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Cryosphere Geophysics
Lin Liu
Graduate Division of Earth and Atmospheric Sciences Faculty of Science, The Chinese University of Hong Kong
Email: [email protected] Website: cryocuhk.github.io
About myself• Grew up in Wuhan, China
• Bachelor degree in geophysics from Wuhan University
• PhD degree, also in geophysics, from University of Colorado at Boulder
• Thompson Postdoc Fellow, Stanford University
• Joined The Chinese University of Hong Kong in 2014
• We use geophysical methods to study changes of the cryosphere (frozen part of the Earth system) in a warming climate.
• Check out our lab website cryocuhk.github.io to learn more
• Send me an email for any questions [email protected]
Lab website
The cryosphere is an important part of the global Earth system
Cryosphere: frozen water on Earth’s surface •Stores 75% of world’s freshwater•Linked to water cycle, sea level change, surface energy and gas exchange
•ALL cryospheric components are undergoing fast warming and area reduction
Sea Ice Greenland Ice Sheet
Antarctica Ice Sheet
Mountain Glaciers
Not shown on this map:• Snow cover• Lake/river ice• Permafrost (frozen ground)
FrozenGroundGreenland
Ice Sheet
Cryosphere
Ice Mass
Balance
Glacial
Dynamics
InSAR
Rock
Glaciers
Active Layer
Thickness
Mercury
Carbon
Taliks
Wildfires
Snow
Freeze/Thaw
Status
Elevation
Changes
Thermokarst
Remote Sensing GeophysicsGNSSSatellite Gravity Deep LearningPassive & Active MicrowaveOptical Radar Surface NMR
Ice Sheet
Hydrology
Interaction with Solid Earth
Glacial
Isostatic
Adjustment
Elastic
Rebound
Space GeodesyAltimetry
SAGI
SGI
AGI
SAGI
IOD
GIODS
GP
GI
IR
IO
GlacialSpeed
Calving
Cryosphere Geophysics Group @ CUHKR
ecen
t res
earc
h pr
ojec
ts
Greenland Ice Mass Loss Permafrost Degradation Rock Glacier Kinematics
See
post
ers
Tom
orro
w!
Geophysical Methods
Altimetry
Global Positioning System
Interferometric Synthetic Aperture Radar
Seismic Methods
Ground Penetrating Radar
Surface Nuclear Magnetic Resonance
Satellite Gravity
Cryospheric Systems
Glaciers
Sea Ice
Lake Ice
Permafrost
Ice Sheets
Combined use of multiple geophysical tools for cryospheric studies
Changes
Glacial Thinning
Glacial Speed
Glacial Isostatic Rebound
Glacial Mass Balance
Sea Ice Dynamics
Lake Ice Growth
Permafrost Surface Subsidence
Thaw Depth
Rock Glacier Flow
Underground Thawing
Ice Sheet Mass Loss
Liu et al., JGR 2010, 2012, 2015Liu et al., The Cryosphere, 2014Liu et al., GRL 2014Liu and Larson, The Cryosphere, 2018Hu et al., GRL 2018Chen et al., JGR 2018
Geophysical Methods
Altimetry
Global Positioning System
Interferometric Synthetic Aperture Radar
Seismic Methods
Ground Penetrating Radar
Surface Nuclear Magnetic Resonance
Satellite Gravity
Cryospheric Systems
Glaciers
Sea Ice
Lake Ice
Permafrost
Ice Sheets
Combined use of multiple geophysical tools for cryospheric studies
Changes
Glacial Thinning
Glacial Speed
Glacial Isostatic Rebound
Glacial Mass Balance
Sea Ice Dynamics
Lake Ice Growth
Permafrost Surface Subsidence
Thaw Depth
Rock Glacier Flow
Underground Thawing
Ice Sheet Mass Loss
Liu et al., GJI 2012, JGR 2017Khan et al., JGR 2010, Nature Climate Change 2014Nelsen et al., JGR 2013Wahr et al., JGR 2013Zhang et al., JGR, 2017, EPSL 2018, EPSL2019
Siberia(Russia)
Iceland
Greenland
Canada
Arctic Ocean
Svalbard
Alaska(USA)
Scandinavia
Greenland contains ice that could raise sea level by 6 m
‘Cool’ facts about Greenland
• Largest island in the world
• 81% of surface is covered by ice • If ice melts completely, global sea level rises by 6 m
Greenland loses ice through surface melting and glacial discharge
Figure modified from van den Broeke et al., 2009
Greenland loses ice through surface melting and glacial discharge
Figure modified from van den Broeke et al., 2009 Rignot and Mouginot, 2012
Snapshot of ice motion speed in 2010
Calving (��) and calving front
Calving front: the terminus of the glacier
Calving: breaking away of ice from glaciers
Significance of calving process
• A great contributor to the mass change of many glacier systems worldwide and global sea level rise.
• Icebergs generated by calving have a cooling effect on ocean, which can substantially influence the broader climate system.
Automatically delineating calving from images using Deep Learning
Developed a novel method based on deep learning to
extract calving front automatically from multiple remote
sensing datasets with no constraint of time and study area.
Manually-designed Method
• Require low computational power• Require extensive prior knowledge and experience • Appropriate for problems with low computational complexity
Deep Learning Method
• Take advantage of increased data volume • Can solve more complex problems
• In the big data era, data volume of remote sensing imagery (and everything else)has increased dramatically, which increases the computational complexity.
• Therefore, deep learning method becomes more appropriate.
Enze Zhang
Image Classification, Segmentation Speech Recognition, Stock Price Prediction
Game Player
Applications of Deep Learning
And many many more!
TerraSAR-X radar image
Landsat-8 optical image
• One of the largest and fastest tidewater glaciers in the world.
• Contributed nearly 1 mm to the global sea level rise from 2000 to 2011
Study target: Jakobshavn glacier
Deep Learning Results
Zhang, E., L. Liu, L. Huang (2019), Automatically delineating the calving front of Jakobshavn Isbræ from multitemporal TerraSAR-X images: a deep learning approach, The Cryosphere, 13, 1729-1741
Enze will give a poster on this study
Why I am excited about cryospheric geophysics
• Innovative and combined usage of state-of-the-art geophysical methods, including deep learning
• Study on-going dramatic changes in various cryosphere systems from interdisciplinary perspectives
• High social impacts: global climate change, sea level rise, etc.
Siberia(Russia)
Scandinavia
Iceland
Greenland
Alaska(USA)
Canada
Arctic Ocean
Svalbard
My previous & current field sites
Tibet(China)
Time for action! (see more photos from our group website)
What kind of PhD students I am looking for
• A driving curiosity to understand how the Earth, esp. the cryosphere works
• Self-motivated
• Independent but capable of working in a team
• Willing to tackle challenging problems
What I can offer you
• Share my passion of science & my vision about cryospheric geophysics
• Train you as an independent scholar through frontier research projects
• International perspectives and professional network
• Always ready to help
• Looking forward to learning from you
Want to learn more about our group’s research this week?
• Tomorrow (Wed) poster session: my PhD students will present four posters
• Group meeting on Thursday • 2:30 pm in this conference room• Lingcao Huang’s rehearsal presentation for PhD thesis defense: “Mapping Non-lake Thermokarst Landforms on the Tibetan Plateau Using Remote Sensing and Deep Learning”
• Talk to me (Room 315) and my group members (Room 308)
• Visit my group website• I’ll put this presentation on my website
Email: [email protected]
Website: cryocuhk.github.io
