Five decades of radioglaciology

Radar sounding is a powerful geophysical approach for characterizing the subsurface conditions of terrestrial and planetary ice masses at local to global scales. As a result, a wide array of orbital, airborne, ground-based, and in situ instruments, platforms and data analysis approaches for radioglaciology have been developed, applied or proposed. Terrestrially, airborne radar sounding has been used in glaciology to observe ice thickness, basal topography and englacial layers for five decades. More recently, radar sounding data have also been exploited to estimate the extent and configuration of subglacial water, the geometry of subglacial bedforms and the subglacial and englacial thermal states of ice sheets. Planetary radar sounders have observed, or are planned to observe, the subsurfaces and near-surfaces of Mars, Earth's Moon, comets and the icy moons of Jupiter. In this review paper, and the thematic issue of the Annals of Glaciology on ‘Five decades of radioglaciology’ to which it belongs, we present recent advances in the fields of radar systems, missions, signal processing, data analysis, modeling and scientific interpretation. Our review presents progress in these fields since the last radio-glaciological Annals of Glaciology issue of 2014, the context of their history and future prospects

Workshop on Science Opportunities for a Multidisciplinary Long-Range Aircraft for Antarctic Research: Program and Abstract Volume

Organizing Committee: Bea Csatho, David H. Bromwich, Michael Studinger, Thomas R. Parish, Robin Muench, and Jeff StithOffice of Polar Programs, National Science Foundatio

NASA Thesaurus. Volume 1: Hierarchical listing

There are 16,713 postable terms and 3,716 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary

NASA thesaurus. Volume 1: Hierarchical Listing

There are over 17,000 postable terms and nearly 4,000 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary and Volume 3 - Definitions

Chemical Impurities and Physical Properties of Polar Ice

The Greenland Ice Sheet and the Antarctic Ice Sheet are the largest reservoirs of freshwater on our planet. They consist of ice which formed over thousands of years out of the precipitation and due to natural densification of snow. As such, polar ice represents a unique archive of the past climate. The large ice masses flow under their own weight causing a transport of ice from the inlands towards the oceans. Numerical flow models are used to simulate the ice dynamics, i. a., in order to project future contributions of the ice sheets to the rising sea level. The viscoplastic deformation of ice on the micro-scale involves similar mechanisms as the deformation of other poly-crystalline materials. The shear of individual crystals is accompanied by recrystallization and the development of characteristic microstructures. Thus, structural-geological concepts and methods can be applied to natural ice samples in order to study their deformation state and active physical processes. Chemical impurities are deposited in snow and ice during the precipitation and reflect the aerosol composition of the atmosphere. As such they play an important role for the reconstructions of the climate of the past. Despite their extremely low concentrations, impurities influence many physical properties of ice, in particular also the deformation rate. The concentrations of the different impurities vary with depth and these variations are correlated with heterogeneities in the flow-velocity profile. This results in the development of localized shear zones in ice. A better understanding of the mechanisms is necessary in order to implement the effect of impurities into the flow models. The presented thesis addresses the relationship between the chemical impurities and the physical properties of polar ice. A central challenge of the project is to understand in which form impurities integrate in ice and where they are located in the bulk, respectively how they interact with it during deformation and recrystallization. A combination of methods for the microstructural analysis was applied to natural ice material from ice cores. The distribution and composition of impurities was analyzed using a confocal cryo-Raman microscope. Within the scope of this thesis, new routines for the acquisition and data processing were developed. The results reveal a complex interplay between impurities, crystal structure and localized deformation in ice. On the one hand, high impurity concentrations cause higher strain rates occurring together with small grain sizes. On the other hand, the deforming ice matrix affects the distribution of impurities and possibly also their chemical composition. The portion of dissociated components in ice could be estimated only qualitatively and through the comparison to the chemical analysis of the meltwater. However, the Raman-spectroscopy data clearly suggest that microscopic inclusions of second phase are present in solid ice in significantly higher concentrations, compared to liquid water. Mixing and chemical reactions of impurities is promoted through the deforming ice matrix. Our image of “ice as a frozen archive” could be replaced by “ice as an effective reactor”, depending on the spatial scales and time spans referred to. The resulting implication for the chrono-stratigraphic integrity of ice-core records may still be positive, because the reaction products often posses lower diffusion rates. A universal mechanism for the impurity effect on ice deformation could not be identified. The localized deformation seems to be in fact an intrinsic property of ice produced by the mechanical anisotropy and triggered by the varying impurity concentrations. However, many questions regarding the form and effect of impurities in ice remain open for future investigations.Der Grönländische und der Antarktische Eisschild sind die größten Süßwasserreservoirs unseres Planeten. Das darin enthaltene Eis bildete sich über Jahrtausende aus dem Niederschlag und durch natürliche Verdichtung von Schnee, und stellt damit ein einzigartiges Klimaarchiv dar. Die großen Eismassen fließen unter ihrem eigenen Gewicht und verfrachten so Eis vom Landesinneren in die Ozeane. Die Eisdynamik wird mithilfe von numerischen Fließmodellen simuliert, u. a. um den zukünftigen Beitrag von Eisschilden zum Meeresspiegelanstieg zu prognostizieren. Die viskoplastische Verformung von Eis auf der Mikroskala involviert ähnliche Mechanismen wie die Deformation anderer polykristalliner Materialen. Die Scherung einzelner Kristalle wird durch Rekristallisation und Bildung bestimmter Mikrostrukturen begleitet. Daher können Konzepte und Vorgehensweisen der Strukturgeologie auf natürliche Eisproben angewandt werden, um ihren Deformationsstatus und die daran beteiligten Prozesse zu studieren. Chemische Spurenstoffe im Schnee und Eis setzen sich mit dem Niederschlag ab und spiegeln die Zusammensetzung der in der Atmosphäre enthaltenen Aerosole wider. Als solche spielen sie eine wichtige Rolle für paläoklimatische Rekonstruktionen. Trotz ihrer extrem niedrigen Konzentrationen beeinflussen Spurenstoffe viele physikalischen Eigenschaften von Eis, insbesondere auch das Deformationsvermögen. Konzentrationschwankungen diverser Spurenstoffkomponenten mit der Tiefe korrelieren mit Heterogenitäten im Fließgeschwindigkeitsprofil und scheinen die Bildung von lokalisierten Scherzonen zu begünstigen. Ein besseres Verständnis dieser Zusammenhänge und der dahinterstehenden Mechanismen ist notwendig um den Effekt von Spurenstoffen realistisch in Fließmodelle implementieren zu können. Die vorgelegte Arbeit befasst sich mit dem Zusammenhang zwischen chemischen Spurenstoffen und physikalischen Eigenschaften von polarem Eis. Eine zentrale Herausforderung ist es zu verstehen, in welcher Form und wo Spurenstoffe in der Eismatrix integriert sind, bzw. wie sie mit ihr während der Deformation und Rekristallisation interagieren. Natürliches Eismaterial aus Eiskernbohrungen wurde mittels einer Kombination verschiedener Methoden zur Mikrostrukturanalyse untersucht. Die Verteilungen und Zusammensetzungen von Spurenstoffen wurden mittels eines konfokalen Kryo-Raman-Mikroskops analysiert. Im Rahmen dieser Arbeit wurden neue Routinen zur Messung und Datenerfassung entwickelt. Die Ergebnisse zeigen ein komplexes Zusammenspiel zwischen Spurenstoffen, Kristallstruktur und lokalisierter Deformation von Eis. Einerseits verursachen hohe Spurenstoffkonzentrationen höhere Deformationsraten, die von feinkörniger Kristallstruktur begleitet werden. Andererseits wird die Verteilung und möglicherweise Zusammensetzung der Spurenstoffe durch die Deformation des Eises beeinflusst. Der Anteil dissoziirter Stoffe im Eis konnte nur qualitativ und indirekt durch den Vergleich der Ramananalyise mit den Ergebnissen einer chemischer Analyse von Schmelzwasser geschätzt werden. Die Ramanspektroskopischen Messungen deuten allerdings klar darauf hin, dass mikroskopische Einschlüsse sekundärer Phasen im Eis einen erheblich höheren Anteil bilden, als im flüssigen Wasser. Das Mischen von Spurenstoffen und chemische Reaktionen zwischen ihnen werden durch die Eisdeformation begünstigt. Unser Bild von “Eis als gefrorenes Archiv” könnte durch “Eis als effektiver Reaktor” ersetzt werden, je nachdem welche zeitlichen und räumlichen Spannen gemeint sind. Die darausfolgende Auswirkung auf die chrono-stratigraphische Integrität von Eiskerndaten ist insgesamt jedoch positiv, da die Reaktionsprodukte oft niedrigere Diffusionsraten besitzen. Ein universeller Mechanismus für die Auswirkung von Spurenstoffen auf die Eisdeformation konnte nicht vollständig aufgedekt werden. Vielmehr scheint Deformationslokalisierung als Folge der mechanischen Anisotropie eine intrinsische Eigenschaft von Eis zu sein, die durch die Variation in Spurenstoffkonzentrationen getriggert wird. Viele Fragen hinsichtlich der Form und Wirkung von Spurenstoffen im Eis stehen allerdings noch offen für zukünftige Forschungsprojekte

7th Annual Jackson School of Geosciences Student Research Symposium, February 3, 2018

ConocoPhillipsGeological Science

NASA thesaurus. Volume 2: Access vocabulary

The Access Vocabulary, which is essentially a permuted index, provides access to any word or number in authorized postable and nonpostable terms. Additional entries include postable and nonpostable terms, other word entries, and pseudo-multiword terms that are permutations of words that contain words within words. The Access Vocabulary contains 40,738 entries that give increased access to the hierarchies in Volume 1 - Hierarchical Listing

NASA thesaurus. Volume 2: Access vocabulary

The access vocabulary, which is essentially a permuted index, provides access to any word or number in authorized postable and nonpostable terms. Additional entries include postable and nonpostable terms, other word entries and pseudo-multiword terms that are permutations of words that contain words within words. The access vocabulary contains almost 42,000 entries that give increased access to the hierarchies in Volume 1 - Hierarchical Listing

NASA Thesaurus. Volume 2: Access vocabulary

The NASA Thesaurus -- Volume 2, Access Vocabulary -- contains an alphabetical listing of all Thesaurus terms (postable and nonpostable) and permutations of all multiword and pseudo-multiword terms. Also included are Other Words (non-Thesaurus terms) consisting of abbreviations, chemical symbols, etc. The permutations and Other Words provide 'access' to the appropriate postable entries in the Thesaurus