geoid modeling at noaa dru a. smith, ph.d. national geodetic survey national ocean service, noaa...
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![Page 1: Geoid Modeling at NOAA Dru A. Smith, Ph.D. National Geodetic Survey National Ocean Service, NOAA November 13, 2000](https://reader036.vdocument.in/reader036/viewer/2022062518/56649e9e5503460f94b9f6f2/html5/thumbnails/1.jpg)
Geoid Modeling at NOAA
Dru A. Smith, Ph.D.National Geodetic SurveyNational Ocean Service, NOAA
November 13, 2000
![Page 2: Geoid Modeling at NOAA Dru A. Smith, Ph.D. National Geodetic Survey National Ocean Service, NOAA November 13, 2000](https://reader036.vdocument.in/reader036/viewer/2022062518/56649e9e5503460f94b9f6f2/html5/thumbnails/2.jpg)
November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
Topics of Discussion
• The many definitions of “height”
• Why does anyone need a geoid model?
• NOAA resources and partnerships
• Geoid modeling 101
• Current status and future directions
![Page 3: Geoid Modeling at NOAA Dru A. Smith, Ph.D. National Geodetic Survey National Ocean Service, NOAA November 13, 2000](https://reader036.vdocument.in/reader036/viewer/2022062518/56649e9e5503460f94b9f6f2/html5/thumbnails/3.jpg)
November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
The many definitions of “height”
• Orthometric Height (H) – Height from the geoid to the Earth’s surface– Frequently (informally) called “height above
mean sea level”– On most topographic maps
• e.g. “The Height of Mount Everest is 8848 meters”
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
![Page 5: Geoid Modeling at NOAA Dru A. Smith, Ph.D. National Geodetic Survey National Ocean Service, NOAA November 13, 2000](https://reader036.vdocument.in/reader036/viewer/2022062518/56649e9e5503460f94b9f6f2/html5/thumbnails/5.jpg)
November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
The many definitions of “height”
• Ellipsoidal Height (h)– Height from the ellipsoid to the Earth’s surface– Usually derived from GPS measurements– Easy to obtain through GPS– Has few physical applications
• e.g. water does not necessarily run ‘downhill’ in ellipsoid heights
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
The many definitions of “height”
• Geoid Height (N)– Height from ellipsoid up to geoid– Also called “geoid undulation”– N = h - H– “N” determined from gravity measurements
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
![Page 8: Geoid Modeling at NOAA Dru A. Smith, Ph.D. National Geodetic Survey National Ocean Service, NOAA November 13, 2000](https://reader036.vdocument.in/reader036/viewer/2022062518/56649e9e5503460f94b9f6f2/html5/thumbnails/8.jpg)
November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
Why do we need a geoid model?
• It saves money
• It saves time (but time = money)
• Additional scientific and economic uses:– Geophysical: Oil and other subsurface features– Oceanographic: Sea level rise and current
modeling
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
Saving money with a geoid model
• The geographic community needs orthometric heights, H
• Old way: H = H0 + H (spirit leveling)
– Time consuming, 4 person team. Expensive!
• New way: H = h - N (GPS & geoid)– Fast, accurate, 1 person team. Cheap!
• Part of NOAA’s “Height Modernization” program
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
Saving money with a geoid model
• Baltimore County GPS project, Phase III– Installed new vertical control benchmarks– 290 square miles (1/3 of Baltimore county)– Traditional leveling: 7 1/2 months / $174,000– GPS and geoid: 3 weeks / $ 49,000
• Savings: $125,000 = 72% !!
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
Saving money with a geoid model
• Baltimore county GPS project, Phase III– 1/3 of 1 county out of 3142 counties– Informal extrapolation:
• The geoid could save 150-1500 million dollars for this application alone
– Depends on achieving an accurate geoid not just in Baltimore, but everywhere
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
NOAA resources / partnerships
• NOAA is uniquely qualified to undertake this research
• Geoid research is cross-disciplinary
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
NOAA resources
• Within NOAA:– NOS : NGS -- gravity database, GPS on leveled
benchmarks and research on high resolution geoid modeling
– NESDIS : NGDC -- Gravity and topography data
– NESDIS : ORA : ORAD -- Satellite altimetry and oceanic gravity
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
NOAA partnerships
• Partner groups:– NIMA -- Significant gravity and DEM data
– USGS -- DEM data
– NASA -- Global gravity field with NIMA
– NTIA -- DEM data
– Universities -- Data and research
– States -- GPS cooperative surveys
– Other countries (Canada, Mexico, Caribbean, Denmark) -- Data and tech transfers
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
Geoid modeling 101
• Gravity measurements every 5-10 km
• Digital elevation models (30-100 m)
• Global gravity field models
• GPS heights on leveled benchmarks
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
![Page 17: Geoid Modeling at NOAA Dru A. Smith, Ph.D. National Geodetic Survey National Ocean Service, NOAA November 13, 2000](https://reader036.vdocument.in/reader036/viewer/2022062518/56649e9e5503460f94b9f6f2/html5/thumbnails/17.jpg)
November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
![Page 18: Geoid Modeling at NOAA Dru A. Smith, Ph.D. National Geodetic Survey National Ocean Service, NOAA November 13, 2000](https://reader036.vdocument.in/reader036/viewer/2022062518/56649e9e5503460f94b9f6f2/html5/thumbnails/18.jpg)
November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
Current Status
• GEOID99 accuracy:
• Absolute +/- 2.5 cm about North American Vertical
Datum of 1988 (NAVD 88)
• Differential +/- 0.2 to 3.5 cm between points 1 to 40+ km
apart
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
Positioning for the Future
• Today: Surveyors can do sub-cm spirit leveling over lines up to 10 km long
• Tomorrow: Surveyors expect to do 100+ km lines at similar accuracy with GPS and geoid (“GPS leveling”)
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
Achieving Higher Accuracies
• 1 cm error budget (absolute and differential)– Better theory– More data (Terabytes, USA; Petabytes, Globe)– More computational power
• Supercomputers?– Occasional, one shot, massive computations– Maui supercomputer: Fall 2000 (UNM/USAFRL)
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
Conclusions
• The geoid is the bridge between historical data sets and new cost-saving GPS technology
• Geoid modeling is an integral part of Height Modernization
• The “1 cm geoid” is achievable in the USA within 10 years
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November 13, 2000Geoid Modeling at NOAA
Dr. Dru A. Smith
Contact Information
• Dr. Dru A. Smith
• 301-713-3202 x 149
• Fax: 301-713-4172
• www.ngs.noaa.gov/GEOID