A5000323767- Cryospheric studies and observations
- Arctic and Antarctic ice dynamics
- Climate change and permafrost
- Winter Sports Injuries and Performance
- Geology and Paleoclimatology Research
- Quantum and electron transport phenomena
- Landslides and related hazards
- Methane Hydrates and Related Phenomena
- Polar Research and Ecology
- Physics of Superconductivity and Magnetism
- Semiconductor Quantum Structures and Devices
- Geophysics and Gravity Measurements
- Arctic and Russian Policy Studies
- Meteorological Phenomena and Simulations
- Geological Studies and Exploration
- Laser-Matter Interactions and Applications
- Quantum optics and atomic interactions
- Species Distribution and Climate Change
- Spectroscopy and Quantum Chemical Studies
- Indigenous Studies and Ecology
- Water resources management and optimization
- Climate variability and models
- Flood Risk Assessment and Management
- Atmospheric and Environmental Gas Dynamics
- Advanced Optical Sensing Technologies
University of Oregon
2021-2024
Brown Foundation
2020-2023
Brown University
1988-2023
Nordland Research Institute
2022
John Brown University
2020-2021
ORCID
2021
University of California, Los Angeles
2017-2019
Aberystwyth University
2014-2018
Delta Air Lines (United States)
2016
Radar (United States)
2016
Abstract. This study presents the application of a cost-effective, unmanned aerial vehicle (UAV) to investigate calving dynamics at major marine-terminating outlet glacier draining western sector Greenland ice sheet. The UAV was flown over Store Glacier on three sorties during summer 2013 and acquired 2000 overlapping, geotagged images front an ~40 cm ground sampling distance. Stereo-photogrammetry applied these enabled extraction high-resolution digital elevation models (DEMs) with vertical...
Abstract. Observations and models agree that the Greenland Ice Sheet (GrIS) surface mass balance (SMB) has decreased since end of 1990s due to an increase in meltwater runoff this trend will accelerate future. However, large uncertainties remain, partly different approaches for modelling GrIS SMB, which have weigh physical complexity or low computing time, spatial temporal resolutions, forcing fields, ice sheet topographies extents, collectively make inter-comparison difficult. Our SMB model...
Greenland’s snowline exhibits large fluctuations and is a primary amplifier of ice sheet surface melt runoff.
Abstract Surface ablation of the Greenland ice sheet is amplified by surface darkening caused light‐absorbing impurities such as mineral dust, black carbon, and pigmented microbial cells. We present first quantitative assessment contribution to darkening, based on field measurements reflectance concentrations impurities, including algae, during 2014 melt season in southwestern part sheet. The impact algae bare study area was greater than that nonalgal yielded a net albedo reduction 0.038 ±...
Abstract. Melting of the Greenland Ice Sheet (GrIS) is largest single contributor to eustatic sea level and amplified by growth pigmented algae on ice surface, which increases solar radiation absorption. This biological albedo-reducing effect its impact upon rise has not previously been quantified. Here, we combine field spectroscopy with a radiative-transfer model, supervised classification unmanned aerial vehicle (UAV) satellite remote-sensing data, runoff modelling calculate biologically...
Significance Meltwater runoff is an important hydrological process operating on the Greenland ice sheet surface that rarely studied directly. By combining satellite and drone remote sensing with continuous field measurements of discharge in a large supraglacial river, we obtained 72 h observations suitable for comparison climate model predictions. The quantify how large, fluvial catchment attenuates magnitude timing delivered to its terminal moulin hence bed. data are used calibrate...
Albedo—a primary control on surface melt—varies considerably across the Greenland Ice Sheet yet specific types that comprise its dark zone remain unquantified. Here we use UAV imagery to attribute seven distinct observed albedo along a 25 km transect dissecting western, ablating sector of ice sheet. Our results demonstrate distributed impurities—an admixture dust, black carbon and pigmented algae—explain 73% spatial variability in are responsible for itself. Crevassing supraglacial water...
Abstract Fine‐scale, subseasonal fluctuations in Arctic‐Boreal surface water reflect regional balance and modulate trace gas emissions to the atmosphere but have eluded detection using traditional satellite remote sensing. We use high‐resolution (~3–5 m), high‐frequency CubeSat sensors measure near‐daily changes lake area through an object‐based tracking method that incorporates machine learning overcome notable limitations of imagery. From ~76,000 images we obtain >2.2 million individual...
Abstract. We document the density and hydrologic properties of bare, ablating ice in a mid-elevation (1215 m a.s.l.) supraglacial internally drained catchment Kangerlussuaq sector western Greenland sheet. find low-density (0.43–0.91 g cm−3, μ = 0.69 cm−3) to at least 1.1 depth below sheet surface. This near-surface, consists alternating layers water-saturated, porous clear solid lenses, overlain by thin (< 0.5 m), even lower (0.33–0.56 0.45 unsaturated weathering crust. Ice data from 10...
Abstract Accurate, transparent knowledge of global reservoir levels is a prerequisite for effective management water resources. However, no complete database exists because gauge data are not globally available and the current generation satellite radar altimeters resolves only world's largest reservoirs. Here, we investigate level changes in reservoirs using ICESat‐2, National Aeronautics Space Administration (NASA)'s new laser altimetry mission. In just first 12 months mission, find that...
Abstract. The Greenland Ice Sheet (GrIS) mass loss has been accelerating at a rate of about 20 ± 10 Gt/yr2 since the end 1990's, with around 60 % this directly attributed to enhanced surface meltwater runoff. However, in climate and glaciology communities, different approaches exist on how model balance (SMB) components using: (1) complex physically-based models which are computationally expensive; (2) intermediate complexity energy models; (3) simple fast positive degree day base their...
Measurements of albedo are a prerequisite for modelling surface melt across the Earth's cryosphere, yet available satellite products limited in spatial and/or temporal resolution. Here, we present practical methodology to obtain centimetre resolution with accuracies 5% using consumer-grade digital camera and unmanned aerial vehicle (UAV) technologies. Our method comprises workflow processing, correcting calibrating raw images white reference target, upward downward shortwave radiation...
Calibration and validation of satellite-derived ice sheet albedo data require high-quality, in situ measurements commonly acquired by up down facing pyranometers mounted on automated weather stations (AWS). However, direct comparison between ground can only be justified when the measured surface is homogeneous at length-scale both satellite pixel footprint. Here we use digital imagery an unmanned aerial vehicle to evaluate point-to-pixel comparisons across western, ablating margin Greenland...
Unmanned aerial vehicle (UAV) photogrammetry has become an important tool for generating multi-temporal, high-resolution ortho-images and digital elevation models (DEMs) to study glaciers their dynamics. In polar regions, the roughness of terrain, strong katabatic winds, unreliability compass readings, inaccessibility due lack infrastructure pose unique challenges UAV surveying. To overcome these issues, we developed open-source, low-cost, high-endurance, fixed-wing equipped with GPS...
We report an inelastic-light-scattering study of the quasi-two-dimensional electron gas in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum-well structures. The spectra intersubband spin-density waves are measured as a function wave vector. Detailed calculations performed using self-consistent-field theory which exchange and correlation included through local-spin-density approximation. find good agreement between experiment for both energy at...
Abstract Surface melting impacts ice sheet sliding by supplying water to the bed, but subglacial processes driving accelerations are complex. We examine linkages between surface runoff, transient storage, and short‐term motion from 168 consecutive hourly measurements of meltwater discharge (moulin input) GPS‐derived for Rio Behar, a ∼60 km 2 moulin‐terminating supraglacial river catchment on southwest Greenland Ice Sheet. Short‐term in speed correlate strongly with lag‐corrected measures ( r...
Abstract The Greenland Ice Sheet harbours a wealth of microbial life, yet the total biomass stored or exported from its surface to downstream environments is unconstrained. Here, we quantify abundance and cellular flux within near-surface weathering crust photic zone western sector ice sheet. Using groundwater techniques, demonstrate that interstitial water flow slow (~10 −2 m d −1 ), while cytometry enumeration reveals this pathway delivers 5 × 10 8 cells supraglacial streams, equivalent...
Abstract Landfast sea ice that forms along the Arctic coastline is of great importance to coastal Alaskan communities. It provides a stable platform for transportation and traditional activities, protects from erosion, serves as critical habitat marine mammals. Here we present full assessment landfast conditions across continuous 7885 km length Alaska over 2000–2022 using satellite imagery. We find maximum extent, usually occurring in March, averaged 67 002 2 during our study period:...
We present a detailed comparison between experiment and theory of the magnitude exchange-correlation Coulomb interaction in collective intersubband spin-density excitation electron gas confined to GaAs/AlGaAs quantum wells. A widely used self-consistent-field which exchange correlation is incorporated through local-density approximation found underestimate slightly interaction, while nonlocal involving variational solution Bethe-Salpeter equation for density-density function compares well...
Abstract Meltwater runoff from the Greenland Ice Sheet (GrIS) significantly contributes to sea level rise and is dominant driver of enhanced mass loss. While most melt occurs during summer, little known about its seasonal and/or interannual retention within GrIS. Here, we document evidence winter, ~4 months after summer melt. Ground‐penetrating radar borehole surveys in proglacial Isortoq River reveal slowly flowing water beneath >0.5 m river ice. Geochemical analysis this indicates...
Abstract The production of meltwater from glacier ice, which is exposed at the margins land ice during summer, responsible for a large proportion mass loss. rate especially sensitive to its physical structure and chemical composition combine determine albedo ice. However, optical properties near-surface are not well known since most prior work has focused on laboratory-grown or deep cores. Here, we demonstrate measurement technique based diffuse propagation nanosecond-duration laser pulses...
The band-gap renormalization of optically excited semiconductor quantum wells due to exchange-correlation effects in the electron-hole system is studied here. first-order self-energies for this two-component plasma are calculated exactly within random-phase approximation. All intersubband interactions included fully, and they found make significant contributions their subband dependences. Particular attention paid dependence renormalization. These calculations made realistic systems with...
Abstract. To quantify the ice-ocean processes which drive dynamic and geometric change at calving outlet glaciers, detailed measurements beyond capability of present satellites are required. This study presents application a cost-effective (< USD 2000), unmanned aerial vehicle (UAV) to investigate frontal dynamics major draining western sector Greenland Ice Sheet. The UAV was flown over Store Glacier on three sorties during summer 2013 acquired 2000 overlapping, geo-tagged images front...