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Who Needs New Datums? NGS Says…. Marti Ikehara California Geodetic Advisor, Sacramento. ftp://ftp.ngs.noaa.gov/pub/marti. Outline. New datums down the road GRAV-D Program, building on GOCE data New datum, epoch for CORS soon Visualizing Geodetic control. What IS a datum?.

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Who Needs New Datums? NGS Says…


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  1. Who Needs New Datums?NGS Says… Marti Ikehara California Geodetic Advisor, Sacramento ftp://ftp.ngs.noaa.gov/pub/marti

  2. Outline • New datums down the road • GRAV-D Program, building on GOCE data • New datum, epoch for CORS soon • Visualizing Geodetic control

  3. What IS a datum? • It is a reference, a basis, for coordinates, so a datum has an origin and/or ‘zero’. • “Underlying” a horizontal datum system is an ELLIPSOID, that represents the global shape of the earth; a DATUM is the ‘continental’ shape as realized with physical marks (passive or active) • Our vertical datum is based on differential leveling

  4. NGVD29 The National Geodetic Vertical Datum of 1929 was referenced to 26 tide gauges in the US and Canada

  5. NAVD88 The North American Vertical Datum of 1988 is referenced to a single tide gauge in Canada

  6. EQUIPOTENTIAL SURFACES

  7. GEOID09 compared to GEOID03 09: teal, good; yellow: State advisor-rejected; red: analysis-rejected 03 (underlying dots): dk blue, kept; orange: rejected

  8. From Helmer’s article in Winter 09/10 issue of California Surveyor

  9. Rationale for new Datums • Terminology • Horizontal becomes GEOMETRIC • Vertical becomes GEOPOTENTIAL • When? 2020+, or when GRAV-D program is completed • Why? But why?! • Primarily need a better vertical datum for “vertical” data(geoid, ortho ht) not obtained by traditional leveling

  10. 2009 National Research Council Report “…uniform national standards for FEMA flood maps cannot be met until an improved orthometric height datum and geoid model exist…”

  11. Rationale for new Datums • Terminology • Horizontal becomes GEOMETRIC • Vertical becomes GEOPOTENTIAL • When? 2018, if GRAV-D program is complete • Why? But why?! • Primarily need a better vertical datum for “vertical” data(geoid, ortho ht) not obtained by traditional leveling • Geodetic Data collection relies upon navigation (GNSS) satellites orbiting around the mass center of the Earth • NAD83 reference frame/datum is not geocentric

  12. Simplified Concept of NAD 83 vs. ITRF00 (or WGS84) h83 h00 Earth’s Surface ITRF 00 Origin 2.2 meters Identically shaped ellipsoids (GRS80) a = 6,378,137.000 meters (semi-major axis) 1/f = 298.25722210088 (flattening) NAD 83 Origin

  13. Z Earth-Centered Earth-Fixed (ECEF) Coordinate System XA, YA,ZA (not NAD83) -Y -X Greenwich Meridian Earth Mass Center X, Y, Z = 0 Y X GRS 80 Ellipsoid -Z

  14. Rationale for new Datums • Terminology • Horizontal becomes GEOMETRIC • Vertical becomes GEOPOTENTIAL • When? 2018, if GRAV-D program is complete • Why? But why?! • Primarily need a better vertical datum for “vertical” data(geoid, ortho ht) not obtained by traditional leveling • Geodetic Data collection relies upon navigation (GNSS) satellites orbiting around the mass center of the Earth • NAD83 reference frame/datum is not geocentric • Earth is not stable in all directions; reference frame must account for this to be as geodetically accurate as possible • Vertical velocities are ignored for NAD83

  15. Horizontal Velocities, relative to ‘stable’ NA tectonic plate, are reflected in HTDP model

  16. Worldwide Tectonic Horizontal Motions

  17. CORS Data allows for Monitoring Vertical Crustal Motion Vertical velocities associated with Glacial Isostatic Adjustment (rebound)

  18. Evolution of Geodetic Datums: from NAD27/NGVD29 to NAD83/NAVD88 to ?/ ? GPS H + V 2 + 1 27, 29 H + V 2 + 1 83(86), 88 H + VE+ VO 2 + 1 + 1 83(92), 88 +VELOCITIES (time) H + Ht+ VE +VO 2 + 2 + 1+ 1 83(07)+HTDP, 88 H + Ht+VE+ VEt 2 + 2 + 1+ 1 GEOMETRIC (VE+G)[+VEt] + Gt 1 + 1 GEOPOTENTIAL H + Ht+VE+ VEt 2 + 2 + 1+ 1 ITRF00 (2002.00) + GRAVITY (geoid model)

  19. The Future of Height Mod: GRAV-D Gravity for the Redefinition of the American Vertical Datum • GRAV-D • Airborne gravity surveys (taking 10 years) • Coastal areas surveyed first • All USA states and territories • www.ngs.noaa.gov/GRAV-D • GOAL: • Orthometric heights-”elevations” – to be good to 2 cm anywhere, anytime with an excellent ellipsoid height from GNSS technology. Currently *this* takes 3-4 hours at 15-second recording and dual-frequency GPS • Height changes much more easily monitored than by leveling, using new technology – GNSS heights and gravity values • Spot-checking/monitoring gravity changes with portable field units

  20. “CONUS” Alaska Guam / Northern Marianas Hawaii Puerto Rico / Virgin Islands American Samoa Planned GRAV-D Coverage

  21. Preliminary GRAV-D Results

  22. Gravity/geoid as measured by GOCE satellitehttp://news.bbc.co.uk/2/hi/science/nature/8767763.stm

  23. 1. Earth is a slightly flattened sphere - it is ellipsoidal in shape • 2. Goce senses tiny variations in the pull of gravity over Earth • 3. The data is used to construct an idealised surface, or geoid • 4. It traces gravity of equal 'potential'; balls won't roll on its 'slopes' • 5. It is the shape the oceans would take without winds and currents • 6. So, comparing sea level and geoid data reveals ocean behaviour • 7. Gravity changes can betray magma movements under volcanoes • 8. A precise geoid underpins a universal height system for the world • 9. Gravity data can also reveal how much mass is lost by ice sheets

  24. New datum, epoch for CORS • Current: ITRF2000, 2002.00 • Near end of year: ITRF2008, 2008.00 and NAD83 (“CORS96A”), 2010.00 for CORS only • No change to passive monumentation, eg, NAD83 (NSRS2007), 2007.00 • About 1000 CORS nationwide • Those with >2 years of data • Changes on the order of mm, but a few outliers are showing several decimeters • List will be prepared, showing amount of change

  25. Visualization of NGS Geodetic Control • Geodetic advisor website, located at Caltrans Office of Land Surveys webpages http://www.dot.ca.gov/hq/row/landsurveys/geodetic • Google Earth kmls • Google Maps online • Shapefiles • DSWorld, NGS partner software

  26. http://www.dot.ca.gov/hq/row/landsurveys/geodetic/geodetic_control.htmlhttp://www.dot.ca.gov/hq/row/landsurveys/geodetic/geodetic_control.html

  27. Kml’s and shapefiles downloadable

  28. http://www.dot.ca.gov/hq/row/landsurveys/geodetic/geodetic_control.htmlhttp://www.dot.ca.gov/hq/row/landsurveys/geodetic/geodetic_control.html

  29. Using NGS DSWORLD software and Google Earth to get any vintage geodetic data from NGSIDB Start by downloading “Google earth” at: http://earth.google.com/download-earth.html Click here

  30. Open the NGS main page atwww.ngs.noaa.gov Mouse-over the “TOOLS” button Click on “DOWNLOAD PC SOFTWARE”

  31. Clickonthe link: “UserContributedSoftwareisalsoavailable…..” Click here

  32. Next, click on the DSWORLD (Version *.**) link. A “file download” window will appear. Choose to save the file where you can easily find it. It will be a zip file, so you will need to unzip it and then double click on the setup.exe file. That will install the program for you. For additional information or assistance, please contact your NGS State Geodetic Advisor

  33. Anything Else?! • Marti.ikehara@noaa.gov • 916-227-7325 • ftp://ftp.ngs. noaa.gov/pub/marti