Flow dynamics of an accumulation basin: a case study of upper Kahiltna Glacier, Mount McKinley, Alaska

We interpreted flow dynamics of the Kahiltna Pass Basin accumulation zone on Mount McKinley, Alaska, USA, using 40, 100 and 900 MHz ground-penetrating radar profiles and GPS surface velocity measurements. We found dipping, englacial surface-conformable strata that experienced vertical thickening as the glacier flowed westward from a steep, higher-velocity (60 m a–1) region into flat terrain associated with a 908 bend in the glacier and lower velocities (15 m a–1) to the south. Stratigraphy near the western side of the basin was surface-conformable to 170 m depth and thinned as flow diverged southward, down-glacier. We found complex strata beneath the conformable stratigraphy and interpret these features as buried crevasses, avalanche debris and deformed ice caused by up-glacier events. We also suggest that basin dimensions, bed topography and the sharp bend each cause flow extension and compression, significantly contributing to conformable and complex strata thickness variations. Our findings show that surface-conformable stratigraphy continuous with depth and consistent strata thicknesses cannot be assumed in accumulation basins, because local and upglacier terrain and flow dynamics can cause structural complexities to occur under and within surfaceconformable layers

Simulated recovery of Europa's global shape and tidal Love numbers from altimetry and radio tracking during a dedicated flyby tour

The fundamental scientific objectives for future spacecraft exploration of Jupiter's moon Europa include confirmation of the existence of subsurface ocean beneath the surface ice shell and constraints on the physical properties of the ocean. Here we conduct a comprehensive simulation of a multiple-flyby mission. We demonstrate that radio tracking data can provide an estimate of the gravitational tidal Love number k2 with sufficient precision to confirm the presence of a liquid layer. We further show that a capable long-range laser altimeter can improve determination of the spacecraft position, improve the k2 determination (2 (3-4% error), which is directly related to the amplitude of the surface tidal deformation. These measurements, in addition to the global shape accurately constrained by the long altimetric profiles, can yield further constraints on the interior structure of Europa. Key Points A multiple-flyby mission to Europa can recover key geophysical parameters Laser altimetry can uniquely and accurately recover the global shape of Europa Laser altimetry enables the recovery of h2 to constrain the ice shell thicknes

Fuzzy heterogeneous neurons for imprecise classification problems

In the classical neuron model, inputs are continuous real-valued quantities. However, in many important domains from the real world, objects are described by a mixture of continuous and discrete variables, usually containing missing information and uncertainty. In this paper, a general class of neuron models accepting heterogeneous inputs in the form of mixtures of continuous (crisp and/or fuzzy) and discrete quantities admitting missing data is presented. From these, several particular models can be derived as instances and different neural architectures constructed with them. Such models deal in a natural way with problems for which information is imprecise or even missing. Their possibilities in classification and diagnostic problems are here illustrated by experiments with data from a real-world domain in the field of environmental studies. These experiments show that such neurons can both learn and classify complex data very effectively in the presence of uncertain information.Peer ReviewedPostprint (author's final draft

Overcoming the Challenges Associated with Image-based Mapping of Small Bodies in Preparation for the OSIRIS-REx Mission to (101955) Bennu

The OSIRIS-REx Asteroid Sample Return Mission is the third mission in NASA's New Frontiers Program and is the first U.S. mission to return samples from an asteroid to Earth. The most important decision ahead of the OSIRIS-REx team is the selection of a prime sample-site on the surface of asteroid (101955) Bennu. Mission success hinges on identifying a site that is safe and has regolith that can readily be ingested by the spacecraft's sampling mechanism. To inform this mission-critical decision, the surface of Bennu is mapped using the OSIRIS-REx Camera Suite and the images are used to develop several foundational data products. Acquiring the necessary inputs to these data products requires observational strategies that are defined specifically to overcome the challenges associated with mapping a small irregular body. We present these strategies in the context of assessing candidate sample-sites at Bennu according to a framework of decisions regarding the relative safety, sampleability, and scientific value across the asteroid's surface. To create data products that aid these assessments, we describe the best practices developed by the OSIRIS-REx team for image-based mapping of irregular small bodies. We emphasize the importance of using 3D shape models and the ability to work in body-fixed rectangular coordinates when dealing with planetary surfaces that cannot be uniquely addressed by body-fixed latitude and longitude.Comment: 31 pages, 10 figures, 2 table

Stacking the Odds for Better GPR: An Antenna Comparison

Ground penetrating radar (GPR) is limited by depth penetration and signal-to-noise ratio (SNR), impacting the ability to resolve subsurface features. Stacking, a process of averaging multiple scans in the same location, improves SNR. Digital antennas are capable of stacking at much higher rates than analog antennas. Four sites were examined using a GSSI SIR-4000 GPR unit with a 400 MHz analog antenna and a 350 MHz digital “hyperstacking” (350 HS) antenna. Sites represent various soil conditions, with known features. Data were compared qualitatively and quantitatively for differences in antenna outputs. Visual inspection of radargrams indicate a reduction in noise in the 350 HS data compared to the 400 MHz data. Quantitative assessments identified significant differences in standard deviation of radar reflection amplitude occurring at depth with both antennas and a reduction in noise and marginal increases in depth of penetration in low-loss conditions with the 350 MHz HS antenna

Geology orbiter comparison study

Instrument requirements of planetary geology orbiters were examined with the objective of determining the feasibility of applying standard instrument designs to a host of terrestrial targets. Within the basic discipline area of geochemistry, gamma-ray, X-ray fluorescence, and atomic spectroscopy remote sensing techniques were considered. Within the discipline area of geophysics, the complementary techniques of gravimetry and radar were studied. Experiments using these techniques were analyzed for comparison at the Moon, Mercury, Mars and the Galilean satellites. On the basis of these comparative assessments, the adaptability of each sensing technique was judged as a basic technique for many targets, as a single instrument applied to many targets, as a single instrument used in different mission modes, and as an instrument capability for nongeoscience objectives

Surface networks

© Copyright CASA, UCL. The desire to understand and exploit the structure of continuous surfaces is common to researchers in a range of disciplines. Few examples of the varied surfaces forming an integral part of modern subjects include terrain, population density, surface atmospheric pressure, physico-chemical surfaces, computer graphics, and metrological surfaces. The focus of the work here is a group of data structures called Surface Networks, which abstract 2-dimensional surfaces by storing only the most important (also called fundamental, critical or surface-specific) points and lines in the surfaces. Surface networks are intelligent and “natural ” data structures because they store a surface as a framework of “surface ” elements unlike the DEM or TIN data structures. This report presents an overview of the previous works and the ideas being developed by the authors of this report. The research on surface networks has fou

Flow Dynamics of an Accumulation Basin: A Case Study of Upper Kahiltna Glacier, Mount McKinley, Alaska

We interpreted flow dynamics of the Kahiltna Pass Basin accumulation zone on Mount McKinley, Alaska, USA, using 40, 100 and 900 MHz ground-penetrating radar profiles and GPS surface velocity measurements. We found dipping, englacial surface-conformable strata that experienced vertical thickening as the glacier flowed westward from a steep, higher-velocity (60 m a−1) region into flat terrain associated with a 90° bend in the glacier and lower velocities (15 m a−1) to the south. Stratigraphy near the western side of the basin was surface-conformable to ∼170 m depth and thinned as flow diverged southward, down-glacier. We found complex strata beneath the conformable stratigraphy and interpret these features as buried crevasses, avalanche debris and deformed ice caused by up-glacier events. We also suggest that basin dimensions, bed topography and the sharp bend each cause flow extension and compression, significantly contributing to conformable and complex strata thickness variations. Our findings show that surface-conformable stratigraphy continuous with depth and consistent strata thicknesses cannot be assumed in accumulation basins, because local and up-glacier terrain and flow dynamics can cause structural complexities to occur under and within surface-conformable layers

3D Restoration of the Sugar Hollow Rift Basin Blue Ridge, Virginia

The tectonic processes of supercontinent breakup create rift structures that are often preserved along the passive margin of continents. The resultant structures and rocks are the foundation from which collisional orogenic structures are eventually created. At Sugar Hollow, 15km northwest of Charlottesville, Virginia, ancient Iapetan rift structures are preserved on the eastern margin of Laurentia in the Virginia Blue Ridge. This location preserves a ~10km2 eastward-thickening graben complex consisting of 8 originally-normal faults that reaches a maximum thickness of ~300m. Some of the 8 faults were reactivated past the null point during the Paleozoic producing apparent thrust geometry. To better understand the original structures that accommodated the opening of the Iapetan Ocean at the close of the Neoproterozoic, the basin was restored to its post-rift state using Midland Valley\u27s Move software. During this process, layers were unfolded and fault blocks were restored to their maximum extensional state, revealing ~12% shortening. However, penetrative ductile deformation was not accounted for during this restoration. Therefore, strain and vorticity analysis were used to better understand the intensity and geometry of ductile deformation across the basin. Using this data, a fully restored 3D model of the Sugar Hollow basin was created. This model revealed additional shortening of ~13%, suggesting that penetrative strain may be at least as important of a restoration consideration as faulting and folding. Consequently, strain and vorticity analysis should be integrated into cross section restoration whenever possible