Key-Rok Choi, Ph.D.
9617 Great Hills Trail #1427
Austin, TX 78759
Phone:(512) 689-5443
E-mail: krchoi@csr.utexas.edu
Residential Status: Permanent Resident (Green Card)

Resume last updated: 13-Nov-2005


SUMMARY:
Have the expertise in GPS systems, satellite orbital mechanics and estimation theory, earned Ph.D. in Aerospace Engineering in University of Texas, Austin. Extensively experienced in Precise Orbit Determination (POD) problem for almost 10 years; Worked with the force model and measurement model improvements; Worked with many kinds of tracking data such as GPS, SLR, PRARE, and DORIS; involved into several NASA projects related to Low-Earth-Orbiter (LEO), such as TOPEX, CHAMP, JASON and GRACE; Experienced with setting up and conducting simulations. I also have many years experience with data analysis, and have worked many years with diverse technical skills and knowledge in various hardware and software.


EDUCATION:
Ph.D. (2003), Aerospace Engineering, The University of Texas at Austin (GPA: 3.90/4.0)
Dissertation title is RJason-1 Precision Orbit Determination by combining GPS with laser and DORIS dataS.
MS(1995) and BS(1991) in Astronomy, SEOUL National University, KOREA (Served the military service in 1992-1993).


WORK EXPERIENCES:
9/2004 -
Present		 Research Engineer/Scientist Associate III, The University of Texas at Austin/Center for Space Research
  • Working Projects: NASAUs JASON Project and the Gravity Recovery and Climate Experiment (GRACE) Project.
  • Successful porting and implementing programs (Fortran 90, C, and Unix batch scripts) from SGI Cray Scalable Vector 1 (SV1, running the UNICOS operating system) to IBM Power4 System (AIX 5.1 operating system) for GRACE orbit processor and gravitational model simulation.
  • GPS final orbit product comparison from JPL and IGS to see the effect on the LEO precision orbit. (UNIX scripts, Fortran/C)
01/1997 -
9/2004		 Research Assistant, The University of Texas at Austin/Center for Space Research
  • Coded the CHAMP satelliteUs attitude determination with Quaternion data (2000).
  • Preprocessed Microwave altimeter data (form of FTP, 8-mm tapes and CD-ROMs) and operated Data Analysis from the TOPEX/POSEIDON satellite to measure sea level on Cray and UNIX workstation environment (1997-1999).
  • Coding/testing programs for GPS Data Preprocessing and Analysis (1999-present)
  • Involved into the GRACE Project for performing/debugging codes for simulation of gravitational data. (1998-1999)
  • Involving Jason and TOPEX/POSEIDON Science Working Team on implementing/modifying/testing the codes for the precise orbit determination. Three tracking data types such as NASA's Global Positioning System (GPS) data, Satellite Laser Ranging (SLR) data, and the French Doppler Orbitography and Radiopositioning Integrated by Satellite System (DORIS) data were employed at once, and successfully implemented to achieve ~1 cm orbit accuracy. (1999-present)
01/1997 -
06/1997		 Teaching Assistant, The University of Texas at Austin
-- Statistics/Dynamics


SKILLS:
Working Knowledge:
  • Significant experience of satellite (ERS-1/2, TOPEX) altimeter data process/analysis
  • Expertise in precise orbit determination and attitude determination of satellites.
  • Excellent knowledge of GPS system; Experiences in developing algorithm, coding to process GPS data and performing research in GPS application.
  • Excellent knowledge of Kalman filter, linear estimation theory; their application for determining satellite orbits and positioning an object on the ground.
  • Satellites of which GPS data I actually processed: GPS satellites, TOPEX/POSEIDON, GFO-2, CHAMP, Jason-1 and GRACE.
  • Software I have experienced and have been working on particularly for orbit determination problem and the GPS process: STK (AGI satellite tool kit); UTOPIA and MSODP (the orbit determination software of UT/CSR); GIPSY/OASIS (the NASA/JPL software).
Computer Systems:
  • Operating System: Programming experience of many years in Unix (SUN/Solaris, HP-UX, AIX, SGI; Cray SV1, J90, T3E) and Linux (Red Hat). MS Windows (Earned credits from the class: "Course 922: Supporting Microsoft Windows NT 4.0 Core Technologies", provided by CBA/GSB Microsoft Authorized Academic Training Program at University of Texas, Austin, 1999), MS-DOS, Macintosh, X-Windows, and VAX/VMS.
  • Programming Language: Proficient in C/C++ (Earned the credits from the class, "Programming Data structure in C++" at University of Texas, Austin.), FORTRAN 77/90, MATLAB, MATHEMATICA, HTML, PERL, Shell Scripts, and IDL; Have basic knowledge in CGI scripts, Python, and Java.
  • Compiler: Xlc/xlc, xlf/xlf90, GNU gcc, cc (SUN, SGI platform). Various Fortran, C/C++ compilers and software debugging tools for several platforms.
  • Internet/Web: HTML, JavaScript, Perl, CGI scripts. Have Web design skill with HTML and ASP.
  • Application: STK, GIPSY/OASIS, MSODP/UTOPIA; Microsoft Office, Tex/LaTex; X-Windows, GNU emacs and vi editors; Adobe Photoshop and IDL for graphics.
  • Future Interest: GPS embedded systems, Hardware Interface (serial port, parallel port, ISA bus, PCI bus, USB), ASM language, Microsoft Visual Studio .NET 2005 (including Visual Basic and Visual C++), Palm OS, Windows CE, Windows API


RESEARCH INTERESTS:
Precision Orbit Determination by combining tracking systems (GPS and SLR/DORIS); Positioning with GPS technique; Gravity Model Determination; Sea Surface Topography and Oceanography; Space Geodesy; GIS(geographic information system) application; GPS embedded systems.


PUBLICATIONS:
  1. Choi, K.-R., J.C.Ries, B.D. Tapley, "Jason-1 Orbit Improvement by Optimal Network Selection of GPS Stations", in preparation, 2005.
  2. Choi, K.-R., J.C.Ries, B.D. Tapley, "Jason-1 Precision Orbit Determination by Combining SLR and DORIS with GPS Tracking Data", Marine Geodesy, 27(1-2), 319-331, 2004.
  3. Choi, K.-R., J.C.Ries, B.D. Tapley, "Jason-1 POD", Jason-1 and T/P Scientific Working Team Meeting, 10-12 June 2002, Biarritz, France, TP2-J0-CR-2156-CNES, Yves Menard (Eds.).
  4. Choi, K.-R., J.C.Ries, B.D. Tapley, "Jason-1 Orbit Improvement by combining GPS with SLR/DORIS", Jason-1 and T/P Scientific Working Team Meeting, New Orleans, Louisiana USA, 21-23 October 2002
  5. Ries, J.C., K.-R. Choi, B.D. Tapley, "Jason-1 and TOPEX/POSEIDON Precision Orbit Determination: Status and Plans", In Minutes of the Third Joint TOPEX/POSEIDON and Jason-1 Science Working Team Meeting, Lee-Lueng Fu (Eds,), JPL D-20240, November 15-17, 2000, Miami, Florida.
  6. Ries, J.C., D.P. Chambers, K.-R. Choi, R.J. Eanes, "Effect of ITRF2000 on TOPEX/POSEIDON Orbit Determination and Mean Sea Level Time Series", G51B-0251, Presented at Fall AGU, 2001, S.F.,CA.
  7. Ries, J.C., K.-R. Choi, and R.J. Eanes, "Jason-1 Precision Orbit Determination: Status and Assessment", Jason-1 and T/P Scientific Working Team Meeting, New Orleans, Louisiana USA, 21-23 October 2002
  8. Ries, J.C., K.-R. Choi "Jason-1 and TOPEX/POSEIDON Precision Orbit Determination: Initial Results" Jason-1 and T/P Scientific Working Team Meeting, 10-12 June 2002, Biarritz, France, TP2-J0-CR-2156-CNES, Yves Menard (Eds.).
  9. Rim, H., S. Yoon, B. Schutz, Z. Kang, P. Nagel, S. Bettadpur, B. Tapley, K. Choi, J. Ries, M. Cheng, "CHAMP POD at CSR", Presented at First CHAMP Science Meeting, Jan. 22-25, 2002, Potsdam, Germany.
  10. Tapley, B., S. Bettadpur, D. Chambers, M. Cheng, K. Choi, B. Gunter, Z. Kang, J. Kim, P. Nagel, J. Ries, H. Rim, P. Roesset and I. Roundhill, "Gravity field determination from CHAMP using GPS tracking and accelerometer data: Initial results", Paper presented at the 2001 Fall AGU meeting, San-Francisco, CA, December 10-14.


REFERENCES:

Dr. Byron Tapley
Center for Space Research
3925 West Braker Lane, Suite 200
Austin, TX 78759-5321
Tel) +1-512-471-5573
Fax) +1-512-471-3570
Email) tapley@csr.utexas.edu

Dr. Bob Schutz
Center for Space Research
3925 West Braker Lane, Suite 200
Austin, TX 78759-5321
Tel) +1-512-471-4267
Fax) +1-512-471-3570
Email) schutz@csr.utexas.edu

Dr. John Ries
Center for Space Research
3925 West Braker Lane, Suite 200
Austin, TX 78759-5321
Tel) +1-512-471-7486
Fax) +1-512-471-3570
Email) ries@csr.utexas.edu

Dr. C. K. Shum
Geodetic Science Laboratory for Space Geodesy and
Remote Sensing Research,
Dept. of Civil and Environmental Engineering and Geodetic Science
The Ohio State University
2070 Neil Ave.
Columbus, OH 43210-1275
Tel) +1-614-292-7118
Fax) +1-614-292-2957
Email) ckshum@osu.edu