g., maximum penetration, resolution). Therefore, the RS data acquired during different air- borne campaigns have a limited coverage and heterogeneous quality. However, during the past decades a large amount of airborne RS data has been acquired and the volume of data is expected to increase during future airborne and forthcoming satellite EO RS missions.
ideal region to show how effectively impact structure mapping can be extended to regional stratigraphy. A decision-tree mapping algorithm can be constructed for the Haughton structure as suggested in Chapter 2, and then a regional-scale remote predictive map can be produced by combining the Pauli decomposition mosaic (or surface roughness map) and spectral maps by Landsat and ASTER data covering central Devon Island into the decision- tree mapping algorithm. The geological units exposed in the Haughton structure can be compared to the regional bedrocks where they originated from. In addition to classifying geological units, polarimetric SAR can quantitatively assess the weathering and deposition processes in the Canadian Arctic by producing the surface roughness map. Northwestern Victoria Island reveals extensive glacial striation features toward Richard Collinson Inlet and Wynniatt Bay from Shaler Mountains. This indicates that glacial movement on the way to the Richard Collinson Inlet has deeply eroded the Tunnunik impact structure, which is quite distinct from the well-preserved Haughton structure. Thus, it is necessary to extract the glacial striation features on the SAR image using an automated lineament extraction algorithm (e.g., Wang and Howarth, 1990), and investigate how they effect the surface roughness. It would also be worthwhile to compare the difference in surface roughness between northwestern Victoria Island and central Devon Island. Furthermore, melting of snow cover and glaciers accelerated by rapid and ongoing climate change in the Arctic (Otto-Bliesner, 2006; Overpeck et al., 1997) and its subsequent surface changes in morphology, roughness, and moisture can be monitored by time-series mapping of polarimetric SAR.
Hurd and Johnsons glaciers are located in Hurd Peninsula, Livingston Island, the second largest island of the South Shetland Islands (SSI) archipelago (Fig. 1). Johnsons is a tidewater glacier, calving small icebergs into the proglacial bay known as Johnsons Dock, while the fronts of the var- ious tongues of Hurd Glacier (Argentina, Las Palmas and Sally Rocks) are land-terminating. The three unnamed small sea-terminating glacier basins draining to False Bay, to the south-east of Hurd Peninsula (U1, U2, U3 in Fig. 1), which are very steep and heavily crevassed, are not covered in the current study. Johnsons and Hurd glaciers are polythermal, though Johnsons, as compared with Hurd, has a higher pro- portion of temperate ice (Navarro et al., 2009). Typical ve- locities near the calving front of Johnsons Glacier are about 50 m yr −1 (Rodríguez, 2014), whereas maximum velocities in Hurd Glacier are reached in its central zone, and are typ- ically around 5 m yr −1 (Molina, 2014), decreasing towards the terminal zones, which have been suggested to be frozen to bed on the basis of ground-penetrating radar studies, glacier velocities and geomorphological evidences (Navarro et al., 2009; Molina et al., 2007). The annual average temperature at Juan Carlos I Station (12 m a.s.l., in Hurd Peninsula) be- tween 1988 and 2011 was − 0.9 ◦ C, with average summer (DJF) and winter (JJA) temperatures of 2.4 and − 4.4 ◦ C, respectively (Osmanoglu et al., 2014). The main glaciolog- ical studies in Hurd Peninsula include cartography of vol- canic ash layers (Palà et al., 1999; Ximenis, 2001; Molina, 2014), shallow ice coring (Furdàda et al., 1999), numerical modeling of glaciers dynamics (Martín et al., 2004; Otero et al., 2010), analysis of glacier volume changes 1957–2000 (Molina et al., 2007), seismic and ground-penetrating radar surveys (Benjumea et al., 1999, 2001, 2003; Navarro et al., 2005, 2009), modeling of melting (Jonsell et al., 2012), mass- balance observations (Ximenis et al., 1999; Ximenis, 2001; Navarro et al., 2013) and geomorphological and glacier dy- namics studies (Ximenis et al., 2000; Molina, 2014). Glacio- logical studies covering the whole Livingston Island include the analysis of Livingston ice cap front position changes 1956–1996 (Calvet et al., 1999), ground-penetrating radar surveys (Macheret et al., 2009) and estimates of ice discharge to the ocean (Osmanoglu et al., 2014). The latter study also includes ice-cap-wide mass balance estimates and ice veloc- ity fields determined from satellite synthetic aperture radar measurements.
Abstract. There is significant uncertainty regarding the spa- tiotemporal distribution of seasonal snow on glaciers, de- spite being a fundamental component of glacier mass bal- ance. To address this knowledge gap, we collected repeat, spatially extensive high-frequency ground-penetrating radar (GPR) observations on two glaciers in Alaska during the spring of 5 consecutive years. GPR measurements showed steep snow water equivalent (SWE) elevation gradients at both sites; continental Gulkana Glacier’s SWE gradient av- eraged 115 mm 100 m −1 and maritime Wolverine Glacier’s gradient averaged 440 mm 100 m −1 (over > 1000 m). We ex- trapolated GPR point observations across the glacier sur- face using terrain parameters derived from digital elevation models as predictor variables in two statistical models (step- wise multivariable linear regression and regression trees). El- evation and proxies for wind redistribution had the great- est explanatory power, and exhibited relatively time-constant coefficients over the study period. Both statistical models yielded comparable estimates of glacier-wide average SWE (1 % average difference at Gulkana, 4 % average difference at Wolverine), although the spatial distributions produced by the models diverged in unsampled regions of the glacier, particularly at Wolverine. In total, six different methods for estimating the glacier-wide winter balance average agreed within ±11 %. We assessed interannual variability in the spa- tial pattern of snow accumulation predicted by the statistical models using two quantitative metrics. Both glaciers exhib- ited a high degree of temporal stability, with ∼ 85 % of the glacier area experiencing less than 25 % normalized abso-
Different animal species, such as dolphins and bats, rely on echolocation for foraging and navigation. Their bio-sonars characteristics and processing scheme share many sim- ilarities with the strategies being adopted in radar sounders design and operations. As an example, some bat species transmit linear frequency modulated signals  and adapt the time between each signal transmission according to the target distance . When hunting preys, bats usually fly in complex environments such as canopies of forests. This suggests that their sonar system should be capable of dealing with unwanted echoes com- ing from the surroundings [67, 68, 69]. Moreover, big brown bats need to face a given prey with their mouth. This implies that their targets will always be oriented toward nadir direction. It is therefore clear that a radar sounder and a big brown bat share a similar acquisition geometry (Fig. 3.1) even if in very different scenarios. Bates et al.  made a major step forward in unveiling the processing scheme of big brown bats (Eptesicus Fuscus) that is associated with their remarkable clutter mitigation performance. The main concept behind the Eptesicus Fuscus clutter reduction technique is to exploit fre- quency diversity. Big brown bats modulate two different harmonics over the same linear frequency modulated signal. The pattern beam-width (i.e. spatial distribution of the transmitted energy) is frequency dependent and narrower for the higher harmonic with respect to the fundamental one. Moreover, the signal attenuation due to atmospheric effects is frequency dependent too. By performing the ratio of the echo power between the two harmonics big brown bats can predict the echo direction of arrival and range. In the present study, we successfully adapt and implement the Eptesicus Fuscus clutter mitigation mechanism to radar geophysical exploration of planetary bodies. We develop a clutter detection model inspired by the bats processing strategy and tailored to the specific case of radar subsurface sounding. This results in a model that provides simple physical conditions for which clutter ambiguities can be resolved. We then apply the proposed bio-inspired model to experimental data acquired over different regions of Mars to assess the effectiveness of the presented approach.
On the other hand, the glacier volumes calculated form GPR-retrieved ice-thickness data are also useful to calibrate the free parameters of the physically-based models relating the ice-thickness distribution with the glacier topography, mass balance and dynamics. These models are the alternative to the V-A relationships to calculate the volume of large populations of glaciers. Moreover, as mentioned earlier, these two families of methods are a usual tool for regional and global projections of mass losses from glaciers, and corresponding sea-level rise, in response to climate scenarios. Finally, the estimate of the total volume of the entire population of glaciers on Earth provides the knowledge of its potential contribution to sea-level rise and allows predicting for how long glaciers will continue to be the largest contributors to sea-level rise.
Abstract—Speckle noise in interferometric synthetic aperture radar (InSAR) phase images seriously degrades the quality of interferogram, disenables interferogram to reflect accurate phase characteristics of the target and increases the difficulty in extracting DEM information of the target area. Therefore, reducing speckle noise by interferogram filtering is a significant step in InSAR processing. First, a noise-included interferometric SAR phase image is simulated based on a terrain model and geometrical parameters of InSAR system. The phase image can be characterized by multilook phase distribution. Then, three interferogram filtering algorithm are explored to remove speckle noise: Goldstain filter, rotating kernel transformation and Lee filter. Proper implementation of three methods is given. Based on experimental results, performances of three different methods are compared. Two aspects need to be comprehensively considered in noise reduction process: the required accuracy in practical application and the processing duration. And also second- time or multiple combined noise reduction is highly recommended.
Auge describes an essentially atomised culture, in which grand narratives have ceased to operate to homogenise culture, a super-modernity in which each member is left to make his own sense of the myriad information which the modern world makes accessible to him. By this analysis, urban explorers are those who have chosen to make meaning out of abandoned places, whilst others might choose to put their energies into stamp collecting, religion or fashion or any other pass-time, belief or interest to give their world meaning. Auge‟s thesis thus offers an explanation of the taxonomic urges of urban exploration – yet linking it with modern urban alienation in the spirit of Simmel (2009 – written 1903). Blain and Wallis (2009) echo this theme when pointing to the active contemporary investment of meaning in the past (in their case stone circles) as a form of „Orientalism‟, an active celebration of an exotic „other‟ in order to rise above the ‟drab present‟ (2009: 99).
implementation of LAPS we used A = 315 and b = 1.5 for liquid precipitation, which is relevant in this study carried out during the summer period. This is a gross simplifica- tion since the drop size and particle shapes vary according to weather situation (drizzle/convective, wet snow/snow grain), as described in Sect. 2.2. Problematic situations include both convective showers with heavy rainfall and the opposite case of drizzle with little precipitation. Although such situations contribute only a fraction of the annual precipitation amount, they might be important during, e.g. flooding events. On the other hand, the same factors have been used for many years in FMI’s other operational radar products, and looking at long- term averages, the radar accumulation data match the gauge accumulation values within reasonable accuracy (Aaltonen et al., 2008). After correcting for vertical profile of reflec- tivity (Sect. 2.2), mainly due to major sampling differences between the two sensors, random errors remain at 2–3 dB, which is a typical, reasonably accurate figure in operational radar measurements (Koistinen et al., 2003; Collier, 1986).
Abstract. Polythermal ice sheets and glaciers contain both cold ice and temperate ice. We present two new models to de- scribe the temperature and water content of such ice masses, accounting for the possibility of gravity- and pressure-driven water drainage according to Darcy’s law. Both models are based on the principle of energy conservation; one addition- ally invokes the theory of viscous compaction to calculate pore water pressure, and the other involves a modification of existing enthalpy gradient methods to include gravity-driven drainage. The models self-consistently predict the evolution of temperature in cold ice and of water content in temper- ate ice. Numerical solutions are described, and a number of illustrative test problems are presented, allowing compari- son with existing methods. The suggested models are simple enough to be incorporated in existing ice-sheet models with little modification.
Second, it provides formal explanation for why DE via conjugate policies is effective in NPG methods. Our theo- retical results show that: (1) maximizing the diversity (in terms of KL divergence) among perturbed policies is in- versely related to the variance of the perturbed gradient esti- mate, contributing to more accurate policy updates; and (2) conjugate policies generated by conjugate vectors maximize pairwise KL divergence among a constrained number of per- turbations. In addition to justifying DE via conjugate poli- cies, these theoretical results explain why parameter space noise (Plappert et al. 2018) improves upon NPG methods but is not optimal in terms of the maximum diversity objec- tive proposed in this work.
It is clear that calving glaciers and ice sheets make a large contribution to sea-level rise, but much uncertainty remains about future ice sheet response to alternative carbon futures. The foremost source of uncertainty is the West Antarctic Ice Sheet, parts of which appear to have already embarked on a process of irreversible retreat . Future rates of ice loss will depend critically on ice shelf response to atmospheric and oceanic forcing, and what happens once buttressing ice shelves are lost and ice-cliﬀ instability kicks in [37,116]. Potentially, this will entail behaviour well beyond the observed range, involving complex interactions between frac- turing, ﬂow of damaged ice, calving, and marine processes. Meeting the challenge of predicting this behaviour will require an integrated approach, drawing upon all available and developing tools, from high-resolution explicit models to the simple calving laws required for long-term simula- tions of ice-sheet evolution.
Basal water plays a central role in the surge mechanism, but observations have not been conclusive about where it comes from. A surge (or mini-surge) can be due to the release of water stored englacially/subglacially or supplied within a short period due to strong ablation or intense rainfall. On many glaciers it has been observed that enhanced water in- put leads to enhanced ice velocities during a limited period of time (e.g. Iken and Bindschadler, 1986; Anderson et al., 2004; Van de Wal et al., 2008). Large glaciers in Svalbard show sudden accelerations in flow even during winter (Dunse et al., 2011), and these can only be explained by water which suddenly finds its way to a larger area of the glacier bed and facilitates sliding by increasing water pressures.