Understanding the mechanics of deformable glacier beds and the coupling of surface meltwater flux with ice flow is an important and challenging problem in modern glaciology. Hofsjökull and Langjökull temperate ice caps, located in central Iceland (map), are natural laboratories for studying basal mechanics due to their relative accessibility and moderate sizes (surface areas ~100 km2), allowing for high resolution observations and models. In collaboration with scientists at NASA's Jet Propulsion Laboratory and the University of Iceland, we collected airborne interferometric synthetic aperture radar (InSAR), GPS, and in situ meteorological data over both of these ice caps in June 2012, February 2014, and May 2015. UAVSAR collected the InSAR data from multiple vantage points allowing us to infer 3D surface velocity fields for both ice caps. We use the velocity fields as boundary conditions in ISSM, a higher-order 3D ice flow modeling software suite, and invert for the basal shear traction using optimal control methods. Temporal variability in basal shear traction in response to surface meltwater flux provides insights into the subglacial hydrological system and the mechanical properties of deformable glacier beds.
Collaborators: Mark Simons, Helgi Björnsson, Finnur Pálsson, Scott Hensley, Eric Larour, and Mathieu Morlighem
B. M. Minchew, M. Simons, H. Björnsson, F. Pálsson, M. Morlighem,
H. Seroussi, E. Larour, and S. Hensley.
Plastic bed beneath Hofsjökull Ice Cap, central Iceland, and the
sensitivity of ice flow to surface meltwater flux.
Journal of Glaciology, 62(231):147-158, 2016.
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B. M. Minchew, M. Simons, S. Hensley, H. Björnsson, and F. Pálsson.
Early melt-season velocity fields of Langjökull and
Hofsjökull ice caps, central Iceland.
Journal of Glaciology, 61(226), 2015.
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Antarctic ice streams
Most grounded ice in Antarctica resides in the slow moving interior and drains to the ocean through relatively fast moving glaciers. Despite their tremendous momentum, glaciers can respond dynamically to external forcing on timescales from hours to millennia. My research focuses on synoptic-scale variability of glacier flow on daily to yearly timescales. I am particularly interested in the response of glaciers to known forcing, such as ocean tidal uplift of floating ice shelves. Examples of processes we can study by observing the response of glaciers to ocean tidal forcing include grounding zone (regions over which ice begins to floating) migration and extent, the mechanics of the ice-bed interface, and the rheology of ice. We use numerous synthetic aperture radar observations, collected from multiple viewing geometries at the highest possible sampling frequency with the COSMO-SkyMed satellite constellation, to infer the time-dependent, 3D surface velocity field along the full length of Rutford Ice Stream, West Antarctica, whose flow is modulated by ocean tides to nearly 100 km inland.
Collaborators: Mark Simons, Hilmar Gudmundsson, Andrew Thompson, Victor Tsai, Bryan Riel, Piyush Agram, Pietro Milillo, and ASIRelevant publications
B. M. Minchew, M. Simons, B. V. Riel, and P. Milillo.
Tidally induced variations in vertical and horizontal motion on
Rutford Ice Stream, West Antarctica, inferred from remotely sensed
Journal of Geophysical Research - Earth Surface, 121:1-24, 2016.
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P. Milillo, B. M. Minchew, P. Agram, B. Riel, and M. Simons.
Inferring 3D deformation field time series using synthetic aperture
radar: Application to tidal-timescale ice-flow variability in Rutford Ice
Stream, West Antarctica.
in revision, 2016.
Slow-moving landslides, or earthflows, are a primary mechanism of landscape erosion and sediment flux in hilly terrain. We used airborne InSAR data, collected by UAVSAR, to identify 150 previously unknown landslides along the creeping section of the San Andreas fault. This concentration of landslides gives the creeping section a significantly greater landslide density than the locked northern section of the fault where larger magnitude earthquakes are frequent. Approximately 75% of landslides in the creeping section exist within 2 km of the fault zone. We hypothesize that the presence of damage within the creeping section, whether advected from the southern locked section or created by fault creep, and the absence of large-scale seismicity are the primary controls on the occurrence and sustainability of earthflows.
Collaborators: Joel Scheingross, Michael Lamb, Mark Simons, and Scott HensleyRelevant publications
J.S. Scheingross, B.M. Minchew, B.H. Mackey, M. Simons, M.P. Lamb, and
Fault zone controls on the spatial distribution of slow-moving
GSA Bulletin, 125(3-4):473-489, 2013.
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Sediment transported as bedload is a fundamental driver of river incision in steep mountain bedrock streams. However, measuring bedload transport using traditional means is a challenging undertaking that requires significant physical effort and can be dangerous during floods, which is when bedload transport and river incision rates should be at a maximum. To help alleviate these measurement limitations, we developed a physical model for the seismic noise generated by saltating sediment. Our model shows that the power spectral density (PSD) of the Rayleigh waves generated by sediment impacting bedrock is a linear function of the number of particles of a given size and scales as the square of the linear momentum. We show that with reliable constraints on grain size distribution, it may be possible to invert seismic noise for estimates of sediment transport.
Collaborators: Victor Tsai, Michael Lamb, and Jean-Paul AmpueroRelevant publications
V.C. Tsai, B.M. Minchew, M.P. Lamb, and J.P. Ampuero.
A physical model for seismic noise generation from sediment transport
Geophysical Research Letters, 39:L02404, 2012.
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Hazard mitigation using existing remote sensing assets
Marine oil spills
On April 20, 2010, the Deepwater Horizon (DWH) oil rig caught fire and sank, killing 11 workers and destroying the riser that connected the rig to a valve on the seafloor. More than 200 million gallons of oil spilled into the Gulf of Mexico over the next 87 days, damaging oceanic and coastal environments and disrupting Gulf Coast fishing and tourism industries. Using fully polarimetric synthetic aperture radar (PolSAR) data collected by NASA's UAVSAR over the former DWH site and within Barataria Bar, Louisiana, we showed that PolSAR data, which can be collected in any lighting and most weather conditions without loss of data quality, are well-suited to locate oil on the sea surface, within bays, and along wetland coast. We also gleaned some characteristics of the spilled oil from PolSAR data. I derived a simple index for determining the extent to which oil is mixed with seawater, an important metric that could help future oil spill cleanup commanders determine the proper response method.
Collaborators: Cathleen Jones, Ben Holt, Scott Hensley, Michael Collins, and Sebastien Angelliaume.
M.J. Collins, M. Denbina, B.M. Minchew, C.E. Jones, and B. Holt.
On the use of simulated airborne compact polarimetric SAR for
characterizing oil-water mixing of the Deepwater Horizon oil spill.
IEEE Journal of Selected Topics in Applied Earth Observations and Remote
Sensing, 8(3):1062-1077, 2015.
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B.M. Minchew, C.E. Jones, and B. Holt.
Polarimetric analysis of backscatter from the deepwater horizon oil
spill using l-band synthetic aperture radar.
Geoscience and Remote Sensing, IEEE Transactions on,
50(10):3812 -3830, 2012.
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C. E. Jones, B. M. Minchew, B. Holt, and S. Hensley.
Studies of the Deepwater Horizon Oil Spill With the
UAVSAR Radar, in Monitoring and Modeling the Deepwater Horizon Oil Spill: A Record-Breaking Enterprise, Geophysical Monograph Series, volume 195, edited by Y. Liu et al., pages 33-50.
AGU, Washington, DC, 2011.
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Each year millions of acres are consumed by wildfires that can threaten homes, destroy businesses, and cost lives. Airborne polarimetric synthetic aperture radar (PolSAR) data might be able provide actionable information to firefighters and responders on the ground concerning the location and velocity of the fire. We have completed a preliminary study using PolSAR data collected with UAVSAR over a number of wildfires in southern California between 2009 and 2015. We compare pre- and post-fire data from a variety of well-known PolSAR decomposition techniques and show that the data robustly delineate the burned area and reveal structure that, in most cases, is comparable to burn severity maps produced from optical data. These results indicate that PolSAR, which can operate day or night and is unhindered by smoke and inclement weather, might be a useful tool to help manage wildfires.
Collaborators: Mark Simons, Sang-Ho Yun, Christine Rains, Jerry Heo, Erika Higa, and Mark Barker