The discovery of year-round subsurface meltwater in Greenland's ice sheet in 2011 changed understanding of its hydrology. Satellite remote sensing could potentially monitor these perennial firn aquifers (PFAs) across time and throughout the year, extending data records. This study explores using microwave brightness temperature data from satellites to identify PFAs, addressing limitations of current monitoring methods. Preliminary results found locations with subsurface melting not explained by surface melt and regions of melt persisting into winter, consistent with known PFAs. Further work could improve identification methods and compare to established datasets.

1. Abstract
The discovery of year-round subsurface meltwater (Perennial Firn
Aquifers/PFAs) in 2011 radically changed the scientific community‘s
understanding of Greenland hydrology. The environmental and time
constraints on current data collection methods leave a significant need to
explore new methods of monitoring PFAs both throughout the year and across
time. If Satellite Remote Sensing proves effective at detecting subsurface melt,
it could significantly extend the record of PFA location and physical and
temporal extent so that hydrologic and climatic results can be better analyzed.
Impacts of PFAs on Greenland Hydrology
• Additional term in Energy Balance Models
• Potential influence on surface melt and glacier dynamics
• Potential buffering of sea level rise to unknown extent
• Greenland is significant in Arctic Climate change, which impacts
Global Climate
• GPR/SAR, ICEBridge-NASA
• Data from 2011-2015, summer months only
• Time consuming to obtain and process
• Thermal Profile
• Point wise
• Depth of PFA
• Temporal changes throughout year
• Modeling
• Mechanism is still poorly understood
Remote Sensing of Subsurface Meltwater
Methods
Results
Analysis
• While this threshold value and frequency appears to identify
subsurface melt water
• Subsurface melt signals may be drowned out by surface melt
signals in the same region
• Subsurface melt may be to deep for 6GHz signal to penetrate in
many locations
• The subsurface melt signal is weak and may be better identified
using a more discerning algorithm
• According to Tedesco et. al. (2006), 6.9 GHz Tb melt-refreeze
signal is between 250 and 260 K, considerably higher than the
220 K threshold used here
Future Work
• Develop a more discerning Tb threshold
• Compare identified melt regions to ICEBridge PFA dataset
• Evaluate record previous to fall and winter 2010-2011
Resources
Forster RR, Box JE, van den Broeke MR, Miège C, Burgess EW, van Angele JH, Lenaerts JTM, Koenig LS, Paden J, Lewis
C, Gogineni SP, Leuschen C and McConnell JR (2014) Extensive liquid meltwater storage in firn within the Greenland Ice
Sheet. Nat. Geo. 7, 95-99, (doi: 10.1038/NGEO2043)
Mote, T. L. 2014. MEaSUREs Greenland Surface Melt Daily 25km EASE-Grid 2.0, Version 1. [indicate subset used]. Boulder,
Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive
Center. http://dx.doi.org/10.5067/MEASURES/CRYOSPHERE/nsidc-0533.001. [March 9, 2015].
Knowles, K., M. Savoie, R. Armstrong, and M. Brodzik. 2006. AMSR-E/Aqua Daily EASE-Grid Brightness Temperatures,
Version 1. [indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active
Archive Center. http://dx.doi.org/10.5067/XIMNXRTQVMOX. [Aug 4, 2015].
Tedesco, M., Kim, E. J., England, A. W., & De Roo, R. D. (2006, December). Brightness Temperatures of Snow
Melting/Refreezing Cycles: Observations and Modeling Using a Multilayer Dense Medium Theory-Based Model. IEEE
Transactions on Geoscience and Remote Sensing, 44(12), 3563-3573. doi:10.1109/TGRS.2006.881759
• Determine likely brightness temperature threshold for 6.9 GHz
• Apply threshold and ice-sheet mask to AMSR-E 6.9 H GHz
Brightness Temperature data
• Compare identified subsurface melt regions to accepted surface
melt measurements during the same time period
• Identify inequivalent regions throughout winter 2010-2011 when
year-round subsurface meltwater is known to exist
• Passive Microwave Remote Sensing
• Commonly used to monitor surface melt
• Daily observations of entire Greenland Ice Sheet
• Data record extends 40+ years
• Microwaves have large skin depth
• 4-10 GHz range can penetrate up to 30 m
• PFA depth below surface is 5-50 m (Forster et. al. 2014)
• Microwaves interact with englacial ice and snow interfaces similar to GPR
• Potential Drawbacks
• Less spatial resolution than GPR
• Attenuated signal
• Surface melt returns signal before reaching PFA depth
Current Monitoring Methods
Extending the Record of Greenland Ice Sheet
Subsurface Meltwater: Exploring New Applications
of Satellite Remote Sensing Data
Margeaux L. Carter,
Hydrology MS Student
Dept. of Earth and
Environmental Science
New Mexico Tech
mcarter@nmt.edu
David B. Reusch
New Mexico Tech
dreusch@ees.nmt.edu
Christopher C. Karmosky
University of Tennessee-Martin
ckarmosk@utm.edu
National Science Foundation’s Division of Polar Programs
award ARC-1304849
C51B-0708
• Consistently identifies locations not equivalent to surface
measurements (Mote 2014)
• Identifies regions associated with subsurface melt (Forster et. al.
2014)
• Identifies melt throughout winter
• Subsurface melt identified regions relatively temporally stable
• Identified subsurface melt is decreasing in area throughout the
winter
• Subsurface melt may be traveling progressively deeper
• Liquid subsurface melt may be refreezing
• Subsurface melt may be decreasing through winter
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