National Readjustment

1. National Readjustment Donald.Mulcare@noaa.gov Geodesist, Texas State Advisor National Geodetic Survey Texas Society of Professional Surveyors October 2007

2. NATIONAL READJUSTMENT • WHAT? • WHY • HOW • WHEN • POST • QUESTIONS

3. NATIONAL SPATIAL REFERENCE SYSTEM • A component of the National Spatial Data Infrastructure (NSDI) - http://www.fgdc.gov/nsdi/nsdi.html • Contains all geodetic control contained in the National Geodetic Survey (NGS) Integrated Data Base: • Horizontal and vertical control points • Geoid models such as GEOID 03 • Gravity • Precise GPS orbits • Continuously Operating Reference Stations (CORS) • National Shoreline data as observed by NGS • Standards and Specifications for data submittal

4. NATIONAL SPATIAL REFERENCE SYSTEM • MULTIPURPOSE – Supports Geodesy, Geophysics, Land Surveying, Navigation, Mapping, Charting and GIS • ACTIVE – Accessible through Continuously Operating Reference Stations (CORS) and derived products • INTEGRATED – Related to International services and standards (e.g. International Earth Rotation Service, International GPS Service etc.) • DOCUMENTED – Complete metadata is provided for elements.

5. NATIONAL GEODETIC SURVEY WEB SITE http://www.ngs.noaa.gov

8. NATIONAL READJUSTMENT WHAT WHY? HOW WHEN POST QUESTIONS

9. The NAD83(86) Adjustment Team

12. NAD83(86) DOPPLER STATIONS

13. Guess who …

14. COMPARISON OF DATUM ELEMENTS NAD 27NAD 83 ELLIPSOID CLARKE 1866 GRS80 a=6,378,206.4 m a=6,378,137 m 1/f = 294.9786982 1/f = 298.257222101 DATUM POINT Triangulation Station NONE Meades Ranch, Kansas Earth Mass Center ADJUSTMENT 25k Stations 250k Stations few hundred Base lines 30k EDMI base lines few hundred Astro Az 5k Astro Azimuths Doppler and VLBI

15. NAD 27 and NAD 83

16. Results of NAD83(86) • Network Accuracy - 1 Meter • Local Accuracy – First-Order (1 part in 100,000)

17. NAD 83(86) NETWORK PROBLEMS Not “GPSABLE” POOR STATION ACCESSIBILITY IRREGULARLY SPACED POSITIONAL ACCURACY

19. HIGH PRECISION GPS NETWORKS “GPSABLE” Clear Horizons for Satellite Signal Acquisition EASY ACCESSIBILITY Few Special Vehicle or Property Entrance Requirements REGULARLY SPACED Always within 20-100 Km HIGH HORIZONTAL ACCURACY A-Order (5 mm + 1:10,000,000) B-Order (8mm + 1:1,000,000)

20. HARN/HPGN ADJUSTMENT A-Order Adjusted to VLBI-Existing FBN-CORS B-Order Adjusted to A-Order Existing Horizontal (Conventional & GPS) Readjusted to A/B-Order New Adjustment Date Tag e.g. NAD83(1991.35)

21. HIGH ACCURACY REFERENCE NETWORK

22. HPGN/HARN & STATEWIDE NETWORK STATUS 1991 GPS222 1996 1992 1996 1991 GPS1048 GPS341 1991 GPS197 1996 GPS805 reos 7/96 GP S291 1993 1994 reos-1996 GPS941 GPS1047 reobs 9/97 1996 GPS730 GPS606 1994 1995 1992 1995 GPS1121 1997 1997 GPS404 GPS887 1994 1991 GPS394 GPS882 GPS GPS260 GPS1178 1997 1997 1995 1993 1200 GPS633 1992 GPS908 1992 1993 GPS1150 GPS1179 GPS610 reos-6/95-GPS904 GPS412 GPS611 1995 GPS419 1992 1990 -GPS120 1997 GPS852 1993 GPS376 GPS1133 1993 1994 1992 GPS725 GPS366 GPS721 1992 GPS585 1990 1992 GPS383 reos 1/96 GPS936 -GPS170 GPS450 1993 GPS667 1997 . GPS & CLASSICAL ADJUSTMENTS COMPLETED GPS ADJUSTMENT COMPLETED GPS577

23. Official policy FEDERAL BASE NETWORK NGS funded and Maintained Minimum 100 KM station spacing Local ACCURACIES Horizontal: 1-cm. Ellipsoid height: 2-cm NAVD 88: 3-cm Gravity: 50 micro-gals REVISIT EVERY 3 TO 5 YEARS

24. FEDERAL BASE NETWORK NGS FUNDED NGS MARK MAINTENANCE MINIMUM 100 KM STATION SPACING A and B-ORDER HORIZONTAL ACCURACY FIRST-ORDER CLASS II ORTHOMETRIC HEIGHTS or SECOND-ORDER CLASS I ORTHOMETRIC HEIGHTS SECOND-ORDER CLASS I ELLIPSOIDAL HEIGHTS REVISIT EVERY 3 TO 5 YEARS

25. FBN/CBN SURVEYS 1998 GPS1340 2000 2002 1999 GPS1492 2001 GPS1686 GPS1394 GPS1641 2000 1998 GPS1506 GPS1333 2002 1999 1997 2000 GPS1687 2001 GPS1377 1999 GPS1207 2001 GPS1514 GPS1596 GPS1397 GPS1712 2003 2000 2000 GPS1752 1999 2003 2000 2003 GPS1481 GPS1463 2002 1999 GPS1519 GPS1356 GPS GPS1825 GPS1731 GPS1370 1850 2001 2000 2000 MEANS GPS1629 2003 2000 2003 GPS1462 1998 GPS1530 GPS1851 2002 GPS1188 GPS1726 GPS1288 GPS-1547 1999 2003GPS1753 2001 1999 2000 GPS1399 1999 GPS1554 GPS1347 GPS1411 GPS1381 1997 1998 GPS1250 1998 GPS1273 1998 GPS1258 1998 GPS1267 1999 GPS1264 GPS1378 2003 GPS READJUSTMENT COMPLETED GPS1682 WILLIAMS FBN GPS ADJUSTMENT COMPLETED

26. http://www.ngs.noaa.gov/PROJECTS/FBN/

27. http://www.ngs.noaa.gov/PROJECTS/FBN/

28. NGS Map version

29. Old Datasheet format

31. Difference is: DN = -0.644 (m) DE = +0.712 (m) DU = 1.195 (m)

32. IMPROVING POSITIONAL ACCURACY TIME NETWORK LOCAL NETWORK SPAN ACCURACY ACCURACY NAD 27 1927-1986 10 METERS (1 part in 100,000) NAD83(86) 1986-1990 1 METER (1 part in 100,000) HARN 1990-1997 0.1 METER B-order (1.0 ppm) A-order (0.1 ppm) CORS 1996 - 0.01 meter 0.01 meter

33. Reasons for Readjustment • Multiple epoch dates • Inconsistencies between states • Need to be Consistent with CORS • Compute Network and Local accuracies September 24, 2003 NGS Executive Steering Committee approved a plan for the readjustment of the horizontal positions and ellipsoid heights for GPS stations in the contiguous United States. Orthometric Height adjustment will not be attempted

34. What about Orthometric Heights? • Decision was made not to perform a National Readjustment of orthometric heights at this time • Control = NAVD 88 not the CORS • Since no change in control most orthometric elevations would not change significantly • Network & Local Accuracy numbers for the orthometric heights would be the primary reason for readjustment • Would require relevant network accuracies for the NAVD 88 network-This would require a complete analysis of the NAVD 88 network

35. Heights h – H – N = 0 + errors in components

42. Tectonic Plates NUVEL-1A

45. http://tsrc.cbi.tamucc.edu/THM/HomePage

47. Geoid Modeling Issues • The new ellipsoid heights will be used in the next hybrid geoid model. • Future efforts will center on improvements to our gravity data. • NGS has acquired an airborne gravity meter. • We plan a comprehensive set of observations to capture gravity throughout the United States and our possessions. • Airborne gravity data supplements terrestrial and satellite based gravity.

49. Gravity Recovery And Climate Experiment http://www.csr.utexas.edu/grace/

50. NATIONAL READJUSTMENT WHAT WHY HOW? WHEN POST QUESTIONS