Expand sub-menus

Dr. Ryan T. Walker

Photo of RYAN WALKER

Dr. Ryan T. Walker

  • SCIENTIFIC SOFTWARE PROGRAMMER
  • NASA/GSFC
  • Mail Code: 698
  • CHANTILLY , VA 20151
  • 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

    Remote sensing of the Moon


    Previous: Modeling of Earth's ice sheets and effects on sea level

    Curious about: Ice throughout the solar system

    Current Projects

    Passive radiometry of the Moon in the near-infrared with LOLA

    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

    2020 - Present

    Senior Software Analyst

    Hexagon US Federal, NASA Goddard Space Flight Center
    2012 - 2018

    Research Scientist

    University of Maryland, NASA Goddard Space Flight Center
    2007 - 2012

    Research Scientist

    Pennsylvania State University, State College, PA

    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
    M.S., Mathematics, New York University (2002)
    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

    Walker, R. T., M. A. Werder, C. F. Dow, and S. M. Nowicki. 2017. "Determining Ice-Sheet Uplift Surrounding Subglacial Lakes with a Viscous Plate Model." Frontiers in Earth Science, 5: [10.3389/feart.2017.00103]

    Dow, C. F., M. A. Werder, S. Nowicki, and R. T. Walker. 2016. "Modeling Antarctic subglacial lake filling and drainage cycles." The Cryosphere, 10 (4): 1381-1393 [10.5194/tc-10-1381-2016]

    Walker, R. T., B. R. Parizek, R. B. Alley, and S. M. Nowicki. 2016. "A Viscoelastic Model of Ice Stream Flow with Application to Stick-Slip Motion." Front. Earth Sci., 4: [10.3389/feart.2016.00002]

    Voytenko, D., A. Stern, D. M. Holland, et al. T. H. Dixon, K. Christianson, and R. T. Walker. 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]

    Alley, R. B., S. Anandakrishnan, K. Christianson, et al. H. J. Horgan, A. Muto, B. R. Parizek, D. Pollard, and R. T. Walker. 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]

    Walker, R. T., B. R. Parizek, R. B. Alley, K. M. Brunt, and S. Anandakrishnan. 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]

    Walker, R., D. M. Holland, B. R. Parizek, et al. R. B. Alley, S. Nowicki, and A. Jenkins. 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]

    Bindschadler, R., S. Nowicki, A. Abe-Ouchi, et al. A. Ashwanden, H. Choi, J. Fastook, G. Granzow, R. Greve, G. Gutowski, U. Herzfeld, C. Jackson, J. Johnson, C. Khroulev, A. Levermann, W. H. Lipscomb, M. A. Martin, M. Morlighem, B. R. Parizek, D. Pollard, S. F. Price, D. Ren, F. Saito, T. Sato, H. Seddik, H. Seroussi, K. Takahashi, R. Walker, and W. L. Wang. 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]

    Parizek, B., K. Christianson, S. Anandakrishnan, et al. R. Alley, R. Walker, R. Edwards, D. Wolfe, G. Bertini, S. Rinehart, R. Bindschadler, and S. Nowicki. 2013. "Dynamic (in)stability of Thwaites Glacier, West Antarctica." J. Geophys. Res. Earth Surf., 118 (2): 638-655 [10.1002/jgrf.20044]

    Nowicki, S., A. Abe-Ouchi, A. Aschwanden, et al. E. Bueler, H. Choi, J. Fastook, G. Granzow, R. Greve, G. Gutowski, U. Herzfeld, C. Jackson, J. Johnson, C. Khroulev, E. Larour, A. Levermann, W. H. Lipscomb, M. A. Martin, M. Morlighem, B. R. Parizek, D. Pollard, S. F. Price, D. Ren, E. Rignot, F. Saito, T. Sato, H. Seddik, H. Seroussi, K. Takahashi, R. Walker, and W. Wang. 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 (Link)] [10.1002/jgrf.20076]

    Nowicki, S., R. A. Bindschadler, A. Abe-Ouchi, et al. A. Aschwanden, E. Bueler, H. Choi, J. Fastook, G. Granzow, R. Greve, G. Gutowski, U. Herzfeld, C. Jackson, J. Johnson, C. Khroulev, E. Larour, A. Levermann, W. H. Lipscomb, M. A. Martin, M. Morlighem, B. R. Parizek, D. Pollard, S. F. Price, D. Ren, E. Rignot, F. Saito, T. Sato, H. Seddik, H. Seroussi, K. Takahashi, R. Walker, and W. L. Wang. 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]

    Walker, R. T., B. Parizek, R. Alley, et al. S. Anandakrishnan, K. Riverman, and K. Christianson. 2013. "Ice-shelf tidal flexure and subglacial pressure variations." Earth and Planetary Science Letters, 361: 422-428 [10.1016/j.epsl.2012.11.008]

    Talks, Presentations and Posters

    Spatially-resolved Lunar Phase Function at 1064 nm from Lunar Orbiter Laser Altimeter (LOLA) Passive Radiometry

     2023

    Lunar and Planetary Sciences Conference (The Woodlands, TX)

    Calibration of Near-Infrared Passive Radiometry from the Lunar Orbiter Laser Altimeter (LOLA) 

     2022

    Lunar and Planetary Sciences Conference (Virtual)

    Spatially-resolved Lunar Phase Function at 1064 nm from Lunar Orbiter Laser Altimeter (LOLA) Passive Radiometry

     2022

    American Geophysical Union Fall Meeting (Chicago, IL)

    Calibration of Near-Infrared Passive Radiometry from the Lunar Orbiter Laser Altimeter (LOLA) 

     2021

    American Geophysical Union Fall Meeting (Virtual)

    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.


    Selected Publications

    Refereed

    Walker, R. T., M. A. Werder, C. F. Dow, and S. M. Nowicki. 2017. "Determining Ice-Sheet Uplift Surrounding Subglacial Lakes with a Viscous Plate Model." Frontiers in Earth Science 5 [10.3389/feart.2017.00103]

    Dow, C. F., M. A. Werder, S. Nowicki, and R. T. Walker. 2016. "Modeling Antarctic subglacial lake filling and drainage cycles." The Cryosphere 10 (4): 1381-1393 [10.5194/tc-10-1381-2016]

    Walker, R. T., B. R. Parizek, R. B. Alley, and S. M. Nowicki. 2016. "A Viscoelastic Model of Ice Stream Flow with Application to Stick-Slip Motion." Front. Earth Sci. 4 [10.3389/feart.2016.00002]

    Voytenko, D., A. Stern, D. M. Holland, et al. T. H. Dixon, K. Christianson, and R. T. Walker. 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]

    Alley, R. B., S. Anandakrishnan, K. Christianson, et al. H. J. Horgan, A. Muto, B. R. Parizek, D. Pollard, and R. T. Walker. 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]

    Walker, R. T., B. R. Parizek, R. B. Alley, K. M. Brunt, and S. Anandakrishnan. 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]

    Walker, R., D. M. Holland, B. R. Parizek, et al. R. B. Alley, S. Nowicki, and A. Jenkins. 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]

    Bindschadler, R., S. Nowicki, A. Abe-Ouchi, et al. A. Ashwanden, H. Choi, J. Fastook, G. Granzow, R. Greve, G. Gutowski, U. Herzfeld, C. Jackson, J. Johnson, C. Khroulev, A. Levermann, W. H. Lipscomb, M. A. Martin, M. Morlighem, B. R. Parizek, D. Pollard, S. F. Price, D. Ren, F. Saito, T. Sato, H. Seddik, H. Seroussi, K. Takahashi, R. Walker, and W. L. Wang. 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]

    Parizek, B., K. Christianson, S. Anandakrishnan, et al. R. Alley, R. Walker, R. Edwards, D. Wolfe, G. Bertini, S. Rinehart, R. Bindschadler, and S. Nowicki. 2013. "Dynamic (in)stability of Thwaites Glacier, West Antarctica." J. Geophys. Res. Earth Surf. 118 (2): 638-655 [10.1002/jgrf.20044]

    Nowicki, S., A. Abe-Ouchi, A. Aschwanden, et al. E. Bueler, H. Choi, J. Fastook, G. Granzow, R. Greve, G. Gutowski, U. Herzfeld, C. Jackson, J. Johnson, C. Khroulev, E. Larour, A. Levermann, W. H. Lipscomb, M. A. Martin, M. Morlighem, B. R. Parizek, D. Pollard, S. F. Price, D. Ren, E. Rignot, F. Saito, T. Sato, H. Seddik, H. Seroussi, K. Takahashi, R. Walker, and W. Wang. 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 (Link)] [10.1002/jgrf.20076]

    Nowicki, S., R. A. Bindschadler, A. Abe-Ouchi, et al. A. Aschwanden, E. Bueler, H. Choi, J. Fastook, G. Granzow, R. Greve, G. Gutowski, U. Herzfeld, C. Jackson, J. Johnson, C. Khroulev, E. Larour, A. Levermann, W. H. Lipscomb, M. A. Martin, M. Morlighem, B. R. Parizek, D. Pollard, S. F. Price, D. Ren, E. Rignot, F. Saito, T. Sato, H. Seddik, H. Seroussi, K. Takahashi, R. Walker, and W. L. Wang. 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]

    Walker, R. T., B. Parizek, R. Alley, et al. S. Anandakrishnan, K. Riverman, and K. Christianson. 2013. "Ice-shelf tidal flexure and subglacial pressure variations." Earth and Planetary Science Letters 361 422-428 [10.1016/j.epsl.2012.11.008]

                                                                                                                                                                                            
    NASA Logo, National Aeronautics and Space Administration
    • NASA Official:
    • Curator:
    • Last Updated: 05/31/2023