Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska

1. 45th Annual Alaska Surveying & Mapping ConferenceFebruary 21-25, 2011 Hilton Anchorage Hotel Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Part II: GRAV-D Airborne Survey Update Daniel R. Roman and Vicki A. Childers

2. Survey Priority Order • Alabama test region • Puerto Rico/US Virgin Islands • Gulf of Mexico (except Florida) • Alaska • Eastern US Seaboard (& FL)/Great Lakes • Western US Seaboard • Hawaii, Guam/CNMI, American Samoa • Interior CONUS • Aleutian Islands

3. GRAV-D Airborne Surveys • Gulf of Mexico 2008-09 (AL08, LA08, LA09, TX09) • Puerto Rico/US Virgin Islands 2009 (PV09) • Alaska 2008-11 (AK08, AK09, AK10-01, AK10-02, AK10-03) • California 2011 (CA11-01) - 11 surveys, ~10% of total area flown Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

4. Gulf of Mexico Surveys Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

5. Gulf of Mexico Preliminary Gravity Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

6. Puerto Rico/US Virgin Islands Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

7. Preliminary Gravity Puerto Rico Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

8. California 2011 Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

9. California Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

10. Alaska Surveys 2011 Plan Fairbanks 2010&11 2009 2010 2011 Plan 2008 Anchorage Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

11. AK Preliminary Gravity Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

12. Basic Airborne Operations • Instrumentation: • Relative gravity meter aboard aircraft • Inertial measurement unit • GNSS receivers included in both instruments • GPS base stations (three for redundancy) • Gravity tie • New absolute measurement • Relative tie to meter height in plane Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

13. GRAV-D Team • Vicki Childers • Theresa Diehl • Sandy Preaux • Justin Dahlberg • Greg Watson • Tim Wilkins • Carly Weil (not pictured) • Also pictured NOAA pilots Scott Price and Mark Sweeney 2010 NGS Convocation

14. Field Capability • Developing the project from scratch • Instrumentation • Acquisition, engineering, installation, troubleshoot • Operating procedures • Data Handling • QC: equipment working, data quality sufficient • Metadata creation, data archival, shipment to HQ

15. Field Capacity: Challenges • Field team depth • Need a dedicated aircraft • Present NOAA capacity is limited • Need both a long- and a shorter-range aircraft • Mods for USGS magnetometer • Needed instrumentation • Inertial measurement unit • Electronics racks

16. Data Processing: Software Development • GPS processing • GrafNav • Kinematic GPS Challenge • Gravity data processing • Aerograv Problem • Newton software • Programmer has created user-friendly version for 2.0 Newton 2.0

17. Airborne Data Flow

18. GRAV-D Web Page • Program events are recorded here • Survey progress will be displayed • Plan to make data and software available here http://www.ngs.noaa.gov/grav-d

19. Project Challenges • Optimum survey heights: 5Kft, 20kft, 35kft? • Alabama AL08 tested flights at all three altitudes • Downward continued noise amplified 7 times in 35kft data, 2 times in 20kft data • Comparisons of gravity field recovery with EGM08 continued to h=0 shows poor results at 35kft • 20,000 ft was identified as best height • Still above most weather • Aliasing issues can be dealt with

20. Newton 1.0 ResidualsΔg: +NGS ‘A-EGMs’ (N=1080) vs. Terr. (h=0m) 35,000 ft 20,000 ft 5,000 ft

21. Improvements to GPS Processing? • GPS Challenge produced 15 solutions from 9 groups • We will look to use the software that yields the best results • GrafNav will continue to be field QC software Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

22. Improvements to Gravity Processing • Thorough analysis of all aspects of gravity data processing • Rigorous treatment of all corrections • Final challenges remain: • Off-level correction • Low-pass filtering Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

23. Early Version Data Residualswith AGM08 Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

24. AK08 Residual Gravity Profiles Min = -50.76 Max = 31.46 Mean = 1.52 SD = 4.42 As compared with Original Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

25. Early Version Crossover Errors Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

26. Crossover Plots for AK08 Min = -12.90 Max = 12.03 Mean = -0.19 SD = 4.29 mGal As compared with Original Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

27. AK08 Residual Gravity Profiles (Airborne – EGM08) Lines 121-124 Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

28. AK08 vs EGM08 AK08 EGM08 Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200

29. Break time! Next up: Geoid Modeling Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Thursday, 0800-1200