GNET station use in ice velocity studies

Lauren AndrewsNASA Postdoctoral FellowNASA GSFC

GNET Planning Meeting25 January 2017

Photo:DanaJ.Caccamise II,courtesyofTheOhioStateUniversity

GNET stations for process-oriented ice motion studies

• Where are GNET stations used and for what purpose?

• Cost – Baseline Analysis• Why use GNET stations?

• Potential future use and requirements

GPS-derived GrIS ice motion• GPS observations of ice motion are critical for studying

the impact of surface melt on ablation zone ice velocities.

GNET use in ice velocity studies

• GNET GPS stations play a small, but important role as base stations for differential GPS processing.• Easily accessible• Well-documented• Reasonable baselines

• GAMIT/GLOBK, TRACK, others

Photo: Leigh Stearns, KU

THU1 (GNET Precursor)Zwally et al., 2002

KULU (GNET Precursor)Zwally et al., 2002

KELY (GNET Precursor)Zwally et al., 2002

KULU (GNET)Hoffman et al., 2011

KAGA (GNET)Das et al., 2008Hoffman et al., 2011Tedesco et al., 2013Stevens et al., 2015Stevens et al., 2016

KELY (GNET)Hoffman et al., 2011Bartholomew et al., 2011Bartholomew et al., 2012Sole et al., 2013Doyle et al., 2015Cowton et al., 2016

GNET station useas base stations

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THU1 (GNET Precursor)Zwally et al., 2002

KULU (GNET Precursor)Zwally et al., 2002

KELY (GNET Precursor)Zwally et al., 2002

KELY (GNET)Hoffman et al., 2011Bartholomew et al., 2011Bartholomew et al., 2012Sole et al., 2013Doyle et al., 2015Cowton et al., 2016

KULU (GNET)Hoffman et al., 2011

KAGA (GNET)Das et al., 2008Hoffman et al., 2011Tedesco et al., 2013Stevens et al., 2015Stevens et al., 2016

GNET station useSubglacial hydrology

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• The magnitude of seasonal acceleration is tied to melt availability.

Ice motion and subglacial evolution

Modified from Zwally et al., 2002Zwally et al., 2002; NASA

• The duration and rate, rather than the volume of meltwater availability controls seasonal pattern of ice acceleration.

Ice motion and subglacial evolution Photo: Pete N

ienow

Photo: Matt Hoffman

Ice motion and subglacial evolution

Hoffman et al., 2011

• The dynamic response of ice sheet motion is driven by changes in subglacial water storage and the deceleration is associated with evolving subglacial efficiency.

Ice motion and subglacial evolution

Photo: Pete Nienow Sole et al., 2013

• The gradual deceleration continues into the winter, with regions experiencing more melt seeing a stronger slowdown in winter ice velocities.

THU1 (GNET Precursor)Zwally et al., 2002

KULU (GNET Precursor)Zwally et al., 2002

KELY (GNET Precursor)Zwally et al., 2002

KULU (GNET)Hoffman et al., 2011

KAGA (GNET)Das et al., 2008Hoffman et al., 2011Tedesco et al., 2013Stevens et al., 2015Stevens et al., 2016

GNET station useSupraglacial lake drainage

KELY (GNET)Hoffman et al., 2011Bartholomew et al., 2011Bartholomew et al., 2012Sole et al., 2013Doyle et al., 2015Cowton et al., 2016

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Supraglacial lake drainage

• High temporal resolution GPS data help constrain the types and mechanisms of lake drainages as well as their ultimate impact on ice velocity.

Stevens et al., 2015

Tedesco et al., 2013

Cost - Baseline Analysis: Why use GNET stations?

• Well-maintained stations with consistent data streams.

• Freely available, well-documented data

• Reasonable temporal sampling.• Near ice stations are proximal to

areas of interest.• Moderate baselines manageable for

current applications.

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Continued GNET station use• Studies are moving higher in latitude

and elevation.• Baseline lengths increasing (a non-

unique problem).• Studies on faster moving glaciers

dictate the need for higher sampling resolution.• Calving and associated

acceleration.

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• PIs will weigh the needs of the project (baseline length, temporal resolution, etc.).

• Continued use of critical stations (KAGA, KELY) and future use of higher latitude stations (RINK, KULL, etc).

• GNET stations will remain an important redundancy for process-oriented ice velocity studies.

Continued GNET station usepolar.dtu.dk

GNET use in ice motion studies

• Cite/ reference GNET station use.• Many papers reference ‘off-ice’

base station.• Some base stations established for

process-based field studies may be useful for GNET-related studies.• Multiple years, high temporal

resolution, installed using UNAVCO standards.

Future use and limitations • Freely available GNET data help minimize logistical

and financial costs for field programs.• Expected continued use for ice motion studies with

some caveats.• GNET stations will always remain an important

redundancy, even with projects installing unique base stations.

• Outlet glacier studies have different needs.• Potential flexibility in data logging rates – not

necessarily a higher iridium transmission rate.