Browsing by Subject "thickness"

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Debris-Covered Glacier Energy Balance Model for Imja-Lhotse Shar Glacier in the Everest Region of Nepal
(2015-12) Rounce, D. R.; Quincey, D. J.; McKinney, D. C.; Rounce, D. R.; McKinney, D. C.
Debris thickness plays an important role in regulating ablation rates on debris-covered glaciers as well as controlling the likely size and location of supraglacial lakes. Despite its importance, lack of knowledge about debris properties and associated energy fluxes prevents the robust inclusion of the effects of a debris layer into most glacier surface energy balance models. This study combines fieldwork with a debris-covered glacier energy balance model to estimate debris temperatures and ablation rates on Imja-Lhotse Shar Glacier located in the Everest region of Nepal. The debris properties that significantly influence the energy balance model are the thermal conductivity, albedo, and surface roughness. Fieldwork was conducted to measure thermal conductivity and a method was developed using Structure from Motion to estimate surface roughness. Debris temperatures measured during the 2014 melt season were used to calibrate and validate a debris-covered glacier energy balance model by optimizing the albedo, thermal conductivity, and surface roughness at 10 debris-covered sites. Furthermore, three methods for estimating the latent heat flux were investigated. Model calibration and validation found the three methods had similar performance; however, comparison of modeled and measured ablation rates revealed that assuming the latent heat flux is zero may overestimate ablation. Results also suggest that where debris moisture is unknown, measurements of the relative humidity or precipitation may be used to estimate wet debris periods, i.e., when the latent heat flux is non-zero. The effect of temporal resolution on the model was also assessed and results showed that both 6 h data and daily average data slightly underestimate debris temperatures and ablation rates; thus these should only be used to estimate rough ablation rates when no other data are available.
Letter to F.E. Turner from H.B. Stenzel on 1938-02-12
(1938-02-12) Stenzel, Henryk B.
Letter to H.B. Stenzel from Stewart Mossom on 1936-10-01
(1936-10-01) Mossom, Stewart
Letter to W.S. Adkins from H.B. Stenzel on 1952-09-10
(1952-09-10) Stenzel, Henryk B.
New Pulsating DB White Dwarf Stars From The Sloan Digital Sky Survey
(2009-01) Nitta, Atsuko; Kleinman, S. J.; Krzesinski, J.; Kepler, S. O.; Metcalfe, T. S.; Mukadam, Anjum S.; Mullally, Fergal; Nather, R. E.; Sullivan, Denis J.; Thompson, Susan E.; Winget, D. E.; Nather, R. E.; Winget, D. E.
We are searching for new He atmosphere white dwarf pulsators (dbVs) based on the newly found white dwarf stars from the spectra obtained by the Sloan Digital Sky Survey. dbVs pulsate at hotter temperature ranges than their better known cousins, the H atmosphere white dwarf pulsators (DAVs or ZZ Ceti stars). Since the evolution of white dwarf stars is characterized by cooling, asteroseismological studies of dbVs give us opportunities to study white dwarf structure at a different evolutionary stage than the DAVs. The hottest dbVs are thought to have neutrino luminosities exceeding their photon luminosities, a quantity measurable through asteroseismology. Therefore, they can also be used to study neutrino physics in the stellar interior. So far we have discovered nine new dbVs, doubling the number of previously known dbVs. Here we report the new pulsators' light curves and power spectra.
Optimized Retinal Nerve Fiber Layer Segmentation Based On Optical Reflectivity And Birefringence For Polarization-Sensitive Optical Coherence Tomography
(2011-09) Wang, Bingqing; Paranjape, Amit S.; Yin, Biwei; Liu, Shuang; Markey, Markey K.; Milner, Thomas E.; Rylander, H. Grady; Wang, Bingqing; Paranjape, Amit S.; Yin, Biwei; Liu, Shuang; Markey, Markey K.; Milner, Thomas E.; Rylander, H. Grady
Segmentation of the retinal nerve fiber layer (RNFL) from swept source polarization-sensitive optical coherence tomography (SS-PSOCT) images is required to determine RNFL thickness and calculate birefringence. Traditional RNFL segmentation methods based on image processing and boundary detection algorithms utilize only optical reflectivity contrast information, which is strongly affected by speckle noise. We present a novel approach to segment the retinal nerve fiber layer (RNFL) using SS-PSOCT images including both optical reflectivity and phase retardation information. The RNFL anterior boundary is detected based on optical reflectivity change due to refractive index difference between the vitreous and inner limiting membrane. The posterior boundary of the RNFL is a transition zone composed of birefringent axons extending from retinal ganglion cells and may be detected by a change in birefringence. A posterior boundary detection method is presented that segments the RNFL by minimizing the uncertainty of RNFL birefringence determined by a Levenberg-Marquardt nonlinear fitting algorithm. Clinical results from a healthy volunteer show that the proposed segmentation method estimates RNFL birefringence and phase retardation with lower uncertainty and higher continuity than traditional intensity-based approaches.
Refined Broad-Scale Sub-Glacial Morphology of Aurora Subglacial Basin, East Antarctica Derived by an Ice-Dynamics-Based Interpolation Scheme
(2011-07) Roberts, J. L.; Warner, R. C.; Young, D.; Wright, A.; van Ommen, T. D.; Blankenship, D. D.; Siegert, M.; Young, N. W.; Tabacco, I. E.; Forieri, A.; Passerini, A.; Zirizzotti, A.; Frezzotti, M.; Young, D.
Ice thickness data over much of East Antarctica are sparse and irregularly distributed. This poses difficulties for reconstructing the homogeneous coverage needed to properly assess underlying sub-glacial morphology and fundamental geometric constraints on sea level rise. Here we introduce a new physically-based ice thickness interpolation scheme and apply this to existing ice thickness data in the Aurora Subglacial Basin region. The skill and robustness of the new reconstruction is demonstrated by comparison with new data from the ICECAP project. The interpolated morphology shows an extensive marine-based ice sheet, with considerably more area below sea-level than shown by prior studies. It also shows deep features connecting the coastal grounding zone with the deepest regions in the interior. This has implications for ice sheet response to a warming ocean and underscores the importance of obtaining additional high resolution data in these marginal zones for modelling ice sheet evolution.