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Geoid Modeling and GRAV-D: Gravity for the Redefinition of the American Vertical Datum

Geoid Modeling and GRAV-D: Gravity for the Redefinition of the American Vertical Datum Beaumont, Texas June 8-9, 2009 Renee Shields Height Modernization Manager. From the NGS 10-Year Plan. Define the NSRS

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Geoid Modeling and GRAV-D: Gravity for the Redefinition of the American Vertical Datum

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  1. Geoid Modeling and GRAV-D: Gravity for the Redefinition of the American Vertical Datum Beaumont, Texas June 8-9, 2009 Renee Shields Height Modernization Manager

  2. From the NGS 10-Year Plan • Define the NSRS • “The NSRS must be more accurate than all activities which build upon it, while still being practicably achievable.” • Maintain the NSRS • “NGS must track all of the temporal changes to the defining points of the NSRS in such a way as to always maintain the accuracy in the NSRS definition.” • Provide Access to the NSRS • “NGS must develop and maintain guidelines for users to access the NSRS at a variety of accuracies.” • “NGS will publish all coordinates of defining points of the NSRS with an epoch tag and will furthermore publish velocities relative to that epoch-tagged set of coordinates” http://geodesy.noaa.gov/INFO/ngs_tenyearplan.pdf

  3. Mission – The NSRS is… • The official national coordinate system of the U.S. federal government which includes: • Geodetic latitude, longitude and height • Scale, gravity, and orientation • How these values change with time • Components include: • National and Cooperative CORS • Network of passive monuments • Official national shoreline • Precise orbits of GNSS satellites used to define NSRS • Models and tools to describe how all of these quantities change over time.

  4. Science of Height mod – 3 kinds of Heights • Orthometric Heights (NAVD88): Traditionally leveling • Ellipsoid Heights (NAD83): GNSS • Geoid Heights (NAD83): gravity and modeling

  5. Ellipsoid, Geoid, and Orthometric Heights H = Orthometric Height (leveling) H = h - N h = Ellipsoidal Height (GPS) N = Geoid Height (model) TOPOGRAPHIC SURFACE h (NAD83) (NAVD88) H N Geoid Height (GEOID03/09) Ellipsoid Geoid

  6. ROD 1 ROD 2 ROD 1 Backsight Foresight Backsight Foresight 5’ 105’ HI 6’ 96’ 7.5’ BM 100’ 4.5’ INSTR 99’ BM INSTR NAVD88 Heights - Conventional Leveling

  7. enter GNSS… Can we get accurate heights with GNSS?

  8. Guidelines to obtain accurate heights through GNSS Equipment requirements Field Procedures/Data Collection Parameters Basic Control Requirements Processing/Analysis Procedures

  9. Equipment Requirements • Dual-frequency, full-wavelength GPS receiver • Required - observations > 10 km • Preferred - ALL observations regardless of length • Geodetic quality antennas with ground planes • Choke ring antennas; highly recommended • Successfully modeled L1/L2 offsets and phase patterns • Use identical antenna types if possible • Corrections must be utilized by processing software when mixing antenna types

  10. Equipment Requirements “Fixed” Height Tripod

  11. Data Collection Parameters • VDOP < 6 for 90% or longer of 30 minute session • Session lengths and sampling rate • Track satellites down to 10° elevation angle • Repeat Baselines • Different days • Different times of day • Detect, remove, reduce effects due to multipath and similar satellite geometry between sessions

  12. Two Days/Same Time -10.254 -10.251 > -10.253 Difference = 0.3 cm “Truth” = -10.276 Difference = 2.3 cm Two Days/ Different Times -10.254 > -10.275 -10.295 Difference = 4.1 cm “Truth” = -10.276 Difference = 0.1 cm

  13. Station pairs with large repeat base line differences also result in large residuals. NGS guidelines for estimating GPS-derived ellipsoid heights require user to re-observe these base lines.

  14. Four Basic Control Requirements • Occupy stations with known NAVD 88 orthometric heights, evenly distributed throughout project • Project areas < 20 km on a side, surround project with at least 4 NAVD 88 bench marks • Project areas > 20 km on a side, keep distances between GPS-occupied NAVD 88 bench marks to less than 20 km • Projects located in mountainous regions, occupy bench marks at base and summit of mountains, even if distance is less than 20 km

  15. Processing: Five Basic Procedures • Perform 3-D minimally constrained (free) adjustment • Analyze adjustment results • Compute differences between GPS-derived orthometric heights from free adjustment and published NAVD88 BMs • Evaluate differences to determine which BMs have valid NAVD88 height values • Perform constrained adjustment with results from previous step

  16. Sample Project • Area: East San Francisco Bay Project • Latitude 37° 50” N to 38° 10” N • Longitude 121° 45” W to 122° 25” W • Receivers Available: 5 • Standards: 2 cm GPS-Derived Heights

  17. 38°20’N CORS HARN NAVD’88 BM New Station D191 10CC 19.0km Primary Base Station 28.7km 25.7km LATITUDE 38.3km 31.6km 38.7km 25.8km LAKE MART 29.6km MOLA 37°50’N 121°40’W 122°35’W LONGITUDE Primary Base Stations

  18. CORS HARN NAVD’88 BM New Station 8.2km GPS-Usable Stations Spacing Station Primary Base Station

  19. 38°16’N 38°16’N Session F Session F Session E Session E CORS HARN NAVD’88 BM New Station Spacing Station CORS HARN NAVD’88 BM New Station Spacing Station Session D Session D Primary Base Station Primary Base Station Session G Session G LATITUDE LATITUDE Session A Session A Session C Session C Session B Session B 37°55’N 37°55’N 121°40’W 121°40’W 122°20’W 122°20’W LONGITUDE LONGITUDE Observation Sessions

  20. Texas Primary Control – CORS TXBM – Beaumont, TX TXME – Memphis, TX TXAN – San Antonio RRP2, TX

  21. Primary Control - Texas High Accuracy Reference Network (1993)

  22. HARN/Control Stations (75 km) 5.5 hr 3 days different times Primary Base (40 km) 5.5 hr 3 days different times Secondary Base (15 km) 0.5 hr 2 days different times Local Network Stations (7 to 10 km) 0.5 hr 2 days different times GPS Ellipsoid Height Hierarchy

  23. = HARN = Primary Base Network = Secondary Base Network = Local Base Network = Existing NGS Level line = New HMP Level line Height Modernization Project HARN - Average 50km, max 75km Secondary - Average 12-15km, max 15km Local – Average 6-8 km, max 10km Primary – 20-25km, max 40km

  24. NGS Datasheet – Leveling • 1 National Geodetic Survey, Retrieval Date = JUNE 6, 2009 • AC6323 *********************************************************************** • AC6323 DESIGNATION - BEA5 B • AC6323 PID - AC6323 • AC6323 STATE/COUNTY- TX/JEFFERSON • AC6323 USGS QUAD - VOTH (1993) • AC6323 • AC6323 *CURRENT SURVEY CONTROL • AC6323 ___________________________________________________________________ • AC6323* NAD 83(2007)- 30 09 15.32032(N) 094 10 50.43369(W) ADJUSTED • AC6323* NAVD 88 - 13.115 (meters) 43.03 (feet) ADJUSTED • AC6323 ___________________________________________________________________ • AC6323 EPOCH DATE - 2002.00 • AC6323 X - -402,394.366 (meters) COMP • AC6323 Y - -5,504,987.110 (meters) COMP • AC6323 Z - 3,185,163.813 (meters) COMP • AC6323 LAPLACE CORR- 0.04 (seconds) DEFLEC99 • AC6323 ELLIP HEIGHT- -14.472 (meters) (02/10/07) ADJUSTED • AC6323 GEOID HEIGHT- -27.51 (meters) GEOID03 • AC6323 DYNAMIC HT - 13.098 (meters) 42.97 (feet) COMP • AC6323 • AC6323 ------- Accuracy Estimates (at 95% Confidence Level in cm) -------- • AC6323 Type PID Designation North East Ellip • AC6323 ------------------------------------------------------------------- • AC6323 NETWORK AC6323 BEA5 B 0.51 0.41 2.04 • AC6323 ------------------------------------------------------------------- • AC6323 MODELED GRAV- 979,314.4 (mgal) NAVD 88 • AC6323 • AC6323 VERT ORDER - FIRST CLASS II

  25. NGS Datasheet – Leveling • AC6323.This is a reference station for the BEAUMONT RRP • AC6323.National Continuously Operating Reference Station (BEA5). • AC6323 • AC6323.The horizontal coordinates were established by GPS observations • AC6323.and adjusted by the National Geodetic Survey in February 2007. • AC6323 • AC6323.The datum tag of NAD 83(2007) is equivalent to NAD 83(NSRS2007). • AC6323.See National for more information. • AC6323.The horizontal coordinates are valid at the epoch date displayed above. • AC6323.The epoch date for horizontal control is a decimal equivalence • AC6323.of Year/Month/Day. • AC6323 • AC6323.The orthometric height was determined by differential leveling • AC6323.and adjusted in July 2002. • AC6323 • AC6323.Photographs are available for this station. • AC6323 • AC6323.The X, Y, and Z were computed from the position and the ellipsoidal ht. • AC6323 • AC6323.The Laplace correction was computed from DEFLEC99 derived deflections. • AC6323 • AC6323.The ellipsoidal height was determined by GPS observations • AC6323.and is referenced to NAD 83. • AC6323 • AC6323.The geoid height was determined by GEOID03. • AC6323.The dynamic height is computed by dividing the NAVD 88 • AC6323.geopotential number by the normal gravity value computed on the • AC6323.Geodetic Reference System of 1980 (GRS 80) ellipsoid at 45 • AC6323.degrees latitude (g = 980.6199 gals.).

  26. NGS Datasheet – Leveling • AC6323.The modeled gravity was interpolated from observed gravity values. • AC6323 • AC6323; North East Units Scale Factor Converg. • AC6323;SPC TXSC - 4,266,792.245 1,064,130.299 MT 0.99996526 +2 21 39.8 • AC6323;SPC TXSC -13,998,634.22 3,491,234.16 sFT 0.99996526 +2 21 39.8 • AC6323;UTM 15 - 3,336,466.860 386,299.039 MT 0.99975949 -0 35 35.3 • AC6323 • AC6323! - Elev Factor x Scale Factor = Combined Factor • AC6323!SPC TXSC - 1.00000227 x 0.99996526 = 0.99996753 • AC6323!UTM 15 - 1.00000227 x 0.99975949 = 0.99976176 • AC6323 • AC6323 SUPERSEDED SURVEY CONTROL • AC6323 • AC6323 ELLIP H (10/23/00) -14.414 (m) GP( ) 4 2 • AC6323 NAD 83(1993)- 30 09 15.31899(N) 094 10 50.43496(W) AD( ) B • AC6323 ELLIP H (08/21/98) -14.386 (m) GP( ) 5 2 • AC6323 NAD 83(1993)- 30 09 15.31917(N) 094 10 50.43466(W) AD( ) B • AC6323 ELLIP H (01/23/98) -14.225 (m) GP( ) 3 2 • AC6323 NAVD 88 (08/21/98) 13.12 (m) 43.0 (f) LEVELING 3 • AC6323 NAVD 88 (01/23/98) 13.26 (m) 43.5 (f) LEVELING 3 • AC6323 • AC6323.Superseded values are not recommended for survey control. • AC6323.NGS no longer adjusts projects to the NAD 27 or NGVD 29 datums. • AC6323.See file dsdata.txt to determine how the superseded data were derived. • AC6323

  27. NGS Datasheet – Leveling • AC6323_U.S. NATIONAL GRID SPATIAL ADDRESS: 15RUP8629936467(NAD 83) • AC6323_MARKER: I = METAL ROD • AC6323_SETTING: 59 = STAINLESS STEEL ROD IN SLEEVE (10 FT.+) • AC6323_STAMPING: BEA5 B 1996 • AC6323_MARK LOGO: NGS • AC6323_PROJECTION: FLUSH • AC6323_MAGNETIC: I = MARKER IS A STEEL ROD • AC6323_STABILITY: A = MOST RELIABLE AND EXPECTED TO HOLD • AC6323+STABILITY: POSITION/ELEVATION WELL • AC6323_SATELLITE: THE SITE LOCATION WAS REPORTED AS SUITABLE FOR • AC6323+SATELLITE: SATELLITE OBSERVATIONS - January 27, 2005 • AC6323_ROD/PIPE-DEPTH: 9.9 meters • AC6323_SLEEVE-DEPTH : 0.9 meters • AC6323 • AC6323 HISTORY - Date Condition Report By • AC6323 HISTORY - 1996 MONUMENTED NGS • AC6323 HISTORY - 19970313 GOOD NGS • AC6323 HISTORY - 20030522 GOOD JCLS • AC6323 HISTORY - 20050127 GOOD USPSQD • AC6323 • AC6323 STATION DESCRIPTION • AC6323 • AC6323'DESCRIBED BY NATIONAL GEODETIC SURVEY 1996 (GAS) • AC6323'IN BEAUMONT, AT THE INTERSECTION OF HIGHWAYS 69, 96, 287, AND CHINN • AC6323'LANE, 70.6 M (231.6 FT) NORTH OF BENCH MARK W 1496, 8.3 M (27.2 FT) • AC6323'EAST OF THE CENTERLINE OF THE NORTHBOUND LANES OF THE HIGHWAY, 0.7 M • AC6323'(2.3 FT) NORTHEAST OF A WITNESS POST, 0.5 M (1.6 FT) EAST OF THE NORTH • AC6323'END OF A GUARDRAIL, AND 0.4 M (1.3 FT) BELOW THE LEVEL OF THE HIGHWAY.

  28. NGS Datasheet – Leveling • BL0243; North East Units Scale Factor Converg. • BL0243;SPC TXSC - 4,258,727.981 1,072,609.864 MT 0.99994722 +2 24 08.7 • BL0243;SPC TXSC -13,972,176.72 3,519,054.20 sFT 0.99994722 +2 24 08.7 • BL0243;UTM 15 - 3,327,978.224 394,350.224 MT 0.99973771 -0 32 58.1 • BL0243 • BL0243! - Elev Factor x Scale Factor = Combined Factor • BL0243!SPC TXSC - 1.00000334 x 0.99994722 = 0.99995056 • BL0243!UTM 15 - 1.00000334 x 0.99973771 = 0.99974105 • BL0243 • BL0243 SUPERSEDED SURVEY CONTROL • BL0243 • BL0243 NAD 83(1993)- 30 04 42.20377(N) 094 05 46.46109(W) AD( ) 1 • BL0243 ELLIP H (03/11/02) -21.256 (m) GP( ) 4 1 • BL0243 NAVD 88 (03/11/02) 6.22 (m) 20.4 (f) LEVELING 3 • BL0243 NGVD 29 (??/??/??) 6.199 (m) 20.34 (f) ADJUSTED 1 1 • BL0243 • BL0243.Superseded values are not recommended for survey control. • BL0243.NGS no longer adjusts projects to the NAD 27 or NGVD 29 datums. • BL0243.See file dsdata.txt to determine how the superseded data were derived. • BL0243 • BL0243 HISTORY - Date Condition Report By • BL0243 HISTORY - 1972 MONUMENTED NGS • BL0243 HISTORY - 1986 GOOD NGS • BL0243 HISTORY - 198902 GOOD USPSQD • BL0243 HISTORY - 19890821 MARK NOT FOUND USPSQD • BL0243 HISTORY - 1990 GOOD USPSQD • BL0243 HISTORY - 19940817 GOOD USPSQD

  29. NGS Datasheet - GPS Height • 1 National Geodetic Survey, Retrieval Date = APRIL 30, 2008 • 1 National Geodetic Survey, Retrieval Date = JUNE 7, 2009 • AC6388 *********************************************************************** • AC6388 DESIGNATION - BPT AP STA B2 • AC6388 PID - AC6388 • AC6388 STATE/COUNTY- TX/JEFFERSON • AC6388 USGS QUAD - PORT ACRES (1993) • AC6388 • AC6388 *CURRENT SURVEY CONTROL • AC6388 ___________________________________________________________________ • AC6388* NAD 83(2007)- 29 56 48.75724(N) 094 00 44.75163(W) ADJUSTED • AC6388* NAVD 88 - 1.4 (meters) 5. (feet) GPS OBS • AC6388 ___________________________________________________________________ • AC6388 EPOCH DATE - 2002.00 • AC6388 X - -387,032.470 (meters) COMP • AC6388 Y - -5,517,618.690 (meters) COMP • AC6388 Z - 3,165,259.584 (meters) COMP • AC6388 . . . • AC6388.The orthometric height was determined by GPS observations and a • AC6388.high-resolution geoid model. • AC6388 • AC6388.The X, Y, and Z were computed from the position and the ellipsoidal ht. • AC6388 • AC6388.The Laplace correction was computed from DEFLEC99 derived deflections. • AC6388

  30. NGS Datasheet - Height Mod GPS • 1 National Geodetic Survey, Retrieval Date = JUNE 6, 2009 • AJ8222 *********************************************************************** • AJ8222 HT_MOD - This is a Height Modernization Survey Station. • AJ8222 DESIGNATION - BASELINE • AJ8222 PID - AJ8222 • AJ8222 STATE/COUNTY- TX/JEFFERSON • AJ8222 USGS QUAD - BEAUMONT WEST (1994) • AJ8222 • AJ8222 *CURRENT SURVEY CONTROL • AJ8222 ___________________________________________________________________ • AJ8222* NAD 83(2007)- 30 05 43.32312(N) 094 12 12.09959(W) ADJUSTED • AJ8222* NAVD 88 - 11.14 (meters) 36.5 (feet) GPS OBS • AJ8222 ___________________________________________________________________ • AJ8222 EPOCH DATE - 2002.00 • AJ8222 X - -404,813.933 (meters) COMP • AJ8222 . . . • AJ8222 The epoch date for horizontal control is a decimal equivalence • AJ8222 of Year/Month/Day. • AJ8222 • AJ8222.The orthometric height was determined by GPS observations and a • AJ8222.high-resolution geoid model using precise GPS observation and • AJ8222.processing techniques. • AJ8222 • AJ8222.The X, Y, and Z were computed from the position and the ellipsoidal ht. • AJ8222 • AJ8222.The Laplace correction was computed from DEFLEC99 derived deflections.

  31. NGS Datasheet – Leveling • 1 National Geodetic Survey, Retrieval Date = JUNE 6, 2009 • AC6323 *********************************************************************** • AC6323 DESIGNATION - BEA5 B • AC6323 PID - AC6323 • AC6323 STATE/COUNTY- TX/JEFFERSON • AC6323 USGS QUAD - VOTH (1993) • AC6323 • AC6323 *CURRENT SURVEY CONTROL • AC6323 ___________________________________________________________________ • AC6323* NAD 83(2007)- 30 09 15.32032(N) 094 10 50.43369(W) ADJUSTED • AC6323* NAVD 88 - 13.115 (meters) 43.03 (feet) ADJUSTED • AC6323 ___________________________________________________________________ • AC6323 EPOCH DATE - 2002.00 • AC6323 X - -402,394.366 (meters) COMP • AC6323 Y - -5,504,987.110 (meters) COMP • AC6323 Z - 3,185,163.813 (meters) COMP • AC6323 LAPLACE CORR- 0.04 (seconds) DEFLEC99 • AC6323 ELLIP HEIGHT- -14.472 (meters) (02/10/07) ADJUSTED • AC6323 GEOID HEIGHT- -27.51 (meters) GEOID03 • AC6323 DYNAMIC HT - 13.098 (meters) 42.97 (feet) COMP • AC6323 • AC6323 ------- Accuracy Estimates (at 95% Confidence Level in cm) -------- • AC6323 Type PID Designation North East Ellip • AC6323 ------------------------------------------------------------------- • AC6323 NETWORK AC6323 BEA5 B 0.51 0.41 2.04 • AC6323 ------------------------------------------------------------------- • AC6323 MODELED GRAV- 979,314.4 (mgal) NAVD 88 • AC6323 H h N NAVD88 – Ellipsoid Ht + Geoid Ht = … 13.115 – (-14.472) – 28.345 = -0.758 USGG2003 13.115 – (-14.472) – 27.506 = +0.081 GEOID03

  32. How accurate is a GPS-derived Orthometric Height? • Relative (local) accuracy in ellipsoid heights between adjacent points will be better than 2 cm, at 95% confidence level • Network accuracy (relative to NSRS) in ellipsoid and orthometric heights will be better than 5 cm, at 95% confidence level • Accuracy of orthometric height is dependent on accuracy of the geoid model – Currently NGS is improving the geoid model with more data, i.e. Gravity and GPS observations on leveled bench marks from Height Mod projects

  33. ? Ellipsoid, Geoid, and Orthometric Heights H = Orthometric Height (leveling) H = h - N h = Ellipsoidal Height (GPS) N = Geoid Height (model) TOPOGRAPHIC SURFACE h (NAD83) (NAVD88) H N Geoid Height (GEOID03/09) Ellipsoid Geoid

  34. In Search of the Geoid… Dr. Dan Roman Dr. Yan Wang Courtesy of Natural Resources Canada www.geod.nrcan.gc.ca/index_e/geodesy_e/geoid03_e.html

  35. Definitions: GEOIDS versus GEOID HEIGHTS • “The equipotential surface of the Earth’s gravity field which best fits, in the least squares sense, (global) mean sea level.”* • Can’t see the surface or measure it directly. • Can be modeled from gravity data as they are mathematically related. • Note that the geoid is a vertical datum surface. • A geoid height is the ellipsoidal height from an ellipsoidal datum to a geoid. • Hence, geoid height models are directly tied to the geoid and ellipsoid that define them (i.e., geoid height models are not interchangeable). *Definition from the Geodetic Glossary, September 1986

  36. LEVEL SURFACES AND ORTHOMETRIC HEIGHTS Earth’s Surface WP Level Surfaces P Plumb Line Mean “Geoid” Sea Level WO PO Ocean Level Surface = Equipotential Surface (W) H (Orthometric Height) = Distance along plumb line (PO to P)

  37. High Resolution Geoid Models • Start with gravity measurements • Add Digital Elevation Data (Continental) • Add a Global Earth Gravity Model (EGM96, EGM08) • Result – A purely Gravitational geoid model – good for scientific applications … But is this what we need?

  38. To use GNSS you need a good geoid model • NGS makes 2 geoid models • Gravitational model: • is good for scientific applications • uses gravity data collected from a variety of sources • “Hybrid” model: • starts with gravitational model • uses GPS on bench marks to enable a fit to NAVD88 GRACE Satellite Gravity

  39. GGPSBM1999: 6,169 total 0 Canada STDEV 9.2 cm (2σ) GGPSBM2003: 14,185 total 579 Canada STDEV 4.8 cm (2σ)

  40. h h h h H h H H H N N N H N N N Gravimetric vs. Hybrid Geoid surface Earth’s Surface Note use of GPS on BMs Gravimetric Geoid systematic misfit to BM’s but best fits “true” heights Hybrid Geoid “converted” to fit local BM’s, so best fits NAVD 88 heights Conversion Surface model of systematic misfit derived from BM’s in IDB Ellipsoid N N N N 0.876 M in Beaumont, TX– 1999 model 0.839 M in Beaumont, TX – 2003 model 1.065M in Beaumont, TX– 2009 Beta model Hybrid Geoid Gravimetric Geoid

  41. Goal of NHMP • Access to accurate, reliable heights nationally • Standards that are consistent across the nation • Data, technology, and tools that yield consistent results regardless of terrain and circumstances • A system/process that will stand the test of time – “Maintain-able”

  42. That was then…. • In the early years of Height Mod NGS felt the Gravimetric geoid was adequate as the base for the Hybrid geoid • What’s changed? • Better accuracy from GNSS-derived heights – can use GNSS to monitor changes in heights • Better understanding of poor condition of vertical network • Gravity holdings at NGS evaluated

  43. NGS Gravity Holdings • Most of the historical NGS data is terrestrial • Multiple observers, multiple processors over the past 60 years • Numerous corrections and datums over time • Metadata maintained in paper records • Very limited aerogravity • Deficit in near-shore gravity data

  44. 20-100 km gravity gaps along coast Terrestrial gravity New Orleans Ship gravity

  45. Gravity Coverage for USGG2003/USGG2008

  46. Is NAVD 88 “Maintainable”? • NAVD88 defined through leveling network • Not practical to re-leveling the country • At $3000 / km, re-leveling NAVD 88 would cost $2.25 Billion • Does not include densifying poorly covered areas in Western CONUS, Alaska • Does not include leveling needed for separate vertical datums on island states and territories • Leveling yields cross-country error build-up; problems in the mountains • Leveling requires leaving behind marks • Bulldozers and crustal motion do their worst

  47. Transition to the Future – GRAV-D Gravity for the Redefinition of the American Vertical Datum • Official NGS policy as of Nov 14, 2007 • $38.5M over 10 years • Airborne Gravity Snapshot • Absolute Gravity Tracking • Re-define the Vertical Datum of the USA by 2017 http:/www.ngs.noaa.gov/GRAV-D/

  48. GRAV-D is the most ambitious project within the National Height Mod Program • National Height Modernization needs to support the NAVD 88 while transitioning (via GRAV-D) to a new vertical datum in 10 years • All National Height Mod funds (internal or grants) should support access to accurate heights, in general, but: • With emphasis on NAVD 88 today • With emphasis on the new vertical datum in 5 years

  49. From NGS’ 10-Year Plan NGS Mission: “Modernize the Geopotential (“Vertical”) Datum “The gravimetric geoid, long used as the foundation for hybrid geoid models, becomes the most critical model produced by NGS.”

  50. Questions Renee Shields Height Modernization Manager 301-713-3231, x116 Renee.shields@noaa.gov Dan Roman Research Geodesist 301-713-3202, x161 Dan.Roman@noaa.gov

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