Ryan T. Walker
(SCIENTIFIC SOFTWARE PROGRAMMER)
| Email: | ryan.t.walker@nasa.gov |
| Org Code: | |
| Address: |
NASA/GSFC Mail Code 698 Greenbelt, MD 20771 |
| Employer: | Hexagon US Federal |
Brief Bio
Ryan joined 698 in summer 2020, and was previously at Goddard from 2012-2018 with the Cryospheric Sciences Laboratory (615). He works on the Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter, primarily handling data processing and scientific analysis for LOLA's passive radiometry observations.
In his previous professional life (he's "early second career") Ryan was a glaciologist working on numerical modeling of ice sheets. He currently enjoys the different mathematical challenges posed by dealing with large datasets, and is becoming curious about ice throughout the solar system.
Research Interests
Previous: Modeling of Earth's ice sheets and effects on sea level
Earth Science: Ice Sheets & GlaciersCurious about: Ice throughout the solar system
Solar System: IceCurrent Projects
Passive radiometry of the Moon in the near-infrared with LOLA
Remote Sensing
When not in altimetry mode, i.e., when the laser is inactive, LOLA can be operated as a near-infrared (1064 nm) passive radiometer. By adjusting the threshold and gain of the detectors, the solar photon counts reflected off the lunar surface that are “noise” for altimetry become the signal. When properly calibrated, these observations constitute a dataset spanning December 2013 to the present that provides information about the reflectance of the Moon's surface across a broad range of viewing angles. Analysis of how the apparent reflectance varies with geometry can produce insights about physical and geological properties of the lunar surface.
Positions/Employment
Senior Software Analyst
Hexagon US Federal - NASA Goddard Space Flight Center
2020 - Present
Research Scientist
University of Maryland - NASA Goddard Space Flight Center
2012 - 2018
Research Scientist
Pennsylvania State University - State College, PA
2007 - 2012
Education
Ph.D., Atmosphere Ocean Science, New York University (2006)
- Thesis: A two-dimensional coupled model for ice shelf-ocean interaction
- Advisor: David M. Holland
B.S., Mathematics, Haverford College (1998)
Awards
2014 NASA Hydrospheric and Biospheric Sciences Annual Award for Outstanding Publication as a member of the international SeaRISE ice-sheet modeling team
Wilhelm Magnus Prize from the Courant Institute of Mathematical Sciences (New York University) for “significant contributions to the mathematical sciences” in Ph.D. dissertation
Selected Publications
Refereed
2024. "Near-infrared Photometry of the Moon’s Surface with Passive Radiometry from the Lunar Orbiter Laser Altimeter (LOLA).", The Planetary Science Journal, 5 (5): 122 [10.3847/psj/ad4467] [Journal Article/Letter]
2018. "Dynamics of active subglacial lakes in Recovery Ice Stream.", Journal of Geophysical Research: Earth Surface, [10.1002/2017jf004409] [Journal Article/Letter]
2017. "Determining Ice-Sheet Uplift Surrounding Subglacial Lakes with a Viscous Plate Model.", Frontiers in Earth Science, 5 [10.3389/feart.2017.00103] [Journal Article/Letter]
2016. "Modeling Antarctic subglacial lake filling and drainage cycles.", The Cryosphere, 10 (4): 1381-1393 [10.5194/tc-10-1381-2016] [Journal Article/Letter]
2016. "A Viscoelastic Model of Ice Stream Flow with Application to Stick-Slip Motion.", Front. Earth Sci., 4 [10.3389/feart.2016.00002] [Journal Article/Letter]
2015. "Tidally driven ice speed variation at Helheim Glacier, Greenland, observed with terrestrial radar interferometry.", Journal of Glaciology, 61 (226): 301-308 [10.3189/2015jog14j173] [Journal Article/Letter]
2015. "Oceanic Forcing of Ice-Sheet Retreat: West Antarctica and More.", Annual Review of Earth and Planetary Sciences, 43 207 -231 [10.1146/annurev-earth-060614-105344] [Journal Article/Letter]
2014. "Ice-shelf flexure and tidal forcing of Bindschadler Ice Stream, West Antarctica.", Earth and Planetary Science Letters, 395 184-193 [10.1016/j.epsl.2014.03.049] [Journal Article/Letter]
2013. "Efficient Flowline Simulations of Ice Shelf–Ocean Interactions: Sensitivity Studies with a Fully Coupled Model.", Journal of Physical Oceanography, 43 (10): 2200–2210 [10.1175/JPO-D-13-037.1] [Journal Article/Letter]
2013. "Ice-sheet model sensitivities to environmental forcing and their use in projecting future sea level (the SeaRISE project).", Journal of Glaciology, 59 (214): 195-224 [10.3189/2013JoG12J125] [Journal Article/Letter]
2013. "Dynamic (in)stability of Thwaites Glacier, West Antarctica.", J. Geophys. Res. Earth Surf., 118 (2): 638-655 [10.1002/jgrf.20044] [Journal Article/Letter]
2013. "Insights into spatial sensitivities of ice mass response to environmental change from the SeaRISE ice sheet modeling project II: Greenland.", J. Geophys. Res. Earth Surf., 118 (2): 1025-1044 [Full Text] [10.1002/jgrf.20076] [Journal Article/Letter]
2013. "Insights into spatial sensitivities of ice mass response to environmental change from the SeaRISE ice sheet modeling project I: Antarctica.", Journal Of Geophysical Research: Earth Surface, 118 (2): 1002-1024 [10.1002/jgrf.20081] [Journal Article/Letter]
2013. "Ice-shelf tidal flexure and subglacial pressure variations.", Earth and Planetary Science Letters, 361 422-428 [10.1016/j.epsl.2012.11.008] [Journal Article/Letter]
Talks, Presentations and Posters
Other
Spatially-resolved Lunar Phase Function at 1064 nm from Lunar Orbiter Laser Altimeter (LOLA) Passive Radiometry
December 2023
Lunar and Planetary Sciences Conference (The Woodlands, TX)
Calibration of Near-Infrared Passive Radiometry from the Lunar Orbiter Laser Altimeter (LOLA)
December 2022
Lunar and Planetary Sciences Conference (Virtual)
Spatially-resolved Lunar Phase Function at 1064 nm from Lunar Orbiter Laser Altimeter (LOLA) Passive Radiometry
December 2022
American Geophysical Union Fall Meeting (Chicago, IL)
Calibration of Near-Infrared Passive Radiometry from the Lunar Orbiter Laser Altimeter (LOLA)
December 2021
American Geophysical Union Fall Meeting (Virtual)