NASA/TM 2012-208641 / Vol 8 ICESat (GLAS) Science Processing Software Document Series The Algorithm Theoretical Basis Document for the Atmospheric Delay Correction to GLAS Laser Altimeter Ranges Thomas A. Herring and Katherine J. Quinn National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, Maryland 20771 October 2012
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NASA/TM 2012-208641 / Vol 8 ICESat (GLAS) Science Processing Software Document Series The Algorithm Theoretical Basis Document for the Atmospheric Delay Correction to GLAS Laser Altimeter Ranges Thomas A. Herring The Massachusetts Institute of Technology, Cambridge, MA Katherine J. Quinn The Massachusetts Institute of Technology, Cambridge, MA National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, Maryland 20771 October 2012
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Table of Contents 1.0 Introduction....................................................... 3 2.0 Algorithm Description............................................... 3 2.1 Group Refractivity Models...................................... 3 2.2 Zenith Delay Equations........................................ 9 2.3 Off-Nadir Pointing Corrections.................................. 11 2.4 NCEP Global Analyses....................................... 14 2.5 Surface Pressure............................................ 16 2.6 Precipitable Water Vapor....................................... 20 2.7 Delay Correction with Respect to Height........................... 20 2.8 Spatial Interpolation........................................... 21 2.9 Temporal Interpolation........................................ 22 2.10 Coordinate Systems........................................... 23 2.11 Processing Flow............................................... 23 3.0 Validation......................................................... 24 4.0 References........................................................ 29 Appendix A Appendix B ICESat Mission Summary Off-Nadir Atmospheric Delay Corrections Addendum 1
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REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188 The public repor ing burden for his collection of informa ion is estimated to average 1 hour per response, including the ime for reviewing instruc ions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collec ion of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD-MM-YYYY) 2. REPORT TYPE 3. DATES COVERED (From - To) 30-10-2012 Technical Memorandum 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER The Algorithm Theoretical Basis Document for the Atmospheric Delay Correction to GLAS Laser Altimeter Ranges 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER Thomas A. Herring, Katherine J. Quinn 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER The Massachusetts Institute of Technology, Cambridge, MA Goddard Space Flight Center Greenbelt, MD 20771 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITOR'S ACRONYM(S) National Aeronautics and Space Administration Washington, DC 20546-0001 12. DISTRIBUTION/AVAILABILITY STATEMENT NASA GSFC 11. SPONSORING/MONITORING REPORT NUMBER NASA/TM-2012-208641/Vol. 8 Unclassified-Unlimited, Subject Category: 2, 43, 47 Report available from the NASA Center for Aerospace Information, 7115 Standard Drive, Hanover, MD 21076. (443)757-5802 13. SUPPLEMENTARY NOTES 14. ABSTRACT NASA s Ice, Cloud, and Land Elevation Satellite (ICESat) mission will be launched late 2001. It s primary instrument is the Geoscience Laser Altimeter System (GLAS) instrument. The main purpose of this instrument is to measure elevation changes of the Greenland and Antarctic icesheets. To accurately measure the ranges it is necessary to correct for the atmospheric delay of the laser pulses. The atmospheric delay depends on the integral of the refractive index along the path that the laser pulse travels through the atmosphere. The refractive index of air at optical wavelengths is a function of density and molecular composition. For ray paths near zenith and closed form equations for the refractivity, the atmospheric delay can be shown to be directly related to surface pressure and total column precipitable water vapor. For ray paths off zenith a mapping function relates the delay to the zenith delay. The closed form equations for refractivity recommended by the International Union of Geodesy and Geophysics (IUGG) are optimized for ground based geodesy techniques and in the next section we will consider whether these equations are suitable for satellite laser altimetry. 15. SUBJECT TERMS Cryospheres, remote sensing, geodesy, satellite instruments, lasers, altimetry, refraction, elevation, algorithms, ice sheet elevation, ice environments, ice 16. SECURITY CLASSIFICATION OF: a. REPORT b. ABSTRACT c. THIS PAGE Unclassified Unclassified Unclassified 17. LIMITATION OF ABSTRACT Unclassified 18. NUMBER OF PAGES 47 19b. NAME OF RESPONSIBLE PERSON Dr. H. Jay Zwally 19b. TELEPHONE NUMBER (Include area code) (301) 614-5643 Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39-18